HK1243832B - Techniques for employing access node clusters in end-to-end beamforming - Google Patents

Description

Techniques for employing access node clustering in end-to-end beamforming

Technical Field

The disclosed systems, methods, and apparatus relate to end-to-end beamforming using end-to-end repeaters in a system.

Background Art

Wireless communication systems, such as satellite communication systems, provide a way to transmit data, including audio, video, and various other types of data, from one location to another. Information originates from a first site, such as a first ground-based site, and is transmitted to a wireless repeater, such as a communication satellite. The information received by the wireless repeater is retransmitted to a second site, such as a second ground-based site. In some wireless relay communication systems, the first site or the second site (or both) are mounted on a vehicle, such as an air vehicle, a water vehicle, or a land vehicle. Information can be transmitted in only one direction (e.g., only from the first ground-based site to the second ground-based site), or in both directions (e.g., also from the second ground-based site to the first ground-based site).

In wireless relay communication systems in which the wireless repeaters are satellites, the satellites may be geostationary satellites, in which case the satellite's orbit is synchronized with the Earth's rotation, causing the satellite's coverage area to remain substantially stationary relative to the Earth. In other cases, the satellites are in orbit around the Earth, which causes the satellite's coverage area to move across the Earth's surface as the satellite traverses its orbital path.

The signal directed to or from the first station can be directed by using an antenna shaped to focus the signal into a narrow beam. Such antennas typically have a parabolic shaped reflector to focus the beam.

In some cases, a beam can be formed electronically by adjusting the gain and phase (or time delay) of the signals transmitted, received, or both from several elements of a phased array antenna. The beam can be steered by appropriately selecting the relative phase and gain transmitted and/or received by each element of the phased array antenna. In most cases, all energy transmitted from a ground-based site is intended to be received by a wireless repeater. Similarly, information received by a second site is typically received from a wireless repeater at the same time. Therefore, the transmit beam formed to transmit information to the wireless repeater (whether by using electronic beamforming or by using an antenna with a shaped reflector) is typically relatively narrow to allow as much transmission energy as possible to be directed to the wireless repeater. Similarly, the receive beam formed to receive information from the wireless repeater is typically narrow to collect energy from the direction of the wireless repeater with minimal interference from other sources.

In many interesting cases, the signal transmitted from a wireless repeater to a first site and a second site is not directed to a single site. Instead, the wireless repeater is capable of transmitting signals over a relatively large geographic area. For example, in a satellite communications system, a satellite may serve the entire continental United States. In this case, the satellite is said to have a satellite coverage area that includes the entire continental United States. However, in order to increase the amount of data that can be transmitted by the satellite, the energy transmitted by the satellite is focused into a beam. The beam can be directed to a geographic area on Earth.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are provided for illustrative purposes only and depict only examples. These drawings are provided to facilitate the reader's understanding of the disclosed methods and apparatus. They do not limit the breadth, scope, or applicability of the claimed invention. For clarity and ease of illustration, the drawings are not necessarily drawn to scale.

FIG1 is a diagram of an example of a satellite communication system.

FIG. 2 is a diagram illustrating an exemplary beam pattern covering the continental United States.

3 is a diagram of an example of a forward link of a satellite communication system in which a satellite has phased array multi-feed carrier-per-beam beamforming capability.

4 is a diagram of an example of a forward link of a satellite communication system with ground-based beamforming.

5 is a diagram of an exemplary end-to-end beamforming system.

6 is a diagram of an exemplary signal path for a signal in the return direction.

7 is a diagram of exemplary signal paths in the return direction from a user terminal.

FIG8 is a simplified diagram of an exemplary end-to-end return channel matrix model.

9 is a diagram of exemplary signal paths in the forward direction.

10 is a diagram of exemplary signal paths in the forward direction for a user terminal located within the user beam coverage area.

11 is a simplified diagram of an exemplary end-to-end return channel matrix model.

12 is an illustration of an exemplary end-to-end repeater satellite supporting forward and return data.

FIG13 is a diagram of an example in which the uplink frequency range is divided into two parts.

14 is a diagram of an exemplary end-to-end repeater time-division multiplexing between forward data and return data.

15 is a block diagram of components of an exemplary end-to-end relay implemented as a satellite.

16 is a block diagram of an exemplary transponder including a phase shifter.

17 is a graph of exemplary signal strength patterns for several antenna elements.

18 is a diagram of exemplary 3dB signal strength profiles for several antenna elements.

19 is a diagram of exemplary overlapping signal strength patterns for several antenna elements.

20A-20E are diagrams of example overlapping 3dB signal strength profiles for several antenna elements.

21 is a diagram of an exemplary enumeration of 16 antenna elements and their overlapping 3dB signal strength profiles.

FIG. 22 is a table showing an exemplary mapping of receive antenna elements to transmit antennas through 16 transponders.

23 is an illustration of a cross section of a parabolic antenna reflector and an array of elements centered at the focus of the parabola.

24 is an illustration of a cross section of a parabolic antenna reflector and an array of elements positioned away from the focus of the parabola.

25 is a diagram of an exemplary repeater coverage area (shown with single cross-hatching) and areas defined by points within the repeater coverage area that are also contained within the coverage areas of six antenna elements (shown with double cross-hatching).

26 is an illustration of an exemplary repeater antenna pattern in which all points within the repeater coverage area are also contained within the coverage areas of at least four antenna elements.

27 is a diagram of an exemplary distribution of access nodes (ANs) and user beam coverage areas.

28 is an exemplary graph of normalized forward link and return link capacity as a function of the number of deployed ANs.

FIG29 is a block diagram of an exemplary ground segment 502 of an end-to-end beamforming system.

30 is a block diagram of an exemplary forward/return beamformer.

31 is a block diagram of an exemplary forward beamformer including multiple return time-slice beamformers with time-domain demultiplexing and multiplexing.

32 is a diagram of a simplified exemplary ground segment showing the operation of a forward time-slice beamformer.

33 is a block diagram of an exemplary return beamformer including multiple return time-slice beamformers with time-domain demultiplexing and multiplexing.

34 is a diagram of a simplified exemplary ground segment showing the operation of a return beamformer employing time domain multiplexing.

35 is a block diagram of an exemplary multi-band forward/return beamformer employing sub-band demultiplexing and multiplexing.

36 and 37 are diagrams of exemplary timing alignment for the forward link.

FIG38 is a block diagram of an exemplary AN.

FIG39 is a block diagram of a portion of an example of an AN.

FIG40 is a block diagram of an exemplary AN 515 in which multiple frequency sub-bands are processed separately.

41 is an illustration of an exemplary end-to-end beamforming system for achieving different user link and feeder link coverage areas.

42 is a diagram of an exemplary model of the signal paths of signals carrying return data on an end-to-end return link.

43 is a diagram of an exemplary model of the signal paths of signals carrying forward data on an end-to-end forward link.

44A and 44B are diagrams of exemplary forward and return signal paths, respectively.

45A, 45B, 45C, 45D, 45E, 45F, and 45G are diagrams of examples of end-to-end repeater visible coverage areas.

46A and 46B are diagrams of examples of end-to-end repeater Earth coverage areas and North American coverage areas, respectively.

47A and 47B are block diagrams of exemplary forward and return signal paths, respectively, each with selective activation of multiple user link antenna subsystems.

48A and 48B are diagrams of examples of end-to-end repeater coverage areas including multiple selectively activated user coverage areas.

49A and 49B are block diagrams of exemplary forward and return signal paths, respectively, each with selective activation of multiple user link antenna subsystems and multiple feeder link antenna subsystems.

50A, 50B, and 50C illustrate examples of one or more user coverage areas with multiple access node coverage areas.

51A and 51B illustrate exemplary forward and return signal paths, respectively, each with selective activation of multiple user link antenna element arrays and multiple feeder link antenna element arrays.

52A and 52B illustrate exemplary forward and return receive/transmit signal paths, respectively, for simultaneous use of multiple AN clusters.

53A and 53B illustrate exemplary transponders that allow selective coupling between multiple feeder link components and a single user link component.

54A and 54B illustrate a forward link transponder and a return link transponder, respectively.

55A, 55B, and 55C illustrate exemplary loopback transponders.

FIG. 56A illustrates an end-to-end repeater including one or more reflectors.

FIG56B shows an antenna subsystem with multiple feed clusters.

Figure 57 shows an antenna subsystem including a composite reflector.

FIG. 58 illustrates an end-to-end relay system with portions disposed on one or more offshore (eg, fixed or floating) platforms.

59A and 59B are diagrams of examples of visible coverage areas for end-to-end repeaters supporting different frequency ranges.

60A and 60B illustrate exemplary forward/return receive/transmit signal paths supporting multiple frequency bands.

61A and 61B illustrate exemplary forward/return receive/transmit signal paths supporting multiple frequency bands.

FIG. 62 illustrates an exemplary antenna element array having spatially interleaved subsets of constituent antenna elements.

63A and 63B are diagrams of exemplary frequency allocations.

64A and 64B are diagrams of exemplary frequency allocations.

65A and 64B are diagrams of exemplary frequency allocations.

66A and 66B illustrate exemplary forward/return receive/transmit signal paths.

Reference numerals (e.g., 100) are used herein to refer to aspects of the drawings. Similar or identical aspects are generally illustrated using the same numerals. A group of similar or identical elements may be collectively referred to by a single reference numeral (e.g., 200), while individual elements of the group may be referred to by reference numerals with additional letters (e.g., 200a, 200b).

The drawings are not intended to be exhaustive or to limit the claimed invention to the precise forms disclosed. The disclosed methods and apparatus can be practiced with modification and alteration, and the invention is limited only by the claims and their equivalents.

DETAILED DESCRIPTION

The detailed description is organized as follows. First, an introduction to a wireless relay communication system using satellite communication and beamforming is described. Second, end-to-end beamforming is described in general and at a system level using satellite end-to-end beamforming as an example, but the application of end-to-end beamforming is not limited to satellite communication. Third, the operation of forward data and return data is described in the context of end-to-end beamforming. Fourth, an end-to-end repeater and its antenna are described using a communication satellite as an example. Next, a ground network for forming end-to-end beams is described, including related aspects such as delay equalization, feeder link impairment cancellation, and beam weight calculation. Finally, end-to-end beamforming with different user link coverage areas and feeder link coverage areas, as well as a system with multiple coverage areas, is described.

Satellite communications

FIG1 is a diagram of an example of a hub-and-spoke satellite communication system 100. An example of a satellite acting as a wireless repeater. Although many examples are described throughout the disclosure with respect to satellites or satellite communication systems, such examples are not intended to be limited to satellites; any other suitable wireless repeater may be used and operate in a similar manner. System 100 includes a ground-based earth station 101, a communication satellite 103, and an earth-based transmission source such as a user terminal 105. A satellite coverage area can be broadly defined as an area in which and/or to which an earth-based transmission source or earth-based receiver such as a ground-based earth station or user terminal can communicate via a satellite. In some systems, the coverage area for each link (e.g., forward uplink coverage area, forward downlink coverage area, return uplink coverage area, and return downlink coverage area) may be different. The forward uplink coverage area and the return uplink coverage area are collectively referred to as the uplink satellite coverage area. Similarly, the forward downlink coverage area and the return downlink coverage area are collectively referred to as the downlink satellite coverage area. Although satellite coverage areas are only valid for satellites in service (e.g., in a serving orbit), satellites can be considered to have (e.g., can be designed to have) a satellite antenna pattern that is independent of the satellite's relative position with respect to the Earth. That is, a satellite antenna pattern is the distribution pattern of energy transmitted from (or received by) a satellite antenna. When a satellite is in a serving orbit, the satellite antenna pattern illuminates (transmits to or receives from) a specific satellite coverage area. The satellite coverage area is defined by the satellite antenna pattern, the orbital position and orbital attitude for which the satellite is designed, and a given antenna gain threshold. Generally speaking, the intersection of the antenna pattern with a specific physical area of interest (e.g., an area on or near the Earth's surface) (at a specific effective antenna gain relative to the peak gain, e.g., 3 dB, 4 dB, 6 dB, 10 dB) defines the antenna's coverage area. Antennas can be designed to provide specific antenna patterns (and/or coverage areas), and such antenna patterns can be determined computationally (e.g., through analysis or simulation) and/or measured experimentally (e.g., at an antenna test range or in actual use).

Although only one user terminal 105 is shown in the figure for simplicity, many user terminals 105 are typically present in the system. Satellite communication system 100 operates as a point-to-multipoint system. That is, an earth station 101 within the satellite's coverage area can send information to and receive information from any user terminal 105 within the satellite's coverage area. However, user terminals 105 communicate only with earth station 101. Earth station 101 receives forward data from communication network 107, modulates the data using feeder link modem 109, and transmits the data to satellite 103 on forward feeder uplink 111. Satellite 103 relays this forward data to user terminal 105 on forward user downlink (sometimes called forward service downlink) 113. In some cases, forward communications from earth station 101 are intended for several user terminals 105 (e.g., information is multicast to user terminals 105). In other cases, forward communications from earth station 101 are intended for only one user terminal 105 (e.g., unicast to a specific user terminal 105). The user terminal 105 transmits return data to the satellite 103 on a return user uplink (sometimes called a return service uplink) 115. The satellite 103 relays the return data to the ground station 101 on a return feeder downlink 117. The feeder link modem 109 demodulates the return data for relaying to the communication network 107. This return link function is typically shared by multiple user terminals 105.

FIG2 is a diagram illustrating an example configuration of beam coverage areas for a satellite serving the continental United States. Seventy beams are shown in the exemplary configuration. First beam 201 covers approximately two-thirds of the state of Washington. Second beam 203, adjacent to first beam 201, covers an area immediately east of first beam 201. Third beam 205 covers approximately the state of Oregon south of first beam 201. Fourth beam 207 covers an area approximately southeast of first beam 201. Typically, there is some degree of overlap between adjacent beams. In some cases, a multi-color multiplexing pattern (e.g., a two-color, three-color, or four-color multiplexing pattern) is used. In the example of a four-color pattern, beams 201, 203, 205, and 207 are individually assigned unique combinations of frequencies (e.g., one or more frequency ranges or one or more channels) and/or antenna polarizations (e.g., in some cases, antennas can be configured to transmit signals using right-hand circular polarization (RHCP) or left-hand circular polarization (LHCP); other polarization techniques are also available). As a result, there may be relatively little mutual interference between signals transmitted on different beams 201, 203, 205, and 207. These combinations of frequency and antenna polarization can then be reused in a repeating, non-overlapping "four-color" multiplexing pattern. In some cases, the desired communication capacity can be achieved using a single color. In some cases, time-sharing between beams and/or other interference mitigation techniques can be used.

Within certain limits, focusing the beams into a smaller area and thus increasing the number of beams increases the satellite's data capacity by allowing more frequency reuse opportunities. However, increasing the number of beams can increase the complexity of the system and, in many cases, the complexity of the satellite.

The complexity of satellite design typically results in larger size, heavier weight, and higher power consumption. Launching satellites into orbit is expensive. The cost of launching a satellite depends in part on the satellite's weight and size. Furthermore, if a satellite is to be launched using currently available rocket technology, there are absolute limits on its weight and size. This leads to trade-offs between possible satellite design features. Furthermore, the amount of power that can be supplied to satellite components is limited. Therefore, weight, size, and power consumption are parameters to consider in satellite design.

Throughout this disclosure, the term receiving antenna element refers to a physical transducer that converts an electromagnetic signal into an electrical signal, and the term transmitting antenna element refers to a physical transducer that transmits an electromagnetic signal when stimulated by an electrical signal. Antenna elements may include horn antennas, diaphragm-polarized horn antennas (e.g., which can be used as two combined elements with different polarizations), multi-port multi-band horn antennas (e.g., dual-band 20 GHz/30 GHz with dual-polarized LHCP/RHCP), cavity-backed slot antennas, inverted-F antennas, slotted waveguide antennas, Vivaldi antennas, helical antennas, loop antennas, patch antennas, or any other configuration of a combination of antenna elements or interconnected subelements. Antenna elements have corresponding antenna patterns that describe how the antenna gain varies with direction (or angle). Antenna elements also have a coverage area corresponding to an area (e.g., a portion of the Earth's surface) or a volume (e.g., a portion of the Earth's surface plus the space above the surface) at which the antenna element provides a desired gain level (e.g., within 3 dB, 6 dB, 10 dB, or other value relative to the peak gain of the antenna element). The coverage area of an antenna element can be modified by various structures such as reflectors, frequency selective surfaces, lenses, radomes, etc. Some satellites, including the satellites described herein, may have several transponders, each of which is capable of independently receiving and transmitting signals. Each transponder is coupled to an antenna element (e.g., a receiving element and a transmitting element) to form a receive/transmit signal path that has a radiation pattern (antenna pattern) that is different from other receive/transmit signal paths, thereby producing a unique beam that can be assigned to different beam coverage areas. Input and/or output multiplexers are typically used to share a single receive/transmit signal path across multiple beams. In both cases, the number of synchronized beams that can be formed is typically limited by the number of receive/transmit signal paths deployed on the satellite.

Beamforming

Beamforming of a communication link can be performed by adjusting the signal phase (or time delay) and sometimes the signal amplitude of signals transmitted and/or received by multiple elements of one or more antenna arrays with overlapping coverage areas. In some cases, some or all of the antenna elements are arranged as arrays of receiving and/or transmitting constituent elements that cooperate to achieve end-to-end beamforming, as described below. For transmission (from the transmitting elements of one or more antenna arrays), the relative phase and sometimes the amplitude of the transmitted signals are adjusted so that the energy transmitted by the transmitting antenna elements will constructively add at the desired location. This phase/amplitude adjustment is often referred to as "applying beam weights" to the transmitted signals. For reception (by the receiving elements of one or more antenna arrays), the relative phase and sometimes the amplitude of the received signals are adjusted (i.e., applying the same or different beam weights) so that the energy received by the receiving antenna elements from the desired location will constructively add at those receiving antenna elements. In some cases, a beamformer calculates the desired antenna element beam weights. In some cases, the term beamforming can refer to the application of beam weights. An adaptive beamformer includes functionality that dynamically calculates beam weights. Calculating beam weights may require discovering communication channel characteristics directly or indirectly. The processes of beam weight calculation and beam weight application may be performed in the same or different system elements.

Antenna beams can be steered, selectively formed, and/or otherwise reconfigured by applying different beam weights. For example, the number of effective beams, the coverage area of the beams, the size of the beams, the relative gain of the beams, and other parameters can change over time. In some cases, this versatility is desirable. Beamforming antennas can typically form relatively narrow beams. Narrow beams can allow signals transmitted on one beam to be distinguished from signals transmitted on other beams (e.g., to avoid interference). Thus, narrow beams can allow for greater reuse of frequencies and polarizations when forming larger beams. For example, a narrowly formed beam can serve two non-overlapping, discontinuous coverage areas. Each beam can use both right-handed and left-handed polarizations. More multiplexing can increase the amount of data transmitted and/or received.

Some satellites use on-board beamforming (OBBF) to electronically steer an array of antenna elements. Figure 3 is an illustration of a satellite system 300 in which a satellite 302 has phased array multiple feed per beam (MFPB) on-board beamforming capabilities. In this example, beam weights are calculated at a ground-based computing center and then transmitted to the satellite or pre-stored in the satellite for application (not shown). The forward link is shown in Figure 3, although this architecture can be used for the forward link, the return link, or both. Beamforming can be used on the user link, the feeder link, or both. The forward link shown is the signal path from one of multiple gateways (GW) 304 to one or more of multiple user terminals within one or more spot beam coverage areas 306. Satellite 302 has a receive antenna array 307, a transmit antenna array 309, a downconverter (D/C) and gain block 311, a receive beamformer 313, and a transmit beamformer 315. Satellite 302 can form beams on both the feeder link 308 and the user link 310. Each of the L elements of receive array 307 receives K signals from K GWs 304. For each of the K feeder link beams to be generated (e.g., one beam per GW 304), receive beamformer 313 applies a different beam weight (e.g., performs phase/amplitude adjustment) to each signal received by each of the L receive antenna array elements (of receive antenna array 307). Therefore, for the K beams to be formed using receive antenna array 307 having L receive antenna elements, K different beam weight vectors of length L are applied to the L signals received by the L receive antenna array elements. Receive beamformer 313 within satellite 302 adjusts the phase/amplitude of the signals received by the L receive antenna array elements to generate K receive beam signals. Each of the K receive beams is focused to receive a signal from one GW 304. Therefore, receive beamformer 313 outputs the K receive beam signals to D/C and gain module 311. One such receive beam signal is formed for the signal received from each transmit GW 304 .

The D/C and gain module 311 downconverts each of the K receive beam signals and adjusts the gain appropriately. The K signals are output from the D/C and gain module 311 and coupled to the transmit beamformer 315. The transmit beamformer 315 applies a vector of L weights to each of the K signals, for a total of L×K transmit beam weights, to form K beams on the user downlink 310.

In some cases, significant processing power may be required within the satellite to control the phase and gain of each antenna element used to form the beam. Such processing power increases the complexity of the satellite. In some cases, the satellite can operate using ground-based beamforming (GBBF) to reduce the complexity of the satellite while still providing the advantages of electronically forming narrow beams.

FIG4 is a diagram of an example of a satellite communication system 400 with forward GBBF. GBBF is performed on the forward user link 317 via an L-element array similar to that described above. The phase/amplitude of the signal transmitted on the user link 317 is weighted to form a beam. The feeder link 319 uses a single feed per beam (SFPB) scheme, where each receive and transmit antenna element of the antenna 324 is dedicated to one feeder link beam.

Prior to transmission from one or more GWs 304, for each of the K forward feeder link beams, a transmit beamformer 321 applies a corresponding one of K beam weight vectors, each of length L, to each of the K signals to be transmitted. Determining K vectors of L weights and applying them to the signals enables the formation of K forward beams on the ground for forward user downlinks 317. On feeder uplink 319, each of the L different signals is multiplexed into a frequency division multiplexed (FDM) signal by multiplexer 323 (or the like). Each FDM signal is transmitted by GW 304 over feeder link 319 to one of the receive antenna elements in antenna 324. An FDM receiver 325 on satellite 327 receives the signal from antenna 324. An analog-to-digital converter (A/D) 326 converts the received analog signal into a digital signal. Digital channel processor 328 demultiplexes the FDM signals, each of which is appropriately weighted by beamformer 321 for transmission through one of the L elements of the transmit antenna element array of transmit antenna 329. Digital channel processor 328 outputs these signals to digital-to-analog converter (D/A) 331 for conversion back to analog form. The analog output of D/A 331 is upconverted and amplified by upconverter (U/C) and gain stage 330 and transmitted by the associated element of transmit antenna 329. The reverse complementary process occurs for the return beam. Note that in this type of system, the FDM feeder link requires up to L times the bandwidth of the user beam, making systems with wide data bandwidths or systems with a large number of elements L impractical.

End-to-end beamforming system

The end-to-end beamforming system described herein forms an end-to-end beam through an end-to-end repeater. The end-to-end beamforming system can connect a user terminal to a data source/data sink. In contrast to the beamforming system described above, in an end-to-end beamforming system, beam weights are calculated at a central processing system (CPS) and the end-to-end beam weights are applied within a ground network (rather than at a satellite). Signals within the end-to-end beam are transmitted and received at an array of access nodes (ANs), which may be satellite access nodes (SANs). As described above, any suitable type of end-to-end repeater can be used in the end-to-end beamforming system, and different types of ANs can be used to communicate with different types of end-to-end repeaters. The term "center" means that the CPS is accessible to the ANs involved in signal transmission and/or reception, and does not refer to a specific geographical location where the CPS resides. The beamformer within the CPS computes a set of end-to-end beam weights that take into account: (1) the wireless signal uplink path up to the end-to-end repeater; (2) the receive/transmit signal path through the end-to-end repeater; and (3) the wireless signal downlink path from the end-to-end repeater. The beam weights can be mathematically represented as a matrix. As described above, OBBF and GBBF satellite systems have a beam weight vector dimension set by the number of antenna elements on the satellite. In contrast, the end-to-end beam weight vector has a dimension set by the number of ANs rather than the number of elements on the end-to-end repeater. Generally speaking, the number of ANs is different from the number of antenna elements on the end-to-end repeater. In addition, the formed end-to-end beam does not terminate at the transmit or receive antenna elements of the end-to-end repeater. Instead, the formed end-to-end beam is effectively relayed because the end-to-end beam has an uplink signal path, a relay signal path (via the satellite or other suitable end-to-end repeater), and a downlink signal path.

Because end-to-end beamforming takes into account both the user link and the feeder link (as well as the end-to-end repeater), only a single set of beam weights is required to form a desired end-to-end user beam (e.g., a forward user beam or a return user beam) in a particular direction. Thus, one set of end-to-end forward beam weights (hereinafter referred to as the forward beam weights) results in the combination of signals transmitted from the AN, through the forward uplink, through the end-to-end repeater, and through the forward downlink to form an end-to-end forward user beam (hereinafter referred to as the forward user beam). Conversely, signals transmitted from the return user, through the return uplink, through the end-to-end repeater, and back downlink have end-to-end return beam weights (hereinafter referred to as the return beam weights), which are applied to form an end-to-end return user beam (hereinafter referred to as the return user beam). Under some conditions, distinguishing the characteristics of the uplink and downlink may be very difficult or impossible. Therefore, the formed feeder link beam, the formed user beam directionality and the individual uplink and downlink carrier-to-interference ratio (C/I) may no longer have their traditional role in system design, while the concepts of uplink and downlink signal-to-noise ratio (Es/No) and end-to-end C/I may still be relevant.

5 is a diagram of an exemplary end-to-end beamforming system 500. System 500 includes: a ground segment 502; an end-to-end repeater 503; and a plurality of user terminals 517. Ground segment 502 includes M ANs 515 that are geographically distributed over an AN area. ANs 515 cooperate to transmit forward uplink signals 521 to form user beams 519, and return downlink signals 527 are jointly processed to recover return uplink transmissions 525. A group of ANs 515 that are within different (e.g., geographically separated or otherwise orthogonally configured) AN areas and that cooperate to perform end-to-end beamforming for forward and/or return user beams is referred to herein as an "AN cluster." In some examples, multiple AN clusters in different AN areas may also cooperate. An AN cluster may also be referred to as an "AN field" or "SAN field." AN 515 and user terminal 517 can be collectively referred to as earth receivers, earth transmitters or earth transceivers according to the specific functions discussed, because they are located on or near the earth and both transmit and receive signals. In some cases, user terminal 517 and/or AN 515 can be located in an air vehicle, a water vehicle or installed on a land vehicle, etc. In some cases, user terminal 517 can be geographically distributed. AN 515 can be geographically distributed. AN 515 exchanges signals with CPS 505 in ground segment 502 via distribution network 518. CPS 505 is connected to a data source (not shown), such as the Internet, a video head end or other such entities.

A user terminal 517 may be grouped with other user terminals 517 in the vicinity (e.g., as shown by user terminals 517a and 517b). In some cases, such user terminal groups 517 are served by the same user beam and therefore reside within the same geographic forward and/or return user beam coverage area 519. A user terminal 517 is within a user beam if it is within the coverage area served by that user beam. Although only one such user beam coverage area 519 is shown in FIG5 as having more than one user terminal 517, in some cases, a user beam coverage area 519 may have any suitable number of user terminals 517. Furthermore, the depiction in FIG5 is not intended to indicate the relative sizes of different user beam coverage areas 519. That is, the user beam coverage areas 519 may all be of approximately the same size. Alternatively, the user beam coverage areas 519 may be of different sizes, with some being much larger than others. In some cases, the number of ANs 515 is not equal to the number of user beam coverage areas 519.

The end-to-end repeater 503 wirelessly relays signals between a user terminal 517 and multiple network access nodes (such as AN515 shown in FIG5 ). The end-to-end repeater 503 has multiple signal paths. For example, each signal path may include at least one receive antenna element, at least one transmit antenna element, and at least one transponder (as discussed in detail below). In some cases, the multiple receive antenna elements are arranged to receive signals reflected by a receive reflector to form a receive antenna array. In some cases, the multiple transmit antenna elements are arranged to transmit signals and thus form a transmit antenna array.

In some cases, the end-to-end repeater 503 is arranged on a satellite. In other cases, the end-to-end repeater 503 is arranged on an aerial vehicle, a blimp, a tower, an underwater structure, or any other suitable structure or vehicle in which the end-to-end repeater 503 can reside. In some cases, the system uses different frequency ranges (in the same or different frequency bands) for uplink and downlink. In some cases, the feeder link and the user link are in different frequency ranges. In some cases, the end-to-end repeater 503 acts as a passive or active reflector.

As described herein, various features of the end-to-end repeater 503 implement end-to-end beamforming. One feature is that the end-to-end repeater 503 includes multiple transponders that induce multipath between the AN 515 and the user terminal 517 in the case of an end-to-end beamforming system. Another feature is that the antenna (e.g., one or more antenna subsystems) of the end-to-end repeater 503 facilitates end-to-end beamforming, such that when appropriately beam-weighted signals are transmitted through the multipath induced by the end-to-end repeater 503, forward and/or return user beams are formed. For example, during forward communication, each of the multiple transponders receives a corresponding superimposed composite of (beam-weighted) forward uplink signals 521 from multiple (e.g., all) ANs 515 (referred to herein as a composite input forward signal), and the transponder outputs a corresponding composite signal (referred to herein as a forward downlink signal). Each of the forward downlink signals can be a unique composite of beam-weighted forward uplink signals 521, which, when transmitted by the transmit antenna elements of the end-to-end repeater 503, are superimposed to form a user beam 519 at a desired location (e.g., in this case, a recovery location within the forward user beam). Return end-to-end beamforming is similarly implemented. Thus, the end-to-end repeater 503 can cause multiple superpositions to occur, thereby achieving end-to-end beamforming on the induced multipath channel.

Return data

FIG6 is a diagram of an exemplary model of the signal path of a signal carrying return data on an end-to-end return link. Return data is data flowing from user terminal 517 to AN 515. The signals in FIG6 flow from right to left. These signals originate from user terminal 517. User terminal 517 transmits a return uplink signal 525 (which has a return user data stream) to end-to-end repeater 503. The return uplink signal 525 from user terminal 517 in K user beam coverage area 519 is received by an array of L receive/transmit signal paths 1702. In some cases, the uplink coverage area of end-to-end repeater 503 is defined by the set of points from which all L receive antenna elements 406 can receive signals. In other cases, the repeater coverage area is defined by the set of points from which a subset of the L receive antenna elements 406 (e.g., greater than one but less than the desired number of all) can receive signals. Similarly, in some cases, the downlink coverage area is defined by the set of points to which all L transmit antenna elements 409 can reliably transmit signals. In other cases, the downlink coverage area of the end-to-end repeater 503 is defined by the set of points to which a subset of transmit antenna elements 409 can reliably transmit signals. In some cases, the size of the subset of receive antenna elements 406 or transmit antenna elements 409 is at least four. In other cases, the size of the subset is 6, 10, 20, 100, or any other number that provides the desired system performance.

For simplicity, some examples are described and/or illustrated as all L receive antenna elements 406 receiving signals from all points in the uplink coverage area and/or all L transmit antenna elements 409 transmitting signals to all points in the downlink coverage area. Such description is not intended to require that all L elements receive and/or transmit signals at significant signal levels. For example, in some cases, a subset of the L receive antenna elements 406 receives uplink signals (e.g., receiving return uplink signals 525 from user terminal 517 or forward uplink signals 521 from AN 515) such that the subset of receive antenna elements 406 receives the uplink signals at a signal level close to the peak received signal level of the uplink signals (e.g., not significantly less than the signal level corresponding to the uplink signal with the highest signal level); the other receive antenna elements in the L receive antenna elements 406 that are not in the subset receive the uplink signals at significantly lower levels (e.g., well below the peak received signal level of the uplink signals). In some cases, the uplink signal received by each receive antenna element of the subset is at a signal level within 10 dB of the maximum signal level received by any receive antenna element 406. In some cases, the subset includes at least 10% of receive antenna elements 406. In some cases, the subset includes at least 10 receive antenna elements 406.

Similarly, on the transmit side, a subset of the L transmit antenna elements 409 transmits downlink signals to an Earth-based receiver (e.g., a return downlink signal 527 to the AN 515 or a forward downlink signal 522 to the user terminal 517) such that the subset of transmit antenna elements 409 transmits the downlink signals to the receiver at a received signal level that is close to the peak transmitted signal level of the downlink signals (e.g., not significantly less than the signal level corresponding to the downlink signal with the highest received signal level). Other transmit antenna elements of the L transmit antenna elements 409 that are not in the subset transmit downlink signals such that the downlink signals are received at a significantly lower level (e.g., much lower than the peak transmitted signal level of the downlink signals). In some cases, the signal level is within 3 dB of the signal level corresponding to the peak gain of the transmit antenna elements 409. In other cases, the signal level is within 6 dB of the signal level corresponding to the peak gain of the transmit antenna elements 409. In other cases, the signal level is within 10 dB of the signal level corresponding to the peak gain of the transmit antenna elements 409.

In some cases, the signals received by each receive antenna element 406 originate from the same source (e.g., one of the user terminals 517) due to overlap in the receive antenna patterns of each receive antenna element. However, in some cases, there may be multiple points within the end-to-end repeater coverage area where user terminals are located and from which not all receive antenna elements can receive signals. In some such cases, there may be a significant number of receive antenna elements that do not (or are unable to) receive signals from user terminals located within the end-to-end repeater coverage area. However, as described herein, multipath induced by the end-to-end repeater 503 can rely on receiving signals by at least two receive elements.

As shown in Figure 6 and discussed in more detail below, in some cases, the receive/transmit antenna path 1702 includes a receive antenna element 406, a transponder 410, and a transmit antenna element 409. In such a case, a return uplink signal 525 is received by each of the multiple transponders 410 via a corresponding receive antenna element 406. The output of each receive/transmit signal path 1702 is a corresponding synthesized return downlink signal 527 corresponding to the received return uplink signal. The return downlink signal is generated by the receive/transmit signal path 1702. The return downlink signal 527 is transmitted to an array of M ANs 515. In some cases, the ANs 515 are placed at geographically distributed locations (e.g., receiving or recovery locations) throughout the end-to-end repeater coverage area. In some cases, each transponder 410 couples a corresponding one of the receive antenna elements 406 to a corresponding one of the transmit antenna elements 409. Thus, there are L different ways for a signal to reach a particular AN 515 from a user terminal 517 located within a user beam coverage area 519. This creates L paths between the user terminal 517 and the AN 515. The L paths between one user terminal 517 and one AN 515 are collectively referred to as an end-to-end return multipath channel 1908 (see FIG8 ). Thus, receiving a return uplink signal 525 from a transmission location within the user beam coverage area 519 via the L transponders 410 generates L return downlink signals 527, each transmitted from one of the transponders 410 (i.e., traversing L collocated communication paths). Each end-to-end return multipath channel 1908 is associated with an uplink radiation matrix _Ar , a vector in the payload matrix E, and a vector in the downlink radiation matrix _Ct . Note that due to the antenna element coverage pattern, in some cases, some of the L paths may have relatively less energy (e.g., 6 dB, 10 dB, 20 dB, 30 dB, or any other suitable power ratio less than the other paths). A superposition 1706 of return downlink 527 signals is received at each AN 515 (e.g., at M geographically distributed receiving or recovery locations). Each return downlink signal 527 includes a superposition of multiple transmitted return downlink signals 527, thereby generating a corresponding composite return signal. The corresponding composite return signal is coupled to the return beamformer 531 (see Figures 5 and 29).

7 illustrates an exemplary end-to-end return link 523 from one user terminal 517 located within user beam coverage area 519 to AN 515. Return uplink signal 525 transmitted from user terminal 517 is received by the array of L receive antenna elements 406 at end-to-end repeater 503 (e.g., or by a subset of the L receive antenna elements 406).

Ar is the L×K return uplink radiation matrix. The values of the return uplink radiation matrix model the signal path from the reference location in the user beam coverage area 519 to the end-to-end repeater receive antenna element 406. For example, Ar _L,1 is the value of one element of the return uplink radiation matrix (i.e., the amplitude and phase of the path) from the reference location in the first user beam coverage area 519 to the Lth receive antenna element. In some cases, all values in the return uplink radiation matrix Ar may be nonzero (e.g., there is a significant signal path from the reference location to each receive antenna element of the receive antenna array).

E (dimension L×L) is the payload matrix and provides a model (amplitude and phase) of the paths from the receive antenna elements 406 to the transmit antenna elements 409. As used herein, the "payload" of an end-to-end repeater 503 generally includes the set of components of the end-to-end repeater 503 that affect and/or are affected by signal communications when received by, relayed by, and transmitted from the end-to-end repeater 503. For example, an end-to-end repeater payload may include antenna elements, reflectors, transponders, etc.; however, an end-to-end repeater may also include batteries, solar cells, sensors, and/or other components that are not considered part of the payload herein (because they do not affect the signal during normal operation). Treating the set of components as the payload enables the overall impact of the end-to-end repeater to be mathematically modeled as a single payload matrix E. The primary paths from each receive antenna element 406 to each corresponding transmit antenna element 409 are modeled by the values located on the diagonal of the payload matrix E. Assuming there is no crosstalk between the receive/transmit signal paths, the off-diagonal values of the payload matrix are zero. In some cases, crosstalk may not be zero. Isolating the signal paths from each other will minimize crosstalk. In some cases, since crosstalk is negligible, the payload matrix E can be estimated using a diagonal matrix. In some cases, the off-diagonal values of the payload matrix (or any other suitable values) may be considered zero, even if there are some signal effects corresponding to those values, to reduce mathematical complexity and/or for other reasons.

Ct is an M×L return downlink radiation matrix. The values of the return downlink radiation matrix model the signal path from the transmit antenna element 409 to the antenna 515. For example, Ct _3,2 is the value of the return downlink radiation matrix (e.g., the gain and phase of the path) from the second transmit antenna element 409 _b to the third antenna 515 _c . In some cases, all values of the downlink radiation matrix Ct can be non-zero. In some cases, some values of the downlink radiation matrix Ct are substantially zero (e.g., the antenna pattern established by the corresponding transmit antenna element 409 of the transmit antenna array causes the transmit antenna element 409 to not transmit a useful signal to some antenna 515).

As can be seen in Figure 7, the end-to-end return multipath channel from a user terminal 517 in a particular user beam coverage area 519 to a particular AN 515 is the sum of L different paths. The end-to-end return multipath channel has multipath induced by the L unique paths passing through the transponder 410 in the end-to-end repeater. As with many multipath channels, the amplitudes and phases of the paths can add up constructively (constructively) to produce a large end-to-end channel gain, or destructively (destructively) to produce a low end-to-end channel gain. When the number L of different paths between a user terminal and an AN is large, the end-to-end channel gain can exhibit a Rayleigh amplitude distribution. With this distribution, it is common to see some end-to-end channel gains from a particular user terminal 517 to a particular AN 515 that are 20 dB or more lower than the average channel gain level from the user terminal 517 to the AN 515. This end-to-end beamforming system intentionally induces a multipath environment for the end-to-end path from any user terminal to any AN.

FIG8 is a simplified illustration of an exemplary model of all end-to-end return multipath channels from a user beam coverage area 519 to an AN 515. There are M×K such end-to-end return multipath channels in the end-to-end return link (i.e., M end-to-end return multipath channels from each of the K user beam coverage areas 519). Channel 1908 connects a user terminal in one user beam coverage area 519 to one AN 515 via L different receive/transmit signal paths 1702, each path passing through a different one of the L receive/transmit signal paths (and associated transponders) of the repeater. Although this effect is referred to herein as "multipath," this multipath differs from conventional multipath (e.g., multipath in mobile radio or multiple-input, multiple-output (MIMO) systems) because the multipath herein is intentionally induced by (and affected by, as described herein, by) the L receive/transmit signal paths. Each of the M×K end-to-end return multipath channels originating from a user terminal 517 within a particular user beam coverage area 519 can be modeled by an end-to-end return multipath channel. Each such end-to-end return multipath channel is from a reference (or recovery) position within the user beam coverage area 519 to one of the ANs 515.

Each of the M×K end-to-end return multipath channels 1908 can be modeled separately to calculate the corresponding elements of the M×K return channel matrices Hret. The return channel matrix Hret has K vectors, each having a dimension equal to M, so that each vector models the end-to-end return channel gain of the multipath communication between the reference position in one of the corresponding K user beam coverage areas and the M AN 515. Each end-to-end return multipath channel couples one of the M AN 515 with the reference position within one of the K return user beams via L transponders 410 (see Figure 7). In some cases, only a subset of the L transponders 410 on the end-to-end repeater 503 is used to generate the end-to-end return multipath channel (i.e., only one subset is considered to be in the signal path by contributing significant energy to the end-to-end return multipath channel). In some cases, the number K of user beams is greater than the number L of transponders in the signal path of the end-to-end return multipath channel. Furthermore, in some cases, the number of ANs, M, is greater than the number of transponders, L, in the signal path of the end-to-end return multipath channel 1908. In one example, element Hret _4,2 of the return channel matrix Hret is associated with the channel from a reference location in the second user beam coverage area 1903 to the fourth AN 1901. Matrix Hret models the end-to-end channel as a matrix product Ct×E×Ar (see FIG6 ). Each element in Hret models the end-to-end gain of an end-to-end return multipath channel 1908. Due to the multipath nature of the channel, the channel may experience deep fades. The return user beam may be formed by the CPS 505. The CPS 505 calculates return beam weights based on the model of these M×K channel paths and forms the return user beam by applying the return beam weights to multiple composite return signals, each weight being calculated for each end-to-end return multipath channel coupling a user terminal 517 in a user beam coverage area to one of the multiple ANs 515. In some cases, the return beam weights are calculated before the composite return signal is received. There is an end-to-end return link from each of the K user beam coverage areas 519 to the M ANs 515. The weighting (i.e., complex relative phase/amplitude) of each signal received by the M ANs 515 allows the beamforming capabilities of the CPS 505 within the ground segment 502 to be used to combine these signals to form a return user beam. The calculation of the beam weight matrix is used to determine how to weight each end-to-end return multipath channel 1908 to form multiple return user beams, as described in more detail below. The user beam is not formed by directly adjusting the relative phase and amplitude of the signal transmitted by one end-to-end relay antenna element relative to the phase and amplitude of the signals transmitted by other end-to-end relay antenna elements. Instead, the user beam is formed by applying the weights associated with the M×K channel matrix to the M AN signals. It is the multiple ANs that provide the receive path diversity (single reflector (user terminal) to multiple receivers (ANs)) to enable successful transmission of information from any user terminal in the presence of an intentionally induced multipath channel.

Forward data

FIG9 illustrates an exemplary model of the signal paths of signals carrying forward data on end-to-end forward link 501. Forward data is data flowing from AN 515 to user terminal 517. Signals in this figure flow from right to left. Signals originate from M ANs 515 located within the coverage area of end-to-end repeater 503. There are K user beam coverage areas 519. Signals from each AN 515 are relayed by L receive/transmit signal paths 2001.

Receive/transmit signal path 2001 transmits the relayed signal to a user terminal 517 in user beam coverage area 519. Therefore, there may be L different ways for a signal to reach a user terminal 517 located in user beam coverage area 519 from a particular AN 515. This results in L paths between each AN 515 and each user terminal 517. Note that due to the antenna element coverage pattern, some of the L paths may have less energy than other paths.

FIG10 illustrates an exemplary end-to-end forward link 501 coupling a plurality of access nodes at geographically distributed locations with a user terminal 517 in a user beam (e.g., at a recovery location within a user beam coverage area 519) via an end-to-end repeater 503. In some cases, a forward data signal is received at a beamformer before generating a forward uplink signal. Multiple forward uplink signals are generated at the beamformer and transmitted to multiple ANs 515. For example, each AN 515 receives a unique (beam-weighted) forward uplink signal generated according to a beam weight corresponding to that AN 515. Each AN 515 has an output for transmitting a forward uplink signal via one of M uplinks. Each forward uplink signal includes a forward data signal associated with a forward user beam. The forward data signal is "associated" with a forward user beam because it is intended to be received by a user terminal 517 served by the user beam. In some cases, the forward data signal includes two or more user data streams. The user data streams may be multiplexed together by time or frequency division multiplexing, etc. In some cases, each user data stream is for transmission to one or more of multiple user terminals within the same forward user beam.

As discussed in more detail below, each forward uplink signal is transmitted in a time-synchronized manner via its corresponding transmit AN 515. The forward uplink signal 521 transmitted from the AN 515 is received by multiple transponders 410 on the end-to-end repeater 503 via the receive antenna elements 406 on the end-to-end repeater 503. The superposition 550 of the forward uplink signals 521 received from the geographically distributed locations produces a composite input forward signal 545. Each transponder 410 receives the composite input forward signal 545 simultaneously. However, due to the differences in the position of the receive antenna elements 406 associated with each transponder 401, each transponder 410 will receive a signal with slightly different timing.

Cr is the L×M forward uplink radiation matrix. The values of the forward uplink radiation matrix model the signal path (amplitude and phase) from AN 515 to the receiving antenna element 406. E is the L×L payload matrix and provides a model of the transponder signal path from the receiving antenna element 406 to the transmitting antenna element 409. The diagonal values of the payload matrix model the direct path gain from each receiving antenna element 406 through a corresponding one of the multiple transponders to each corresponding transmitting antenna element 409. As described above with respect to the return link, assuming no crosstalk between the antenna elements, the non-diagonal elements of the payload matrix are zero. In some cases, crosstalk may not be zero. Isolating the signal paths from each other will minimize crosstalk. In this example, each transponder 410 couples a corresponding one of the receiving antenna elements 406 to a corresponding one of the transmitting antenna elements 409. Thus, the forward downlink signal 522 output from each transponder 410 is transmitted by each of the plurality of transponders 410 via the transmit antenna element 409 (see FIG. 9 ), such that the forward downlink signal 522 forms a forward user beam (by constructively and destructively adding to form a beam in the desired geographic recovery location). In some cases, multiple user beams are formed, each corresponding to a geographic user beam coverage area 519 serving a respective set of user terminals 517 within the user beam coverage area 519. The path from the first transmit antenna element 409a (see FIG. 10 ) to the reference (or recovery) location in the first user beam coverage area 519 is given by the At ₁₁ value of the forward downlink radiation matrix. As noted with respect to the return link, this end-to-end beamforming system intentionally induces a multipath environment for the end-to-end path from any AN 515 to any user terminal 517. In some cases, a subset of the transmit antenna elements 409 transmits a forward downlink signal 522 with significant energy to the user terminal 517. The user terminal 517 (or more generally, a reference or recovered location in the user beam coverage area 519 for reception and/or recovery) receives a plurality of forward downlink signals 522 and recovers at least a portion of a forward data signal from the received plurality of forward downlink signals 522. The transmitted forward downlink signals 522 can be received by the user terminal 517 at a signal level within 10 dB of the maximum signal level of any other signal transmitted by the transmit antenna elements 409 in the subset. In some cases, the subset of transmit antenna elements includes at least 10% of the plurality of transmit antenna elements present in the end-to-end repeater 503. In some cases, the subset of transmit antenna elements includes at least 10 transmit antenna elements, regardless of the number of transmit antenna elements 409 present in the end-to-end repeater 503. In one case, receiving the plurality of forward downlink signals includes receiving a superposition 551 of the plurality of forward downlink signals.

FIG11 is a simplified illustration of a model of the entire end-to-end forward multipath channel 2208 from M ANs 515 to K user beam coverage areas 519. As shown in FIG11 , an end-to-end forward multipath channel 2208 couples each AN 515 to each user beam coverage area 519. Each channel 2208 from an AN 515 to a user beam coverage area 519 has multipath induced by L unique paths from the AN 515 through multiple transponders to the user beam coverage area 519. Thus, the K×M multipath channels 2208 can be individually modeled, and the model of each multipath channel serves as an element of a K×M forward channel matrix Hfwd. The forward channel matrix Hfwd has M vectors, each of which has a dimension equal to K, such that each vector models the end-to-end forward gain of multipath communication between a corresponding one of the M ANs 515 and a reference (or recovery) location in the K forward user beam coverage areas. Each end-to-end forward multipath channel couples one of the M ANs 515 to a user terminal 517 served by one of the K forward user beams via L transponders 410 (see FIG. 10 ). In some cases, only a subset of the L transponders 410 on the end-to-end repeater 503 is used to generate the end-to-end forward multipath channel (i.e., in the signal path of the end-to-end forward multipath channel). In some cases, the number of user beams, K, is greater than the number of transponders, L, in the signal path of the end-to-end forward multipath channel. Furthermore, in some cases, the number of ANs, M, is greater than the number of transponders, L, in the signal path of the end-to-end forward multipath channel.

H-fwd can represent the end-to-end forward link as the matrix product At×E×Cr. Each element in Hfwd is the end-to-end forward gain due to the multipath nature of the path and may be subject to deep fades. Appropriate beam weights can be calculated by the CPS 505 within the ground segment 502 for each of the multiple end-to-end forward multipath channels 2208 to form a forward user beam from the set of M ANs 515 to each user beam coverage area 519. Multiple ANs 515 provide transmission path diversity to a single receiver (user terminal) by using multiple transmitters (ANs), enabling successful transmission of information to any user terminal 517 in the presence of intentionally induced multipath channels.

Combined forward and return data

Figure 12 shows an exemplary end-to-end repeater that supports both forward communication and return communication. In some cases, both the end-to-end forward link 501 and the end-to-end return link 523 can use the same end-to-end relay signal path (e.g., a set of receiving antenna elements, transponders, and transmitting antenna elements). Some other cases include forward link transponders and return link transponders that may or may not share receiving antenna elements and transmitting antenna elements. In some cases, system 1200 has multiple ANs and user terminals that are located in the same general geographic area 1208 (the general geographic area can be, for example, a specific state, an entire country, a region, an entire visible area, or any other suitable geographic area 1208). A single end-to-end repeater 1202 (set on a satellite or any other suitable end-to-end repeater) receives a forward uplink signal 521 from the AN and transmits a forward downlink signal 522 to the user terminal. At alternating times or frequencies, the end-to-end repeater 1202 also receives return uplink signals 525 from the user terminal and transmits return downlink signals 527 to the AN. In some cases, the end-to-end repeater 1202 is shared between the forward data and the return data using techniques such as time domain multiplexing, frequency domain multiplexing, etc. In some cases, time domain multiplexing between the forward data and the return data uses the same frequency range: the forward data is transmitted during a different (non-overlapping) time interval than the time interval used to transmit the return data. In some cases, with frequency domain multiplexing, different frequencies are used for the forward data and the return data, thereby allowing concurrent, non-interfering transmission of the forward data and the return data.

Figure 13 is a diagram that the uplink frequency range is divided into two parts. The lower limit frequency (left) part of the range is allocated to the forward uplink, and the upper limit frequency (right) part of the range is allocated to the return uplink. The uplink range can be divided into a plurality of parts of forward data or return data.

Figure 14 is a diagram of forward data and return data being time-division multiplexed. A data frame cycle is shown, wherein forward data is transmitted during the first time interval of the frame and return data is transmitted during the last time interval of the frame. An end-to-end repeater receives from one or more access nodes during a first (forward) receive time interval and receives from one or more user terminals during a second (return) receive time interval that does not overlap with the first receive time interval. An end-to-end repeater transmits to one or more user terminals during a first (forward) transmit time interval and transmits to one or more access nodes during a second (return) transmit time interval that does not overlap with the first receive time interval. The data frame may repeat or may change dynamically. A frame may be divided into multiple (e.g., non-contiguous) parts for forward data and return data.

End-to-end beamforming satellite

In some cases, the end-to-end repeater 503 is implemented on a satellite, such that the satellite is used to relay signals from an AN (which in such cases may be referred to as a satellite access node (SAN)) to a user terminal, and vice versa. In some cases, the satellite is in geostationary orbit. An exemplary satellite operating as an end-to-end repeater has an array of receive antenna elements, an array of transmit antenna elements, and multiple transponders connecting the receive antenna elements to the transmit antenna elements. These arrays have a large number of antenna elements with overlapping antenna element coverage areas, similar to traditional single-link phased array antennas. It is the overlapping antenna element coverage areas on both the transmit antenna elements and the receive antenna elements that creates the multipath environment described previously. In some cases, the antenna patterns established by the corresponding antenna elements are identical to the antenna patterns that produce overlapping antenna element coverage areas (e.g., overlapping component beam antenna patterns). For the purposes of this disclosure, the term "identical" means that they essentially follow the same power distribution at a given set of points in space, allowing the antenna elements to serve as reference points for locating points in space. However, they are rarely identical. Therefore, patterns with relatively small deviations from one pattern to another are within the scope of "identical" patterns. In other cases, the receive component beam antenna patterns may not be identical, and in fact may be significantly different.Such antenna patterns may also result in an overlap of antenna element coverage areas, however, the resulting coverage areas will not be identical.

Antenna types include, but are not limited to, array-fed reflectors, confocal arrays, direct radiating arrays, and other forms of antenna arrays. Each antenna may be a system that includes additional optical components, such as one or more reflectors, to assist in receiving and/or transmitting signals. In some cases, satellites include components to assist in system timing alignment and beamforming calibration.

15 is a diagram of an exemplary satellite 1502 that can be used as an end-to-end repeater 503. In some cases, satellite 1502 has an array-fed reflector transmit antenna 401 and an array-fed reflector receive antenna 402. Receive antenna 402 includes a receive reflector (not shown) and an array of receive antenna elements 406. Receive antenna element 406 is illuminated by the receive reflector. Transmit antenna 401 includes a transmit reflector (not shown) and an array of transmit antenna elements 409. Transmit antenna elements 409 are arranged to illuminate the transmit reflector. In some cases, the same reflector is used for both reception and transmission. In some cases, one port of an antenna element is used for reception and the other port is used for transmission. Some antennas are capable of distinguishing signals with different polarizations. For example, an antenna element may include four waveguide ports, one for right-hand circular polarization (RHCP) reception, one for left-hand circular polarization (LHCP) reception, one for RHCP transmission, and one for LHCP transmission, respectively. In some cases, dual polarization can be used to increase the capacity of the system; in other cases, single polarization can be used to reduce interference (eg, to utilize other systems that use different polarizations).

Exemplary satellite 1502 also includes multiple transponders 410. Transponder 410 connects the output from one receive antenna element 406 to the input of transmit antenna element 409. In some cases, transponder 410 amplifies the received signal. Each receive antenna element outputs a unique received signal. In some cases, a subset of receive antenna elements 406 receives signals from an Earth-based transmitter, such as user terminal 517 in the case of a return link signal or network access 515 in the case of a forward link signal. In some cases, the gain of each receive antenna element in the subset for the received signal is within a relatively small range. In some cases, the range is 3 dB. In other cases, the range is 6 dB. In other cases, the range is 10 dB. Thus, the satellite receives a signal at each of the satellite's multiple receive antenna elements 406, the communication signal originating from the Earth-based transmitter, such that the subset of receive antenna elements 406 receives the communication signal at a signal level that is substantially no less than the signal level corresponding to the peak gain of receive antenna element 406.

In some cases, at least 10 transponders 410 are disposed within satellite 1502. In another case, at least 100 transponders 410 are disposed within satellite 1502. In another case, the number of transponders per polarity may be in the range of 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, or a number therebetween or greater. In some cases, transponder 410 includes a low noise amplifier (LNA) 412, a frequency converter and associated filter 414, and a power amplifier (PA) 420. In some cases where the uplink frequency and the downlink frequency are the same, the transponder does not include a frequency converter. In other cases, multiple receive antenna elements operate at a first frequency. Each receive antenna element 406 is associated with a transponder 410. Receive antenna element 406 is coupled to the input of LNA 412. Thus, the LNA independently amplifies the unique receive signal provided by the receive antenna element associated with transponder 410. In some cases, the output of LNA 412 is coupled to a frequency converter 414. Frequency converter 414 converts the amplified signal to a second frequency.

The output of the transponder is coupled to an associated one of the transmit antenna elements. In these examples, there is a one-to-one relationship between the transponder 410, the associated receive antenna element 406, and the associated transmit antenna element 409, such that the output of each receive antenna element 406 is connected to the input of one and only one transponder, and the output of that transponder is connected to the input of one and only one transmit antenna element.

FIG16 is a diagram of an exemplary transponder 410. The transponder 410 can be an example of a transponder of the end-to-end repeater 503 as described above (e.g., satellite 1502 of FIG15 ). In this example, in addition to the LNA 412, the frequency converter and associated filter 414, and the power amplifier (PA) of the transponder 410, the transponder also includes a phase shifter 418. As shown in FIG16 , the exemplary transponder 410 can also be coupled to a phase shift controller 427. For example, the phase shift controller 427 can be coupled (directly or indirectly) to each of some or all of the transponders of the end-to-end repeater 503 so that the phase shift controller 427 can individually set the phase of each transponder. The phase shifter can, for example, facilitate calibration, as described below.

antenna

To create a multipath environment, the antenna element coverage area can overlap with the antenna element coverage area of at least one other antenna element of the same polarization, frequency, and type (transmit or receive, respectively). In some cases, multiple receive component beam antenna patterns that can operate with the same receive polarization and receive frequency (e.g., at least a portion of the receive frequencies are common) overlap with each other. For example, in some cases, at least 25% of the receive component beam antenna pattern that can operate with the same receive polarization and receive frequency (e.g., at least a portion of the receive frequencies are common) overlaps with at least five other receive component beam antenna patterns of the receive antenna element. Similarly, in some cases, at least 25% of the transmit component beam antenna pattern that can operate with the same transmit polarization and transmit frequency (e.g., at least a portion of the transmit frequencies are common) overlaps with at least five other transmit component beam antenna patterns. The amount of overlap will vary from system to system. In some cases, at least one of the receive antenna elements 406 has a component beam antenna pattern that overlaps with the antenna patterns of other receive antenna elements 406 that may operate at the same receive frequency (e.g., at least a portion of the receive frequency is common) and at the same receive polarization. Thus, at least some of the multiple receive antenna elements are capable of receiving the same signal from the same source. Similarly, at least one of the transmit antenna elements 409 has a component beam antenna pattern that overlaps with the antenna patterns of other transmit antenna elements 409 that may operate at the same transmit frequency (e.g., at least a portion of the receive frequency is common) and at the same transmit polarization. Thus, at least some of the multiple transmit antenna elements are capable of transmitting signals having the same frequency with the same polarization to the same receiver. In some cases, the overlapping component beam antenna patterns may have gains that differ by less than 3 dB (or any other suitable value) within a common geographic area. Antenna elements (whether receive or transmit) may have wide component beam antenna patterns and, therefore, have relatively wide antenna element coverage areas. In some cases, signals transmitted by an earth-based transmitter, such as a user terminal 517 or access node 515, are received by all receive antenna elements 406 of an end-to-end repeater (e.g., a satellite). In some cases, a subset of elements 406 receives signals from an earth-based transmitter. In some cases, the subset includes at least 50% of the transmit antenna elements. In other cases, the subset includes at least 75% of the transmit antenna elements. In other cases, the subset includes at least 90% (e.g., up to and including all) of the receive antenna elements. Different subsets of receive antenna elements 406 may receive signals from different earth-based transmitters. Similarly, in some cases, a subset of elements 409 transmits signals that can be received by a user terminal 517. In some cases, the subset includes at least 50% of the transmit antenna elements. In other cases, the subset includes at least 75% of the transmit antenna elements. In other cases, the subset includes at least 90% (e.g., up to and including all) of the transmit antenna elements. Different subsets of elements 409 may transmit signals received by different user terminals. Furthermore, a user terminal may be within the coverage area 519 of the formed user beams. For purposes of this disclosure, an antenna pattern is a distribution pattern of energy transmitted to or received from an antenna. In some cases, energy may be radiated directly from/to an antenna element. In other cases, energy from one or more transmitting antenna elements may be reflected by one or more reflectors that shape the antenna element pattern. Similarly, a receiving element may receive energy directly or after the energy is reflected off one or more reflectors. In some cases, an antenna may be comprised of several elements, each having a component beam antenna pattern that establishes a coverage area for the corresponding antenna element. Similarly, all or a subset of the receive and transmit antenna elements that receive and transmit signals to an AN 515 may overlap, such that multiple receive antenna elements receive signals from the same AN 515 and/or multiple transmit antenna elements transmit signals to the same AN 515.

FIG17 is an illustration of component beam antenna patterns generated by several antenna elements (receive antenna element 406 or transmit antenna element 409) that intersect at the 3 dB point. Component beam antenna pattern 1301 of the first antenna element has a peak component beam antenna gain along boresight 1303. Component beam antenna pattern 1301 is shown to be attenuated by approximately 3 dB before intersecting component beam antenna pattern 1305. Because each pair of two adjacent component beam antenna patterns overlaps only over a relatively small portion of the component beam antenna pattern about 3 dB line 1307, the antenna elements that generate these component beam antenna patterns are considered non-overlapping.

Figure 18 shows idealized 3dB antenna profiles 3901, 3902, 3903 for several elements 406, 409 with peak gains marked with the letter "x". Profiles 3901, 3902, 3903 are referred to herein as "idealized" because they are shown as circular for simplicity. However, profiles 3901, 3902, 3903 are not necessarily circular. Each profile indicates a location where the transmitted or received signal is 3dB below the peak level. Outside the profile, the signal is more than 3dB below the peak. Inside the profile, the signal is less than 3dB below the peak (i.e., within 3dB of the peak). In a system where the coverage area of a receive component beam antenna pattern is all points where the receive component beam antenna gain is within 3dB of the peak receive component beam antenna gain, the area within the profile is referred to as the antenna element coverage area. The 3dB antenna profiles for each element 406, 409 are non-overlapping. That is, only a relatively small portion of the area within the 3dB antenna profile 3901 overlaps with the area within the adjacent 3dB antenna patterns 3902 , 3903 .

19 is a diagram of antenna patterns 1411, 1413, 1415 for several antenna elements (receive antenna element 406 or transmit antenna element 409). Compared to the component beam antenna pattern of FIG. 17, the component beam antenna pattern shown in FIG. 19 intersects 1417 above the 3dB line 1307.

Figures 20A to 20E show the 3dB antenna profiles of several antenna elements 406, 409, with the beam center point (peak gain) marked with the letter "x". Figure 20A shows a specific antenna profile 1411 of the first antenna element 406. Figure 20B shows the 3dB antenna profiles 1411, 1413 of two specific elements 406. Figure 20C shows the 3dB antenna profiles of three elements 406. Figure 20D shows the 3dB antenna profiles of four antenna elements 406. Figure 20E shows the 3dB antenna profile of an array of 16 antenna elements 406. The 3dB antenna profiles are shown as overlapping with 1418 (for example, 16 such 3dB antenna profiles are shown). The antenna elements in a receiving antenna or a transmitting antenna can be arranged in any of several different configurations. For example, if the element has a generally circular feed horn, the elements can be arranged in a honeycomb configuration to tightly pack the elements into a small amount of space. In some cases, the antenna elements are aligned in horizontal rows and vertical columns.

FIG21 is an exemplary illustration of the relative positions of receive antenna 3dB antenna profiles associated with receive antenna elements 406. The beam centers of elements 406 are numbered 1 through 16, with element ₄₀₆₄ identified by the number "4" in the upper left corner of the beam center indicator "x." In some cases, there may be more than 16 receive antenna elements 406. However, for simplicity, only 16 are shown in FIG21. The corresponding array of transmit antenna elements 409 and their associated 3dB antenna profiles would appear similar to FIG21. Therefore, for simplicity, only the array of receive antenna elements 406 is shown. The area 2101 in the center is where the coverage areas of all antenna elements overlap.

In some cases, at least one point within the repeater's coverage area (e.g., satellite coverage area) falls within the 3dB antenna profiles of the component beams of several antenna elements 406. In one such case, at least one point is within the 3dB antenna profiles of at least 100 different antenna elements 406. In another case, at least 10% of the repeater's coverage area is within the 3dB antenna profiles of at least 30 different antenna elements. In another case, at least 20% of the repeater's coverage area is within the 3dB antenna profiles of at least 20 different antenna elements. In another case, at least 30% of the repeater's coverage area is within the 3dB antenna profiles of at least 10 different antenna elements. In another case, at least 40% of the repeater's coverage area is within the 3dB antenna profiles of at least eight different antenna elements. In another case, at least 50% of the repeater's coverage area is within the 3dB antenna profiles of at least four different antenna elements. However, in some cases, more than one of these relationships may be true.

In some cases, the end-to-end repeater has a repeater coverage area (e.g., a satellite coverage area) in which at least 25% of the points in the uplink repeater coverage area are within (e.g., across) the overlapping coverage areas of at least six receive antenna elements 406. In some cases, 25% of the points in the uplink repeater coverage area are within (e.g., across) the overlapping coverage areas of at least four receive antenna elements 406. In some cases, the end-to-end repeater has a coverage area in which at least 25% of the points in the downlink repeater coverage area are within (e.g., across) the overlapping coverage areas of at least six transmit antenna elements 409. In some cases, 25% of the points in the downlink repeater coverage area are within (e.g., across) the overlapping coverage areas of at least four transmit antenna elements 409.

In some cases, the receive antenna 402 may be pointed toward approximately the same coverage area as the transmit antenna 401, such that some receive antenna element coverage areas may naturally correspond to specific transmit antenna element coverage areas. In these cases, the receive antenna elements 406 may be mapped to their corresponding transmit antenna elements 409 via the transponder 410, thereby producing similar transmit and receive antenna element coverage areas for each receive/transmit signal path. However, in some cases, it may be advantageous to map the receive antenna elements 406 to transmit antenna elements 409 that do not correspond to the same component beam coverage area. Thus, the mapping of the elements 406 of the receive antenna 402 to the elements 409 of the transmit antenna 401 may be randomly (or otherwise) arranged. Such an arrangement includes situations in which the receive antenna elements 406 are not mapped to transmit antenna elements 409 located in the same relative position within the array or having the same coverage area. For example, each receive antenna element 406 within the receive antenna element array may be associated with the same transponder 410 as a transmit antenna element 409 located in a mirrored position within the transmit antenna element array. Any other arrangement may be used to map the receive antenna elements 406 to the transmit antenna elements 409 according to an arrangement (e.g., pairing each receive antenna element 406 with the same transponder coupled with an associated transmit antenna element 409 according to a particular arrangement of receive antenna elements 406 and transmit antenna elements 409).

22 is a table 4200 illustrating an exemplary mapping of receive antenna elements 406 to transmit antenna elements 409 via 16 transponders 410. Each transponder 410 has an input uniquely coupled to an associated receive antenna element 406 and an output uniquely coupled to an associated transmit antenna element 409 (e.g., there is a one-to-one relationship between each receive antenna element 406, one transponder 410, and one transmit antenna element 409). In some cases, other receive antenna elements, transponders, and transmit antenna elements may exist on an end-to-end repeater (e.g., a satellite) that is not configured in a one-to-one relationship (and is not operating as part of an end-to-end beamforming system).

The first column 4202 of table 4200 identifies transponders 410. The second column 4204 identifies the receive antenna elements 406 coupled to the transponders 410 in the first column. The third column 4206 of table 4200 identifies the associated transmit antenna elements 409 coupled to the outputs of transponders 410. Each receive antenna element 406 is coupled to the input of the transponder 410 identified in the same row of table 4200. Similarly, each transmit antenna element 409 is coupled to the output of the transponder 410 identified in the same row of table 4200. The third column of table 4200 illustrates an example of direct mapping, where each receive antenna element 406 of the receive antenna array is coupled to the same transponder 410 as the transmit antenna element 409 in the same relative position within the transmit antenna array. The fourth column 4208 of table 4200 illustrates an example of staggered mapping, where the first receive antenna element 406 is coupled to the first transponder 410 and the tenth transmit antenna element 409. The second receive antenna element 406 is coupled to the second transponder 410 and the ninth transmit antenna element 409, etc. Some cases have other permutations, including random mappings, where the particular pairings of receive antenna elements 406 and transmit elements 409 with transponders 410 are randomly selected.

Direct mapping, which attempts to make the transmit antenna element coverage area and the receive antenna element coverage area as similar as possible for each receive/transmit signal path, generally produces the highest overall system capacity. Random and interleaved permutations generally produce slightly less capacity but provide a more robust system in the face of AN failures, fiber failures in the terrestrial network, or loss of receive/transmit signal paths due to electronic failures on end-to-end repeaters (e.g., in one or more transponders). Random and interleaved permutations allow the use of less expensive, non-redundant ANs. They also result in less variation in capacity between the best-performing beam and the worst-performing beam. Random and interleaved permutations may also be more suitable for initially operating the system with only a small fraction of the ANs, resulting in only a small fraction of the total capacity being available but with no loss of coverage area. An example of this is gradual AN rollout, where the system initially operates with only 50% of the ANs deployed. This provides less than full capacity while still allowing operation throughout the coverage area. As demand increases, more ANs can be deployed to increase capacity until full capacity is achieved with all ANs active. In some cases, changes in the composition of the ANs result in a recalculation of the beam weights. A composition change may include changing the number or characteristics of one or more ANs. This may require re-estimation of the end-to-end forward and/or return gains.

In some cases, the antenna is an array-fed reflector antenna having a parabolic reflector. In other cases, the reflector does not have a parabolic shape. The array of receiving antenna elements 406 can be arranged to receive signals reflected by the reflector. Similarly, the array of transmitting antenna elements 409 can be arranged to form an array for illuminating the reflector. One way to provide elements with overlapping component beam antenna patterns is to defocus (unfocus) the elements 406, 409 due to the focal plane of the reflector being behind (or in front of) the array of elements 406, 409 (i.e., the receiving antenna array is positioned outside the focal plane of the receiving reflector).

FIG23 is an illustration of a cross-section of a center-fed parabolic reflector 1521. A focal point 1523 is located on a focal plane 1525 that is perpendicular to a central axis 1527 of the reflector 1521. Received signals striking the reflector 1521 parallel to the central axis 1527 are focused onto the focal point 1523. Similarly, signals transmitted from an antenna element positioned at the focal point and striking the reflector 1521 will be reflected from the reflector 1521 parallel to the central axis 1527 in a focused beam. This type of arrangement is typically used in single-feed-per-beam systems to maximize the directivity of each beam and minimize overlap with beams formed by adjacent feeds.

FIG24 is an illustration of another parabolic reflector 1621. By positioning antenna elements 1629 (receive antenna elements or transmit antenna elements 406, 409, 3416, 3419, 3426, 3429) outside the focal plane (e.g., in front of the focal plane 1625 of reflector 1621), the paths of transmitted signals 1631 striking reflector 1621 are not parallel to one another when they reflect off reflector 1621, thereby forming a wider beamwidth than would be the case if focused. In some cases, reflectors with shapes other than parabolic are used. Such reflectors can also cause antenna defocusing. An end-to-end beamforming system can use this type of defocused antenna to create overlap in the coverage areas of adjacent antenna elements and, therefore, provide a larger number of useful receive/transmit paths for a given beam position in the repeater's coverage area.

In one case, a repeater coverage area is established where, when an end-to-end repeater is deployed (e.g., an end-to-end satellite repeater is in a serving orbit), 25% of the points within the repeater coverage area are within the antenna element coverage areas of at least six component beam antenna patterns. Alternatively, 25% of the points within the repeater coverage area are within the antenna element coverage areas of at least four receive antenna elements. Figure 25 is an illustration of an exemplary repeater coverage area (also referred to as a satellite coverage area for an end-to-end satellite repeater) 3201 (shown with single cross shading) and an area 3203 (shown with double cross shading) defined by points within the repeater coverage area 3201 that are also contained within the six antenna element coverage areas 3205, 3207, 3209, 3211, 3213, 3215. Coverage area 3201 and antenna element coverage areas 3205, 3207, 3209, 3211, 3213, 3215 can be either receive antenna coverage areas or transmit antenna element coverage areas and can be associated with only the forward link or only the return link. The size of antenna element coverage areas 3205, 3207, 3209, 3211, 3213, 3215 is determined by the desired performance to be provided by the system. Systems with greater error tolerance may have larger antenna element coverage areas than systems with less error tolerance. In some cases, each antenna element coverage area 3205, 3207, 3209, 3211, 3213, 3215 is all points where the component beam antenna gain is within 10 dB of the peak component beam antenna gain of the antenna element that establishes the component beam antenna pattern. In other cases, each antenna element coverage area 3205, 3207, 3209, 3211, 3213, 3215 is all points where the component beam antenna gain is within 6 dB of the peak component beam antenna gain. In other cases, each antenna element coverage area 3205, 3207, 3209, 3211, 3213, 3215 is all points where the component beam antenna gain is within 3 dB of the peak component beam antenna gain. Even when the end-to-end repeater has not yet been deployed (e.g., the end-to-end satellite repeater is not in a serving orbit), the end-to-end repeater still has a component beam antenna pattern that conforms to the above definition. That is, even when the end-to-end repeater is not in a serving orbit, the antenna element coverage area corresponding to the end-to-end repeater in orbit can be calculated based on the component beam antenna pattern. The end-to-end repeater may include additional antenna elements that do not contribute to beamforming and therefore may not have the above characteristics.

26 is an illustration of an end-to-end repeater (e.g., satellite) antenna pattern 3300 in which all points within a repeater coverage area 3301 (e.g., satellite coverage area) are also contained within at least four antenna element coverage areas 3303, 3305, 3307, 3309. Additional antenna elements may be present on the end-to-end repeater and may have antenna element coverage areas 3311 that include fewer than all points within the repeater coverage area 3301.

The system can operate in any suitable spectrum. For example, an end-to-end beamforming system can operate in C, L, S, X, V, Ka, Ku, or one or more other suitable frequency bands. In some such systems, the receiving device operates in C, L, S, X, V, Ka, Ku, or one or more other suitable frequency bands. In some cases, the forward uplink and the return uplink can operate in the same frequency range (e.g., approximately 30 GHz); and the return downlink and the forward downlink can operate in non-overlapping frequency ranges (e.g., approximately 20 GHz). The end-to-end system can use any suitable bandwidth (e.g., 500 MHz, 1 GHz, 2 GHz, 3.5 GHz, etc.). In some cases, the forward link and the return link use the same transponder.

To help with system timing alignment, in some cases, for example, by selecting appropriate cable lengths, the path lengths between the L transponders are set to match the signal path time delay. In some cases, the end-to-end repeater (e.g., satellite) has a delayed beacon generator 426 (satellite beacon) within the calibration support module 424 (see Figure 15). The beacon generator 426 generates a delayed beacon signal. The end-to-end repeater broadcasts the repeater beacon signal to further help with system timing alignment and support feeder link calibration. In some cases, the repeater beacon signal is a pseudo-random (called PN) sequence, such as a PN direct sequence spread spectrum signal running at a high chip rate (e.g., 100 million, 200 million, 400 million, or 800 million chips per second (Mcp) or any other suitable value). In some cases, a linearly polarized repeater (e.g., satellite) beacon, which can be received by both the RHCP antenna and the LHCP antenna, is broadcast or coupled to one or more transponders 410 in a wide coverage area by an antenna such as an antenna horn (not shown) for transmission via the associated transmitting antenna element 409. In an exemplary system, beams are formed across multiple 500 MHz bandwidth channels on the Ka band, and the 400 Mcps PN code is filtered or pulse-shaped to fit within the 500 MHz bandwidth channels. When multiple channels are used, the same PN code can be transmitted in each channel. The system can employ one beacon for each channel, or one beacon for two or more channels.

Since there may be a large number of receive/transmit signal paths in an end-to-end repeater, redundancy of separate receive/transmit signal paths may not be required. In the event of a receive/transmit signal path failure, the system can still perform very close to its previous performance level, but the loss can be accounted for using modifications to the beamforming coefficients.

Ground network

The terrestrial network of an exemplary end-to-end beamforming system comprises a plurality of geographically distributed access node (AN) earth stations pointing to a common end-to-end repeater. Looking first at the forward link, a central processing system (CPS) calculates beam weights for transmitting user data and interfacing to the AN through a distribution network. The CPS also interacts with data sources provided to user terminals. The distribution network can be implemented in various ways, such as using a fiber optic cable infrastructure. The timing between the CPS and the SAN can be deterministic (e.g., using a circuit-switched channel) or non-deterministic (e.g., using a packet-switched network). In some cases, the CPS is implemented at a single site, for example, using a customized application-specific integrated circuit (ASIC), to perform signal processing. In some cases, the CPS is implemented in a distributed manner, such as using cloud computing technology.

Returning to the example of FIG. 5 , the CPS 505 may include multiple feeder link modems 507. For the forward link, each feeder link modem 507 receives a forward user data stream 509 from various data sources, such as the internet, a video headend (not shown), and the like. The received forward user data stream 509 is modulated by the modem 507 into K forward beam signals 511. In some cases, K may be in the range of 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, or a number therebetween or greater. Each of the K forward beam signals carries a forward user data stream to be transmitted on one of the K forward user beams. Thus, if K=400, there are 400 forward beam signals 511, each of which will be transmitted on an associated one of the 400 forward user beams to a forward user beam coverage area 519. The K forward beam signals 511 are coupled to a forward beamformer.

If M access nodes 515 are present in the ground segment 502, the output of the forward beamformer is M access node-specific forward signals 516, each of which includes a weighted forward beam signal corresponding to some or all of the K forward beam signals 511. The forward beamformer can generate the M access node-specific forward signals 516 based on the matrix product of K×M forward beam weight matrices and the K forward data signals. The distribution network 518 distributes each of the M access node-specific forward signals to a corresponding one of the M access node-specific forward signals 515. Each AN 515 transmits a forward uplink signal 521 containing the corresponding access node-specific forward signal 516. Each AN 515 transmits its corresponding forward uplink signal 521 to be relayed to one or more (e.g., up to and including all) of the forward receive/transmit signal paths of the end-to-end repeater in the forward user beam coverage area. The transponders 410, 411 within the end-to-end repeater 503 receive a composite input forward signal comprising a superposition 550 of forward uplink signals 521 transmitted by multiple (e.g., up to and including all) ANs 515. Each transponder (e.g., each receive/transmit signal path through the repeater) relays the composite input forward signal as a corresponding forward downlink signal to the user terminal 517 via the forward downlink.

Figure 27 is a diagram of an exemplary distribution of ANs 515. Each smaller numbered circle represents the location of an AN 515. Each larger circle represents a user beam coverage area 519. In some cases, the ANs 515 are spaced approximately evenly within the coverage area of the end-to-end repeater 503. In other cases, the ANs 515 may be unevenly distributed throughout the coverage area. In other cases, the ANs 515 may be evenly or unevenly distributed within one or more sub-areas of the repeater coverage area. Generally, system performance is best when the ANs 515 are evenly distributed throughout the coverage area. However, considerations may dictate a compromise in AN placement. For example, the ANs 515 may be placed based on the amount of interference, rain or other environmental conditions, real estate costs, access to the distribution network, and the like. For example, for a satellite-based end-to-end relay system that is sensitive to rain, more ANs 515 may be placed in areas less likely to experience rain-induced attenuation (e.g., the western United States). As another example, ANs 515 can be placed more densely in high rainfall areas (eg, the southeastern United States) to provide some diversity gain to offset the effects of rain fade. ANs 515 can be located along fiber routes to reduce the distribution costs associated with ANs 515.

The number M of ANs 515 is an optional parameter that can be selected based on several criteria. Fewer ANs can result in a simpler, lower cost ground segment and lower operating costs for the distribution network. More ANs can result in a larger system capacity. Figure 28 is a simulation of the normalized forward link and return link capacity as a function of the number of ANs deployed in an example system. The normalized capacity is the capacity obtained with M ANs divided by the capacity obtained with the maximum number of ANs in the simulation. The capacity increases with the number of ANs, but does not increase indefinitely. Both the forward link capacity and the return link capacity approach an asymptotic limit as the number of ANs increases. This simulation was performed with L = 517 transmit and receive antenna elements and with ANs uniformly distributed across the coverage area, but this asymptotic behavior of capacity can be achieved with other values of L and other spatial distributions of ANs. The same curves as shown in Figure 28 can be helpful in selecting the number M of ANs to deploy and in understanding how the system capacity can be phased as the ANs are incrementally deployed, as previously described.

FIG29 is a block diagram of an exemplary ground segment 502 of an end-to-end beamforming system. FIG29 may, for example, illustrate the ground segment 502 of FIG5 . Ground segment 502 includes CPS 505, distribution network 518, and AN 515. CPS 505 includes beam signal interface 524, forward/return beamformer 513, distribution interface 536, and beam weight generator 910.

For the downlink, the beam signal interface 524 obtains a forward beam signal (FBS) 511 associated with each of the forward user beams. The beam signal interface 524 may include a forward beam data multiplexer 526 and a forward beam data stream modulator 528. The forward beam data multiplexer 526 may receive a forward user data stream 509 including forward data for transmission to the user terminal 517. The forward user data stream 509 may include, for example, data packets (e.g., TCP packets, UDP packets, etc.) for transmission to the user terminal 517 via the end-to-end beamforming system 500 of FIG. 5 . The forward beam data multiplexer 526 groups (e.g., multiplexes) the forward user data stream 509 according to their respective forward user beam coverage areas to obtain a forward beam data stream 532. The forward beam data multiplexer 526 can use, for example, time domain multiplexing, frequency domain multiplexing, or a combination of multiplexing techniques to generate the forward beam data stream 532. The forward beam data stream modulator 528 can modulate the forward beam data stream 532 according to one or more modulation schemes (e.g., mapping data bits to modulation symbols) to produce forward beam signals 511, which are passed to the forward/return beamformer 513. In some cases, the modulator 528 can frequency division multiplex multiple modulated signals to produce the multi-carrier beam signal 511. The beam signal interface 524 can, for example, implement the functionality of the feeder link modem 507 discussed with reference to FIG5.

The forward/return beamformer 513 may include a forward beamformer 529 and a return beamformer 531. The beam weight generator 910 generates an M×K forward beam weight matrix 918. Techniques for generating the M×K forward beam weight matrix 918 are discussed in more detail below. The forward beamformer 529 may include a matrix multiplier that calculates the M access node-specific forward signals 516. For example, this calculation may be based on a matrix product of the M×K forward beam weight matrix 918 and a vector of the K forward beam signals 511. In some examples, each of the K forward beam signals 511 may be associated with one of the F forward frequency subbands. In this case, the forward beamformer 529 can generate M samples of the access node-specific forward signal 516 for each of the F forward frequency subbands (e.g., for a corresponding subset of the K forward beam signals 511, effectively implementing a matrix product operation for each of the F subbands). The distribution interface 536 distributes the M access node-specific forward signals 516 (e.g., via the distribution network 518) to the corresponding AN 515.

For the return link, the distribution interface 536 obtains a composite return signal 907 from the AN 515 (e.g., via the distribution network 518). Each return data signal from the user terminal 517 may be included in multiple composite return signals (e.g., up to and including all) in the composite return signal 907. The beam weight generator 910 generates a K×M return beam weight matrix 937. Techniques for generating the K×M return beam weight matrix 937 are discussed in more detail below. The return beamformer 531 calculates K return beam signals 915 for the K return user beam coverage areas. For example, this calculation may be based on a matrix product of the return beam weight matrix 937 with a vector of the corresponding composite return signal 907. The beam signal interface 524 may include a return beam signal demodulator 552 and a return beam data demultiplexer 554. The return beam signal demodulator 552 may demodulate each of the return beam signals to obtain K return beam data streams 534 associated with the K return user beam coverage areas. The return beam data demultiplexer 554 can demultiplex each of the K return beam data streams 534 into a corresponding return user data stream 535 associated with a return data signal transmitted from the user terminal 517. In some examples, each of the return user beams can be associated with one of the R return frequency subbands. In this case, the return beamformer 531 can generate a corresponding subset of the return beam signals 915 associated with each of the R return frequency subbands (e.g., effectively implementing a matrix product operation for each of the R return frequency subbands to generate a corresponding subset of the return beam signals 915).

FIG30 is a block diagram of an exemplary forward/return beamformer 513. The forward/return beamformer 513 includes a forward beamformer 529, a forward timing module 945, a return beamformer 531, and a timing module 947. The forward timing module 945 associates each of the M access node-specific forward signals 516 with a timestamp (e.g., multiplexing the timestamp with the access node-specific forward signal in a multiplexed set of access node-specific forward signals) that indicates the expected time of arrival of the signal at the end-to-end repeater. In this way, the data of the K forward beam signals 511, split in the splitting module 904 within the forward beamformer 529, can be transmitted by each of the ANs 515 at the appropriate time. The timing module 947 aligns the received signals based on the timestamps. Samples of the M AN composite return signals (CRSs) 907 are associated with timestamps that indicate when the particular sample was transmitted from the end-to-end repeater. Timing considerations and generation of timestamps are discussed in more detail below.

The forward beamformer 529 has a data input 925, a beam weight input 920, and an access node output 923. The forward beamformer 529 applies the values of the M×K beam weight matrix to each of the K forward data signals 511 to generate M access node-specific forward signals 521, each of which has K weighted forward beam signals. The forward beamformer 529 can include a splitting module 904 and M forward weighting and summing modules 533. The splitting module 904 splits (e.g., replicates) each of the K forward beam signals 511 into M groups 906 of K forward beam signals, with each of the M forward weighting and summing modules 533 receiving one group 906. Thus, each forward weighting and summing module 533 receives all K forward data signals 511.

Forward beam weight generator 917 generates an M×K forward beam weight matrix 918. In some cases, forward beam weight matrix 918 is generated based on a channel matrix in which the elements are estimates of the end-to-end forward gain for each of the K×M end-to-end forward multipath channels used to form the forward channel matrix, as discussed further below. The estimation of the end-to-end forward gain is performed in channel estimator module 919. In some cases, the channel estimator has a channel data storage area 921 that stores data related to various parameters of the end-to-end multipath channel, as discussed in further detail below. Channel estimator 919 outputs the estimated end-to-end gain signal to allow forward beam weight generator 917 to generate forward beam weight matrix 918. Each of weighting and summing modules 533 is coupled to receive a corresponding vector of beamforming weights for forward beam weight matrix 918 (only one such connection is shown in FIG. 30 for simplicity). The first weighting and summing module 533 applies a weight equal to the value of the 1,1 element of the M×K forward beam weight matrix 918 to the first of the K forward beam signals 511 (as discussed in more detail below). A weight equal to the value of the 1,2 element of the M×K forward beam weight matrix 918 is applied to the second of the K forward beam signals 511. The remaining weights of the matrix are applied in a similar manner until the Kth forward beam signal 511, which is weighted with a value equal to the 1,K element of the M×K forward beam weight matrix 918. Each of the K weighted forward beam signals 903 is then summed and output from the first weighting and summing module 533 as an access node-specific forward signal 516. The access node-specific forward signal 516 output by the first weighting and summing module 533 is then coupled to the timing module 945. The timing module 945 outputs the access node-specific forward signal 516 to the first AN 515 via the distribution network 518 (see FIG5 ). Similarly, each of the other weighting and summing modules 533 receives K forward beam signals 511 and weights and sums the K forward beam signals 511. The output from each of the M weighting and summing modules 533 is coupled to the associated M ANs 515 via the distribution network 518, so that the output from the mth weighting and summing module is coupled to the mth AN 515. In some cases, jitter and uneven delays through the distribution network, as well as some other timing considerations, are handled by the timing module 945 by associating timestamps with the data. Details of exemplary timing techniques are provided below with respect to FIG36 and FIG37 .

Signals transmitted from the AN 515 through the end-to-end repeaters 503 form user beams due to the beam weights applied by the forward beamformer 529 at the ground segment 502. The size and location of the beams that can be formed can be a function of the number of ANs 515 deployed, the number and antenna pattern of the repeater antenna elements through which the signal passes, the location of the end-to-end repeaters 503, and/or the geographic spacing of the ANs 515.

5, a user terminal 517 within one of the user beam coverage areas 519 transmits signals up to the end-to-end repeater 503. These signals are then relayed down to the ground segment 502. These signals are received by the AN 515.

Referring again to FIG. 30 , M return downlink signals 527 are received by M ANs 515 as composite return signals 907, coupled from the M ANs 515 via distribution network 518, and received at access node input 931 of return beamformer 531. Timing module 947 aligns the composite return signals from the M ANs 515 with one another and outputs the time-aligned signals to return beamformer 531. Return beam weight generator 935 generates return beam weights as a K×M return beam weight matrix 937 based on information stored in channel data storage area 941 within channel estimator 943. Return beamformer 531 has a beam weight input 939 through which it receives return beam weight matrix 937. Each of the M AN composite return signals 907 is coupled to an associated one of M splitters and weighting modules 539 within return beamformer 531. Each splitter and weighting module 539 splits the time-aligned signal into K replicas 909. The splitter and weighting module 539 weights each of the K replicas 909 using the k,m elements of a K×M return beam weight matrix 937. Additional details regarding the K×M return beam weight matrix are provided below. Each set of K weighted composite return signals 911 is then coupled to a combining module 913. In some cases, the combining module 913 combines the kth weighted composite return signal 911 output from each splitter and weighting module 539. The return beamformer 531 has a return data signal output 933 that outputs K return beam signals 915, each of which has samples associated with one of the K return user beams 519 (e.g., samples received by each of the M ANs). Each of the K return beam signals 915 may have samples from one or more user terminals 517. The K combined and aligned beamformed return beam signals 915 are coupled to the feeder link modem 507 (see FIG5 ). Note that return timing adjustments can be performed after splitting and weighting. Similarly, for the forward link, forward timing adjustments can be performed before beamforming.

As described above, the forward beamformer 529 can perform a matrix product operation on the input samples of the K forward beam signals 511 to calculate M access node-specific forward signals 516 in real time. As the beamwidth increases (e.g., to support shorter symbol durations) and/or K and M become larger, the matrix product operation becomes computationally intensive and may exceed the capabilities of a single compute node (e.g., a single compute server, etc.). The operations of the return beamformer 531 are similarly computationally intensive. Various methods can be used to partition the computational resources of the multiple compute nodes in the forward/return beamformer 513. In one example, the forward beamformer 529 of FIG. 30 can be partitioned into a separate weighting and summing module 533 for each of the M access nodes 515, which can be assigned to different compute nodes. Generally, implementation considerations include cost, power consumption, scalability with respect to K, M, and bandwidth, system availability (e.g., due to node failures, etc.), upgradeability, and system latency. The above examples are arranged in rows (or columns). Other ways of grouping matrix operations can also be considered (for example, dividing into four, where [1, 1 to K/2, M/2], […] are calculated separately and added).

In some cases, the forward/return beamformer 513 may include a time-domain multiplexing architecture for processing beam weighting operations by a time-slice beamformer. FIG31 is a block diagram of an exemplary forward beamformer 529 including multiple forward time-slice beamformers with time-domain demultiplexing and multiplexing. The forward beamformer 529 includes a forward beam signal demultiplexer 3002, N forward time-slice beamformers 3006, and a forward access node signal multiplexer 3010.

The forward beam signal demultiplexer 3002 receives the forward beam signal 511 and demultiplexes the K forward beam signals 511 into the forward time slot input 3004 for input into the N forward time slot beamformers 3006. For example, the forward beam signal demultiplexer 3002 sends a first time-domain subset of samples of the K forward beam signals 511 to the first forward time slot beamformer 3006, which generates samples associated with M access node-specific forward signals corresponding to the first time-domain subset of samples. The forward time slot beamformer 3006 outputs the samples associated with the M access node-specific forward signals of the first time-domain subset of samples to the forward access node signal multiplexer 3010 via its forward time slot output 3008. The forward time slot beamformer 3006 can utilize synchronization timing information used by the access node (e.g., corresponding time slot index, etc.) to output samples associated with each of the M access node-specific forward signals, causing the corresponding access node-specific forward signals to be synchronized (e.g., through pre-correction) when received by the end-to-end repeater. The forward access node signal multiplexer 3010 multiplexes time-domain subsets of the samples of the M access node-specific forward signals received via the N forward time slot outputs 3008 to generate the M access node-specific forward signals 516. Each of the forward time slot beamformers 3006 can include a data buffer that implements a matrix product operation, a beam matrix buffer, and a beam weight processor. In other words, each of the forward time slot beamformers 3006 can implement computations mathematically equivalent to the splitting module 904 and the forward weighting and summing module 533 shown for the forward beamformer 529 of FIG. 30 during the processing of samples for one time slot index. The updating of the beam weight matrix can be performed incrementally. For example, the beam weight matrix buffer for the forward time slice beamformer can be updated by the N forward time slice beamformers 3006 in the rotation of the time slice index t during idle time. Alternatively, each forward time slice beamformer can have two buffers that can be used in a reciprocating configuration (e.g., one can be used while the other is updated). In some cases, multiple buffers can be used to store beam weights corresponding to multiple user beam patterns (e.g., multiple user coverage areas). The beam weight buffer and data buffer for the forward time slice beamformer 3006 can be implemented as any type of memory or storage device including dynamic or static random access memory (RAM). The beam weight processing can be implemented in an application specific integrated circuit (ASIC) and/or a field programmable gate array (FPGA) and can include (e.g., in a cloud computing environment) one or more processing cores. In addition or alternatively, the beam weight buffer, data buffer and beam weight processor can be integrated into one component.

FIG32 illustrates a simplified exemplary ground segment illustrating the operation of the forward time-slice beamformer 529. In the example of FIG32, the forward beamformer 529 receives four forward beam signals (e.g., K=4), generates access node-specific forward signals for five ANs (e.g., M=5), and has three forward time-slice beamformers (e.g., N=3). The forward beam signals are denoted as FBk:t, where k is the forward beam signal index and t is the time-slice index (e.g., corresponding to a time-domain subset of samples). The forward beam signal demultiplexer 3002 receives four time-domain subsets of samples of the forward beam signals associated with the four forward user beams and demultiplexes each forward beam signal such that one forward time-slice input 3004 includes a time-domain subset of samples from each of the forward beam signals 511 for a particular time-slice index t. For example, the time-domain subsets may be single samples, blocks of consecutive samples, or blocks of discontinuous (e.g., interleaved) samples, as described below. The forward time slice beamformer 3006 generates each of the M access node-specific forward signals, denoted as AFm:t, for time slice index t (e.g., based on the forward beam signal 511 and the forward beam weight matrix 918). For example, for time slice index t=0, the time domain subset of samples FFB1:0, FB2:0, FB3:0, and FB4:0 are input to the first forward time slice beamformer TSBF[1] 3006, which generates corresponding samples of the access node-specific forward signals AF1:0, AF2:0, AF3:0, AF4:0, and AF5:0 at the forward time slice output terminal 3008. For subsequent time slice index values t=1, 2, the time-domain subsets of samples of the forward beam signal 511 are demultiplexed by the forward beam signal demultiplexer 3002 for input to the second and third forward time slice beamformers 3006, which generate access node-specific forward signals associated with the corresponding time slice index t at the forward time slice output 3008. FIG32 also shows that, for time slice index value t=3, the first forward time slice beamformer generates an access node-specific forward signal associated with the corresponding time slice index 3. The matrix product operation performed by each forward time slice beamformer 3006 for one time slice index value t may require a longer time (e.g., the number of samples S multiplied by the sampling rate _tS ) than the actual time of the time-domain subset of samples. However, each forward time slice beamformer 3006 may process only one time-domain subset of samples for every N time slice indices t. The forward access node signal multiplexer 3010 receives the forward time slice output 3030 from each of the forward time slice beamformers 3006 and multiplexes the time domain subset of the samples to generate M access node specific forward signals 516 for distribution to the corresponding ANs.

33 is a block diagram of an exemplary return beamformer 531 including multiple return time slice beamformers with time domain demultiplexing and multiplexing. The return beamformer 531 includes a return composite signal demultiplexer 3012, N return time slice beamformers 3016, and a return beam signal multiplexer 3020. The return composite signal demultiplexer 3012 receives M composite return signals 907 (e.g., from M ANs) and demultiplexes the M composite return signals 907 into return time slice inputs 3014 for input to the N return time slice beamformers 3016. Each of the return time slice beamformers 3016 outputs samples associated with K return beam signals 915 for a corresponding time domain subset of samples to the return beam signal multiplexer 3020 via a corresponding return time slice output 3018. The return beam signal multiplexer 3020 multiplexes time-domain subsets of the samples of the K return beam signals received via the N return time slice outputs 3018 to generate K return beam signals 915. Each of the return time slice beamformers 3016 can include a data buffer that implements a matrix product operation, a beam matrix buffer, and a beam weight processor. That is, each of the return time slice beamformers 3016 can perform computations mathematically equivalent to the splitter and weighting module 539 and the combining module 913 shown for the return beamformer 531 of FIG. 30 during processing of samples indexed by a time slice. As discussed above with respect to the forward time slice beamformer, a reciprocating beam weight buffer configuration can be used to incrementally perform updates to the beam weight matrix (e.g., one can be used while another is being updated). In some cases, multiple buffers can be used to store beam weights corresponding to multiple user beam patterns (e.g., multiple user coverage areas). The beam weight buffer and data buffer for the return time slice beamformer 3016 can be implemented as any type of memory or storage device, including dynamic or static random access memory (RAM). The beam weight processing can be implemented in an application specific integrated circuit (ASIC) and/or a field programmable gate array (FPGA) and can include one or more processing cores. In addition or alternatively, the beam weight buffer, data buffer, and beam weight processor can be integrated into a single component.

FIG34 illustrates a simplified exemplary ground segment, illustrating the operation of the return beamformer 531 employing time-domain multiplexing. In the example of FIG33 , the return beamformer 531 receives five composite return signals (e.g., M=5), generates return beam signals for four return user beams (e.g., K=5), and has three time-slice beamformers (e.g., N=3). The composite return signal is represented as RCm:t, where m is the AN index and t is the time-slice index (e.g., corresponding to a time-domain subset of samples). The return composite signal demultiplexer 3012 receives four time-domain subsets of samples of the composite return signal from the five ANs and demultiplexes each composite return signal so that one return time-slice input 3014 includes the corresponding time-domain subset of samples from each of the composite return signals 907 for a particular time-slice index t. For example, the time-domain subsets may be single samples, blocks of consecutive samples, or blocks of discontinuous (e.g., interleaved) samples, as described below. The return time slice beamformer 3016 generates (e.g., based on the synthesized return signal 907 and the return beam weight matrix 937) each of the K return beam signals, denoted as RBk:t, for time slice index t. For example, for time slice index t=0, a time domain subset of samples RC1:0, RC2:0, RC3:0, RC4:0, and RC5:0 is input to the first return time slice beamformer 3016, which generates corresponding samples of return beam signals RB1:0, RB2:0, RB3:0, and RB4:0 at the return time slice output terminal 3018. For subsequent time slice index values t = 1, 2, the time domain subsets of samples of the composite return signal 907 are demultiplexed by the return composite signal demultiplexer 3012 for input to the second and third return time slice beamformers 3016, respectively, which generate samples of the return beam signal associated with the corresponding time slice index t at the return time slice output 3018. FIG34 also illustrates that, at time slice index value t = 3, the first return time slice beamformer generates samples of the return beam signal associated with the corresponding time slice index 3. The matrix product operation performed by each return time slice beamformer 3016 for one time slice index value t may be longer than the actual time of the time domain subset of samples (e.g., the number of samples S multiplied by the sampling rate _tS ). However, each return time slice beamformer 3016 may process only one time domain subset of samples for every N time slice indices t. The return beam signal multiplexer 3020 receives the return time slice output 3018 from each of the return time slice beamformers 3016 and multiplexes the time domain subsets of the samples to generate K return beam signals 915.

While Figures 31 through 34 illustrate the same number N of forward time-slice beamformers 3006 relative to the return time-slice beamformers 3016, some implementations may have more or fewer forward time-slice beamformers 3006 than return time-slice beamformers 3016. In some examples, the forward beamformer 529 and/or the return beamformer 531 may have spare capacity to gain robustness against node failures. For example, if each forward time-slice beamformer 3006 takes t _FTS to process one sample set for a time-slice index t, which has a real time-slice duration t _D , where t _FTS = N·t _D , then the forward beamformer 529 may have N+E forward time-slice beamformers 3006. In some examples, each of the N+E forward time-slice beamformers 3006 is used in operation, with each forward time-slice beamformer 3006 having an effective excess capacity of E/N. If one forward time-slice beamformer 3006 fails, operations can be transferred to another forward time-slice beamformer 3006 (e.g., by adjusting how time-domain samples (or groups of samples) are routed through time-domain demultiplexing and multiplexing). Thus, the forward beamformer 529 can tolerate the failure of up to E forward time-slice beamformers 3006 before system performance is affected. Furthermore, the additional capacity allows for system maintenance and upgrades of the time-slice beamformers while the system is operating. For example, upgrades of the time-slice beamformers can be performed incrementally because the system can tolerate different performance between time-slice beamformers. Data samples associated with a time-slice index t can be interleaved. For example, a first time-slice index _t0 can be associated with samples 0, P, 2P, ... (S-1)*P, while a second time-slice index _t1 can be associated with samples 1, P+1, 2P+1 ... (S-1)*P+1, and so on, where S is the number of samples in each sample set and P is the interleaving duration. Interleaving can also make the system more robust to time-slice beamformer failures, because each time-slice beamformer block of samples is separated in time, so that the error due to a lost block will be distributed in time, similar to the advantage that arises from interleaving in forward error correction. In fact, the distributed error caused by time-slice beamformer failure can cause an effect similar to noise and will not cause any errors in the user data, especially if forward error correction coding is employed. Although an example has been shown where N = 3, other values of N can also be used, and N does not need to have any specific relationship with K or M.

As described above, the forward beamformer 529 and return beamformer 531 shown in Figures 31 and 33, respectively, can perform time-domain demultiplexing and multiplexing of time-slice beamforming for a channel or frequency subband. An additional subband multiplexing/demultiplexing switching layer can be used to independently process multiple subbands. Figure 35 is a block diagram of an exemplary multi-band forward/return beamformer 513 employing subband demultiplexing and multiplexing. The multi-band forward/return beamformer 513 can support F forward subbands and R return subbands.

The multi-band forward/return beamformer 513 includes F forward sub-band beamformers 3026, R return sub-band beamformers 3036, and a sub-band multiplexer/demultiplexer 3030. For example, the forward beam signal 511 can be divided into F forward sub-bands. Each of the F forward sub-bands can be associated with a subset of K forward user beam coverage areas. That is, the K forward user beam coverage areas can include multiple subsets of forward user beam coverage areas associated with different (e.g., different frequency and/or polarization, etc.) frequency sub-bands, where the forward user beam coverage areas within each of these subsets can be non-overlapping (e.g., at a 3dB signal profile, etc.). Therefore, each of the forward sub-band beamformer inputs 3024 can include a subset K ₁ of the forward beam signal 511. Each of the F forward beamformers 3026 can include the functionality of the forward beamformer 529, thereby generating a forward subband beamformer output 3028 including M access node-specific forward signals associated with a subset of the forward beam signals 511 (e.g., a matrix product of the K ₁ forward beam signals and the M×K ₁ forward beam weight matrix). Thus, each of the ANs 515 can receive multiple access node-specific forward signals associated with different frequency subbands (e.g., each of the F forward subbands). The AN can combine (e.g., add) the signals in the different subbands in the forward uplink signal, as discussed in more detail below. Similarly, the AN 515 can generate multiple composite return signals 907 for the R different return subbands. Each of the R return subbands can be associated with a subset of the K return user beam coverage areas. That is, the K return user beam coverage areas may include multiple subsets of return user beam coverage areas associated with different frequency sub-bands, where the return user beam coverage areas within each of these subsets may be non-overlapping (e.g., at a 3 dB signal profile, etc.). The sub-band multiplexer/demultiplexer 3030 may split the composite return signal 907 into R return sub-band beamformer inputs 3034. Each of the return sub-band beamformers 3036 may then generate a return sub-band beamformer output 3038, which may include the return beam signal 915 for the subset of return user beams (e.g., to the feeder link modem 507 or the return beam signal demodulator, etc.). In some examples, the multi-band forward/return beamformer 513 may support multiple polarizations (e.g., right-hand circular polarization (RHCP), left-hand circular polarization (LHCP), etc.), which in some cases may effectively double the number of sub-bands.

In some cases, time slice multiplexing and demultiplexing (e.g., beam signal demultiplexer 3002, forward access node signal multiplexer 3010, return composite signal demultiplexer 3012, return beam signal multiplexer 3020) and subband multiplexing/demultiplexing (subband multiplexer/demultiplexer 3030) for the forward beamformer 529 and return beamformer 531 can be performed by packet switching (e.g., Ethernet switching, etc.). In some cases, time slice and subband switching can be performed in the same switching node or in a different order. For example, a fabric switching architecture can be used, where each fabric switching node can be coupled to a subset of the AN 515, the forward time slice beamformer 3006, the return time slice beamformer 3016, or the feeder link modem 507. The fabric switching architecture can allow, for example, any AN to connect (e.g., via switches and/or switch fabric interconnects) to any forward time-slice beamformer or return time-slice beamformer in a low-latency hierarchical plane architecture. In one example, a system supporting K≤600, M≤600, and 500 MHz bandwidth (e.g., per subband) with fourteen subbands for forward or return links can be implemented by a commercially available interconnect switch platform with 2048 10GigE ports.

Delay Balancing

In some cases, the difference in propagation delay on each path between the end-to-end repeater 503 and the CPS 505 is not significant. For example, on the return link, when the same signal (e.g., data to or from a particular user) is received by multiple ANs 515, each instance of the signal can arrive at the CPS substantially aligned with every other instance of the signal. Similarly, when the same signal is transmitted to a user terminal 517 via several ANs 515, each instance of the signal can arrive at the user terminal 517 substantially aligned with every other instance of the signal. In other words, the signals can be phase- and time-aligned with sufficient accuracy so that the signals combine coherently, making the path delay and beamforming effects small relative to the transmission symbol rate. As an illustrative example, if the difference in path delay is 10 microseconds, the beamforming bandwidth can be on the order of tens of kHz, and a narrow bandwidth signal, say, ≈10 ksps, can be used with minimal performance degradation. The symbol duration of a 10 ksps signaling rate is 100 microseconds, and a delay spread of 10 microseconds is only one-tenth of the symbol duration. In these cases, for purposes of system analysis, it can be assumed that signals received by an end-to-end repeater at one instant will be repeated and transmitted at substantially the same time, as previously described.

In other cases, the propagation delay may vary significantly relative to the signaling interval (transmission symbol duration) of the signal transmitted from the transmit antenna element 409 to the AN 515. The path that the signal takes from each AN 515 through the distribution network 518 may contain significant delay variations. In these cases, delay equalization may be employed to match the path delays.

For the end-to-end return link signals received by the CPS 505 through the distribution network 518, the signals can be time-aligned by using the repeater beacon signal (e.g., the PN beacon as described above) transmitted from the end-to-end repeater. Each AN 515 can use the repeater beacon signal as a reference to time-stamp the composite return signal. Therefore, different ANs 515 can receive the same signal at different times, but the signals received in each AN 515 can be time-stamped to allow the CPS 505 to time-align them. The CPS 505 can buffer the signals so that beamforming is achieved by combining signals with the same time stamp.

Returning to Figures 33 and 34, delay equalization of the return link can be performed by demultiplexing the composite return signal to the return time slice beamformer 3016. For example, each AN can split the composite return signal into a set of samples associated with a time slice index t, which can include interleaved samples of the composite return signal. The time slice index t can be determined based on the repeater beacon signal. The AN can send a subset of samples multiplexed with the corresponding time slice index t (e.g., as a multiplexed composite return signal) to the return beamformer 531, and these corresponding time slice indices can be used as synchronization timing information on the return link. The subset of samples from each AN can be demultiplexed (e.g., via switching), and one return time slice beamformer 3016 can receive a subset of samples from each AN for time slice index t (in some cases, for one of multiple subbands). By performing a matrix product of the return beam weight matrix with a subset of samples from each of the M composite return signals associated with time slice index t, the return time slice beamformer 3016 can align the signals simultaneously relayed by the end-to-end repeaters for application of the return beam weight matrix.

For the forward link, the beamformer 513 within the CPS 505 can generate a timestamp indicating the expected time at which each access node-specific forward signal transmitted by the AN 515 arrives at the end-to-end repeater 503. Each AN 515 can transmit an access node beacon signal 2530, such as a looped PN signal. Each such signal can be looped back and transmitted back to the AN 515 by the end-to-end repeater 503. The AN 515 can receive the repeater beacon signal and the repeated (looped) access node beacon signal from any or all of the ANs. The timing of the received access node beacon signal relative to the reception timing of the repeater beacon signal indicates the time at which the access node beacon signal arrives at the end-to-end repeater. The timing of the access node beacon signal is adjusted so that the access node beacon signal, after being relayed by the end-to-end repeater, arrives at the AN at the same time as the repeater beacon signal, forcing the access node beacon signal to arrive at the end-to-end repeater synchronously with the repeater beacon. Having all ANs perform this function enables all access node beacon signals to arrive at the end-to-end repeater in synchronization with the repeater beacon. The last step in the process is to have each AN transmit its access node-specific forward signal in synchronization with its access node beacon signal. This can be done using the timestamps described later. Alternatively, the CPS can manage delay equalization (e.g., where the timing performed via the distribution network is deterministic) by sending corresponding access node-specific forward signals offset by corresponding time domain offsets to the AN. In some cases, the feeder link frequency range may be different from the user link frequency range. When the feeder link downlink frequency range (e.g., the frequency range in the V band) does not overlap with the user link downlink frequency range (e.g., the frequency range in the Ka band) and the AN is within the user coverage area, the AN may include an antenna and receiver operable within the user link downlink frequency range to receive the relayed access node beacon signal via the receive/transmit signal path of the end-to-end repeater. In this case, the end-to-end repeater may include a first repeater beacon generator that generates a first repeater beacon signal in a user link downlink frequency range to support feeder link synchronization. The end-to-end repeater may also include a second repeater beacon generator that generates a second repeater beacon signal in a feeder link downlink frequency range to support removal of feeder link impairments from the return downlink signal.

FIG36 is a diagram illustrating PN sequences used to align system timing. The horizontal axis of the figure represents time. AN ₁ PN sequence 2301 transmits chip 2303 in an access node beacon signal from a first AN. PN sequence 2305 depicts the relative time of arrival of this sequence at an end-to-end repeater. Due to propagation delay from the AN to the end-to-end repeater, PN sequence 2305 is time-shifted relative to AN ₁ PN sequence 2301. Repeater PN beacon sequence 2307 is generated within and transmitted from the end-to-end repeater in the repeater beacon signal. PN chip 2315 of repeater PN beacon sequence 2307 at time _T0 is aligned with PN chip 2316 of AN ₁ PN receive signal 2305 at time _T0 . PN chips 2316 of AN ₁ PN receive signal 2305 are aligned with PN chips 2315 of repeater PN beacon 2307 when AN ₁ transmit timing is adjusted by the appropriate amount. PN sequence 2305 is looped back from the end-to-end repeater, and PN sequence 2317 is received at AN _1. PN sequence 2319, transmitted from the end-to-end repeater in the repeater PN beacon, is received at AN _1. Note that PN sequences 2317, 2319 are aligned at AN ₁ , indicating that they are aligned at the end-to-end repeater.

Figure 37 shows an example of AN ₂ , which has not correctly adjusted the timing of the PN sequence generated in AN _2. Note that the PN sequence 2311 generated by AN ₂ is received at the end-to-end repeater, shown as sequence 2309, which is offset by an amount dt relative to the repeater PN beacon PN sequence 2307. This offset is caused by a timing error used to generate the sequence in AN _2. Also, note that AN ₂ PN sequence 2321 arrives at AN ₂ offset by the same amount dt relative to the repeater PN beacon PN sequence arriving at AN ₂ 2323. The signal processing in AN ₂ will observe this error and can make a correction to the transmission timing by adjusting the timing by an amount dt to align PN sequences 2321 and 2323.

In Figures 36 and 37, the same PN chip rate has been used for the repeater PN beacon and all AN (loopback) PN signals to facilitate the explanation of this concept. The same timing concept can be applied using different PN chip rates. Returning to Figures 31 and 32, the time slice index t can be used to synchronize the access node-specific forward signal received from each AN at the end-to-end repeater. For example, the time slice index t can be multiplexed using the access node-specific forward signal 516. Each AN can transmit a sample of the access node-specific forward signal using a specific time slice index t aligned with the corresponding timing information in the PN sequence of the code chip transmitted in the corresponding access node beacon signal. Since the corresponding access node beacon signal has been adjusted to compensate for the corresponding path delay and phase shift between the AN and the end-to-end repeater, the sample associated with the time slice index t will arrive at the end-to-end repeater when it is correctly timed synchronously and phase-aligned with each other.

In the event that the AN receives its own access node beacon signal, the access node beacon signal can be looped back using the same end-to-end repeater communication hardware that also carries the forward communication data. In these cases, the relative gain and/or phase of the transponders in the end-to-end repeaters can be adjusted as described subsequently.

38 is a block diagram of an exemplary AN 515. AN 515 includes a receiver 4002, a receive timing and phase adjuster 4024, a repeater beacon signal demodulator 2511, a multiplexer 4004, a network interface 4006, a controller 2523, a demultiplexer 4060, a transmit timing and phase compensator 4020, and a transmitter 4012. The network interface 4006 can be connected to, for example, the CPS 505 via a network port 4008.

On the return link, receiver 4002 receives a return downlink signal 527. The return downlink signal 527 may include, for example, a composite of a return uplink signal and a repeater beacon signal relayed by an end-to-end repeater (e.g., via multiple receive/transmit signal paths, etc.). Receiver 4002 may perform, for example, downconversion and sampling. Repeater beacon signal demodulator 2511 may demodulate the repeater beacon signal in the digitized composite return signal 907 to obtain repeater timing information 2520. For example, repeater beacon signal demodulator 2511 may perform demodulation to recover the chip timing associated with the repeater PN code and generate a timestamp corresponding to the transmission time from the end-to-end repeater for samples of the digitized composite return signal 527. The multiplexer 4004 may multiplex the repeater timing information 2520 with samples of the digitized composite return signal to be sent to the CPS 505 (e.g., via the network interface 4006) (e.g., to form a multiplexed composite return signal). Multiplexing the repeater timing information 2520 may include generating a subset of samples corresponding to the time slice index t for transmission to the CPS 505. For example, the multiplexer 4004 may output a subset of samples associated with each time slice index t for input to the return time slice beamforming architecture described above with reference to Figures 33, 34, and 35. The multiplexer 4004 may include an interleaver 4044 for, in some cases, interleaving the samples of each subset of samples.

On the forward link, the network interface 4006 can obtain an AN input signal 4014 (e.g., via the network port 4008). The demultiplexer 4060 can demultiplex the AN input signal 4014 to obtain an access node-specific forward signal 516 and forward signal transmission timing information 4016 indicating the transmission timing of the access node-specific forward signal 516. For example, the access node-specific forward signal 516 may include forward signal transmission timing information (e.g., multiplexed with data samples, etc.). In one example, the access node-specific forward signal 516 includes a set of samples (e.g., in a data packet), where each sample set is associated with a time slice index t. For example, each sample set can be a sample of the access node-specific forward signal 516 generated according to the forward time slice beamforming architecture discussed above with reference to Figures 31, 32, and 35. The demultiplexer 4060 may include a deinterleaver 4050 for deinterleaving samples associated with the time slice index t.

The transmission timing and phase compensator 4020 can receive and buffer the access node-specific forward signal 516 and output forward uplink signal samples 4022 for transmission by the transmitter 4012 at the appropriate time as the forward uplink signal 521. The transmitter 4012 can perform digital-to-analog conversion and upconversion to output the forward uplink signal 521. The forward uplink signal samples 4022 can include the access node-specific forward signal 516 and the access node beacon signal 2530 (e.g., a loopback PN signal), which can include transmission timing information (e.g., PN code chip timing information, frame timing information, etc.). The transmission timing and phase compensator 4020 can multiplex the access node-specific forward signal 516 with the access node beacon signal 2530 so that the forward signal transmission timing and phase information 4016 is synchronized with the corresponding transmission timing and phase information in the access node beacon signal 2530.

In some examples, generation of the access node beacon signal 2530 is performed locally at the AN 515 (e.g., in the access node beacon signal generator 2529). Alternatively, generation of the access node beacon signal 2530 can be performed in a separate component (e.g., the CPS 505) and sent (e.g., via the network interface 4006) to the AN 515. As described above, the access node beacon signal 2530 can be used to compensate the forward uplink signal 521 for path differences and phase shifts between the AN and the end-to-end repeater. For example, the access node beacon signal 2530 can be transmitted in the forward uplink signal 521 and relayed by the end-to-end repeater so as to be received back at the receiver 4002. The controller 2523 can compare the relayed transmit timing and phase information 4026 obtained from the relayed access node beacon signal (e.g., by demodulation, etc.) with the receive timing and phase information 4028 obtained from the repeater beacon signal (e.g., by demodulation, etc.). The controller 2523 can generate a timing and phase adjustment 2524 for input to the transmission timing and phase compensator 4020 to adjust the access node beacon signal 2530 to compensate for path delay and phase shift. For example, the access node beacon signal 2530 can include a PN code and frame timing information (e.g., one or more bits of a frame number, etc.). The transmission timing and phase compensator 4020 can, for example, adjust the frame timing information used for coarse compensation of path delay (e.g., the output frame timing information in the access node beacon signal so that the relayed access node beacon signal will coarsely align the relayed transmission frame timing information with the corresponding frame timing information in the repeater beacon signal, thereby changing which code chip of the PN code is considered to be the LSB, etc.). In addition or alternatively, the transmission timing and phase compensator 4020 can perform a timing and phase adjustment on the forward uplink signal samples 4022 to compensate for the timing or phase difference between the relayed transmission timing and phase information 4026 and the received timing and phase information 4028. For example, where the access node beacon signal 2530 is generated based on a local oscillator, the timing or phase difference between the local oscillator and the received repeater beacon signal can be corrected by adjusting the timing and phase of the forward uplink signal samples 4022. In some examples, demodulation of the access node beacon signal is performed locally at the AN 515 (e.g., in the access node beacon signal demodulator 2519). Alternatively, demodulation of the access node beacon signal can be performed in a separate component (e.g., CPS 505), and the relayed transmission timing and phase information 4026 can be obtained in other signaling (e.g., via the network interface 4006). For example, deep fading can make the AN's own relayed access node beacon signal difficult to receive and demodulate without having to transmit at a higher power than other signaling, which can reduce the power budget of the communication signal. Therefore, combining the reception of relayed access node beacon signals from multiple ANs 515 can improve the effective received power and demodulation accuracy of the relayed access node beacon signal. Thus, demodulation of access node beacon signals from a single AN 515 may be performed using downlink signals received at multiple ANs 515. Demodulation of access node beacon signals may be performed at the CPS 505 based on a composite return signal 907, which may also include signal information of access node beacon signals from most or all of the ANs 515. If desired, end-to-end beamforming of access node beacon signals may be performed taking into account access node beacon uplinks (e.g., _Cr ), repeater loopbacks (e.g., E), and/or access node beacon downlinks (e.g., _Ct ).

Feeder link damage elimination

In addition to delay equalization of the signal paths from all ANs to the end-to-end repeater, phase shifts induced by the feeder links can be eliminated before beamforming. The phase shift for each link between the end-to-end repeater and the M ANs will be different. The reasons for the different phase shifts for each link include, but are not limited to, propagation path length, atmospheric conditions such as scintillation, Doppler shift, and different AN oscillator errors. These phase shifts are typically different for each AN and are time-varying (due to differences in scintillation, Doppler shift, and AN oscillator errors). By eliminating dynamic feeder link impairments, the rate of beam weight adaptation can be slower than an alternative solution in which the beam weights adapt quickly enough to track the dynamic characteristics of the feeder link.

In the return direction, the feeder downlink impairments of the AN are common to both the repeater PN beacon and the user data signal (e.g., the return downlink signal). In some cases, coherent demodulation of the repeater PN beacon provides channel information for eliminating most or all of these impairments from the return data signal. In some cases, the repeater PN beacon signal is a known PN sequence that is continuously transmitted and located in-band with the communication data. The equivalent (or effective) isotropic radiated power (EIRP) of the in-band PN signal is set so that the interference with the communication data is no greater than the maximum acceptable level. In some cases, the feeder link impairment cancellation process for the return link involves coherent demodulation and tracking of the received timing and phase of the repeater PN beacon signal. For example, the repeater beacon signal demodulator 2511 can determine the receive timing and phase adjustment 2512 based on comparing the repeater PN beacon signal with a local reference signal (e.g., a local oscillator or PLL) to compensate for the feeder link impairments. The recovered timing and phase differences are then removed from the return downlink signal (e.g., by the receive timing and phase adjuster 4024), thereby removing the feeder link impairments from the communication signal (e.g., the return downlink signal 527). After the feeder link impairments are removed, the return link signal from the beam will have a common frequency error at all ANs and is therefore suitable for beamforming. The common frequency error may include, but is not limited to, contributions from user terminal frequency error, user terminal uplink Doppler error, end-to-end repeater frequency conversion frequency error, and repeater PN beacon frequency error.

In the forward direction, the access node beacon signal from each AN can be used to help eliminate feeder uplink impairments. Feeder uplink impairments will be imposed on the forward link communication data (e.g., access node-specific signals) as well as the access node beacon signal. Coherent demodulation of the access node beacon signal can be used to recover the timing and phase difference of the access node beacon signal (e.g., relative to the repeater beacon signal). The recovered timing and phase difference is then removed from the transmitted access node beacon signal so that the access node beacon signal arrives in phase with the repeater beacon signal.

In some cases, the forward feed link cancellation process is a phase-locked loop (PLL) with a path delay from the AN to the end-to-end repeater and back within a loop structure. In some cases, the round-trip delay from the AN to the end-to-end repeater and back to the AN may be large. For example, a geostationary satellite acting as an end-to-end repeater will generate a round-trip delay of approximately 250 milliseconds (ms). In order to maintain the stability of the loop in the presence of large delays, a very low loop bandwidth can be used. For a delay of 250ms, the PLL closed-loop bandwidth may typically be less than 1 Hz. In this case, both the satellite and the AN can use a high-stability oscillator to maintain a reliable phase lock, as shown in block 2437 in Figure 39 (see below).

In some cases, the access node beacon signal is a burst signal transmitted only during the calibration interval. During the calibration interval, no communication data is transmitted to eliminate this interference with the access node beacon signal. Since no communication data is transmitted during the calibration interval, the transmission power of the access node beacon signal can be much greater than that required when it is broadcast during the communication data period. This is because interference with the communication data is not considered (communication data is not present at this time). When the access node beacon signal is transmitted during the calibration interval, this technique enables the access node beacon signal to have a strong signal-to-noise ratio (SNR). The frequency of the calibration interval is the inverse of the elapsed time between calibration intervals. Since each calibration interval provides a phase sample to the PLL, the calibration frequency is the sampling rate of the discrete-time PLL. In some cases, the sampling rate is high enough to support the closed-loop bandwidth of the PLL with a low amount of aliasing. The product of the calibration frequency (loop sampling rate) and the calibration interval represents the fraction of time that the end-to-end repeater cannot use for communication data without additional interference from the channel sounding probe signal. In some cases, a value less than 0.1 is used, and in some cases, a value less than 0.01 is used.

FIG39 is a block diagram of an exemplary AN transceiver 2409. An input 2408 of the AN transceiver 2409 receives an end-to-end return link signal (e.g., for one of a plurality of frequency sub-bands) received by the AN 515. Input 2408 is coupled to an input 2501 of a down converter (D/C) 2503. The output of the D/C 2503 is coupled to an analog-to-digital converter (A/D) 2509. The output of the A/D 2509 is coupled to a receive timing adjuster 2515 and/or a receive phase adjuster 2517. The receive timing adjuster 2515 and the receive phase adjuster 2517 can illustrate various aspects of the receive timing and phase adjuster 4024 of FIG38. The D/C 2503 is an orthogonal down converter. Therefore, the D/C 2503 outputs in-phase and quadrature outputs to the A/D 2509. The received signal may include a communication signal (e.g., a synthesis of return uplink signals transmitted by user terminals), an access node beacon signal (e.g., transmitted from the same AN and/or other ANs), and a repeater beacon signal. The digital samples are coupled to a repeater beacon signal demodulator 2511. The repeater beacon signal demodulator 2511 demodulates the repeater beacon signal. In addition, the repeater beacon signal demodulator 2511 generates a time control signal 2513 and a phase control signal 2514 to eliminate feeder link impairments based on the received repeater beacon signal. Such impairments include Doppler error, AN frequency error, scintillation effects, path length variations, etc. By performing coherent demodulation of the repeater beacon signal, a phase-locked loop (PLL) can be used to correct most or all of these errors. By correcting the errors in the repeater beacon signal, corresponding errors in the communication signals and access node beacon signals on the feeder link are also corrected (e.g., because such errors are common to the repeater beacon signal, the access node beacon signal, and the communication signals). After the feeder link impairments are removed, the end-to-end return link communication signals from the user terminal 517 nominally have the same frequency error at each of the M ANs 515. This common error includes user terminal frequency error, user link Doppler error, end-to-end repeater frequency translation error, and repeater beacon signal frequency error.

The digital samples from which the feeder link impairments have been removed are coupled to a multiplexer 2518, which can be an example of the multiplexer 4004 of FIG. 38 . The multiplexer 2518 associates (e.g., timestamps) these samples with repeater timing information 2520 from the repeater beacon signal demodulator 2511. The output of the multiplexer 2518 is coupled to the output port 2410 of the AN transceiver 2409. The output port 2410 is coupled to the multiplexer 2413 and to the CPS 505 via the interface 2415 (see FIG. 40 ). The CPS 505 can then use the timestamps associated with the received digital samples to align the digital samples received from each AN 515. Additionally or alternatively, feeder link impairment removal can be performed at the CPS 505. For example, digital samples of an end-to-end return link signal with an embedded repeater beacon signal can be sent from AN 515 to CPS 505, and CPS 505 can use the synchronization timing information (e.g., the embedded repeater beacon signal) in each of the composite return signals to determine corresponding adjustments to the corresponding composite return signals to compensate for downlink channel impairments.

2408 . The access node beacon signal 2530 may be generated locally by an access node beacon signal generator 2529. The access node beacon signal demodulator 2519 demodulates the access node beacon signal received by the AN 515 (e.g., after the access node beacon signal is relayed by the end-to-end repeater and received at the input 2408). The repeater beacon signal demodulator 2511 provides the received repeater timing and phase information signal 2521 to the controller 2523. The controller 2523 also receives the relayed transmit timing and phase information signal 2525 from the access node beacon signal demodulator 2519. The controller 2523 compares the received repeater timing and phase information with the relayed transmit timing and phase information and generates a coarse time adjustment signal 2527. The coarse time adjustment signal 2527 is coupled to the access node beacon signal generator 2529. The access node beacon signal generator 2529 generates an access node beacon signal 2530 with embedded transmit timing information for transmission from the AN 515 to the end-to-end repeater 503. As noted in the above discussion, the difference between the repeater timing and phase information (embedded in the repeater beacon signal) and the transmit time and phase information (embedded in the access node beacon signal) is used to adjust the transmit timing and phase information so that the relayed transmit timing and phase information is synchronized with the received repeater timing and phase information. The access node beacon signal generator 2529 is coarsely time-adjusted by signal 2527, and the receive time adjuster 2539 is finely time-adjusted by signal 2540. With the transmission timing and phase information 2525 relayed from the access node beacon signal demodulator 2519 synchronized with the received repeater timing and phase information 2521, the access node beacon signal generator 2529 generates a timestamp 2531 that helps synchronize the access node beacon signal 2530 with the access node-specific forward signal from the transmitted CPS 505. That is, data samples from the CPS 505 are received on the input port 2423 along with a timestamp 2535 indicating the expected time of arrival of the associated data sample at the end-to-end repeater 503. The buffer time alignment and addition module 2537 buffers the data samples coupled from the CPS 505 and adds them to the samples from the access node beacon signal generator 2529 based on the timestamps 2535, 2531. PN samples and communication data samples having the same time (as indicated by the timestamp) are added together. In this example, multiple beam signals (x _k (n)*b _k ) are added together in the CPS 505 , and a synthesized access node-specific forward signal including the multiple beam signals is sent by the CPS 505 to the AN.

When properly aligned by the ANs, data samples arrive at the end-to-end repeater 503 at the desired time (e.g., at the same time as the same data samples from other ANs arrive). The transmit timing adjuster 2539 performs fine timing adjustments based on the fine timing controller output signal 2540 from the time controller module 2523. The transmit phase adjuster 2541 performs phase adjustments on the signal in response to the phase control signal 2542 generated by the access node beacon signal demodulator 2519. The transmit timing adjuster 2539 and the transmit phase adjuster 2541 can illustrate aspects of the transmit timing and phase compensator 4020 of FIG. 38, for example.

The output of the transmit phase adjuster 2541 is coupled to the input of a digital-to-analog converter (D/A) 2543. The quadrature analog output of the D/A 2543 is coupled to an upconverter (U/C) 2545 for transmission by the HPA 2433 (see FIG. 40 ) to the end-to-end repeater 503. An amplitude control signal 2547 provided by the access node beacon signal demodulator 2519 provides amplitude feedback to the U/C 2545 to compensate for terms such as uplink rain fade.

In some cases, the PN code used by each AN for access node beacon signal 2530 is different from the PN code used by each other AN. In some cases, the PN code in the access node beacon signal is different from the repeater PN code used in the repeater beacon signal. Thus, each AN 515 can be able to distinguish its own access node beacon signal from the access node beacon signals of other ANs 515. AN 515 can distinguish its own access node beacon signal from the repeater beacon signal.

As previously mentioned, the end-to-end gain from any point in the coverage area to any other point in the area is a multipath channel with L different paths, which can cause very deep fading in some point-to-point channels. Transmission diversity (forward link) and reception diversity (return link) are very effective in mitigating deep fading and enabling communication systems to work. However, for access node beacon signals, there is no transmission and reception diversity. Therefore, the point-to-point link of the loopback signal (i.e., the signal transmission from the AN back to the same AN) can experience an end-to-end gain much lower than the average. In the case of a large number of receive/transmit signal paths (L), a value 20dB lower than the average may occur. These low end-to-end gains cause the SNR of these ANs to decrease and can make link closure challenging. Therefore, in some cases, a higher gain antenna is used at the AN. Alternatively, with reference to the exemplary transponder of Figure 16, a phase adjuster 418 can be included in each of the receive/transmit signal paths. Phase adjusters 418 can be individually adjusted by phase shift controller 427 (e.g., controlled by a telemetry, tracking, and command (TT&C) link from an Earth-based control center). Adjusting the relative phase can help increase the end-to-end gain of the low-gain loopback path. For example, the goal can be to select a phase shift setting that increases the worst-case loopback gain (the gain from the AN back to itself). Note that the choice of phase does not generally change the distribution of gain when evaluating all points in the coverage area to the distribution of gain when evaluating all other points in the coverage area, but it can increase the gain of the low-gain loopback path.

To illustrate, consider the set of gains from each of the M ANs 515 to all other ANs 515. There are ^M² gains, of which only M are gains for the loop paths. Consider two gain distributions. The first is the total distribution of all paths ( ^M² ), which can be estimated by compiling a histogram of all ^M² paths. For ANs that are uniformly distributed throughout the coverage area, this distribution can represent the distribution of end-to-end gain from any point in the coverage area to any other point. The second distribution is the loop gain distribution (loop distribution), which can be estimated by compiling a histogram of only the M loop paths. In many cases, custom selection of receive/transmit signal path phase settings (and optionally, gain settings) does not significantly change the total distribution. This is especially true for random or interleaved mapping of transmit elements to receive elements. However, in most cases, the loop distribution can be improved by custom selection of phase (and optionally, gain) settings (as opposed to random values). This is because the loop gain set consists of M paths (as opposed to ^M² total paths), and the number of degrees of freedom in phase and gain adjustment is L. Typically, L is of the same order as M, which allows for significant improvements in low loop-back gains through custom phase selection. From another perspective, custom phase selection does not necessarily eliminate low end-to-end gains, but rather moves them from the loop-back gain set (M members in the set) to the non-loop-back gain set ( ^M2 -M members). For non-trivial values of M, the larger set is typically much larger than the former.

AN 515 can process one or more frequency sub-bands. Figure 40 is a block diagram of an exemplary AN 515 in which multiple frequency sub-bands are processed separately. On the end-to-end return link 523 (see Figure 5), AN 515 receives a return downlink signal 527 from the end-to-end repeater 503 via LNA 2401. The amplified signal is coupled from LNA 2401 to power divider 2403. Power divider 2403 divides the signal into multiple output signals. Each signal is output at one of the output ports 2405, 2407 of power divider 2403. One of the output ports 2407 can be set as a test port. The other ports 2405 are coupled to the input port 2408 of a corresponding one of a plurality of AN transceivers 2409 (only one is shown). AN transceiver 2409 processes the signal received on the corresponding sub-band. AN transceiver 2409 performs several functions discussed in detail above. The output 2410 of the AN transceiver 2409 is coupled to the input port 2411 of the sub-band multiplexer 2413. These outputs are combined in the sub-band multiplexer 2413 and output to the distribution network interface 2415. The interface 2415 provides an interface for data from the AN 515 to the CPS 505 or from the CPS 505 to the AN 515 via the distribution network (see FIG. 5 ). Processing frequency sub-bands can help reduce the performance requirements of the RF components used to implement end-to-end repeaters and ANs. For example, by dividing a 3.5 GHz bandwidth (e.g., as may be used in a Ka-band system) into seven sub-bands, each sub-band is only 500 MHz wide. That is, each of the access node-specific forward signals can include multiple sub-signals associated with different sub-bands (e.g., associated with different subsets of the forward user beam coverage area), and the AN transceiver 2409 can up-convert the sub-signals to different carrier frequencies. This bandwidth division can allow the use of lower tolerance components because amplitude and phase variations between different sub-bands can be compensated for by separate beamforming weights, calibration, etc. for different sub-bands. Of course, other systems may use a different number of sub-bands and/or test ports. Some cases may use a single sub-band and may not include all of the components shown here (e.g., omitting power splitter 2403 and multiplexer 2413).

On the end-to-end repeater link 501, data is received from the CPS 505 by the interface 2415. The received data is coupled to the input port 2417 of the sub-band demultiplexer 2419. The sub-band demultiplexer 2419 divides the data into multiple data signals. These data signals are coupled from the output port 2421 of the sub-band demultiplexer 2419 to the input port 2423 of the AN transceiver 2409. The output port 2425 of the AN transceiver 2409 is coupled to the input port 2427 of the adder module 2429. The adder module 2429 adds the signals output from the seven AN transceivers 2409. The output port 2431 of the adder module 2429 couples the output of the adder module 2429 to the input port 2433 of the high power amplifier (HPA) 2435. The output of the HPA 2435 is coupled to an antenna (not shown) that transmits the signal output to the end-to-end repeater 503. In some cases, an ultrastable oscillator 2437 is coupled to the AN transceiver 2409 to provide a stable reference frequency source.

Beam weight calculation

Returning to FIG8 , which is an exemplary description of signals on a return link, a mathematical model of an end-to-end return link can be used to describe the link as:

in,

x is a K×1 column vector of the transmitted signal. In some cases, the square of the magnitude of each element in x is defined to be unity (equal transmit power). In some cases, this is not always the case.

y is a K x 1 column vector of the received signal after beamforming.

Ar is the L×K return uplink radiation matrix. Element a _lk contains the gain and phase of the path from the reference position located in beam K to the lth (letter "el") receive antenna element 406 in the receive array. In some cases, the values of the return uplink radiation matrix are stored in channel data storage area 941 (see FIG. 30 ).

E is an L×L payload matrix. Elements e _ij define the signal gain and phase from the jth antenna element 406 in the receive array to the i-th antenna element 409 in the transmit array. In some cases, the E matrix is diagonal, excluding occasional crosstalk between paths (caused by finite isolation of electronic components). Matrix E can be normalized so that the sum of the squared magnitudes of all elements in the matrix is L. In some cases, the values of the payload matrix are stored in channel data repository 941 (see FIG. 29 ).

Ct is an M×L return downlink radiation matrix. The element c _ml contains the gain and phase of the path from the lth (letter "el") antenna element in the transmit array to the mth AN 515 among the M ANs 515. In some cases, the values of the return downlink radiation matrix are stored in the channel data repository 941 (see Figure 29).

Hret is the M×K return channel matrix, which is equal to the product Ct×E×Ar.

n _ul is an L × 1 noise vector of complex Gaussian noise. The covariance of the uplink noise is the identity matrix.

^σ2 is the noise variance. is experienced on the uplink, while is experienced on the downlink.

n _dl is an M × 1 noise vector of complex Gaussian noise. The covariance of the downlink noise is the identity matrix.

Bret is the K×M matrix of end-to-end return link beam weights.

Generally speaking, multiple examples (e.g., referring to Figures 6 to 11) are described above in a manner assuming that there are some similarities between the forward end-to-end multipath channel and the return end-to-end multipath channel. For example, generally speaking, the forward and return channel matrices are described above with reference to M, K, E and other models. However, these descriptions are only used to simplify the description to increase clarity, and are not limited to the situation where the example is only limited to the forward and return directions with the same configuration. For example, in some cases, the same transponder is used for both forward traffic and return traffic, and therefore the payload matrix E can be identical for both forward and return end-to-end beamforming (and corresponding beam weight calculation). In other cases, different transponders are used for forward traffic and return traffic, and different forward payload matrices (Efwd) and return payload matrices (Eret) can be used to model the corresponding end-to-end multipath channel and calculate the corresponding beam weight. Similarly, in some cases, identical M ANs 515 and K user terminals 517 are considered to be a part of both forward and return end-to-end multipath channels. In other cases, M and K may refer to different subsets of ANs 515 and/or user terminals 517, and/or different numbers of ANs 515 and/or user terminals 517 in the forward and return directions.

The beam weights can be calculated in many ways to meet system requirements. In some cases, they are calculated after the end-to-end repeater is deployed. In some cases, the payload matrix E is measured before deployment. In some cases, the beam weights are calculated with the goal of increasing the signal-to-noise-and-interference ratio (SINR) of each beam and can be calculated as follows:

where R is the covariance of the received signal, and (*) ^H is the conjugate transpose (Hermetian) operator.

The k,m elements of the K×M return beam weight matrix Bret provide weights to form a beam from the user terminal in the k-th user beam to the m-th AN 515. Therefore, in some cases, each of the return beam weights used to form the return user beam is calculated by estimating the end-to-end return gain (i.e., an element of the channel matrix Hret) for each of the end-to-end multipath channels (e.g., each of the end-to-end return multipath channels).

Equation 2 is true where R is the covariance of the received signal provided in Equation 3. Therefore, when all matrices of Equations 1, 2, and 3 are known, the beam weights used to form end-to-end beams can be determined directly.

This set of weights reduces the mean square error between x and y. It also increases the end-to-end signal to interference plus noise ratio (SINR) of each of the K end-to-end return link signals 525 (originating from each of the K beams).

The first term in Equation 3 is the covariance of the downlink noise (which is uncorrelated). The second term in Equation 3 is the covariance of the uplink noise (which is correlated at the AN). The third term HH ^H in Equation 3 is the covariance of the signal. Setting the variance of the uplink to zero and ignoring the last term (HH ^H ) results in a set of weights that increase the downlink signal-to-noise ratio by phase-aligning the received signals on each of the M ANs 515. Setting the downlink noise variance to zero and ignoring the third term results in a set of weights that increase the uplink SINR. Setting both the uplink and downlink noise variances to zero results in a decorrelated receiver that increases the carrier-to-interference (C/I) ratio.

In some cases, the beam weights are normalized so that the sum of the squared magnitudes of any row of Bret is unity.

In some cases, the solution to Equation 2 is determined by a priori knowledge of the matrices Ar, Ct, and E and the variances of the noise vectors _null and _ndl . Knowledge of the matrix element values can be obtained during measurements performed during the manufacture and testing of the relevant components of the end-to-end repeater. This may work well for systems that do not expect the values in the matrices to change significantly during system operation. However, for some systems, particularly those operating in higher frequency bands, such expectations may not exist. In this case, the matrices Ar, Ct, and E can be estimated after deploying a vehicle (such as a satellite) on which the end-to-end repeater is disposed.

In some cases where no a priori information is used to set the weights, the solution to Equation 2 can be determined by estimating the values of R and H. In some cases, a designated user terminal 517 located at the center of each user beam coverage area 519 transmits a known signal x during the calibration period. The vector received at AN 515 is:

u＝H x+Ct E n _ul +n _dl Equation 4

In one example, the CPS 505 estimates the values of R and H based on the following relationship;

is an estimate R of the covariance matrix R, is an estimate of the channel matrix H and is an estimate of the correlation vector, is the conjugate of the kth component of the transmitted vector with the frequency error caused by the uplink transmission. In some cases, no return communication data is transmitted during the calibration period. That is, during the calibration period, only calibration signals known to AN are transmitted on the end-to-end repeater so that the allowed values are determined based on the received vector u using the above equation. This in turn allows the determined values. Both the covariance matrix estimate and the channel matrix estimate are determined based on the information received during the calibration period.

In some cases, the CPS 505 can estimate the covariance matrix in the presence of communication data (e.g., even when x is unknown). This can be seen from the fact that is determined based solely on the received signal u. Nevertheless, the value of is estimated based on signals received during a calibration period during which only calibration signals are transmitted on the return link.

In some cases, when transmitting communication data on the return link, an estimate of both the channel matrix and the covariance matrix is made. In this case, the covariance matrix is estimated as indicated above. However, the value of x is determined by demodulating the received signal. Once the value of x is known, the channel matrix can be estimated as indicated above in Equations 6 and 7.

The beamformed signal and its interference component are contained in the vector Bret H x. The signal and interference power for each of these beams is contained in the K×K matrix Bret H. The power of the kth diagonal element of Bret H is the desired signal power from beam k. The sum of the squared magnitudes of all elements in row k, excluding the diagonal elements, is the interference power in beam k. Therefore, the C/I for beam k is:

where s _kj are the elements of Bret H. The uplink noise is contained in the vector Bret Ct En _ul , which has a K×K covariance matrix. The kth diagonal element of the covariance matrix contains the uplink noise in beam k. The uplink signal-to-noise ratio for beam k is then calculated as:

where _tkk is the kth diagonal element of the uplink covariance matrix. The downlink noise is contained in the vector _Bretndl , which has covariance with the help of the normalized beam weights. Therefore, the downlink signal-to-noise ratio is:

The end-to-end SINR is a combination of equations 8 to 10:

The above equations describe how to calculate the end-to-end SINR taking into account the payload matrix E. The payload matrix can be constructed by intelligently selecting the gain and phase of each element of E. The gain and phase of the diagonal elements of E that optimize some utility metric (which is typically a function of the K-beam SINR calculated as described above) can be selected and implemented by providing a phase shifter 418 in each of the L transponders 411. Candidate utility functions include, but are not limited to, the sum of SINR _k (total SINR), the sum of Log(1+SINR _k ) (proportional to the total throughput), or the total power in the channel matrix H. In some cases, the improvement in the utility function by customizing the gain and phase is very small and insignificant. This is sometimes the case when using random or interleaved mapping of antenna elements. In some cases, the utility function can be improved by a non-trivial amount by customizing the gain and phase of the receive/transmit signal.

Returning to FIG. 9 , the mathematical model of the end-to-end forward link 501 can be used to describe the link 501 as:

y＝AtE[CrBfwdx+n _ul ]+n _dl

=Hfwd Bfwdx+ _AEnul + _ndlEquation 12

in,

x is a K×1 column vector of the transmitted signal. The square of the magnitude of each element in x is defined as unity (equal signal power). In some cases, unequal transmit power can be achieved by selecting forward beam weights.

y is a K×1 column vector of the received signal.

Cr is the L×M forward uplink radiation matrix. The element c _lm contains the gain and phase of the path 2002 from the mth AN 515 to the lth (letter "el") receive antenna element 406 of the receive antenna array on the end-to-end repeater 503. In some cases, the values of the forward uplink radiation matrix are stored in the channel data repository 921 (see Figure 29).

E is an L×L payload matrix. The elements e _ij define the gain and phase of the signal from the jth receive array antenna element to the ith antenna element in the transmit array. Aside from occasional crosstalk between paths (caused by finite isolation of electronic components), the E matrix is a diagonal matrix. In some cases, the matrix E is normalized so that the sum of the squared magnitudes of all elements in the matrix is L. In some cases, the values of the payload matrix are stored in the channel data repository 921 (see FIG. 29 ).

At is the K×L forward downlink radiation matrix. The elements a _kl contain the gain and phase of the path from antenna element L (letter "el") in the transmit array of end-to-end repeater 503 to the reference position in user beam k. In some cases, the values of the forward downlink radiation matrix are stored in channel data repository 921 (see FIG29 ).

Hfwd is a K×M forward channel matrix, which is equal to the product A _t EC _r .

n _ul is the L×1 noise vector of complex Gaussian noise. The covariance of the uplink noise is:

where _IL is the L×L identity matrix.

n _dl is a K×1 noise vector of complex Gaussian noise. The covariance of the downlink noise is:

where I _K is the K×K identity matrix.

Bfwd is the M×K beam weight matrix of the end-to-end forward link beam weights.

The beam weight for user beam k is the element in column k of Bfwd. Unlike the return link, the C/I of beam k is not determined by the beam weight of beam k. The beam weight of beam k determines the uplink signal-to-noise ratio (SNR) and downlink SNR as well as the carrier (C) power in the C/I. However, the interference power in beam k is determined by the beam weights of all other beams except beam k. In some cases, the beam weight of beam k is selected to increase the SNR. Since C increases, such beam weights also increase the C/I of beam k. However, interference may occur in other beams. Therefore, unlike the case of the return link, the optimal beam weight is not calculated on a beam-by-beam basis (independent of other beams).

In some cases, the beam weights (including the radiation matrix and payload matrix used to calculate them) are determined after the end-to-end repeater is deployed. In some cases, the payload matrix E is measured before deployment. In some cases, the beam weight set can be calculated by using the interference caused by beam k in other beams and taking it as the interference count in beam k. Although this approach may not calculate the optimal beam weights, it can be used to simplify the weight calculations. This allows the weight set to be determined for each beam independently of all other beams. The resulting forward beam weight is then calculated similarly to the return beam weight:

Bfwd＝H ^H R ⁻¹ , where Equation 13

The first term in Equation 14 is the covariance of the downlink noise (uncorrelated). The second term is the covariance of the uplink noise (which is correlated at the AN). The third term, HH ^H , is the covariance of the signal. Setting the variance of the uplink noise to zero and ignoring the last term (HH ^H ) results in a set of weights that increase the downlink signal-to-noise ratio by phase-aligning the signals received at the M ANs 515. Setting the downlink noise variance to zero and ignoring the third term results in a set of weights that increase the uplink SNR. Setting both the uplink and downlink noise variances to zero results in a decorrelated receiver that increases the C/I ratio. For the forward link, downlink noise and interference generally dominate. Therefore, these terms are typically useful in beam weight calculations. In some cases, the second term (uplink noise) in Equation 14 is negligible compared to the first term (downlink noise). In such cases, the second term can be ignored in the covariance calculation, further simplifying the calculation while still producing a set of beam weights that increases the end-to-end SINR.

As with the return link, the beam weights can be normalized. For transmitter beam weights where equal power is allocated to all K forward link signals, each column of Bfwd can be scaled so that the sum of the squared amplitudes of the elements in any column adds to one. Equal power sharing will provide each signal with the same portion of the total AN power (the total power obtained from all ANs allocated to signal x _k ). In some cases, for the forward link, unequal power sharing between forward link signals is implemented. Therefore, in some cases, some beam signals receive more than one equal share of the total AN power. This can be used to equalize the SINR among all beams, or to provide a larger SINR for more important beams than for less important beams. To generate beam weights for unequal power sharing, the M×K equal power beam weight matrix Bfwd is right-multiplied by the K×K diagonal matrix P, so that the new Bfwd = Bfwd P. Assume

Then the square value of the kth diagonal element represents the power allocated to user signal _xk . The power sharing matrix P is normalized so that the sum or square of the diagonal elements is equal to K (the off-diagonal elements are zero).

In some cases, the solution to Equation 13 is determined by a priori knowledge of the matrices At, Cr, and E, and the variances of the noise vectors _null and _ndl . In some cases, knowledge of the matrices can be obtained during measurements performed during the manufacture and testing of the relevant components of the end-to-end repeater. This may work well for systems where the values in the matrices are not expected to change significantly from previously measured values during system operation. However, this may not be the case for some systems, particularly those operating in higher frequency bands.

In some cases where a priori information is not used to set the weights, the values of R and H for the forward link can be estimated to determine the solution to Equation 13. In some cases, the AN transmits a channel sounding probe during the calibration period. The channel sounding probe can be many different types of signals. In one case, different, orthogonal and known PN sequences are transmitted by each AN. The channel sounding probe can be pre-corrected in time, frequency and/or phase to eliminate feeder link impairments (as further discussed below). All communication data can be turned off during the calibration interval to reduce interference with the channel sounding probe. In some cases, the channel sounding probe can be the same signal as the signal used for feeder link impairment cancellation.

During the calibration interval, the terminal located at the center of each beam can be designated to receive and process the channel sounding probe. The Kx1 vector u received during the calibration period is u=Hx+ _AtEnul + _ndl , where x is the Mx1 vector of the transmitted channel sounding probe. In some cases, each designated terminal first removes the occasional frequency error (caused by Doppler shift and terminal oscillator error) and then correlates the resulting signal with each of M known orthogonal PN sequences. The correlation results are M complex numbers (amplitude and phase) for each terminal, and these results are transmitted back to the CPS via the return link. The M complex numbers calculated by the terminal located at the center of the kth beam can be used to form the kth row of the estimate of the channel matrix. By using the measurements obtained from all K designated terminals, an estimate of the entire channel matrix is obtained. In many cases, it is useful to combine the measurements from multiple calibration intervals to improve the estimate of the channel matrix. Once the estimate of the channel matrix is determined, the estimate of the covariance matrix can be determined according to Equation 14 using a value of 0 for the second term. If the uplink noise (the second term in Equation 14) is negligible relative to the downlink noise (the first term in Equation 14), this may be a very accurate estimate of the covariance matrix. The forward link beam weights can then be calculated by using the channel matrix in Equation 13 and the estimate of the covariance matrix. Therefore, in some cases, the calculation of the beam weights includes estimating the end-to-end forward gain (i.e., the value of the element of the channel matrix Hfwd) for each of the end-to-end forward multipath channels between the AN 515 and a reference position in the user beam coverage area. In other cases, the calculation of the beam weights includes estimating the end-to-end forward gain of K×M end-to-end forward multipath channels from the M ANs 515 to the reference position located within the K user beam coverage areas.

The beamformed signal and its interference component are contained in the vector HBfwdx (the product of H, Bfwd, and x). The signal and interference power for each of these beams is contained in the K×K matrix HBfwd. The power of the kth diagonal element of HBfwd is the desired signal power intended for beam k. The sum of the squared magnitudes of all elements in row k, excluding the diagonal elements, is the interference power in beam k. Therefore, the C/I for beam k is:

where s _kj are the elements of HB fwd. The uplink noise is contained in the vector _AtE n _ul , which has a K×K covariance matrix. The kth diagonal element of the covariance matrix contains the uplink noise in beam k. The uplink signal-to-noise ratio for beam k is then calculated as:

where _tkk is the kth diagonal element of the uplink covariance matrix. The downlink noise is contained in the vector _ndl , which has covariance. Therefore, the downlink signal-to-noise ratio is:

The end-to-end SINR is a combination of Equations 15 to 17:

The above equations describe how to calculate the end-to-end SINR considering the payload matrix E. The payload matrix can be constructed by intelligently selecting the gain and phase of each element of E. The gain and phase of the diagonal elements of E that optimize some utility metric (which is typically a function of the K-beam SINR calculated as described above) can be selected and implemented by providing a phase shifter 418 in each of the L transponders 411. Candidate utility functions include, but are not limited to, the sum of SINR _k (total SINR), the sum of Log(1+SINR _k ) (proportional to the total throughput), or the total power in the channel matrix H. In some cases, the improvement in the utility function by customizing the gain and phase is very small and insignificant. This is sometimes the case when using random or interleaved mapping of antenna elements. In some cases, the utility function can be improved by a non-trivial amount by customizing the gain and phase of the received/transmitted signal.

Different coverage areas

Some of the examples described above assume that the end-to-end repeater 503 is designed to serve a single coverage area shared by both the user terminals 517 and the ANs 515. For example, some scenarios describe a satellite with an antenna system that illuminates the satellite coverage area, and both the ANs 515 and the user terminals 517 are geographically distributed throughout the satellite coverage area (e.g., as shown in FIG27 ). The number of beams that can be formed in the satellite coverage area and the size of these beams (beam coverage areas) can be affected by various aspects of the antenna system design such as the number and arrangement of antenna elements, reflector size, etc. For example, achieving very large capacity can involve deploying a large number of ANs 515 (e.g., hundreds) with sufficient spacing between the ANs 515 to achieve end-to-end beamforming. For example, as noted above with reference to FIG28 , increasing the number of ANs 515 can increase system capacity, although the return decreases as the number increases. When one antenna subsystem supports both user terminals 517 and ANs 515, achieving such a deployment with sufficient spacing between ANs 515 can force the ANs 515 to have a very wide geographical distribution (e.g., across the entire satellite coverage area, as shown in FIG27 ). In practice, achieving such a distribution can involve placing ANs 515 in undesirable locations, such as in areas with poor access to high-speed networks (e.g., backed up to poor fiber infrastructure of CPS 505, etc.), in multiple legal jurisdictions, or in expensive and/or densely populated areas. Therefore, the placement of ANs 515 often involves various trade-offs.

Some examples of end-to-end repeaters 503 are designed with multiple antenna subsystems, thereby enabling separate service of two or more different coverage areas by a single end-to-end repeater 503. As described below, the end-to-end repeater 503 may include at least a first antenna subsystem that serves an AN area 3450 and at least a second antenna subsystem that serves a user coverage area 3460. Because the user coverage area 3460 and the AN area 3450 can be served by different antenna subsystems, each antenna subsystem can be designed to meet different design parameters, and each coverage area can be at least partially different (e.g., geographically, in beam size and/or density, in frequency band, etc.). For example, using such a multiple antenna subsystem approach can enable user terminals 517 distributed across one or more relatively large geographic areas 3460 (e.g., the entire United States) to be served by a large number of ANs 515 distributed across one or more relatively small geographic areas (e.g., a portion of the eastern United States). For example, the physical area of the AN area 3450 may be a small portion (e.g., less than half, less than a quarter, less than a fifth, less than a tenth) of the user coverage area 3460.

FIG41 is a diagram of an exemplary end-to-end beamforming system 3400. System 3400 is an end-to-end beamforming system that includes: a plurality of geographically distributed ANs 515; an end-to-end repeater 3403; and a plurality of user terminals 517. End-to-end repeater 3403 can be an example of an end-to-end repeater 503 as described herein. ANs 515 are geographically distributed within an AN area 3450, and user terminals 517 are geographically distributed within a user coverage area 3460. AN area 3450 and user coverage area 3460 are both within the visible Earth coverage area of end-to-end repeater 3403, but AN area 3450 is distinct from user coverage area 3460. In other words, AN area 3450 is not coextensive with user coverage area 3460, but may at least partially overlap with user coverage area 3460. However, the AN area 3450 may have a substantial (non-trivial) area that does not overlap with the user coverage area 3460 (e.g., more than one-tenth, one-quarter, one-half, etc. of the AN area 3450). For example, in some cases, at least half of the AN area 3450 does not overlap with the user coverage area 3460. In some cases, the AN area 3450 and the user coverage area 3460 may not overlap at all, as described with reference to FIG45C. As described above (e.g., in FIG5), the AN 515 may exchange signals with the CPS 505 within the ground segment 502 via the distribution network 518, and the CPS 505 may be connected to a data source.

End-to-end repeater 3403 includes a separate feeder link antenna subsystem 3410 and a user link antenna subsystem 3420. Each of feeder link antenna subsystem 3410 and user link antenna subsystem 3420 is capable of supporting end-to-end beamforming. For example, as described below, each antenna subsystem may have its own array of one or more coordinated antenna elements, its own array of one or more reflectors, etc. Feeder link antenna subsystem 3410 may include an array 3415 of coordinated feeder link component receive elements 3416 and an array 3415 of coordinated feeder link component transmit elements 3419. User link antenna subsystem 3420 may include an array 3425 of coordinated user link component receive elements 3426 and an array 3425 of coordinated user link component transmit elements 3429. The components are "coordinated" in the sense that their arrays have features that make their respective antenna subsystems suitable for use in beamforming systems. For example, a given user link component receive element 3426 may receive a superimposed composite of return uplink signals 525 from multiple (e.g., some or all) user beam coverage areas 519 in a manner that facilitates forming a return user beam. A given user link component transmit element 3429 may transmit a forward downlink signal 522 in a manner that is superimposed with corresponding transmissions from other user link component transmit elements 3429 to form some or all forward user beams. A given feeder link component receive element 3416 may receive a superimposed composite of forward uplink signals 521 from multiple (e.g., all) ANs 515 in a manner that facilitates forming a forward user beam (e.g., by inducing multipath at the end-to-end repeater 3403). A given feeder link component transmit element 3419 may transmit a return downlink signal 527 in a manner that is superimposed with corresponding transmissions from other feeder link component transmit elements 3419 to facilitate forming some or all return user beams (e.g., by enabling the ANs 515 to receive a composite return signal that can be beam-weighted to form a return user beam).

The exemplary end-to-end repeater 3403 includes a plurality of forward link transponders 3430 and a plurality of return link transponders 3440. These transponders can be any suitable type of bent-pipe signal path between the antenna subsystems. Each forward link transponder 3430 couples a corresponding one of the feeder link component receiving elements 3416 to a corresponding one of the user link component transmitting elements 3429. Each return link transponder 3440 couples a corresponding one of the user link component receiving elements 3426 to a corresponding one of the feeder link component transmitting elements 3419. Some examples are described as having a one-to-one correspondence between each user link component receiving element 3426 and a corresponding feeder link component transmitting element 3419 (or vice versa), or as each user link component receiving element 3426 being coupled to "one and only one" feeder link component transmitting element 3419 (or vice versa), etc. In some such cases, one side of each transponder is coupled to a single receiving element, and the other side of the transponder is coupled to a single transmitting element. In other such cases, one or both sides of a transponder may be selectively coupled to one of multiple elements (e.g., via a switch, splitter, combiner, or other device as described below). For example, an end-to-end repeater 3403 may include one feeder link antenna subsystem 3410 and two user link antenna subsystems 3420; and each transponder may be coupled to a single feed circuit element on one side and selectively coupled to a single user link element of the first user link antenna subsystem 3420 or to a single user link element of the second user link antenna subsystem 3420 on the other side. In such selective coupling cases, each side of each transponder may still be considered to be coupled to "one and only one" element at any given time (e.g., for a particular signal-related transaction), and so on.

For forward communications, transmissions from AN 515 may be received by feeder link component receiving element 3416 (via feeder uplink 521), relayed by forward link transponder 3430 to user link component transmitting element 3429, and transmitted by user link component transmitting element 3429 (via user downlink 522) to user terminal 517 in user coverage area 3460. For return communications, transmissions from user terminal 517 may be received by user link component receiving element (via user uplink signal 525), relayed by return link transponder 3440 to feeder link component transmitting element 3419, and transmitted by feeder link component transmitting element 3419 to AN 515 in AN area 3450 (via feeder downlink signal 527). The full signal path from AN 515 via end-to-end repeater 3403 to user terminal 517 is referred to as end-to-end forward link 501; and the full signal path from user terminal 517 via end-to-end repeater 3403 to AN 515 is referred to as end-to-end return link 523. As described herein, end-to-end forward link 501 and end-to-end return link 523 can each include multiple multipath channels for forward and return communications.

In some cases, each of the plurality of geographically distributed ANs 515 has an end-to-end beam-weighted forward uplink signal 521 output. The end-to-end repeater 3403 includes an array 3415 of cooperating feeder link component receive elements 3416 for wireless communication with the distributed ANs 515, an array 3425 of cooperating user link component transmit elements 3429 for wireless communication with the plurality of user terminals 517, and a plurality of forward link transponders 3430. The forward link transponders 3430 may be "bent-pipe" (or non-processing) transponders, such that each transponder outputs a signal corresponding to the signal it receives with little or no processing. For example, each forward link transponder 3430 may amplify and/or frequency convert the signal it receives, but may not perform more complex processing (e.g., no analog-to-digital conversion, demodulation and/or modulation, no satellite carrier beamforming, etc.). In some cases, each forward link transponder 3430 receives input at a first frequency range (e.g., 30 GHz LHCP) and outputs at a second frequency range (e.g., 20 GHz RHCP), and each return link transponder 3440 receives input at a first frequency range (e.g., 30 GHz RHCP) and outputs at a second frequency range (e.g., 20 GHz LHCP). Any suitable combination of frequency and/or polarization may be used, and the user link and feeder link may use the same or different frequency ranges. As used herein, a frequency range refers to a set of frequencies used for signal transmission/reception, and may be a continuous range or include multiple non-continuous ranges (e.g., such that a given frequency range may include frequencies from more than one frequency band, a given frequency band may include multiple frequency ranges, etc.). Each forward link transponder 3430 is coupled between a corresponding one of the feeder link component receiving elements 3416 and a corresponding one of the user link component transmitting elements 3419 (e.g., in a one-to-one correspondence). The forward link transponder 3430 converts the superposition of multiple beam-weighted forward uplink signals 521 received via the feeder link component receiving element 3416 into a forward downlink signal 522. The transmission of the forward downlink signal 522 by the user link component transmitting element 3429 facilitates the formation of a forward user beam that serves at least some of the plurality of user terminals 517 (e.g., which may be grouped into one or more user beam coverage areas 519 for transmission via corresponding beamformed forward user beams). As described herein, the forward uplink signals 521 may be end-to-end beam-weighted and synchronized (e.g., phase synchronized, and, if desired, time synchronized) prior to transmission from the AN 515, which may achieve the desired superposition of those signals 521 at the feeder link component receiving element 3416.

As described herein, the transmission of forward uplink signal 521 facilitates the formation of a forward user beam, and in this sense, beamforming is end-to-end; beamforming is the result of multiple steps, including: calculating and applying appropriate weights to forward uplink signal 521 prior to transmission from AN 515 to the repeater; inducing multipath reception by multiple forward link transponders 3430 of end-to-end repeater 3403; and transmitting forward downlink signal 522 from multiple user link component transmit elements 3429. However, for simplicity, some descriptions may refer to the forward beam as being formed by the superposition of the transmitted forward downlink signals 522. In some cases, each of the multiple user terminals 517 wirelessly communicates with the array 3425 of cooperating user link component transmit elements 3429 to receive a composite (e.g., superposition) of the transmitted forward downlink signals 522.

In some cases, the end-to-end repeater 3403 also includes an array 3425 of user link component receive elements 3426 that wirelessly communicate with the user terminals 517, an array 3415 of cooperating feeder link component transmit elements 3419 that wirelessly communicate with the distributed AN 515, and a plurality of return link transponders 3440. The return link transponders 3440 can be similar or identical to the forward link transponders 3430 (e.g., bent pipe transponders), except that each is coupled between a respective one of the user link component receive elements 3426 and a respective one of the feeder link component transmit elements 3419. Receipt of the return uplink signal 525 via the array of cooperating user link component receive elements 3426 allows formation of a return downlink signal 527 in the return link transponder 3440. In some cases, each return downlink signal 527 is a respective superposition of return uplink signals 525 received by the user link component receiving element 3426 from multiple user terminals 517 (e.g., from one or more user beam coverage areas 519). In some such cases, each of the multiple user terminals 517 wirelessly communicates with an array of cooperating user link component receiving elements 3426 to transmit a respective return uplink signal 525 to the multiple user link component receiving elements 3426.

In some cases, return downlink signals 527 are transmitted by feeder link component transmit elements 3419 to geographically distributed ANs 515. As described herein, each AN 515 may receive a superposition composite of return downlink signals 527 transmitted from feeder link component transmit elements 3419. This superposition composite may be an example of superposition 1706 described with reference to FIG6. The received return downlink signals 527 (which may be referred to as composite return signals) may be coupled to a return beamformer 531, which may combine, synchronize, beam-weight, and perform any other suitable processing. For example, the return beamformer 531 may weight the received superposition 1706 of the return downlink signals 527 before combining them (e.g., applying return beam weights to the composite return signal). The return beamformer 531 may also synchronize the composite return signals 1706 before combining them to account for at least the respective path delay differences between the end-to-end repeater 3403 and the AN 515. In some cases, synchronization may be based on received beacon signals (received by one or more or all of AN 515).

Due to the end-to-end nature of beamforming, the appropriate application of return beam weights by the return beamformer 531 enables the formation of a return user beam, even though the return beamformer 531 may be coupled to the feeder link side of the end-to-end multipath channel and may form a user beam at the user link side of the end-to-end multipath channel. Thus, the return beamformer 531 may be said to facilitate the formation of a return user beam (several other aspects of the system 3400 also facilitate end-to-end return beamforming, such as multipath induced by the return link transponder 3440 of the end-to-end repeater 3403). However, for simplicity, the return beamformer 531 may be said to form a return user beam.

In some cases, the end-to-end repeater 3403 also includes a feeder link antenna subsystem 3410 for illuminating an AN area 3450 in which the ANs 515 are distributed. The feeder link antenna subsystem 3410 includes an array 3415 of feeder link component receive elements 3416. In some cases, the end-to-end repeater 3403 also includes a user link antenna subsystem 3420 for illuminating a user coverage area 3460 in which a plurality of user terminals 517 are geographically distributed (e.g., within a plurality of user beam coverage areas 519). The user link antenna subsystem 3420 includes an array 3425 of user link component transmit elements 3429. In some cases, the user link antenna subsystem 3420 includes a user link receive array and a user link transmit array (e.g., a separate half-duplex array of user link component elements). The user link receive array and the user link transmit array can be spatially interleaved (e.g., directed toward the same reflector), spatially separated (e.g., directed toward a receive reflector and a transmit reflector, respectively), or arranged in any other suitable manner (e.g., as described with reference to FIG62). In other cases, the user link antenna subsystem 3420 includes full-duplex elements (e.g., each user link component transmit element 3429 shares a radiating structure with a corresponding user link component receive element 3426). Similarly, in some cases, the feeder link antenna subsystem 3410 includes a feeder link receive array and a feeder link transmit array, which can be spatially related in any suitable manner and can directly radiate toward a single reflector, toward separate transmit and receive reflectors, etc. In other cases, the feeder link antenna subsystem 3410 includes full-duplex elements. The feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 can have the same or different aperture sizes. In some cases, the feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 may operate in the same frequency range (e.g., a frequency range within the K/Ka band, etc.). In some cases, the feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 may operate in different frequency ranges (e.g., the feeder link uses the V/W band, the user link uses the K/Ka band, etc.). In some cases, the feeder link antenna subsystem 3410 and/or the user link antenna subsystem 3420 may operate in multiple frequency ranges (e.g., the feeder link uses the V/W band and the K/Ka band, as described below with reference to FIG. 64A , 64B, 65A, or 65B).

In examples such as that shown in FIG41 , the AN area 3450 is distinct from the user coverage area 3460. The AN area 3450 may be a single, continuous coverage area or a plurality of non-intersecting coverage areas. Similarly (and regardless of whether the AN area 3450 is single or multiple), the user coverage area 3460 may be a single, continuous coverage area or a plurality of non-intersecting coverage areas. In some cases, the AN area 3450 is a subset of the user coverage area 3460. In some cases, at least half of the user coverage area 3460 does not overlap with the AN area 3450. As described below, in some cases, the feeder link antenna subsystem 3410 further includes one or more feeder link reflectors, and the user link antenna subsystem 3420 further includes one or more user link reflectors. In some cases, the feeder link reflector is significantly larger than the user link reflector (e.g., the physical area of the feeder link reflector is at least two times, at least five times, ten times, fifty times, eighty times, etc., that of the user link reflector). In some cases, the feeder link reflector is approximately the same physical area as the user link reflector (the physical area of the feeder link reflector is within 5%, 10%, 25% of the physical area of the user link reflector).

In some cases, system 3400 operates with terrestrial network functionality, as described with reference to FIG5 . For example, end-to-end repeater 3403 communicates with AN 515, which communicates with CPS 505 via distribution network 518. In some cases, CPS 505 includes forward beamformer 529 and/or return beamformer 531, for example, as described with reference to FIG29 . As described above, forward beamformer 529 can participate in forming a forward end-to-end beam by applying calculated forward beam weights (e.g., supplied by forward beam weight generator 918) to forward uplink signal 521; and return beamformer 531 can participate in forming a return end-to-end beam by applying calculated return beam weights (e.g., supplied by return beam weight generator 935) to return downlink signal 527. As described above, the end-to-end forward beam weights and/or the end-to-end return beam weight sets can be calculated based on the estimated end-to-end gains of the end-to-end multipath channels, each of which communicatively couples a corresponding one of the distributed ANs 515 to a corresponding location in the user coverage area 3460 (e.g., the user terminal 517 or any suitable reference location) via a corresponding plurality of forward link bent pipe transponders 3430 and/or via a corresponding plurality of return link bent pipe transponders 3440. In some cases, although not shown, the end-to-end repeater 3403 includes a beacon signal transmitter. The beacon signal transmitter can be implemented as described above with reference to the beacon signal generator and calibration support module 424 of FIG. 15. In some cases, the generated beacon signal can be used to enable time-synchronized wireless communication between the plurality of distributed ANs 515 and the end-to-end repeater 3403 (e.g., utilizing a plurality of feeder link composition receiving elements 3416 based on the beacon signal).

In some cases, system 3400 includes a system for forming multiple forward user beams using end-to-end beamforming. Such cases include means for transmitting multiple forward uplink signals 521 from multiple geographically distributed locations, wherein the multiple forward uplink signals 521 are formed by a weighted combination of multiple user beam signals, and wherein each user beam signal corresponds to one and only one user beam. For example, the multiple geographically distributed locations may include multiple ANs 515, and the means for transmitting the multiple forward uplink signals 521 may include some or all of the forward beamformer 529, the distribution network 518, and the geographically distributed ANs 515 (in communication with the end-to-end repeater 3403). Such cases may also include means for relaying the multiple forward uplink signals 521 to form multiple forward downlink signals 522. Each forward downlink signal 522 is formed by amplifying a unique superposition of multiple forward uplink signals 521, and the multiple forward downlink signals 522 are superimposed to form multiple user beams, wherein each user beam signal is dominant within the corresponding user beam coverage area 519. For example, an apparatus for relaying multiple forward uplink signals 521 to form multiple forward downlink signals 522 may include an end-to-end repeater 3403 (in communication with one or more user terminals 517 in the user beam coverage area 519) having multiple signal paths co-located therewith, the multiple signal paths including a forward link transponder 3430 and a return link transponder 3440.

Some such scenarios include a first apparatus for receiving a first superposition of multiple forward downlink signals 522 and recovering a first user beam signal from the multiple user beam signals. Such a first apparatus may include a user terminal 517 (e.g., including a user terminal antenna and a modem or other components for recovering the user beam signal from the forward downlink signal). Some such scenarios also include a second apparatus (e.g., including a second user terminal 517) for receiving a second superposition of multiple forward downlink signals 522 and recovering a second user beam signal from the multiple user beam signals. For example, the first apparatus for receiving is located within the first user beam coverage area 519, and the second apparatus for receiving is located within the second user beam coverage area 519.

FIG42 is a diagram of an exemplary model of the signal paths of signals carrying return data on an end-to-end return link 523. The exemplary model can operate similarly to the model described with reference to FIG6 through FIG8 , except that the end-to-end repeater 3403 includes a return link signal path 3502 dedicated to return link communications. Each return link signal path 3502 may include a return link transponder 3440 coupled (e.g., selectively coupled) between a user link component receiving element 3426 and a feeder link component transmitting element 3419. Signals originating from user terminals 517 within the K user beam coverage areas 519 are transmitted (as return uplink signals 525) to the end-to-end repeater 3403, received by the array of L user link component receiving elements 3426, transmitted to L corresponding feeder link component transmitting elements 3419 via L return link signal paths 3502 (e.g., via L return link transponders 3440), and transmitted by each of the L feeder link component transmitting elements 3419 to some or all of the M ANs 515 (similar to that shown in FIG7 ). In this manner, multiple return link signal paths 3502 (e.g., return link transponders 3440) induce multipath in the return link communications. For example, the output of each return link signal path 3502 is a received composite return downlink signal 527 corresponding to return uplink signals 525 transmitted from multiple user beam coverage areas 519, and each return downlink signal 527 is transmitted to some or all of the M ANs 515 (e.g., geographically distributed across the AN area 3450). Thus, each AN 515 may receive a superposition 1706 of some or all of the return downlink signals 527, which may then be passed to the return beamformer 531. As described above, there are L (or at most L) different ways for a signal to enter a particular AN 515 from a user terminal 517 located in a user beam coverage area 519. The end-to-end repeater 3403 thereby creates L paths between the user terminal 517 and the AN 515, which are collectively referred to as end-to-end return multipath channels 1908 (e.g., similar to FIG8 ).

The end-to-end return multipath channel can be modeled in the same manner as described above. For example, Ar is the L×K return uplink radiation matrix, Ct is the M×L return downlink radiation matrix, and Eret is the L×L return payload matrix for the path from the user link component receive element 3426 to the feeder link component transmit element 3419. As described above, the end-to-end return multipath channel from a user terminal 517 in a particular user beam coverage area 519 to a particular AN 515 is the net effect of L different signal paths induced by the L unique return link signal paths 3502 passing through the end-to-end repeater 3403. In the case of K user beam coverage areas 519 and M ANs 515, there can be M×K induced end-to-end return multipath channels in the end-to-end return link 523 (via the end-to-end repeater 3403), and each can be modeled separately to calculate the corresponding element of the M×K return channel matrix Hret ( _Ct ×Eret×Ar). As described above (e.g., with reference to Figures 6-8), not all ANs 515, user beam coverage areas 519, and/or return link transponders 3440 must participate in the end-to-end return multipath channel. In some cases, the number of user beams, K, is greater than the number of transponders, L, in the signal path of the end-to-end return multipath channel; and/or the number of ANs 515, M, is greater than the number of return link transponders, L, in the signal path of the end-to-end return multipath channel. As described with reference to Figure 5, the CPS 505 can enable the formation of return user beams by applying return beam weights to the received downlink return signal 527 (the received signal, after being received by the AN 515, is referred to as the composite return signal 907, as further explained below). The return beam weights can be calculated based on a model of the M×K signal paths of each end-to-end return multipath channel that couples a user terminal 517 in one user beam coverage area 519 to one of the multiple ANs 515.

FIG43 is a diagram illustrating an exemplary model of the signal paths of signals carrying forward data on an end-to-end forward link 501. The exemplary model can operate similarly to the model described with reference to FIG9 through FIG11, except that the end-to-end repeater 3403 includes a forward link signal path 3602 dedicated to forward link communications. Each forward link signal path 3602 may include a forward link transponder 3430 coupled between a feeder link component receiving element 3416 and a user link component transmitting element 3429. As described above, each forward uplink signal 521 is beam-weighted (e.g., at a forward beamformer 529 in a CPS 505 of the ground segment 502) prior to transmission from the AN 515. Each AN 515 receives a unique forward uplink signal 521 and transmits the unique forward uplink signal 521 via one of the M uplinks (e.g., in a time-synchronized manner). Forward uplink signals 521 are received by some or all of the forward link transponders 3430 from geographically distributed locations (e.g., from AN 515) in a superimposed manner to produce a composite input forward signal 545. The forward link transponders 3430 receive the respective composite input forward signals 545 simultaneously, but with slightly different timing due to differences in the location of each receiving feeder link component receiving element 3416 associated with each forward link transponder 3430. For example, even though each feeder link component receiving element 3416 may receive a composite of the same plurality of forward uplink signals 521, the received composite input forward signals 545 may be slightly different. The composite input forward signal 545 is received by L forward link transponders 3430 via corresponding feeder link component receiving elements 3416, transmitted by the L forward link transponders 3430 to L corresponding user link component transmitting elements 3429, and transmitted by the L user link component transmitting elements 3429 to one or more of the K user beam coverage areas 519 (e.g., as forward downlink signals 522, each corresponding to a corresponding one of the received composite input forward signals 545). In this manner, multiple forward link signal paths 3602 (e.g., forward link transponders 3430) induce multipath in the forward link communication. As described above, there are L (or up to L) different ways for a signal to reach a particular user terminal 517 in the user beam coverage area 519 from the AN 515. The end-to-end repeater 3403 thereby induces multiple (e.g., up to L) signal paths 3602 between an AN515 and a user terminal 517 (or a user beam coverage area 519), which can be collectively referred to as an end-to-end forward multipath channel 2208 (e.g., similar to FIG10).

The end-to-end forward multipath channel 2208 can be modeled in the same manner as described above. For example, Cr is the L×M forward uplink radiation matrix, At is the K×L forward downlink radiation matrix, and Efwd is the L×L forward payload matrix for the path from the feeder link component receive element 3416 to the user link component transmit element 3429. In some cases, the forward payload matrix Efwd and the return payload matrix Eret can be different to reflect the difference between the forward link signal path 3602 and the return link signal path 3502. As described above, the end-to-end forward multipath channel from a particular AN 515 to a user terminal 517 in a particular user beam coverage area 519 is the net effect of the L different signal paths induced by the L unique forward link signal paths 3602 passing through the end-to-end repeater 3403. Given K user beam coverage areas 519 and M ANs 515, there can be M×K induced end-to-end forward multipath channels in the end-to-end forward link 501, each of which can be individually modeled to compute a corresponding element of the M×K forward channel matrix Hfwd(At×Efwd×Cr). As noted with reference to the return direction, not all ANs 515, user beam coverage areas 519, and/or forward link transponders 3430 necessarily participate in the end-to-end forward multipath channel. In some cases, the number of user beams, K, is greater than the number, L, of forward link transponders 3430 in the signal path of the end-to-end forward multipath channel; and/or the number, M, of ANs 515 is greater than the number, L, of forward link transponders 3430 in the signal path of the end-to-end forward multipath channel. As described with reference to FIG5 , appropriate beam weights can be calculated by the CPS 505 for each of the multiple end-to-end forward multipath channels to form a forward user beam. The use of multiple transmitters (AN 515) for a single receiver (user terminal 517) can provide transmission path diversity to enable successful transmission of information to any user terminal 517 in the presence of an intentionally induced multipath channel.

Figures 41 to 43 illustrate an end-to-end repeater 3403 implemented using separate forward link transponders 3430 and return link transponders 3440. Figures 44A and 44B illustrate diagrams of an exemplary forward signal path 3700 (similar to the forward signal path 3602 of Figure 43) and a return signal path 3750 (similar to the return signal path 3502 of Figure 42), respectively. As described above, the forward signal path 3700 includes a forward link transponder 3430 coupled between the feeder link component receiving element 3416 and the user link component transmitting element 3429. The return signal path 3750 includes a return link transponder 3440 coupled between the user link component receiving element 3426 and the feeder link component transmitting element 3419. In some cases, each forward link transponder 3430 and each return link transponder 3440 is a cross-pole transponder.

Figure 63A shows an exemplary spectrum allocation 6300 according to various embodiments of the present disclosure. The exemplary spectrum allocation 6300 of Figure 63A shows two frequency ranges 6325a and 6330a. Although shown as separate, the frequency ranges 6325a and 6330a may alternatively be adjacent (e.g., one continuous range). As shown in FIG63A, the forward link transponder 3430 receives a forward uplink signal 6340a (for example, which may be an example of the forward uplink signal 521 of FIG41) with left-hand circular polarization (LHCP) at the uplink frequency range 6330a, and outputs a forward downlink signal 6345a (for example, which may be an example of the forward downlink signal 522 of FIG41) with right-hand circular polarization (RHCP) at the downlink frequency range 6325a; and each return link transponder 3440 receives a return uplink signal 6350a (for example, which may be an example of the return uplink signal 525 of FIG41) with right-hand circular polarization (RHCP) at the uplink frequency range 6330a, and outputs a return downlink signal 6355a (for example, which may be an example of the return downlink signal 527 of FIG41) with left-hand circular polarization (LHCP) at the downlink frequency range 6325a. One such case (i.e., after the polarization described in the previous example) is shown only by following the solid lines of Figures 44A and 44B, and the other such case (i.e., after the polarization opposite to that described in the previous example) is shown only by following the dotted lines of Figures 44A and 44B.

In other cases, some or all of transponders can provide bipolar signal path pairs.For example, by following the solid line and dotted line of Figure 44 A and Figure 44 B, forward link transponder 3430 and return link transponder 3440 can receive forward uplink signal 521 by these two polarizations (LHCP and RHCP) under identical or different uplink frequencies, and can export forward downlink signal 522 by these two polarizations (LHCP and RHCP) under identical or different downlinks.This type of situation can use the interference of any appropriate type to alleviate technology (for example, use time division, frequency division, spatial separation etc.) and can make multiple systems can parallel operation.In the exemplary frequency allocation 6301 of Figure 63 B, show the specific implementation of a kind of this type of frequency division. In exemplary frequency allocation 6301, each forward link transponder 3430 receives a forward uplink signal 6340b within a first portion of an uplink frequency range 6330b (e.g., using two polarizations) and outputs a forward downlink signal 6345b within a first portion of a downlink frequency range 6325b (e.g., using two polarizations); and each return link transponder 3440 receives a return uplink signal 6350b within a second portion of an uplink frequency range 6330b (e.g., using two polarizations) and outputs a return downlink signal 6355a within a second portion of a downlink frequency range 6325b (e.g., using two polarizations). In some cases, the bandwidths of the first and second portions of frequency ranges 6330b and 6325b may be equal. In other examples, the bandwidths of the first and second portions may be different. For example, when traffic flows primarily through the end-to-end repeater 3403 in the forward direction (represented by the ETE forward link 501 in FIG. 41 ), the bandwidth of the first portion of the frequency ranges 6330b and 6325b used for forward link communications may be greater (e.g., significantly greater) than the bandwidth of the second portion used for return link communications.

In some cases, end-to-end repeater 3403 includes a large number of transponders, such as 512 forward link transponders 3430 and 512 return link transponders 3440 (for example, 1,024 transponders in total). Other specific implementations may include a smaller number of transponders, such as 10 or any other suitable number of transponders. In some cases, antenna element is implemented as a full-duplex structure so that each receiving antenna element shares a structure with a corresponding transmitting antenna element. For example, each shown antenna element can be implemented as two of the four waveguide ports of the radiating structure suitable for transmitting and receiving signals. In some cases, only feed link element or only user link element are full-duplex. Other specific implementations can use different types of polarization. For example, in some specific implementations, transponder can be coupled between receiving antenna element and transmitting antenna element with the same polarity.

Both the exemplary forward link transponder 3430 and the return link transponder 3440 may include some or all of an LNA 3705, a frequency converter and associated filter 3710, a channel amplifier 3715, a phase shifter 3720, a power amplifier 3725 (e.g., a traveling wave tube amplifier (TWTA), a solid-state power amplifier (SSPA), etc.), and a harmonic filter 3730. In the bipolar embodiment shown, each pole has its own signal path with its own set of transponder components. Some embodiments may have more or fewer components. For example, in the case where the uplink frequency and the downlink frequency are different, the frequency converter and associated filter 3710 may be useful. As an example, each forward link transponder 3430 may accept input at a first frequency range and output at a second frequency range; and each return link transponder 3440 may accept input at a first frequency range and output at a second frequency range.

In some cases, multiple sub-bands are used (e.g., seven 500 MHz sub-bands, as described above). For example, in some cases, transponders operating on the same sub-bands as used in a multiple sub-band implementation of a terrestrial network can be provided, effectively implementing multiple independent and parallel end-to-end beamforming systems (each end-to-end beamforming system operating in a different sub-band) through a single end-to-end repeater. In this case, each transponder may include multiple frequency converters and associated filters 3710 and/or other components dedicated to processing one or more sub-bands. The use of multiple frequency sub-bands can relax the requirements on the amplitude and phase response of the transponder because the terrestrial network can separately determine the beam weights used in each sub-band, thereby effectively calibrating out the passband amplitude and phase variations of the transponder. For example, in the case of separate forward and return transponders, and by using 7 sub-bands, a total of 14 different beam weights can be used for each beam (i.e., 7 sub-bands × 2 directions (forward and return)). In other cases, a wide bandwidth end-to-end beamforming system may use multiple sub-bands in the terrestrial network, but pass one or more (or all) of the sub-bands through a wideband transponder (e.g., passing seven sub-bands, each 500 MHz wide, through a 3.5 GHz bandwidth transponder). In some cases, each transponder path includes only an LNA 3705, a channel amplifier 3715, and a power amplifier 3725. Some implementations of the end-to-end repeater 3403 include a phase shift controller and/or other controller that can individually set the phase and/or other characteristics of each transponder as described above.

The antenna elements can transmit and/or receive signals in any suitable manner. In some cases, the end-to-end repeater 3403 has one or more array feed reflectors. For example, the feed link antenna subsystem 3410 can have a feed link reflector for both transmission and reception, or a separate feed link transmit reflector and a feed link receive reflector. In some cases, the feed link antenna subsystem 3410 can have multiple feed link reflectors for transmission, reception, or both. Similarly, the user link antenna subsystem 3420 can have a user link reflector for both transmission and reception, or a separate user link transmit reflector and a user link receive reflector. In some cases, the user link antenna subsystem 3420 can have multiple user link reflectors for transmission, reception, or both. In one exemplary embodiment, the feed link antenna subsystem 3410 includes an array of radiating structures, and each radiating structure includes a feed link component receive element 3416 and a feed link component transmit element 3419. In this case, feed link antenna subsystem 3410 may also include a feed link reflector that illuminates feed link component receive element 3416 and is illuminated by feed link component transmit element 3419. In some cases, the reflector is implemented as a plurality of reflectors, which may have different shapes, sizes, orientations, etc. In other cases, feed link antenna subsystem 3410 and/or user link antenna subsystem 3420 are implemented without a reflector, for example, as a direct radiating array.

As described above, achieving a relatively uniform distribution of ANs 515 across a given user coverage area may involve placing the ANs 515 in undesirable locations. Accordingly, the present disclosure describes techniques for enabling the ANs 515 to be geographically distributed within AN areas 3450 that are smaller (sometimes significantly smaller) than the user coverage area 3460. For example, in some cases, the AN area 3450 may be less than half, less than a quarter, less than a fifth, or less than a tenth of the physical area of the user coverage area 3460. In addition, multiple AN areas 3450 may be used simultaneously, or multiple AN areas 3450 may be activated for use at different times. As described herein, these techniques include using reflectors of different sizes, one or more composite reflectors, selectively coupled transponders, different user link and feeder link antenna subsystems, and the like.

As described above, separating the feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 can enable service of one or more AN areas 3450 that are distinct from one or more user coverage areas 3460. For example, the feeder link antenna subsystem 3410 can be implemented with a reflector having a much larger physical area than the reflector of the user coverage area 3460. The larger reflector can allow a large number of ANs 515 to be geographically distributed in significantly smaller AN areas 3450, such as in a small subset of the user coverage areas 3460. Some examples are shown in Figures 45A to 45G. Alternatively, the AN areas 3450 that are subsets of the user coverage areas can be deployed using a single antenna subsystem for both the feeder link and the user link by using different frequency ranges for the feeder link and the user link. For example, an AN area 3450 that is one-quarter the area of the user coverage area 3460 can be deployed using a feeder link carrier frequency that is approximately twice the user link carrier frequency. In one example, the user link may use a frequency range (or multiple ranges) in the K/Ka band (e.g., approximately 30 GHz), while the feeder link uses one or more frequency ranges in the V/W band (e.g., approximately 60 GHz). In this case, the AN area 3450 will be concentric with the user coverage area 3460.

FIG45A shows an example of an end-to-end repeater 3403 (e.g., a satellite) visible Earth coverage area 3800. In the exemplary end-to-end repeater 3403, the feeder link antenna subsystem 3410 includes an 18-meter feeder link reflector, and the user link antenna subsystem 3420 includes a 2-meter user link reflector (e.g., the area of the feeder link reflector is approximately eight times the area of the user link reflector). Each antenna subsystem also includes an array of 512 coordinated combined receive/transmit elements. The exemplary end-to-end repeater 3403 may include 512 forward link transponders 3430 (e.g., forming 512 forward signal paths 3700 as shown in FIG44A) and 512 return link transponders 3440 (e.g., forming 512 return signal paths 3750 as shown in FIG44B). From the geosynchronous orbital location of the end-to-end repeater 3403, the user link antenna subsystem 3420 illuminates a user coverage area 3460 that extends substantially across the visible Earth coverage area 3800, while the feed link reflector illuminates an AN area 3450, which is a small portion of the user coverage area 3460. Although the AN area 3450 is a small subset of the large user coverage area 3460, end-to-end beamforming with a large number of ANs 515 (e.g., coordinated in an AN cluster) in the AN area 3450 can be used to support a large system capacity including a large number of user beams. For example, hundreds of coordinated ANs 515 can be geographically distributed within the AN area 3450, which is shown as the shaded area in the eastern United States in FIG. 45A . In one example, 597 ANs 515 are geographically distributed within the AN area 3450.

46A shows visible earth coverage with end-to-end beamforming applied between AN 515 in AN area 3450 and user coverage area 3460. User coverage area 3460 includes 625 user beam coverage areas 519 that provide service to user terminals 517 within visible earth coverage area 3800.

FIG45B illustrates an example of an end-to-end repeater 3403 (e.g., satellite) continental United States (CONUS) coverage area 3900. The exemplary end-to-end repeater 3403 is similar to the example shown in FIG45A, except that the feeder link antenna subsystem 3410 uses an 18-meter feeder link reflector, while the user link antenna subsystem 3420 includes a 5-meter user link reflector (e.g., the area of the feeder link reflector is approximately thirteen times the area of the user link reflector). The AN area 3450 (e.g., the area containing the matching AN cluster) is the same as the AN area of FIG45A: an area in the eastern United States with, for example, 597 ANs 515 distributed as a small subset of the user coverage area 3460.

46B shows a CONUS coverage area 3900 with end-to-end beamforming applied between the AN 515 in the AN area 3450 and the user coverage area 3460. The user coverage area 3460 includes 523 user beam coverage areas 519 that provide services to user terminals 517 within the CONUS coverage area.

The present disclosure supports various geographic and relative locations of AN clusters. As described herein, end-to-end repeaters 3403 (such as those shown in Figures 49A and 49B) can provide communication services between one or more user coverage areas 3460 and ANs 515 located in one or more AN areas 3450. In some examples (such as the example shown in Figure 45B), AN areas 3450 may overlap user coverage areas 3460 or be completely located within user coverage areas 3460. Additionally or alternatively, AN areas 3450 may not overlap user coverage areas 3460, as shown in Figure 45C. In some cases, such an arrangement may require the use of a special loopback mechanism, which is discussed below with reference to Figures 55A to 55C.

As another example of a possible geographic arrangement, an AN cluster (e.g., AN area 3450) may at least partially overlap with a low-demand area of user coverage area 3460. An example is shown in FIG. 45D , where AN area 3450 is located in a low-demand area of user coverage area 3460. In some cases, a low-demand area may be determined based on demand for communication services being below a demand threshold. For example, a low-demand area may have an average demand that is less than a fraction (e.g., half, a quarter, etc.) of the average demand of other service areas across user coverage area 3460. Such a deployment may support increased system capacity in higher-demand areas (e.g., by allowing portions of the spectrum associated with feeder link communications in the low-demand area to be used for user beams in the higher-demand area). That is, a given system bandwidth (which may be a continuous frequency range or multiple discontinuous frequency ranges) may be used primarily or entirely to serve user beams in areas outside the low-demand area and may be allocated primarily to feeder link communications within the low-demand area, while user beams in the low-demand area are allocated a smaller portion (e.g., less than half) of the system bandwidth. Thus, in some cases, user link communications in higher demand areas may use at least a portion of the same frequency bandwidth used for feeder link communications in lower demand areas where access node area 3450 is located. In this example, AN area 3450 is fully contained within user coverage area 3460, but the two may only partially overlap in some cases.

In some cases, an AN cluster may be located within (e.g., on the surface of) a body of water (e.g., a lake, sea, or ocean). An example is shown in FIG. 45E , which illustrates a user coverage area 3460 encompassing the United States and an AN area 3450 located off the east coast of the United States. In some cases, an AN area may at least partially overlap with a continent (e.g., some ANs 515 may not be located within the body of water). Thus, the examples discussed with respect to FIG. 45E include scenarios in which only one AN 515 is located within the body of water, all ANs 515 are located within the body of water, or some intermediate number of ANs 515 are located within the body of water. Advantages of locating part or all of an AN cluster on a body of water include the ability to use a large area for the AN cluster near a continent where user coverage is desired, the ability to flexibly place ANs 515 within the AN area 3450, and reduced competition for spectrum rights. For example, when an AN cluster is not located in a specific country or continent, regulatory considerations such as interference with other services and frequency band sharing can be reduced.

AN 515 located within the body of water may be located on a fixed or floating platform. Examples of fixed platforms for AN 515 include fixed oil platforms, fixed offshore wind turbines, or other platforms mounted on pile foundations. Examples of floating platforms include barges, buoys, offshore oil platforms, floating offshore wind turbines, etc. Some fixed or floating platforms may already have a power source, while other fixed or floating platforms dedicated to AN clusters may be configured with a power generation device (e.g., a generator, a solar power plant, a wind turbine, etc.). Distribution of access node-specific forward signals 521 from beamformers 529 to AN 515 and composite return signals 1706 from AN 515 to beamformers 531 may be provided via a distribution network 518 including wired or wireless links between one or more beamformers or distribution platforms and AN 515. In some cases, the distribution network 518 may include a submarine cable coupled to one or more beamformers and AN 515 distributed within the body of water, as discussed with reference to FIG. 45G . The submarine cable may also provide power. The distribution network may additionally or alternatively include wireless RF links (e.g., microwave backhaul links) or free space optical links. In some examples, one or more beamformers, distribution points for one or more beamformers, or the entire distribution network 518 may be located within a body of water. For example, FIG58 illustrates a CPS 505 located on an offshore (e.g., fixed or floating) platform 5805 that delivers traffic to a terrestrial network node and is coupled to an AN 515 in the body of water via the distribution network 518.

In some cases, at least some of the ANs 515 in the AN cluster may be mobile (e.g., may be located on a movable platform). For example, ANs 515 in a body of water may be located on a vessel or barge that can be controlled to reposition its position, as shown by the floating platform 5805 in FIG. 58 . Similarly, ground-based ANs 515 may be located on a vehicle-mounted platform, while airborne ANs 515 may be located on a mobile platform (such as an aircraft, balloon, drone, etc.). In some examples, mobile ANs 515 may be used to optimize the distribution of ANs 515 within an AN area 3450. For example, ANs 515 may be repositioned to achieve better geographical distribution within an AN area 3450, or ANs 515 may be repositioned (e.g., to redistribute available ANs 515) when one or more ANs 515 fail. Beamforming weights may be recalculated for the new position, and the ANs 515 may resynchronize transmission timing and phase to accommodate the new position, as described above.

In some examples, the AN area 3450 can be relocated using mobile ANs 515 (e.g., one or more ANs 515 in the AN cluster can be located on a mobile platform). An example is shown in FIG. 45F , which shows that the initial AN area 3450a includes multiple ANs 515 geographically distributed within the AN area 3450a. For various reasons, the AN cluster can be relocated within the new AN area 3450b. For example, the mobile AN cluster can be used to adapt to changes in the position of the end-to-end repeater 3403. In one example, the orbital position or orientation of the satellite end-to-end repeater 3403 changes due to a deployment change to a new orbital gap or due to orbital drift or alignment, and the change in the AN area 3450 adapts to the new orbital position or orientation. The mobile AN 515 can be moved to a new position within the new AN area 3450b. In addition, although the mobile AN cluster is shown as being located within a body of water, some or all of the ANs 515 can be located on land (e.g., the mobile AN 515 need not be located in a body of water). In some cases, one or more ANs 515 may be located on an aircraft (e.g., an airplane, a balloon, a drone, etc.). Additionally, although the current example describes a first AN area 3450a and a second AN area 3450b of similar size located at different locations, the AN areas 3450 located at different locations may be (e.g., significantly) different (e.g., due to differences in the tilt range or adaptation of antenna assemblies on the end-to-end repeater). For example, the first AN area 3450a and the second AN area 3450b may have the same (or similar) center point, but have significantly different physical dimensions (e.g., due to a combination of orbital gap shifting and re-pointing of the end-to-end repeater antennas).

For example, the AN cluster may initially be located at a first location 3450a. While located at the first location 3450a, each AN 515 of the AN cluster may receive an access node-specific forward signal for transmission to one or more user terminals in the user coverage area 3460 via the end-to-end repeater 3403. In various aspects, the access node-specific forward signal may be received from a forward beamformer 529 via a distribution network 518, which may be a free-space optical link or any other suitable link. As described above, the access node-specific forward signal may be appropriately weighted by the forward beamformer 529 before being received at the AN 515. While located at the first location 3450a, each AN 515 may synchronize its forward uplink signal 521 for reception at the end-to-end repeater 3403 such that the forward uplink signal 521 is aligned in time and phase with other forward uplink signals 521 from other ANs 515 in the AN cluster. Synchronization may be accomplished using any of the techniques described herein (eg, using repeater beacons).

Subsequently, the AN cluster (or portion thereof) may move to a second location 3450b. The movement may be made in response to some stimulus (e.g., a change in the location of an end-to-end repeater, weather conditions, etc.). At the second location 3450b, the AN 515 of the AN cluster may obtain a weighted access node-specific forward signal (e.g., generated using an updated beam weight matrix determined based on the new location of the AN 515 within the new AN area 3450b), synchronize transmissions, and transmit a forward uplink signal 521 to the end-to-end repeater 3403. Although described as being performed at the second location, one or more of these steps may be performed before arriving at the second location.

In some cases, the location and shape of the AN cluster can be configured to leverage existing network infrastructure. For example, as shown in FIG45G , the AN area 3450 can be located near an existing submarine cable 4551 (e.g., a fiber optic cable used in Internet backbone communications, etc.). The submarine cable 4551 can also provide power. The distribution network 518 (e.g., between ANs) may additionally or alternatively include wireless RF links (e.g., microwave backhaul links) or free space optical links. In some examples, one or more beamformers, distribution points for beamformers, or the distribution network 518 as a whole may be located within a body of water. As shown in FIG45G , one or more AN areas 3450 can be shaped (e.g., using appropriately shaped reflectors, etc.) so as to minimize the total distance between the AN 515 and the submarine cable 4551. The example of FIG45G shows an elliptical AN area 3450, but any suitable shape may be used. 45G , there may be multiple AN areas 3450 (eg, located along the same submarine cable 4551 or different submarine cables 4551). The multiple AN areas 3450 may be disjoint or at least partially overlapping.

Multiple coverage areas

In the exemplary end-to-end repeater 3403 described above, the user link antenna subsystem 3420 is described as a single antenna subsystem (e.g., having a single user link reflector), and the feeder link antenna subsystem 3410 is described as a single antenna subsystem (e.g., having a single feeder link reflector). In some cases, the user link antenna subsystem 3420 may include one or more antenna subsystems (e.g., comprising two or more subarrays of antenna elements) associated with one or more user link reflectors, and the feeder link antenna subsystem 3410 may include one or more antenna subsystems associated with one or more feeder link reflectors. For example, some end-to-end repeaters 3403 may have a user link antenna subsystem 3420 that includes a first set of user link component receive/transmit elements associated with a first user link reflector (e.g., each element is arranged to illuminate the first user link reflector and/or be illuminated by the first user link reflector) and a second set of user link component receive/transmit elements associated with a second user link reflector. In some cases, the physical areas of the two user link reflectors are approximately the same as each other (within 5%, 10%, 25%, etc. of each other). In some cases, one user link reflector is significantly larger than the other (e.g., the physical area of one user link reflector is 50% larger than the other, at least twice the size of the other, etc.). Each set of user link component receive/transmit elements and their associated user link reflectors can illuminate a corresponding different user coverage area 3460. For example, multiple user coverage areas can be non-overlapping, partially overlapping, completely overlapping (e.g., a smaller user coverage area can be contained within a larger user coverage area), etc. In some cases, multiple user coverage areas can be active (illuminated) simultaneously. Other situations, as described below, can enable selective activation of different portions of the user link component receive/transmit elements, thereby activating different user coverage areas at different times. Similarly, selective activation of different portions of the feeder link component receive/transmit elements can activate different AN areas 3450 at different times. Switching between multiple coverage areas can be coordinated using the CPS 505. For example, beamforming calibration, beam weight calibration, and beam weight application can occur in two parallel beamformers, one for each of two different coverage areas. The application of appropriate weights in the beamformers can be timed to correspond to the operation of the end-to-end repeater. For example, switching between multiple coverage areas can be coordinated to occur at time-slice boundaries when using a time-slice beamformer.

FIG47A and FIG47B illustrate exemplary forward signal paths 4000 and return signal paths 4050, respectively, each with selective activation of multiple user link antenna subsystems 3420. Forward signal paths 4000 (and other forward signal paths described herein) may be examples of forward signal paths 3602 described with reference to FIG43. Return signal paths 4050 (and other return signal paths described herein) may be examples of return signal paths 3502 described with reference to FIG42. For example, each forward signal path 4000 may have a transponder 3430 coupled between component antenna elements. In FIG47A, forward link transponder 3430b is similar to that described with reference to FIG44A, except that the output side of forward link transponder 3430b is selectively coupled to one of two user link component radiating elements 3429, each portion of a separate user link antenna subsystem 3420 (e.g., each portion of a separate array 3425 of associated user link component radiating elements 3429). As described above, the forward link transponder 3430b may include some or all of the following: an LNA 3705a; a frequency converter and associated filter 3710a; a channel amplifier 3715a; a phase shifter 3720a; a power amplifier 3725a; and a harmonic filter 3730a.

The forward link transponder 3430b of FIG47A further includes a switch 4010a (forward link switch) that selectively couples the transponder to a first user link component transmitting element 3429a (of the first user link antenna element array 3425a) via a first set of power amplifiers 3725a and harmonic filters 3730a, or to a second user link component transmitting element 3429b (of the second user link antenna element array 3425b) via a second set of power amplifiers 3725a and harmonic filters 3730a. For example, in a first switching mode, the forward link transponder 3430b effectively forms a signal path between the feeder link component receiving element 3416 and the first user link component transmitting element 3429a; and in a second switching mode, the forward link transponder 3430b effectively forms a signal path between the same feeder link component receiving element 3416 and the second user link component transmitting element 3429b. Switch 4010a can be implemented using any suitable switching device (such as an electromechanical switch, a repeater, a transistor, etc.). Although shown as switch 4010a, other implementations may use any other suitable device for selectively coupling the input of forward link transponder 3430 to multiple outputs. For example, power amplifier 3725a can function as a switch (e.g., providing high gain when "on" and zero gain (or loss) when "off"). Switch 4010a is an example of a switch that selectively couples one input to one of two or more outputs.

In FIG47B , the return link transponder 3440 b functionally mirrors the forward link transponder 3430 of FIG47A . Rather than selectively coupling the output side of the transponder as in the forward link case of FIG47A , the input side of the return link transponder 3440 b is selectively coupled to one of two user link component receive elements 3426. Similarly, each user link component receive element 3426 may be part of a separate array of cooperating user link component receive elements 3426, which may be part of the same user link antenna subsystem 3420 or a different user link antenna subsystem 3420. As described above (e.g., in FIG44B ), the return link transponder 3440 may include some or all of the following: an LNA 3705 b; a frequency converter and associated filter 3710 b; a channel amplifier 3715 b; a phase shifter 3720 b; a power amplifier 3725 b; and a harmonic filter 3730 b.

The return link transponder 3440b of FIG47B also includes a switch 4010b (return link switch) that selectively couples the transponder to a first user link component receiving element 3426a (of the first user link antenna element array 3425a) via a first set of LNAs 3705b, or to a second user link component receiving element 3426b (of the second user link antenna element array 3425b) via a second set of LNAs 3705b. For example, in a first switching mode, the return link transponder 3440b effectively forms a signal path between the first user link component receiving element 3426a and the feeder link component transmitting element 3419; and in a second switching mode, the return link transponder 3440b effectively forms a signal path between the second user link component receiving element 3426b and the same feeder link component transmitting element 3419. The switch 4010b can be implemented using any suitable switching device, such as an electromechanical switch, a repeater, a transistor, or the like. Although shown as switch 4010b, other implementations may use any other suitable means for selectively coupling the output of forward link transponder 3440b to multiple inputs. For example, power amplifier 3705b may function as a switch (e.g., providing high gain when "on" and zero gain (or loss) when "off"). Switch 4010b may be an example of a switch that selectively couples one of two or more inputs to a single output.

An example of an end-to-end repeater 3403 may include a switch controller 4070 to selectively switch some or all of the switches 4010 (or other suitable selective coupling devices) according to a switching schedule. For example, the switching schedule may be stored in a storage device on the end-to-end repeater 3403. In some cases, the switching schedule effectively selects which user link antenna element array 3425 will be activated (e.g., which user beam set will be illuminated) in each of a plurality of time intervals (e.g., time slots). In some cases, switching allocates equal time to the plurality of user link antenna element arrays 3425 (e.g., each of the two arrays is activated approximately half the time). In other cases, switching may be used to achieve capacity sharing objectives. For example, one user link antenna element array 3425 may be associated with a more demanding user and may be allocated a larger portion of the time in the schedule, while another user link antenna element array 3425 may be associated with a less demanding user and may be allocated a smaller portion of the time in the schedule.

Figures 48A and 48B show examples of end-to-end repeater 3403 coverage areas 4100 and 4150, respectively, including multiple selectively activated user coverage areas 3460a, 3460b. The exemplary end-to-end repeater 3403 is similar to the repeaters in Figures 38 and 39, except that different antenna subsystems are present. In this example, the user link antenna subsystem 3420 includes two 9-meter user link reflectors, and the transponder is configured to selectively activate only half of the user beam coverage area 519 at any given time (for example, the transponder is implemented as shown in Figures 47A and 47B). For example, during the first time interval, as shown in Figure 48A, the user coverage area 3460a includes 590 active user beam coverage areas 519. The active user beam coverage area 519 effectively covers half of the western United States. The AN area 3450 (AN cluster) is the same as Figures 38 and 39: a region in the eastern United States with, for example, 597 ANs 515. During the first time interval, AN area 3450 does not overlap with active user coverage area 3460a. During the second time interval, as shown in FIG48B , user coverage area 3460a includes an additional 590 active user beam coverage areas 519. Active user beam coverage areas 519 effectively cover half of the eastern United States during the second time interval. AN area 3450 does not change. However, during the second time interval, AN area 3450 completely overlaps with active user coverage area 3460b (being a subset of the active user coverage areas). Capacity can be flexibly allocated to various regions (e.g., between eastern and western user coverage areas 3460) by dynamically adjusting the time ratio allocated to the corresponding user link antenna subsystem 3420.

Although the previous example illustrates two user coverage areas 3460 of similar size, other numbers of user coverage areas 3460 (e.g., three or more) may be provided, and may have different sizes (e.g., global coverage, only continental United States, only the United States, only regions, etc.). In the case of multiple user coverage areas 3460, the user coverage areas 3460 may have any suitable geographical relationship. In some cases, the first user coverage area and the second user coverage area 3460 partially overlap (e.g., as shown in Figures 48A and 48B). In other cases, the second user coverage area 3460 may be a subset of the first user coverage area 3460 (e.g., as shown in Figures 46A and 46B). In other cases, the first user coverage area and the second user coverage area 3460 do not overlap (e.g., are disjoint).

In some cases, it may be desirable for services in specific geographic areas to terminate in their respective regions. Figure 50A shows a first AN area 3450a in North America for providing communication services to a first user coverage area 3460a in North America, and a second AN area 3450b for providing communication services to a second user coverage area 3460b in South America. In some cases, the AN within the first AN area 3450a exchanges signals with a first CPS (e.g., located within or near the AN area 3450a), and the AN within the second AN area 3450b exchanges signals with a second CPS that is separate and distinct from the first CPS (e.g., located within or near the AN area 3450b). For example, the first AN end-to-end repeater 3403 shown in Figures 49A and 49B can support multiple user coverage areas and multiple AN areas as shown in Figure 50A. Each combination of an AN area and a user coverage area can adopt a frequency allocation 6300 or 6301 as shown in Figure 63A or Figure 63B.

FIG49A illustrates an exemplary forward signal path 4900 for an end-to-end repeater 3403 supporting multiple user coverage areas and multiple AN areas 3450. The exemplary forward signal path 4900 includes a first forward link transponder 3430c coupled between a first feeder link component receiving element 3416a of a first feeder link antenna element array 3415a and a first user link component transmitting element 3429a of a first user link antenna element array 3425a. Additionally, the exemplary forward signal path 4900 includes a second forward link transponder 3430c coupled between a second feeder link component receiving element 3416b of a second feeder link antenna element array 3415b and a second user link component transmitting element 3429b of a second user link antenna element array 3425b. As described above, each of the forward link transponders 3430 may include some or all of the following: an LNA 3705a; a frequency converter and associated filter 3710a; a channel amplifier 3715a; a phase shifter 3720a; a power amplifier 3725a; and a harmonic filter 3730a.

FIG49B illustrates an exemplary return signal path 4950 for an end-to-end repeater 3403 supporting multiple user coverage areas and multiple AN areas 3450. The exemplary return signal path 4950 includes a first return link transponder 3440c coupled between a first user link component receiving element 3426a of a first user link antenna element array 3425a and a first feeder link component transmitting element 3419a of a first feeder link antenna element array 3415a. Additionally, the exemplary return signal path 4950 includes a second return link transponder 3440c coupled between a second user link component receiving element 3426b of a second user link antenna element array 3425b and a second feeder link component transmitting element 3419b of a second feeder link antenna element array 3415b. As described above, each of the return link transponders 3440 may include some or all of the following: an LNA 3705b; a frequency converter and associated filter 3710b; a channel amplifier 3715b; a phase shifter 3720b; a power amplifier 3725b; and a harmonic filter 3730b.

In some cases, feed link antenna element arrays 3415a and 3415b are part of a single feed link antenna subsystem 3410. Alternatively, a single feed link antenna subsystem 3410 may include both feed link antenna element arrays 3415a and 3415b (e.g., via the use of a single reflector, as described in more detail below with reference to FIG56A and FIG56B). Similarly, user link antenna element arrays 3425a and 3425b may be part of the same or a separate user link antenna subsystem 3420. The forward signal path 4900 and return signal path 4950 of FIG49A and FIG49B may be used to support multiple independent end-to-end beamforming systems using a single end-to-end repeater payload. For example, end-to-end beamforming between the first AN area 3450a and the first user coverage area 3460a shown in Figure 50A can be supported by one beamformer and distribution system, while a separate and independent beamformer and distribution system supports end-to-end beamforming between the second AN area 3450b and the second user coverage area 3460b. Figures 49A and 49B illustrate examples where the component receive elements can be the same as the component transmit elements, and therefore only one polarization is shown in each direction. However, other examples may employ different component receive elements and component transmit elements, and may use multiple polarizations in each direction.

Figures 47A and 47B describe signal path selection on the user link side. However, alternatively or in addition, some scenarios include signal path switching on the feeder link side. Figure 51A shows an exemplary forward signal path 5100 with selective activation of multiple user link antenna element arrays 3425 (which may be part of the same or different user link antenna subsystems 3420) and multiple feeder link antenna element arrays 3415 (which may be part of the same or different feeder link antenna subsystems 3410). The signal path has a forward link transponder 3430d coupled between the component antenna elements. As described above, the forward link transponder 3430d may include some or all of the following: an LNA 3705a; a frequency converter and associated filter 3710a; a channel amplifier 3715a; a phase shifter 3720a; a power amplifier 3725a; and a harmonic filter 3730a. The input side of the forward link transponder 3430d is selectively coupled to one of the two feeder link component receiving elements 3416 (e.g., using switch 4010b, or any other suitable path selection device). Each feeder link component receiving element 3416 can be part of a separate feeder link antenna element array 3415 (e.g., each part of a separate array of feeder link component receiving elements 3416). The output side of the forward link transponder 3430d is selectively coupled to one of the two user link component transmitting elements 3429 (e.g., using switch 4010a, or any other suitable path selection device). Each user link component transmitting element 3429 can be part of a separate user link antenna element array 3425 (e.g., each part of a separate array of user link component transmitting elements 3429). One or more switching controllers 4070 (not shown) may be included in the end-to-end repeater 3403 to select between some or all of the four possible signal paths enabled by the forward link transponder 3430d. For example, switch controller 4070 may operate forward link transponder 3430d according to one of several switching patterns, which may be determined based on which AN areas 3450 are used to support user coverage areas 3460. In one example, switch controller 4070 applies a first switching pattern to switch 4010 to couple forward link transponder 3430d between first feeder link antenna element array 3415a and first user link antenna element array 3425a, and applies a second switching pattern to switch 4010 to couple forward link transponder 3430d between second feeder link antenna element array 3415b and second user link antenna element array 3425b. Alternatively, a first switching mode for switch 4010 may couple the forward link transponder 3430d between the first feeder link antenna element array 3415a and the second user link antenna element array 3425b, and a second switching mode for switch 4010 may couple the forward link transponder 3430d between the second feeder link antenna element array 3415b and the first user link antenna element array 3425a.

FIG51B illustrates an exemplary selectively activated return signal path 5150 having a plurality of user link antenna element arrays 3425 (e.g., which may be part of the same or different user link antenna subsystem 3420) and a plurality of feeder link antenna element arrays 3415 (e.g., which may be part of the same or different feeder link antenna subsystem 3410). The signal path has a return link transponder 3440d coupled between the constituent antenna elements. As described above, the return link transponder 3440d may include some or all of the following: an LNA 3705b; a frequency converter and associated filter 3710b; a channel amplifier 3715b; a phase shifter 3720b; a power amplifier 3725b; and a harmonic filter 3730b. The input side of the return link transponder 3440d is selectively coupled to one of the two user link constituent receive elements 3426a, 3426b (e.g., using a switch 4010b or any other suitable path selection device). Each user link component receiving element 3426a, 3426b can be part of a separate user link antenna element array 3425a, 3425b (e.g., each part of a separate array of user link component receiving elements 3426). The output side of the return link transponder 3440d is selectively coupled to one of the two feeder link component transmitting elements 3419a or 3419b (e.g., using switch 4010a or any other suitable path selection device). Each feeder link component transmitting element 3419a or 3419b can be part of a separate feeder link antenna element array 3415a or 3415b (e.g., each part of a separate array of feeder link component transmitting elements 3419). One or more switching controllers 4070 (not shown) can be included in the end-to-end repeater 3403 to select between some or all of the four possible signal paths enabled by the return link transponder 3440d. For example, the switch controller 4070 may operate the return link transponder 3440d according to one of several switching patterns, which may be determined based on which AN areas 3450 are used to support the user coverage areas 3460. In one example, the switch controller 4070 applies a first switching pattern to the switch 4010 to couple the return link transponder 3440d between the first user link antenna element array 3425a and the first feeder link antenna element array 3415a, and applies a second switching pattern to the switch 4010 to couple the return link transponder 3440d between the second user link antenna element array 3425b and the second feeder link antenna element array 3415b. Alternatively, a first switching mode for the switch 4010 may couple the return link transponder 3440d between the first user link antenna element array 3425a and the second feeder link antenna element array 3415b, and a second switching mode for the switch 4010 may couple the return link transponder 3440d between the second user link antenna element array 3425b and the first feeder link antenna element array 3415a.

The transponders of Figures 47A, 47B, 51A, and 51B are intended to illustrate only some of the many possible scenarios for an end-to-end repeater 3403 employing routing. Additionally, some scenarios may include routing between more than two user link antenna element arrays 3425 or user link antenna subsystems 3420 and/or more than two feeder link antenna element arrays 3415 or feeder link antenna subsystems 3410.

As shown in Figures 51A and 51B, an end-to-end repeater 3403 can support multiple user coverage areas 3460 and multiple AN areas 3450. As described above, it may be desirable for services in specific geographic areas to terminate in their respective regions. For example, an end-to-end repeater 3403 with or without a paired transponder (such as those shown in Figures 51A and 51B) can use a first AN area 3450a in North America to provide communication services to a first user coverage area 3460a in North America, and use a second AN area 3450b to provide communication services to a second user coverage area 3460b in South America, as shown in Figure 50A. By using path selection (e.g., switching) in the transponder, a single end-to-end repeater 3403 (e.g., a single satellite) can use the AN 515 in the North American AN area 3450a (or use the AN 515 in the South American AN area 3450b) to serve traffic associated with the North American user coverage area 3460a, and use the AN 515 in the South American AN area 3450b (or use the AN 515 in the North American AN area 3450a) to serve traffic associated with the South American user coverage area 3460b. Capacity can be flexibly allocated to various regions (e.g., between the North American user coverage area and the South American user coverage area 3460) by dynamically adjusting the time ratio allocated to the corresponding antenna subsystem.

Figure 50B illustrates a second possible deployment with multiple AN areas 3450 and multiple user coverage areas 3460. For example, the deployment shown in Figure 50B can be supported by the end-to-end repeater 3403 shown in Figures 51A and 51B. As shown in Figure 50B, the end-to-end repeater 3403, with routing in the transponder, uses a first AN area 3450a to serve traffic in a first user coverage area 3460a, and uses a second AN area 3450b to serve traffic in a second user coverage area 3460b. Because the first AN area 3450a does not overlap with the first user coverage area 3460a, the same or overlapping bandwidth portions can be used for uplink or downlink communications between the end-to-end repeater 3403 and user terminals or ANs. Furthermore, in this example, because the AN areas 3450a or 3450b and their corresponding user coverage areas 3460a or 3460b, respectively, do not overlap, a special loopback mechanism can be employed to synchronize transmissions from the AN 515. An exemplary loopback mechanism in the form of a loopback transponder is discussed with reference to Figures 55A, 55B, and 55C. For example, with reference to Figure 63A, the system may have a total of 3.5 GHz uplink bandwidth 6330a and 3.5 GHz downlink bandwidth 6325a available. In a first switching configuration, the entire 3.5 GHz uplink bandwidth (e.g., using two orthogonal polarizations) can be used simultaneously for return uplink transmissions 525 from the first user coverage area 3460a and forward uplink transmissions 521 from the AN area 3450a. Similarly, the entire 3.5 GHz downlink bandwidth (e.g., using two orthogonal polarizations) can be used simultaneously for forward downlink transmissions 522 to the first user coverage area 3460a and return downlink transmissions 527 to the first AN area 3450a. The entire uplink and downlink bandwidth can also be used for the second user coverage area 3460b and the second AN area 3450b in a second switching configuration. Although two AN areas 3450 and two user coverage areas 3460 are discussed with respect to FIG 50B for simplicity, any suitable number of AN areas 3450 and user coverage areas 3460 is possible. In addition, aspects discussed above with respect to a single AN cluster (e.g., mobility, location in a body of water, etc.) may apply to one or both of the AN clusters in this example.

The above example describes AN area 3450a as serving non-overlapping user coverage areas 3460a. As an alternative example, AN area 3450a may serve user coverage area 3460b (e.g., user coverage area 3460 may include its associated AN area 3450 or a portion thereof). A similar example is generally discussed with reference to FIG50A in the context of a first AN area 3450a located in North America (e.g., which may correspond to AN coverage area 3450a of FIG50B) serving user coverage area 3460a located in North America, while a second AN area 3450b located in South America serves user coverage area 3460b located in South America. However, FIG50B shows that user coverage areas 3460 served by different AN coverage areas may also overlap to provide aggregated user coverage areas for a particular region. In this case, the handover transponders shown in FIG51A and FIG51B may be used to utilize user coverage areas 3460 at different time intervals. Alternatively, user coverage areas 3460a and 3460b may be served simultaneously by access node areas 3450a and 3450b using the multiple transponder paths shown in Figures 49A and 49B (where access node area 3450a serves user coverage area 3460a and access node area 3450b serves user coverage area 3460b, or where access node area 3450b serves user coverage area 3460a and access node area 3450a serves user coverage area 3460b). In this case, the uplink and downlink resources used for the user beams in user coverage areas 3460a and 3460b may be orthogonal (different frequency resources, different polarizations, etc.), or the user beams in user coverage areas 3460a and 3460b may use the same resources (same frequency range and polarization), where interference mitigation techniques such as adaptive coding and modulation (ACM), interference cancellation, space-time coding, etc. are used to mitigate interference.

As a third example, in some cases, AN coverage areas 3450a and 3450b combine to serve user coverage area 3460b (or user coverage area 3460a). In this case, a special loopback mechanism may not be necessary because a subset of ANs 515 is contained within user coverage area 3460. In some cases, the ANs 515 of AN coverage areas 3450a and 3450b can be considered coordinated in the sense that forward uplink signals 521 from each of the AN coverage areas 3450 can be combined to serve a single user beam coverage area 519. Alternatively, the ANs 515 of AN coverage area 3450a can serve a first subset of the user beam coverage area 519 of user coverage area 3460b, while the ANs 515 of AN coverage area 3450b can serve a second subset of the user beam coverage area 519 of user coverage area 3460b. In some cases of this example, there may be some overlap between the first subset and the second subset of user beam coverage areas 519 (e.g., such that AN coverage area 3450 may be considered to cooperate in some user beam coverage areas 519 and not cooperate in other user beam coverage areas). For another example, AN coverage area 3450a may serve user coverage area 3460b at a first time interval (or a first set of time intervals), and AN coverage area 3450b may serve user coverage area 3460b at a second time interval (or a second set of time intervals). In some examples, AN coverage areas 3450a and 3450b may cooperate to serve user coverage area 3460b during one or more first time intervals, and may cooperate to serve user coverage area 3460a during one or more second time intervals.

Generally speaking, the features of the end-to-end repeater 3403 described in FIG. 41 enable the use of ANs 515 geographically distributed within at least one AN area 3450, which is a physical area distinct from the user beam coverage area 3460, to serve at least one user beam coverage area 3460. In some cases, one or more AN clusters can provide high capacity to a large user coverage area 3460. FIG. 45A to 45F, 46A, 46B, 48A, 48B, 50A, and 50B illustrate various examples of such AN cluster implementations. Deploying a large number of ANs 515 in a relatively small geographic area can provide many benefits. For example, it can be easier to ensure that more (or even all) ANs 515 are deployed closer to high-speed networks (e.g., in areas with good fiber connectivity to CPS 505), within the borders of a single country or region, in accessible areas, and so on, with less deviation from the ideal AN 515 distribution. Enabling different coverage area services through path selection (e.g., as shown in FIG. 47A and 47B) can provide additional features. For example, as described above, a single AN cluster (and a single end-to-end repeater 3403) can be used to selectively serve multiple user coverage areas 3460. Similarly, a single end-to-end repeater 3403 can be used to differentiate and service area traffic.

In some cases, different coverage area services implemented through path selection can enable various interference management and/or capacity management features. For example, returning to Figures 48A and 48B, four types of communication links can be considered: forward link communication from the AN cluster to the western active user coverage area 3460a ("Link A"); forward link communication from the AN cluster to the eastern active user coverage area 3460b ("Link B"); return link communication from the western active user coverage area 3460a to the AN cluster ("Link C"); and return link communication from the eastern active user coverage area 3460b to the AN cluster ("Link D"). During a first time interval, the eastern user coverage area 3460b is active, allowing communication to proceed via Link B and Link D. Due to the complete overlap between AN area 3450 and the eastern user coverage area 3460b, Link B and Link D are likely to interfere. Therefore, during the first time interval, Link B can be allocated a first portion of the bandwidth (e.g., 2 GHz), and Link D can be allocated a second portion of the bandwidth (e.g., 1.5 GHz). In the second time interval, the western user coverage area 3460a is active, so that communication is carried out through link A and link C. Since there is no overlap between AN area 3450 and western user coverage area 3460a, link A and link C can use the full bandwidth of end-to-end repeater 3403 (e.g., 3.5 GHz) during the second time interval. For example, during the first time interval, the forward uplink signal 521 can be received using a first frequency range, and the return uplink signal 525 can be received using a second frequency range different from the first frequency range. And during the second time interval, the forward uplink signal 521 and the return uplink signal 525 can be received using the same frequency range (e.g., the first, second, or other frequency range). In some cases, frequency reuse can be performed during the first time interval and the second time interval, wherein other interference mitigation techniques are used during the first time interval. In some cases, path selection timing can be selected to compensate for this difference in bandwidth allocation during different time intervals. For example, the first time interval may be longer than the second time interval so that links B and D are allocated less bandwidth more of the time, thereby compensating for allocating more bandwidth for shorter times to links A and C. Other alternative frequency allocations are discussed below.

In some cases, a first return uplink signal 525 is received by a plurality of cooperating user link composition receiving elements 3426a during a first time interval from a first portion of a plurality of user terminals 517 geographically distributed over some or all of a first user coverage area 3460 (e.g., eastern user coverage area 3460b), and a second return uplink signal 525 is received by a plurality of cooperating user link composition receiving elements 3426b during a second time interval from a second portion of a plurality of user terminals 517 geographically distributed over some or all of a second user coverage area 3460 (e.g., western user coverage area 3460a). When an AN area 3450 (AN cluster) is a subset of the first user coverage area 3460b (e.g., as shown in FIG. 48B ), the AN 515 timing can be calibrated using the end-to-end repeater 3403 during a first time frame (e.g., when there is overlap between the user coverage area 3460b and the AN area 3450).

As described above, some cases may include determining a corresponding relative timing adjustment for each of the multiple ANs 515 so that the associated transmissions from the multiple ANs 515 arrive at the end-to-end repeater 3403 in a synchronized manner (e.g., sufficiently timed relative to the symbol duration, which is typically a fraction of the symbol duration such as 10%, 5%, 2%, or other suitable value). In this case, the forward uplink signal 521 is transmitted by the multiple ANs 515 according to the corresponding relative timing adjustment. In some such cases, at least some of the multiple ANs 515 receive a synchronization beacon signal (e.g., a PN signal generated by a beacon signal generator as described above) from the end-to-end repeater 3403, and the corresponding relative timing adjustment is determined based on the synchronization beacon signal. In other such cases, some or all of the ANs 515 may receive a loopback transmission from the end-to-end repeater 3403 and determine the corresponding relative timing adjustment based on the loopback transmission. Various methods of calibrating the ANs 515 may depend on the ability of the ANs 515 to communicate with the end-to-end repeater 3403. Thus, some situations may require calibrating the AN 515 only during time intervals when the appropriate coverage area is illuminated. For example, loopback transmissions via the user link antenna subsystem 3420 may only be used during time intervals when there is some overlap between the AN area 3450 and the user coverage area 3460 (e.g., the AN 515 communicates via loopback beams that may utilize both the feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 of the end-to-end repeater 3403). In some situations, proper calibration may further rely on some overlap between the feeder downlink frequency range and the user downlink frequency range.

As described above, an end-to-end repeater 3403 with or without a selectively coupled transponder (such as those shown in Figures 49A, 49B, 51A and 51B) can use an AN 515 within a first AN area 3450 overlapping with the first user coverage area 3460 (for example, both are in North America) to serve user terminals within the first user coverage area 3460, and use an AN 515 within a second AN area 3450 overlapping with the second user coverage area 3460 (for example, both are in South America) to serve user terminals within the second user coverage area 3460. Alternatively, the end-to-end repeater 3403 (such as the end-to-end repeater of Figures 51A and 51B) can use the AN 515 within the first AN area 3450 that does not overlap with the first user coverage area 3460 to serve the user terminals within the first user coverage area 3460, and use the AN 515 within the second AN area 3450 that does not overlap with the second user coverage area 3460 to serve the user terminals within the second user coverage area 3460, as shown in Figure 50B. As also shown in Figure 50B, the first user coverage area and the second user coverage area 3460 can be configured to at least partially overlap with each other to provide continuous coverage for a given area (e.g., the CONUS area, the visible earth coverage area, etc.). Other similar implementations are also possible.

50B may, for example, include a forward beamformer 529 that generates an access node-specific forward signal for each of the plurality of ANs 515 within the AN area 3450. Each of the plurality of ANs 515 within a given AN area 3450 may obtain the access node-specific forward signal from the forward beamformer 529 (e.g., via the distribution network 518) during a time window in which a given AN cluster is active, and transmit a corresponding forward uplink signal 521 to the end-to-end repeater 3403. If a time-sliced beamformer architecture is employed as described above, the time window in which a given AN cluster is active may include one or more time slices.

As described above, the system may include means for pre-correcting the forward uplink signal 521 to compensate for, for example, path delay, phase offset, etc., between the corresponding AN and the end-to-end repeater 3403. In some cases, the pre-correction may be performed by the forward beamformer 529. Additionally or alternatively, the pre-correction may be performed by the AN 515 itself. For example, each of the ANs 515 may transmit an access node beacon signal to the end-to-end repeater 3403 and receive signaling from the end-to-end repeater 3403 that includes the repeater beacon signal and a relayed access node beacon signal (e.g., relayed from the end-to-end repeater 3403). In this example, each AN 515 may adjust its respective forward uplink signal 521 based on the relayed access node beacon signal (e.g., may adjust timing and/or phase information associated with the signal transmission). For example, AN 515 can adjust the forward uplink signal 521 to align the relayed access node beacon signal with the received repeater beacon signal in time and phase. In some cases, the signaling described in this example (e.g., access node beacon signal, repeater beacon signal, and relayed access node beacon signal) can be received or transmitted via the feeder link antenna subsystem 3410, as described above. Therefore, in some cases, although not shown, the end-to-end repeater 3403 includes a beacon signal transmitter. The beacon signal transmitter can be implemented as described above with reference to the beacon signal generator and calibration support module 424 of Figure 15.

Although portions of the above description have discussed techniques for end-to-end beamforming between a single active AN area 3450 (e.g., selected between two or more AN areas 3450) and a single active user coverage area 3460 (e.g., selected between two or more user coverage areas 3460), in some cases, it may be desirable to have multiple different AN areas 3450 simultaneously (e.g., cooperatively) used to provide service to a single user coverage area 3460. An example of such a system is shown with respect to FIG50C , which includes AN areas 3450a and 3450b and a user coverage area 3460.

50C , an exemplary system may include multiple AN clusters (e.g., two relatively dense AN clusters). Each AN cluster may include multiple ANs 515 geographically distributed within a corresponding AN area 3450, wherein each AN 515 is operable to transmit a corresponding pre-corrected forward uplink signal 521 to the end-to-end repeater 3403. Multiple AN clusters can be used in conjunction to provide service to user terminals 517 within a user coverage area 3460. Multiple AN clusters can be used in conjunction using a variety of technologies. In one example, the end-to-end repeater 3403 can employ a feeder link antenna subsystem 3410 having a single feeder link antenna element array 3415 and a composite reflector that illuminates multiple AN clusters.

FIG57 illustrates a feeder link antenna subsystem 3410c having a single feeder link antenna element array 3415 and a compound reflector 5721. Each of the multiple zones of the compound reflector 5721 may have a focal point 1523 (which may be at the same or different distances from the compound reflector). FIG57 illustrates a first example, in which the compound reflector 5721 has a single focal point (or zone) 1523a. The feeder link antenna element array 3415 may be positioned at a defocused focal point of the compound reflector. As shown, the feeder link antenna element array 3415 is located within the focal point 1523a (i.e., closer to the compound reflector 5721 than the focal point 1523a). Alternatively, the feeder link antenna element array 3415 may be located outside the focal point 1523a (i.e., farther from the compound reflector 5721 than the focal point 1523a). A second example is shown in Figure 57, in which a compound reflector 5721 has two focal points (or zones) 1523b and 1523c. In this example, the feed link antenna element array 3415 is shown as being located inside the focal points 1523b and 1523c. Alternatively, the feed link antenna element array 3415 may be located outside the focal points 1523b and 1523c. In yet another embodiment, the feed link antenna element array 3415 may be located inside one focal point (e.g., focal point 1523b) and outside another focal point (e.g., focal point 1523c). In some cases, focal point 1523b may be associated with the top portion of the compound reflector 5721, while focal point 1523c is associated with the bottom portion of the compound reflector 5721. Alternatively, focal point 1523b may be associated with the bottom portion of the compound reflector 5721, while focal point 1523c is associated with the top portion of the compound reflector 5721. Feeder link antenna element array 3415 may include feeder link constituent transmit elements 3419 and feeder link constituent receive elements 3416, which in some cases may be the same antenna elements (e.g., different polarizations or frequencies for transmission and reception, etc.).

In the transmit direction, the output of the feed link component transmit element 3419 can be reflected from the reflector 5721 to form a first beam group 5705a that illuminates the first AN area 3450 (e.g., AN area 3450a in FIG. 50C ) and a second beam group 5705b that reflects the second AN area 3450 (e.g., AN area 3450b in FIG. 50C ). Although not shown, in the receive direction, the signals from the first AN area 3450a and the second AN area 3450b can be reflected using the compound reflector 5721 to the feed link component receive element 3416 of the feed link antenna element array 3415.

Returning to FIG. 50C , multiple AN areas 3450 may be used independently or together (e.g., in coordination). For example, the AN of only one of the AN areas 3450a or 3450b may be activated at a given time, and beamforming coefficients may be generated for forming user beam coverage areas 519 within user coverage areas 3460 from the ANs 515 of the active AN cluster. Alternatively, beamforming coefficients may be generated for forming user beams within user coverage areas 3460 using both AN clusters simultaneously (e.g., in coordination). In the forward direction, the forward beamformer 529 may apply the beamforming coefficients (e.g., by matrix product between the forward beam signal and the forward beam weight matrix) to obtain multiple access node-specific forward signals for the ANs 515 within both clusters to generate the desired forward user beams. In the return direction, the return beamformer 531 may obtain composite return signals from the ANs 515 within the two clusters and apply a return beam weight matrix to form a return beam signal associated with a return user beam.

In some cases, AN areas 3450a and 3450b may not overlap (e.g., not intersect). Alternatively, AN areas 3450a and 3450b may overlap (e.g., at least partially). In addition, at least one of AN areas 3450a and 3450b may at least partially overlap with user coverage area 3460. Alternatively, at least one of AN areas 3450a and 3450b may not overlap (e.g., not intersect) with user coverage area 3460. As discussed above, in some cases, at least one of the ANs 515 in one or both of AN areas 3450a or 3450b may be disposed on a mobile platform and/or located in a body of water.

50B or 50C , each of the multiple AN areas 3450 can be illuminated using a separate feeder link antenna element array 3415. In some cases, the separate feeder link antenna element arrays 3415 can be used simultaneously (e.g., multiple AN areas 3450 can be used cooperatively) to support services provided to a single user coverage area 3460. Referring again to FIG. 50C , the end-to-end repeater 3403 can have a separate feeder link antenna element array 3415 that illuminates each of the AN areas 3450a and 3450b. In some examples, the end-to-end repeater 3403 can have separate feeder link antenna subsystems 3410, each of which includes a feeder link antenna element array 3415 and a reflector. FIG56A illustrates an end-to-end repeater 3403 having a feeder link antenna subsystem 3410a, which includes a first feeder link antenna element array 3415a illuminating a first AN area 3450a via a first reflector 5621a and a second feeder link antenna element array 3415b illuminating a second AN area 3450b via a second reflector 5621b. The first and second feeder link antenna element arrays 3415a, 3415b may each include a feeder link component receive element 3416 and a feeder link component transmit element 3419. FIG56B illustrates a feeder link antenna subsystem 3410b, which includes a first and second feeder link antenna element arrays 3415a, 3415b illuminating corresponding AN areas 3450 via a single reflector 5621. As shown in FIG56B , the feeder link element arrays 3415 may be positioned in a defocused position relative to the focal point 1523 of the reflector 5621. Although the feed link element array 3415 is shown as being located outside the focal point 1523 of the reflector 5621 , it may alternatively be located closer to the reflector 5621 than the focal point 1523 .

Similarly, multiple user coverage areas 3460 can be implemented using separate user link antenna element arrays 3425 and separate reflectors (similar to FIG. 56A ) or a single reflector (similar to FIG. 56B ). Thus, the multiple AN areas 3450 and multiple user coverage areas 3460 in FIG. 50B can be deployed using any combination of a single feeder link reflector or multiple feeder link reflectors and a single user link reflector or multiple user link reflectors. In another example, a deployment similar to that shown in FIG. 50B can be implemented using a reflector shared between a feeder link and a user link using different feeder link and user link frequency bands. For example, a single antenna element array can have feeder link components and user link components (e.g., in an interleaved pattern, such as that shown in FIG. 62 ). The feeder link can use a higher (e.g., 1.5 times or more than 2 times) frequency range to provide higher gain using a shared reflector. In one example, the user link may use a frequency range (or multiple ranges) in the K/Ka band (e.g., approximately 30 GHz), while the feeder link uses one or more frequency ranges in the V/W band (e.g., approximately 60 GHz). Due to the narrower beamwidth at higher frequencies, the AN area 3450 sharing the common antenna element array (and therefore the reflector) will be an area smaller than (and concentric with) the user coverage area. Thus, one antenna subsystem comprising a single antenna element array and a reflector may be used to illuminate the user coverage area 3450a and the AN area 3450b, while a second antenna subsystem comprising a single antenna element array and a reflector may be used to illuminate the user coverage area 3450b and the AN area 3450a. In yet another example of a deployment similar to FIG50B , a single antenna subsystem may include a single reflector and two antenna element arrays, as shown in FIG56B , where each antenna element array includes a feeder link component element and a user link component element.

Referring again to FIG. 56B , in some cases, the first feeder link antenna element array 3415a can be coupled to a first subset of the multiple receive/transmit signal paths associated with the end-to-end repeater 3403, while the second feeder link antenna element array 3415b can be coupled to a second subset of the multiple receive/transmit signal paths. Thus, a first set of forward uplink signals 521 from an AN cluster having AN area 3450a can be carried via the first subset of the multiple receive/transmit signal paths associated with the end-to-end repeater 3403. Additionally, a second set of forward uplink signals 521 from an AN cluster having AN area 3450b can be carried via the second subset of the multiple receive/transmit signal paths. In some cases, both the first set of forward uplink signals and the second set of forward uplink signals can contribute to forming a forward user beam associated with at least one of the multiple forward user beam coverage areas 519 in the user coverage area 3460.

52A and 52B illustrate exemplary forward and return receive/transmit signal paths for use with multiple AN clusters, each associated with a separate feeder link antenna element array 3415. Referring first to FIG52A, an exemplary forward signal path 5200 is illustrated. The forward signal path 5200 includes a first forward link transponder 3430e coupled between a feeder link component receive element 3416a of a first feeder link antenna element array 3415a and a first user link component transmit element 3429 of a user link antenna element array 3425, and a second forward link transponder 3430e coupled between a feeder link component receive element 3416b of a second feeder link antenna element array 3415b and a second user link component transmit element 3429 of the same user link antenna element array 3425. The end-to-end repeater 3403 may have a first set of forward link transponders 3420 coupled by a first forward link transponder 3430e as shown, and a second set of forward link transponders 3430 coupled by a second forward link transponder 3430e as shown. Thus, the feeder link component receiving elements 3416a of the first feeder link antenna element array 3415a may be coupled to a first subset of the user link component transmitting elements 3429 of the user link antenna element array 3425 via the first set of forward link transponders 3430e, while the feeder link component receiving elements 3416b of the second feeder link antenna element array 3415b may be coupled to a second subset of the user link component transmitting elements 3429 of the same user link antenna element array 3425 via the second set of forward link transponders 3430e. The first and second sets of user link component transmitting elements 3429 may be spatially interleaved (e.g., alternating in rows and/or columns, etc.) within the user link antenna element array 3425 (e.g., as shown in FIG. 62 ).

FIG52B illustrates an exemplary return signal path 5250. The return signal path 5250 includes a first return link transponder 3440e coupled between the user link component receiving element 3426a of the user link antenna element array 3425 and the first feeder link component transmitting element 3419a of the first feeder link antenna element array 3415a. The return signal path 5250 also includes a second return link transponder 3440e coupled between the user link component receiving element 3426b of the same user link antenna element array 3425 and the second feeder link component transmitting element 3419b of the second feeder link antenna element array 3415b. The end-to-end repeater 3403 may have a first set of return link transponders 3440 coupled by the first return link transponder 3440e as shown, and a second set of return link transponders 3440 coupled by the second return link transponder 3440e as shown. Thus, a first subset of the user link component receiving elements 3426a of the user link antenna element array 3425 can be coupled to the feeder link component transmitting elements 3419a of the first feeder link antenna element array 3415a via a first set of return link transponders 3440e, while a second subset of the user link component receiving elements 3426b of the same user link antenna element array 3425 can be coupled to the feeder link component transmitting elements 3419b of the second feeder link antenna element array 3415b via a second set of return link transponders 3440e. As described above, the user link component receiving elements 3426 and the user link component transmitting elements 3429 can be the same physical antenna element. Similarly, the feeder link component receiving elements 3416 and the feeder link component transmitting elements 3419 of a given feeder link antenna element array 3415 can be the same physical antenna element.

The first and second groups of user link component receive elements 3426 may be spatially interleaved (e.g., alternating rows and/or columns, etc.) within the user link antenna element array 3425. FIG62 illustrates an exemplary antenna element array 6200 having spatially interleaved subsets of component antenna elements 6205. While each component antenna element 6205 is illustrated as a circular antenna element and the interleaved subsets are illustrated as being arranged in alternating rows, the component antenna elements 6205 may have any shape (e.g., square, hexagonal, etc.) and be arranged in any suitable pattern (e.g., alternating rows or columns, a checkerboard, etc.). Each component antenna element 6205 may be an example of a user link component receive element 3416 or a user link component transmit element 3419, or both (e.g., an element used for both transmission and reception).

52A and 52B , where user link antenna element array 3425 is implemented as antenna element array 6200 of FIG. 62 , a first group of forward link transponders 3430e may each couple its output to one of the first group of user link antenna elements 6205a, while a second group of forward link transponders 3430e may each couple its output to one of the second group of user link antenna elements 6205b. Furthermore, a first group of return link transponders 3440e may each couple its input to one of the first group of user link antenna elements 6205a, while a second group of return link transponders 3440e may each couple its input to one of the second group of user link antenna elements 6205b.

In some cases, the end-to-end repeater 3403 includes a large number of transponders, such as 512 forward link transponders 3430 and 512 return link transponders 3440 (e.g., a total of 1,024 transponders). Thus, the first group of forward link transponders 3430e in Figure 52A may include 256 transponders, and the second group of forward link transponders 3430e may include 256 transponders.

In some cases, support for the use of multiple AN clusters is provided by features of the transponder associated with the end-to-end repeater 3403. In addition or alternatively, support for the use of multiple AN clusters can be provided using one or more appropriately designed reflectors. Some exemplary transponders are described above (e.g., with respect to Figures 49A, 49B, 51A, 51B, 52A, and 52B). Additional examples of transponder designs are discussed below. It should be understood that the techniques described with reference to any one of the exemplary forward link transponder 3430 and the return link transponder 3440 may be applicable to any other exemplary transponder in some cases. In addition, the components of the transponder may be rearranged in any suitable manner without departing from the scope of this disclosure.

For clarity, only a single polarization of the receive/transmit path (e.g., a cross-pole transponder) is shown in Figures 49A, 49B, 52A, and 52B. For example, the forward link transponder 3430 receives a forward uplink signal 521 at the uplink frequency using left circular polarization (LHCP) and outputs a forward downlink signal 522 at the downlink frequency using right circular polarization (RHCP); and each return link transponder 3440 receives a return uplink signal 525 at the uplink frequency using right circular polarization (RHCP) and outputs a return downlink signal 527 at the downlink frequency using left circular polarization (LHCP). In other cases, some or all transponders may provide a bipolar signal path pair. In some embodiments, the repeater 3403 can be implemented as a plurality of repeaters, such as 512 forward link transponders 3430 and 512 return link transponders 3440 (for example, 1,024 transponders in total). Other specific implementations may include a small number of transponders, such as 10 or any other suitable number of transponders. In some cases, antenna element is implemented as a full-duplex structure so that each receiving antenna element and corresponding transmitting antenna element share structure. For example, each antenna element shown in can be implemented as two of the four waveguide ports of the radiation structure suitable for transmitting and receiving signals. In some cases, only the feeder link element or only the user link element is full duplex. Other implementations may use different types of polarization. For example, in some implementations, the transponder may be coupled between a receive antenna element and a transmit antenna element having the same polarization.

Exemplary forward link transponder 3430 and return link transponder 3440 both can comprise some or all of LNA 3705, frequency converter and associated filter 3710, channel amplifier 3715, phase shifter 3720, power amplifier 3725 (for example, TWTA, SSPA etc.) and harmonic filter 3730.In the bipolar specific implementation as shown in the figure, each pole has its own signal path, and this signal path has its own transponder component set.Some specific implementations can have more or less components.For example, when uplink frequency and downlink frequency are different, frequency converter and associated filter 3710 can be useful.As an example, each forward link transponder 3430 can accept input under the first frequency range and can output under the second frequency range; And each return link transponder 3440 can accept input under the first frequency range and can output under the second frequency band. Additionally or alternatively, each forward link transponder 3430 may accept input at a first frequency range and may output at a second frequency range; and each return link transponder 3440 may accept input at a second frequency range and may output at a first frequency range.

For example, the transponders of Figures 52A and 52B can be implemented in a system similar to the system of Figure 50C. In this example, some or all of the ANs 515 in AN area 3450a can cooperate with some or all of the ANs 515 in AN area 3450b to transmit forward uplink signals 521. The forward uplink signals from the two AN clusters can thus be combined to serve user terminals in user coverage area 3460. In this example, some AN clusters may only affect some user link antenna elements (e.g., some AN clusters may be associated with a subset of feeder link component receive elements 3416, which may be coupled to a corresponding subset of user link component transmit elements 3429). Although the above example discusses the use of two clusters, other implementations using more clusters are also possible.

Another exemplary forward signal path 5300 is shown in FIG53A. Forward signal path 5300 may include some combination of an LNA 3705a, a frequency converter and associated filter 3710a, a channel amplifier 3715a, a phase shifter 3720a, a power amplifier 3725a (e.g., a TWTA, SSPA, etc.), and a harmonic filter 3730a. The input side of the forward link transponder 3430f is selectively coupled to one of the feeder link component receive elements 3416a or 3416b (e.g., using a switch 4010b, or any other suitable path selection device). Each feeder link component receive element 3416a or 3416b may be part of a separate feeder link antenna element array 3415 (e.g., each part of a separate array 3415 of feeder link component receive elements 3416). The output side of the forward link transponder 3430f is coupled to the user link component transmit element 3429 of the user link antenna element array 3425 (e.g., which is part of the user link antenna element subsystem 3420). One or more switching controllers 4070 (not shown) may be included in the end-to-end repeater 3403 to select between some or all of the possible signal paths enabled by the forward link transponder 3430f. Thus, while the exemplary transponder 3430b of FIG. 47A allows, for example, selective coupling between a single feeder link component receive element 3416 and multiple user link component transmit elements 3429, the exemplary transponder 3430f of FIG. 53A allows, for example, selective coupling between multiple feeder link component receive elements 3416a, 3416b and a single user link component transmit element 3429.

An exemplary return signal path 5350 is shown in FIG53B. The return signal path 5350 may include some combination of an LNA 3705b, a frequency converter and associated filter 3710b, a channel amplifier 3715b, a phase shifter 3720b, a power amplifier 3725b (e.g., a TWTA, SSPA, etc.), and a harmonic filter 3730b. The output side of the return link transponder 3440f is selectively coupled to one of the feeder link component transmit elements 3419a or 3419b (e.g., using a switch 4010a or any other suitable path selection device). Each feeder link component transmit element 3419a or 3419b may be part of a separate feeder link antenna element array 3415 (e.g., each part of a separate array 3415 of feeder link component transmit elements 3419). The input side of the return link transponder 3440f is coupled to the user link component receiving element 3426 of the user link antenna element array 3425 (e.g., which is part of the user link antenna element subsystem 3420). One or more switching controllers 4070 (not shown) may be included in the end-to-end repeater 3403 to select between some or all of the possible signal paths enabled by the return link transponder 3440f. Thus, while the exemplary return link transponder 3440b of FIG. 47B allows, for example, selective coupling between a single feeder link component transmitting element 3419 and multiple user link component receiving elements 3426, the exemplary transponder 3440f of FIG. 53B allows, for example, selective coupling between a single user link component receiving element 3426 and multiple feeder link component transmitting elements 3419.

For example, forward link transponder 3430f in FIG. 53A may be implemented in a system similar to the system in FIG. 50C . In this example, some or all of the ANs 515 in AN area 3450a may transmit forward uplink signals 521 during a first time interval. Some or all of the ANs 515 in AN area 3450b may transmit forward uplink signals 521 during a second time interval. Using some appropriate path selection mechanism (e.g., a switch), forward link transponder 3430f may receive input from AN area 3450a during the first time interval (e.g., via a first cooperating feeder link constituting an array of receive elements 3416a) and receive input from AN area 3450b during the second time interval (e.g., via a second cooperating feeder link constituting an array of receive elements 3416b). In some such scenarios, each AN area 3450 may include a complete set of ANs 515 (e.g., so that each AN area 3450 can provide appropriate beamforming across the entire user coverage area 3460).

For example, the return link transponder 3440f of FIG. 53B may be implemented in a system similar to the system of FIG. 50C . In this example, some or all of the ANs 515 in AN area 3450a may receive the return downlink signal 527 during a first time interval. Some or all of the ANs 515 in AN area 3450b may receive the return downlink signal 527 during a second time interval. Using some appropriate path selection mechanism (e.g., a switch), the return link transponder 3440f may output to AN area 3450a during the first time interval (e.g., via a first cooperating feeder link forming an array of transmit elements 3419a) and to AN area 3450b during the second time interval (e.g., via a second cooperating feeder link forming an array of transmit elements 3419b). In some such scenarios, each AN area 3450 may include a complete set of ANs 515 (e.g., so that a single AN area 3450 can provide appropriate beamforming across the entire user coverage area 3460).

Figure 54A and Figure 54B show forward link transponder and return link transponder 3430g and 3440g respectively.These transponders are similar to the transponders of Figure 51A and Figure 51B, and difference is that these components have been rearranged so that switch 4010a follows one or more harmonic filters 3730.As above, other rearrangement modes of components are possible.In some cases, this exemplary arrangement mode may need less power amplifier 3725 and/or harmonic filter 3730.Similar to Figure 51A and Figure 51B, this type of arrangement mode can realize the selective association between AN cluster and user coverage area 3460.This selective association can allow flexibly allocating capacity between two (or more) user areas, and carries out frequency reuse (for example, it can increase system capacity) between user link and feeder link.

As discussed above with reference to FIG. 46B , in some cases, there may be no overlap between the AN area 3450 and the user coverage area 3460, which may require the use of a loopback mechanism separate from the loopback mechanism discussed above. In some cases, a separate loopback mechanism may include the use of a loopback transponder 5450, such as the loopback transponder shown in FIG. 55A , 55B , or 55C . In some embodiments, the loopback transponder 5450 may receive an AN loopback beacon (e.g., an AN loopback beacon transmitted from each AN), which may be an example of the access node beacon signal 2530 discussed with reference to FIG. 38 . The loopback transponder 5450 may retransmit the access node beacon signal 2530 and transmit a satellite beacon (e.g., which may be generated using the repeater beacon generator 426 as described above). In some examples below, the input side of the loopback transponder 5450 is coupled to the feeder link antenna element. Alternatively, the input side of the loopback transponder 5450 may be coupled to a loopback antenna element that is separate and distinct from the one or more feeder link antenna element arrays. Similarly, in some examples below, the output side of the loopback transponder 5450 is coupled to a feeder link antenna element or a user link antenna element. Alternatively, the output side of the loopback transponder 5450 may be coupled to a loopback antenna element that is distinct from the one or more feeder link antenna element arrays and the one or more user link antenna element arrays, and the loopback antenna element may be the same as or different from the loopback antenna element coupled to the input side of the loopback transponder 5450.

55A , the loopback transponder 5450a may include some combination of an LNA 3705c, a frequency converter and associated filter 3710c, a channel amplifier 3715c, a phase shifter 3720c, a power amplifier 3725c (e.g., a TWTA, SSPA, etc.), and a harmonic filter 3730c. Additionally, as shown in FIG55B , where the end-to-end repeater 3403 has multiple feeder link antenna element arrays 3415, the input side of the loopback transponder 5450 may be selectively coupled to one of the first feeder link component receiving element 3416a of the first feeder link antenna element array 3415a or the second feeder link component receiving element 3416b of the second feeder link antenna element array 3415b (e.g., using a switch 4010b or any other suitable path selection device). FIG55A shows that the output side of the exemplary loopback transponder 5450a is coupled to the feeder link component transmitting element 3419. 55B illustrates the output side of the exemplary loopback transponder 5450b being selectively coupled (e.g., using switch 4010a or any other suitable path selection device) to either a feeder link component transmit element 3419a or a feeder link component transmit element 3419b, which may be part of the same feeder link antenna element array 3415 or a different feeder link antenna element array. That is, the feeder link component transmit element 3419b may be part of the same antenna element array 3415 as the feeder link component transmit element 3419a and/or the feeder link component receive element 3416b. As shown, the feeder link component transmit element 3419b is part of the same antenna element array 3415b as the feeder link component receive element 3416b. Similarly, the input side of the loopback transponder 5450b can be selectively coupled (e.g., using switch 4010b or any other suitable path selection device) to a feeder link component receiving element 3416a or 3416b, which can be a component of the same or different feeder link antenna element array 3415. The loopback transponder 5450b of FIG. 55B can be employed in situations where the end-to-end repeater 3403 supports selective use of one of multiple access node regions 3450 (e.g., as discussed in some examples shown in FIG. 50B). Thus, the switch 4010a can be set to a first position when the first access node region 3450 is active to provide the output of the loopback transponder 5450b to the feeder link component transmitting element 3419a, and can be set to a second position when the second access node region 3450 is active to provide the output of the loopback transponder 5450b to the feeder link component transmitting element 3419b. In some cases, there may be two or more feeder link component transmit elements 3419, and each may be part of a separate feeder link antenna element array 3415 (e.g., to support selective use of one access node region 3450 from two or more access node regions 3450). Referring to FIG55B, one or more switching controllers 4070 (not shown) may be included in the end-to-end repeater 3403 to select between some or all of the possible signal paths enabled by the loopback link transponder 5450b. In some cases, the feeder link component receive element 3416 and the feeder link component transmit element 3419 may be associated with the same physical structure, as described above. In some cases, the AN 515 may be able to synchronize transmissions based on a comparison of retransmitted access node beacon signals 2530 with satellite beacons (e.g., transmissions from ANs 515 within one or more AN clusters may be aligned in time and phase based on the comparison).

In some cases, the feeder link frequency range may be different from the user link frequency range. When the feeder link downlink frequency range does not overlap with the user link downlink frequency range, a transponder that is shifted from the feeder link uplink frequency range to the user link downlink frequency range (e.g., using frequency converter 3710) cannot be used to relay access node beacon signals (e.g., because the AN cannot receive and process the user link downlink frequency range). In such cases, the loopback transponder 5450 can solve this problem by shifting the access node beam signal from the feeder link uplink frequency range to the feeder link downlink frequency range. For example, feeder link communications (e.g., forward uplink signal 521 and return downlink signal 527) may be in a first frequency range (e.g., a frequency range within the V/W band), and user link communications (e.g., forward downlink signal 522 and return uplink signal 525) may be in a second frequency range (e.g., a frequency range within the K/Ka band). Therefore, even in the case where the AN area 3450 overlaps the user coverage area 3460, the AN 515 may still be unable to receive the AN loopback signal relayed via the receive/transmit signal path of the end-to-end repeater 3403 (e.g., the forward responder 3430 and/or the return responder 3440).

Figure 55C shows an exemplary loopback transponder 5450c, which receives all AN loopback signals in the feeder link uplink frequency range and relays these AN loopback signals in the feeder link downlink frequency range. Loopback transponder 5450c can be used in any access node cluster deployment (e.g., with reference to at least some deployments discussed in Figures 45C, 45E, 45F, 45G or 50B) that the access node area 3450 does not overlap with the user coverage area 3460. The feeder link uplink frequency range and the feeder link downlink frequency range can be a part of the same frequency band (e.g., K/Ka band, V band, etc.) or different frequency bands. The AN loopback signal can be received via antenna element 3455, which can be a part of feeder link antenna element array 3415 or can be a separate loopback antenna element. The relayed AN loopback signal can be transmitted via the same antenna element 3455 or via different antenna elements in some cases as shown in the figure. The loopback transponder 5450c includes a loopback frequency converter 5460 that can convert the AN loopback signal from one carrier frequency within the feeder link uplink frequency range to a different carrier frequency within the feeder link downlink frequency range. The loopback transponder 5450c may additionally include one or more of an LNA 3705c, a channel amplifier 3715 (not shown), a phase shifter 3720 (not shown), a power amplifier 3725c, and a harmonic filter (not shown).

Referring again to the exemplary end-to-end beamforming system 3400 of FIG. 41 , aspects of system 3400 can be modified to support coordinated operation of multiple AN clusters using different frequency ranges. FIG. 59A and FIG. 59B illustrate examples of possible geographic coverage areas for multiple access node areas 3450, each operating within a different frequency range, to coordinately provide end-to-end beamforming for user coverage areas 3460. In the example shown in FIG. 59A , AN area 3450a may be associated with Ka-band transmissions, while AN area 3450b may be associated with V-band transmissions. As shown in FIG. 59A , AN areas 3450a and 3450b may not intersect. In some cases, AN area 3450b associated with V-band transmissions may be smaller than AN area 3450a associated with Ka-band transmissions (e.g., to cover a smaller geographic area). In some cases, AN area 3450a and AN area 3450b may be illuminated by separate feeder link antenna element arrays 3415. For example, AN area 3450a can be illuminated by the first feeder link antenna element array 3415a of the feeder link antenna subsystem 3410b shown in FIG56B, and AN area 3450b can be illuminated by the second feeder link antenna element array 3415b of the feeder link antenna subsystem 3410b shown in FIG56B. As in the example where the first AN cluster in access node area 3450a is operating in the Ka band and the second AN cluster in access node area 3450b is operating in the V band, the size of access node area 3450b can be set based on the gain difference provided by a single reflector (e.g., which can be the example of reflector 5621 in FIG56B) in different frequency ranges. Alternatively, the separate feeder link antenna element arrays 3415 illuminating AN area 3450a and AN area 3450b can be illuminated by separate reflectors (e.g., which can be the example of reflector 5621 discussed with reference to FIG56A), which can have the same or different sizes. Alternatively, AN area 3450a and AN area 3450b may be illuminated by the same feeder link antenna element array 3415 having multiple groups of feeder link antenna elements 3416, 3419 and a compound reflector 5721, as shown in Figure 57. Different frequency ranges for different AN clusters may provide a higher degree of isolation of different feeder link element subsets within a single feeder link antenna element array, which may result in higher system capacity than multiple AN clusters operating in the same frequency range.

FIG59B illustrates an alternative arrangement of multiple AN clusters using separate frequency ranges used in conjunction. As shown in FIG59B , the two AN clusters may at least partially overlap (or one may be completely contained within the other as shown). FIG59B may illustrate an example in which a single feeder link antenna element array 3415 may illuminate both AN coverage area 3450a and AN coverage area 3450b (e.g., simultaneously receiving or transmitting signals to both coverage areas in different frequency ranges). In some cases, a given AN 515 (e.g., an AN located within AN coverage area 3450b) may be associated with multiple AN clusters and communicate via feeder links in multiple frequency ranges (e.g., which may be contained in different frequency bands).

Figures 60A and 60B illustrate exemplary receive/transmit signal paths for cooperating AN clusters operating in different frequency ranges, in accordance with various aspects of the present disclosure. The forward receive/transmit signal path 6000 of Figure 60A includes a forward link transponder 3430h coupled between a feeder link component receive element 3416a and a user link component transmit element 3429a, and a forward link transponder 3430i coupled between a feeder link component receive element 3416b and a user link component transmit element 3429b. As described above, the various user link antenna elements may be part of different user link antenna element arrays 3425, which may be positioned to provide non-overlapping access node areas 3450, as shown in Figure 59A, or overlapping access node areas 3450, as shown in Figure 59B. Alternatively, the various user link antenna elements may be part of the same feeder link antenna element array 3415, in which case the access node areas 3450 will overlap, as shown in Figure 59B. The feed link component receive elements 3416a and the feed link component receive elements 3416b may be interwoven within the same feed link antenna element array 3415 as shown in FIG. 62 .

As described above, forward link transponder 3430h may include some or all of the following: LNA 3705a; frequency converter and associated filter 3710h; channel amplifier 3715a; phase shifter 3720a; power amplifier 3725a; and harmonic filter 3730a. Similarly, forward link transponder 3430i may include some or all of the following: LNA 3705a; frequency converter and associated filter 3710i; channel amplifier 3715a; phase shifter 3720a; power amplifier 3725a; and harmonic filter 3730a. In some cases, frequency converter 3710h may be operable to convert signals from a first feeder link uplink frequency range to a user link downlink frequency range, while frequency converter 3710i may be operable to convert signals from a second feeder link uplink frequency range to the same user link downlink frequency range.

The return receive/transmit signal path 6050 of FIG60B includes a return link transponder 3440h coupled between a user link component receive element 3426a and a corresponding feeder link component transmit element 3419a, and a return link transponder 3440i coupled between a user link component receive element 3426b and a corresponding feeder link component transmit element 3419b. As described above, the return link transponder 3440h may include some or all of the following: an LNA 3705b; a frequency converter and associated filter 3710j; a channel amplifier 3715b; a phase shifter 3720b; a power amplifier 3725b; and a harmonic filter 3730b. Similarly, the return link transponder 3440i may include some or all of the following: an LNA 3705b; a frequency converter and associated filter 3710k; a channel amplifier 3715b; a phase shifter 3720b; a power amplifier 3725b; and a harmonic filter 3730b. In some cases, frequency converter 3710j may be operable to convert signals from a user link uplink frequency range to a first feeder link downlink frequency range (e.g., which may be the same range as the first feeder link uplink frequency range described in reference FIGURE 60A), and frequency converter 3710k may be operable to convert signals from the user link uplink frequency range to a second feeder link downlink frequency range (e.g., which may be the same range as the second feeder link uplink frequency range described in reference FIGURE 60A).

As described above, the various user link antenna elements may be part of the same or different user link antenna element arrays 3425, and the various feeder link antenna elements may be part of the same or different feeder link antenna element arrays 3415. Feeder link component radiating elements 3419a and feeder link component radiating elements 3419b may be interleaved within the same feeder link antenna element array 3415, as shown in FIG62. In the event that the frequencies supported by forward link transponders 3430h and 3430i and return link transponders 3440h and 3440i for the feeder links are significantly different (e.g., one differs from the other by a factor of more than 1.5, etc.), the different element subsets 6205a, 6205b of the antenna element array 6200 may be appropriately sized for the different supported frequency ranges (e.g., component antenna element 6205b supporting a higher frequency range than component antenna element 6205a may have a smaller waveguide/horn, etc.).

FIG64A illustrates an exemplary spectrum allocation 6400, in which four frequency ranges are shown (frequency ranges 6425a, 6430a, 6435a, and 6436a). In the example shown, frequency ranges 6425a and 6430a are frequency ranges within the K/Ka band (e.g., between 17 GHz and 40 GHz), while frequency ranges 6435a and 6436a are within the V/W band (e.g., between 40 GHz and 110 GHz). FIG64A may illustrate the operation of multiple AN clusters operating in different frequency ranges as shown in FIG59A and FIG59B.

As an example, spectrum allocation 6400 can be used in the scenario shown in FIG. 59A , which uses an end-to-end repeater 3403 having forward receive/transmit signal paths and return receive/transmit signal paths 6000 and 6050 as shown in FIG. 60A and FIG. 60B . In this example, forward uplink signals 6440a from AN area 3450a can be transmitted within frequency range 6430a (e.g., using RHCP), while forward uplink signals 6440b from AN area 3450b can be transmitted within frequency range 6436a (e.g., using RHCP). The first set of forward uplink signals 6440a can be received by feeder link component receive element 3416a, while the second set of forward uplink signals 6440b can be received by feeder link component receive element 3416b. For simplicity, a signal can be illustrated by its span over some or all of a frequency range (e.g., forward uplink signal 6440a illustrates the frequency span of an example of forward uplink signal 521 within frequency range 6430a). In some cases, a given signal may span one or more frequency ranges. As discussed with reference to Figure 60A, these two groups of forward uplink signals 6440 are frequency converted by forward link transponders 3430h and 3430i (e.g., the two groups of forward uplink signals are down-converted to the same frequency range 6425a in the Ka band). Subsequently, the output of forward link transponder 3430h is transmitted as a first group of forward downlink signals 6445a by user link composition transmitting element 3429a, and the output of forward link transponder 3430i is transmitted as a second group of forward downlink signals 6445b by user link composition transmitting element 3429b. In this example, these user link component transmit elements 3429a and 3429b belong to the same user link antenna element array 3425 and illuminate the same user coverage area 3460. Therefore, the ANs 515 in the access node areas 3450a and 3450b can be said to be coordinated because a portion of the ANs 515 in each area are combined to serve the same user coverage area 3460. That is, at least one beamformed forward user beam serving the user terminal 517 within the corresponding user beam coverage area 519 is formed by forward uplink signals 6440a from at least a subset of the ANs 515 in the first access node area 3450a and by forward uplink signals 6440b from at least a subset of the ANs 515 in the second access node area 3450b.

Spectrum allocation 6400 also illustrates an example of frequency allocation for return link transmissions for the scenario shown in FIG59A, using an end-to-end repeater 3403 having forward receive/transmit signal paths and return receive/transmit signal paths 6000 and 6050 as shown in FIG60A and FIG60B. Return uplink signals 6450 (e.g., LHCP signals) originating from user terminals 517 distributed throughout user coverage area 3460 may be transmitted within frequency range 6430a (e.g., using LHCP) and received by user link component receive elements 3426a and 3426b of FIG60B, which belong to the same user link antenna element array 3425. As described with reference to FIG60B , the return uplink signal 6450 may be fed to the return link transponders 3440h and 3440i, respectively, and frequency converted to the appropriate frequency ranges 6425a (e.g., using RHCP) and 6435a (e.g., using LHCP). The frequency converted signals 6455a and 6455b may then be transmitted by the feeder link composition transmit elements 3419a and 3419b, respectively (e.g., belonging to separate feeder link antenna element arrays 3415a and 3415b, respectively) to the AN 515 in the access node regions 3450b and 3450a. It will be appreciated that the frequency allocation 6400 is an example and that various other frequency allocations may be used. For example, the return uplink signal 6450 may be in a frequency range different from the forward uplink signal 6440a (e.g., a different frequency range in the K/Ka band), and the forward downlink signal 6445 may be in a frequency range different from the return downlink signal 6455a (e.g., a different frequency range in the K/Ka band). This may, for example, allow the use of bipolar transponders in the forward receive/transmit signal path and the return receive/transmit signal path 6000 and 6050. In addition or alternatively, the forward uplink signal 6440b may be allocated in a frequency range different from the return downlink signal 6455b (e.g., a different frequency range in the V band), as shown in the figure. Other arrangements in which the forward uplink/downlink signal and the return uplink/downlink signal are in different frequency ranges may also be considered. For example, the return uplink signal may be allocated in the same frequency range as the forward downlink signal (e.g., using orthogonal polarization). Additionally or alternatively, the forward uplink signal 6440a from the AN in the first access node region 3450a can be allocated in the same frequency range as the return downlink signal 6455a (e.g., using orthogonal polarization). The coupling of the forward receive/transmit signal path and the return receive/transmit signal path 6000 and 6050 to the various user link and feeder link component transmit/receive elements can be selected based on the desired frequency range allocation.

In some examples where a single feeder link antenna element array 3415 supports multiple AN clusters (such as the multiple AN clusters shown in FIG. 59B ), each feeder link component receive element 3416 and feeder link component transmit element 3419 can be coupled to multiple forward link transponders 3430. FIG. 61A and FIG. 61B illustrate exemplary receive/transmit signal paths supporting cooperating AN clusters operating in different frequency ranges according to aspects of the present disclosure. The forward receive/transmit signal path 6100 of FIG. 61A includes multiple forward link transponders 3430 coupled between the feeder link component receive element 3416 and multiple user link component transmit elements 3429. In some examples, the feeder link component receive element 3416 receives a composite of forward uplink signals 521 from ANs 515 in multiple AN regions 3450. In some embodiments, the uplink signal of the present invention is sent to the user downlink transponder 522.After being formed receiving element 3416 by feeder link reception, forward uplink signal can be split (for example, using splitter 6005), and split signal can serve as the input to forward link transponder 3430j and 3430k.In some examples, splitter 6005 splits signal based on frequency range (for example, makes the received forward uplink signal occupying the first frequency range be fed to forward link transponder 3430j, and occupies the received forward uplink signal of the second frequency range be fed to forward link transponder 3430k).In such case, splitter 6005 can alternatively be the example of filter.Therefore, frequency converter 3710d and 3710e are operable to accept input at different frequency ranges, and output signal for being superimposed on user downlink signal 522 at same frequency range.

FIG61B shows a return receive/transmit signal path 6150, where a return link transponder 3440 couples multiple user link component receive elements 3426a and 3426b to a single user link component transmit element 3419. The user link component receive elements 3426a and 3426b can be part of the same user link antenna element array 3425 or separate user link antenna element arrays 3425a and 3425b (as shown). The user link component receive element 3426a can serve as an input to the return link transponder 3440j, while the user link component receive element 3426b can serve as an input to the return link transponder 3440k. The output of the return link transponder 3440 can be fed to a signal combiner 6010 and then transmitted by the feeder link component transmit element 3419 to the AN 515 in the AN region 3450. In some cases, components of receive/transmit signal paths 6000 and 6050 may be rearranged (or omitted), such that, for example, signal combiner 6010 may follow harmonic filter 3430b, splitter 6005 may precede LNA 3705a, and so on.

FIG64B illustrates an exemplary spectrum allocation 6401, which is shown with four frequency ranges (frequency ranges 6425b, 6430b, 6435b, and 6436b). In the example shown, frequency ranges 6425b and 6430b are frequency ranges within the K/Ka band (e.g., between 17 GHz and 40 GHz), while frequency ranges 6435b and 6436b are within the V/W band (e.g., between 40 GHz and 110 GHz). For example, frequency ranges 6425b, 6430b, 6435b, and 6436b may be the same as frequency ranges 6425a, 6430a, 6435a, and 6436a shown in FIG64A. FIG64B may illustrate the operation of multiple AN clusters operating in different frequency ranges as shown in FIG59A or FIG59B.

As an example, spectrum allocation 6401 can be used in the scenario shown in FIG. 59B , which uses an end-to-end repeater 3403 having forward receive/transmit signal paths and return receive/transmit signal paths 6100 and 6150 as shown in FIG. 61A and FIG. 61B . In this example, forward uplink signals 6440c from AN area 3450a can be transmitted within frequency range 6430b (e.g., using RHCP), while forward uplink signals 6440d from AN area 3450b can be transmitted within frequency range 6436b (e.g., using RHCP). The first set of forward uplink signals 6440c can be received by feeder link component receiving element 3416a of forward receive/transmit signal path 6100, while the second set of forward uplink signals 6440d can be received by feeder link component receiving element 3416b of forward receive/transmit signal path 6100. As discussed with reference to Figure 61A, these two groups of forward uplink signals 6440 are frequency converted by forward link transponders 3430j and 3430k (e.g., they are down-converted to the same frequency range 6425b in the Ka band). Subsequently, the output of forward link transponder 3430j is transmitted by user link component transmitting element 3429a as a first group of forward downlink signals 6445c, while the output of forward link transponder 3430k is transmitted by user link component transmitting element 3429b as a second group of forward downlink signals 6445d. In this example, these user link component transmitting elements 3429a, 3429b belong to the same user link antenna element array 3425 and illuminate the same user coverage area 3460. Therefore, the ANs 515 in access node areas 3450a and 3450b can be said to be coordinated because some portion of the ANs 515 in each area serve the same user coverage area 3460 by combining. That is, at least one beamformed forward user beam providing service to the user terminal 517 within the corresponding user beam coverage area 519 is formed by a forward uplink signal 6440c from at least a subset of AN 515 in the first access node area 3450a and a forward uplink signal 6440d from at least a subset of AN 515 in the second access node area 3450b.

Spectrum allocation 6401 also illustrates an example of a frequency allocation for return link transmissions for the scenario shown in FIG59B, using an end-to-end repeater 3403 having forward receive/transmit signal paths and return receive/transmit signal paths 6100 and 6150 as shown in FIG61A and FIG61B. Return uplink signals 6450a originating from user terminals 517 distributed throughout user coverage area 3460 may be transmitted within frequency range 6425b (e.g., using RHCP) and received by user link component receive elements 3426a and 3426b of FIG61B, which belong to the same user link antenna element array 3425. As described with reference to FIG61B, return uplink signals 6450 may be fed to return link transponders 3440j and 3440k, respectively, and frequency translated to appropriate frequency ranges 6430b (e.g., using LHCP) and 6435b (e.g., using LHCP). The frequency converted signals may then be combined (e.g., summed, etc.) by a signal combiner 6010 and transmitted by the feeder link composition transmit element 3419 to the AN 515 in the access node regions 3450a and 3450b. It will be appreciated that frequency allocation 6401 is an example and that various other frequency allocations may be used. For example, the return uplink signal 6450a may be in a different frequency range (e.g., a different frequency range within the K/Ka band) than the forward downlink signals 6445c and 6445d. Similarly, the forward uplink signal 6440c may be in a different frequency range (e.g., a different frequency range within the K/Ka band) than the return downlink signal 6455a, and the forward uplink signal 6440d may be allocated in a different frequency range (e.g., a different frequency range within the V/W band, as shown) than the return downlink signal 6455d. This may, for example, allow the use of bipolar transponders in the forward receive/transmit signal paths 6100 and 6150. The coupling of the forward receive/transmit signal paths 6100 and 6150 to the various user link and feeder link constituent transmit/receive elements may be selected based on the desired frequency range allocation.

In some cases, the available bandwidth for feeder link transmissions and user link transmissions in a given frequency band (e.g., K-band, Ka-band, etc.) may be unequal (e.g., significantly different). Additionally or alternatively, the available bandwidth for uplink and downlink transmissions within a given frequency band may be (e.g., significantly) unequal. For example, a regulatory body may specify portions of the spectrum that may be used for various types of transmissions.

Figures 65A and 65B illustrate exemplary spectrum allocations 6500 and 6501, wherein three frequency ranges (frequency ranges 6520a, 6525a, and 6530a) are used for the forward link and three frequency ranges (frequency ranges 6520b, 6525b, and 6530b) are used for the return link. In the example shown, frequency ranges 6520a, 6520b, 6525a, and 6525b are frequency ranges within the K/Ka band (e.g., between 17 GHz and 40 GHz), while frequency ranges 6530a and 6530b are within the V/W band (e.g., between 40 GHz and 110 GHz). Figures 65A and 65B may illustrate the operation of multiple AN clusters operating in different frequency ranges as shown in Figures 59A or 59B.

65A , forward uplink signals 6540a from AN coverage area 3450a may be transmitted within frequency range 6525a (e.g., using RHCP), while forward uplink signals 6540b from AN coverage area 3450b may be transmitted within frequency range 6530a (e.g., using RHCP). As discussed with reference to FIG60A or FIG61A , these two sets of forward uplink signals 6540 are frequency-converted to frequency range 6520a by forward link transponder 3430. In the example shown in FIG65A , the combined bandwidth of frequency ranges 6525a and 6530a is equal to the bandwidth of frequency range 6520a. Thus, forward uplink signal 6540a is frequency converted (e.g., via a frequency converter in a forward link transponder of forward receive/transmit signal path 6000 or 6100) to become forward downlink signal 6545 spanning a first portion 6521a of frequency range 6520a, while forward uplink signal 6540b is frequency converted (e.g., via a frequency converter in a forward link transponder of forward receive/transmit signal path 6000 or 6100) to become forward downlink signal 6545 spanning a second portion 6521b of frequency range 6520a. A given beamformed user beam in user coverage area 3460 may span the entire frequency range 6520a, in which case the user beam is formed by both forward uplink signals 6540a and 6540b. In the case where each user beam formed by the forward downlink signal 6545 uses a subset of the frequency range 6520a, some user beams may be formed by the first portion 6521a of the frequency range 6520a, and some user beams may be formed by the second portion 6521b of the frequency range 6520a. Additionally or alternatively, in some cases, some user beams may be formed by the coordinated superposition of the forward downlink signal 6545 associated with the frequency range 6521a and the forward downlink signal 6545 associated with the frequency range 6521b (e.g., the frequency ranges 6521a and 6521b may partially overlap to enable coordinated formation of user beams using forward uplink signals 6540 from different AN clusters in the user coverage area 3460). In another example, one or both of frequency ranges 6525a or 6530a may have the same bandwidth as frequency range 6520a (e.g., or the combined bandwidth of frequency ranges 6525a and 6530a may exceed the bandwidth of frequency range 6520a), and thus up to all forward user beams may be formed by the coordinated superposition of forward downlink signals associated with frequency ranges 6521a and 6521b.

FIG65B illustrates an exemplary return link allocation in which at least one access node area 3450 utilizes a frequency range in a frequency band different from the frequency band used for the user coverage area 3460. Specifically, the user terminal 517 may transmit return uplink signals 6550 in a frequency range 6520b (e.g., in the K/Ka band), which may be received by two sets of user link component receiving elements 3416 as shown in FIG60B or FIG61B and frequency-converted (e.g., via a frequency converter in the return link transponder 3440 of the return receive/transmit signal path 6050 or 6150) into a first set of return downlink signals 6555a in a frequency range 6525b and a second set of return downlink signals 6555b in a frequency range 6530b. The first and second groups of return downlink signals 6555a, 6555b can be transmitted from the same feeder link component transmitting element 3419 (as shown in FIG. 61B ), or from different feeder link component transmitting elements 3419 (as shown in FIG. 60B ). As in FIG. 65A , the combined bandwidth of frequency ranges 6525b and 6530b is shown to be equal to the bandwidth of frequency range 6520b. Thus, a first portion 6560a of the return uplink signal 6550 can be frequency converted and transmitted by the first group of return link transponders 3440 as the return downlink signal 6555a, while a second portion 6560b (which may or may not overlap with the first portion 6560a) can be frequency converted and transmitted by the second group of return link transponders 3440 as the return downlink signal 6555b. Thus, some return user beams may be formed by performing return link beamforming processing on portions of the return downlink signal 6555a, and some return user beams may be formed by performing return link beamforming processing on portions of the return downlink signal 6555b. Additionally or alternatively, some return user beams may be formed by performing return link beamforming processing on portions of the return downlink signal 6555a and the return downlink signal 6555b (e.g., portions of the return downlink signals 6555a and 6555b may cooperate to form a single return user beam). In some cases, one or both of the frequency ranges 6525b or 6530b may have the same bandwidth as the frequency range 6520b (e.g., or the combined bandwidth of the frequency ranges 6525b and 6530b may exceed the bandwidth of the frequency range 6520b), and thus up to all return user beams may be formed by the cooperative superposition of the return downlink signals 6555a and 6555b.

Figures 66A and 66B illustrate exemplary receive/transmit signal paths supporting cooperating AN clusters operating in different frequency ranges, in accordance with various aspects of the present disclosure. The forward receive/transmit signal path 6600 of Figure 66A includes a forward link transponder 3430l coupled between the feeder link component receive element 3416a and the user link component transmit element 3429, and a forward link transponder 3430m coupled between the feeder link component receive element 3416b and the user link component transmit element 3429. As described above, the forward link transponder 3430l may include some or all of the following: an LNA 3705a; a frequency converter and associated filter 3710l; a channel amplifier 3715a; a phase shifter 3720a; a power amplifier 3725a; and a harmonic filter 3730a. Similarly, forward link transponder 3430m may include some or all of the following: LNA 3705a; frequency converter and associated filter 3710m; channel amplifier 3715a; phase shifter 3720a; power amplifier 3725a; and harmonic filter 3730a. In some cases, frequency converter 3710l may be operable to convert signals from a first feeder link uplink frequency range (e.g., frequency range 6525a of FIG. 65A) to a first portion of a user link downlink frequency range (e.g., frequency range 6521a of FIG. 65A), while frequency converter 3710m may be operable to convert signals from a second feeder link uplink frequency range (e.g., frequency range 6530a of FIG. 65A) to a second portion of the same user link downlink frequency range (e.g., frequency range 6521b of FIG. 65A). The forward link transponder 3430 couples multiple feeder link component receiving elements 3416a and 3416b to a single user link component transmitting element 3429. The feeder link component receiving elements 3416a and 3416b can be part of the same feeder link antenna element array 3415 or separate feeder link antenna element arrays 3415a and 3415b (as shown). The feeder link component receiving element 3416a can serve as an input to the forward link transponder 3430l, while the feeder link component receiving element 3416b can serve as an input to the forward link transponder 3430m. The output of the forward link transponder 3430 can be fed into a signal combiner 6610 and then transmitted by the user link component transmitting element 3429 to the user terminal 517 in the user coverage area 3460. In some cases, components of receive/transmit signal paths 6600 and 6650 may be rearranged (or omitted), such that, for example, signal combiner 6610 may follow harmonic filter 3430b, splitter 6605 may precede LNA 3705a, and so on.

The return receive/transmit signal path 6650 of FIG66B includes a return link transponder 34401 coupled between the user link component receive element 3426 and the corresponding feeder link component transmit element 3419a, and a return link transponder 3440m coupled between the user link component receive element 3426 and the corresponding feeder link component transmit element 3419b. As described above, the return link transponder 34401 may include some or all of the following: an LNA 3705b; a frequency converter and associated filter 3710n; a channel amplifier 3715b; a phase shifter 3720b; a power amplifier 3725b; and a harmonic filter 3730b. Similarly, the return link transponder 3440m may include some or all of the following: an LNA 3705b; a frequency converter and associated filter 3710o; a channel amplifier 3715b; a phase shifter 3720b; a power amplifier 3725b; and a harmonic filter 3730b. In some cases, frequency converter 3710n may be operable to convert signals from a first portion of the user link uplink frequency range (e.g., frequency range 6560a of FIG. 65B ) to a first feeder link downlink frequency range (e.g., frequency range 6525b of FIG. 65B , which may be the same range as the first feeder link uplink frequency range described with reference to FIG. 66A ), while frequency converter 3710o may be operable to convert signals from a second portion of the user link uplink frequency range (e.g., frequency range 6560b of FIG. 65B ) to a second feeder link downlink frequency range (e.g., frequency range 6530b of FIG. 65B , which may be the same range as the second feeder link uplink frequency range described with reference to FIG. 66A ). After being received by user link component receive element 3426, the return uplink signal may be split (e.g., using splitter 6605), and the split signals may serve as inputs to return link transponders 3440l and 3440m. In some examples, splitter 6605 splits the signal based on frequency range (e.g., such that a received return uplink signal occupying a first frequency range is fed to forward link transponder 3430l, and a received return uplink signal occupying a second frequency range is fed to forward link transponder 3430m). In such cases, splitter 6605 can be an example of one or more filters. Thus, frequency converters 3710n and 3710o can be operated to accept inputs at different frequency ranges or portions of a frequency range and output signals of different frequency ranges in feeder downlink signal 522.

As described above, the various feeder link antenna elements may be part of the same or different feeder link antenna element arrays 3415. Feeder link component radiating elements 3419a and feeder link component radiating elements 3419b may be interleaved within the same feeder link antenna element array 3415, as shown in FIG62. In situations where the frequencies supported by forward link transponders 3430l and 3430m and return link transponders 3440l and 3440m for the feeder links are significantly different (e.g., one differs from the other by a factor of more than 1.5, etc.), the different element subsets 6205a, 6205b of the antenna element array 6200 may be appropriately sized for the different supported frequency ranges (e.g., a component antenna element 6205b supporting a higher frequency range than a component antenna element 6205a may have a smaller waveguide/horn, etc.).

Access nodes supporting multiple independent feeder link signals

In some examples, one or more ANs 515 may support multiple feeder links (e.g., transmission of multiple forward uplink signals and/or reception of multiple return downlink signals). In some cases, ANs 515 supporting multiple feeder links may be used to reduce the number of ANs. For example, instead of having M ANs 515, each of which supports one feeder link, the system may have M/2 ANs 515, each of which supports two feeder links. Although having M/2 ANs 515 may reduce the spatial diversity of the ANs 515, signals at different frequencies between the ANs 515 and the end-to-end repeaters will experience different channels, which also results in channel diversity between the two feeder links. Each AN 515 may receive multiple access node-specific forward signals 516, wherein each access node-specific forward signal 516 is weighted according to a beamforming coefficient determined based on a channel matrix associated with the corresponding transmission frequency range. Therefore, in the case where each AN 515 supports two feeder links, a forward signal specific to the first access node determined in part based on a first forward uplink channel matrix for the forward uplink channel between the AN 515 and the end-to-end repeater 3403 can be provided to each AN 515 in a first frequency range, and a forward signal specific to the second access node determined in part based on a second forward uplink channel matrix for the forward uplink channel between the AN 515 and the end-to-end repeater 3403 can be provided in a second frequency range. Similarly, on the return link, each AN 515 can obtain a first synthetic return signal based on the first return downlink signal in a third frequency range (which can be the same frequency range as the first frequency range or in the same frequency band as the first frequency range), and obtain a second synthetic return signal based on the second return downlink signal in a fourth frequency range (which can be the same frequency range as the second frequency range or in the same frequency band as the second frequency range). Each AN 515 may provide corresponding first and second synthesized return signals to a return beamformer 513, which may apply beamforming coefficients determined in part based on a first return downlink channel matrix for a return downlink channel between the end-to-end repeater 3403 and the AN 515 to the first synthesized return signal within a third frequency range, and apply beamforming coefficients determined in part based on a second return downlink channel matrix for the return downlink channel to the second synthesized return signal within a fourth frequency range.

A system employing M/2 ANs 515 may have a reduced system capacity when compared to a system having M ANs 515, but the system cost may be significantly reduced (e.g., including establishment and maintenance costs) while still providing acceptable performance. In addition, a number of ANs 515 other than M/2 may be used, such as 0.75·M, which may provide similar or stronger performance at a reduced cost when compared to M ANs 515 each supporting only one feeder link. Generally speaking, where M ANs 515 each supporting a single feeder link (e.g., a single feeder uplink frequency range and a single feeder downlink frequency range) are to be used, X·M ANs 515 may be used, where each AN 515 supports multiple feeder links, where X is in the range of 0.5 to 1.0.

45A and 45B , X·M ANs 515 may be distributed within the access node area 3450 and may serve user terminals 517 within the user coverage area 3460 via beamformed user beams, where one or more user beams are beamformed using multiple feeder link signals from at least one AN 515. Multiple feeder links may be supported via a single set of feeder link constituent antenna elements (e.g., a single feeder link antenna element array 3415) or separate feeder link constituent antenna elements (a separate feeder link antenna element array 3415 for each feeder link).

A single feeder link antenna element array 3415 and a single reflector can be used to support multiple feeder links for each AN 515 using the forward receive/transmit signal paths and return receive/transmit signal paths 6000, 6050 of Figures 60A and 60B (e.g., separate subsets of feeder link component antenna elements within the same feeder link antenna element array 3415), or the forward receive/transmit signal paths and return receive/transmit signal paths 6100, 6150 of Figures 61A and 61B (e.g., a splitter and combiner for multiplexing multiple feeder links using the same set of feeder link component antenna elements). In cases where the frequency ranges between the multiple feeder links differ significantly (which may be desirable to increase channel diversity), the size of the access node area 3450 may be determined by the higher frequency feeder link. For example, in cases where a first feeder link is supported in the frequency range of approximately 30 GHz and a second feeder link is supported in the frequency range of approximately 60 GHz, the access node area is limited to the area illuminated by the single feeder link antenna element array 3415 via a single reflector. 5 , 3415b, and 3416. Thus, some path diversity for the lower frequency range may be lost. Alternatively, the first feeder link antenna element array 3415a may be used to support the first frequency range, while the second feeder link antenna element array 3415b may be used to support the second frequency range. In this case, separate reflectors may be used and their sizes may be appropriately set to provide coverage of the same access node area 3450 at different frequencies. For example, where the first feeder link antenna element array 3415a and the first reflector support the first feeder link in the frequency range of approximately 30 GHz, and the second feeder link antenna element array 3415b and the second reflector support the second feeder link in the frequency range of approximately 60 GHz, the first reflector may be larger than the second reflector (e.g., having twice the reflector area) to account for the difference in antenna gain at the different frequencies.

Frequency allocation for different feeder links can be performed in various ways, including the ways shown in Figures 64A, 64B, 65A, or 65B. That is, a first feeder link can use carrier frequencies within frequency ranges 6425a and 6430a (e.g., in the K/Ka band), while a second feeder link uses frequency range 6435a (e.g., in the V/W band), as shown in Figure 64A. Alternatively, a first feeder link can use carrier frequencies within frequency range 6430b (e.g., in the K/Ka band), while a second feeder link uses frequency range 6435b (e.g., in the V/W band), as shown in Figure 64B. In yet another alternative, the first feeder link and the second feeder link can each use a different frequency than the user link, as shown in Figures 65A and 65B, where the first feeder link uses frequency ranges 6525a and 6525b (e.g., in the V/W band) and the second feeder link uses frequency ranges 6530a and 6530b (e.g., in the V/W band). In some examples, the first feeder link and the second feeder link can use significantly different frequency ranges (e.g., the lowest frequency in one frequency range can be 1.5 or 2 times the lowest frequency in the other frequency range). As described above, the bandwidth used for each feeder link frequency range can be less than the bandwidth used for the user link frequency range, or one or more of the feeder link frequency ranges can have the same bandwidth as the user link frequency range. In some cases, the correlation of the signals associated with the first feeder link and the second feeder link may be inversely proportional to the bandwidth separation between the two signals (e.g., such that two signals with adjacent frequency ranges within the Ka-band are more correlated than a Ka-band signal and a V-band signal, or two signals with non-adjacent frequency ranges within the Ka-band). This effect occurs because signals with adjacent frequency ranges experience similar atmospheric effects, while signals with greater bandwidth separation experience different atmospheric effects, which contribute to multipath.

in conclusion

Although the methods and apparatus disclosed herein have been described above with reference to various examples, scenarios, and specific implementations, it should be understood that specific features, aspects, and functions described in one or more individual examples may be applicable to other examples. Accordingly, the breadth and scope of the present invention as claimed is not limited by any of the examples provided above, but rather by the appended claims.

Unless expressly stated otherwise, the terms and phrases used in this document, and variations thereof, are to be considered open ended rather than restrictive. As examples of the foregoing: the term "including" is used to mean "including but not limited to," etc.; the term "example" is used to provide an example of an instance of the item in question, rather than an exhaustive or limiting list; the term "a" or "an" means "at least one," "one or more," etc.

Throughout this specification, the terms "couple" or "coupled" are used broadly to refer to a physical or electrical connection (including a wireless connection) between components. In some cases, a first component can be coupled to a second component via an intermediate third component disposed between the first and second components. For example, components can be coupled via direct connections, impedance matching networks, amplifiers, attenuators, filters, DC current blocks, AC current blocks, and the like.

A group of items connected with the conjunction "and" is not intended to require that each and every one of those items be present in the group, and is intended to include all or any subset of all unless specifically stated otherwise. Similarly, a group of items connected with the conjunction "or" is not intended to require that each and every one of those items be mutually exclusive in the group, and is intended to include all or any subset of all unless specifically stated otherwise. Furthermore, although items, elements, or components of the disclosed methods and apparatus may be described or claimed in the singular, the plural is considered to be within the scope of the invention unless specifically stated to be limited to the singular.

In some cases, the presence of expanded words and phrases such as "one or more," "at least," or other similar phrases does not mean that a narrower context is expected or required where such expanded words may not be present. Additionally, the terms "plurality" and "many" may be used synonymously herein.

Although reference signs are included in the claims, these are provided merely to make the claims easier to understand, and the inclusion (or omission) of reference signs shall not be construed as limiting the scope of the claimed subject matter.

Claims (129)

1. A system for providing communication services to user terminals geographically distributed within a user coverage area via an end-to-end repeater comprising multiple receive/transmit signal paths, comprising: A beam signal interface that receives multiple forward user data streams for transmission to the user terminal grouped by multiple forward user beam coverage areas; A beam weight generator that generates a forward beam weight matrix for end-to-end beamforming of the plurality of forward user beam coverage areas via the end-to-end repeater. A beamformer coupled to the beam signal interface and the beam weight generator, the beamformer including a forward matrix multiplier that obtains multiple access node-specific forward signals based on the matrix product of the forward beam weight matrix and the vectors of the forward beam signals; and Multiple access node clusters, wherein each access node cluster is associated with a corresponding access node region among multiple access node regions, and wherein each of the multiple access node clusters includes: Multiple access nodes are geographically distributed within the corresponding access node regions, wherein each access node cluster receives a corresponding set of access node-specific forward signals, and wherein each of the multiple access nodes in each access node cluster includes a transmitter that transmits a corresponding forward uplink signal to the end-to-end repeater based on one of the corresponding sets of the multiple access node-specific forward signals, and wherein the corresponding forward uplink signal is pre-calibrated to compensate for corresponding path delays and phase offsets introduced between the multiple access nodes and the end-to-end repeater. 2. The system according to claim 1, wherein each access node region in the plurality of access node regions does not overlap with other access node regions in the plurality of access node regions. 3. The system according to claim 1, wherein at least one access node region among the plurality of access node regions partially overlaps with at least one other access node region among the plurality of access node regions. 4. The system of claim 1, wherein at least one of the plurality of access node regions overlaps at least partially with the user coverage area. 5. The system according to claim 1, wherein at least one of the plurality of access node areas does not overlap with the user coverage area. 6. The system according to any one of claims 1 to 5, wherein at least one access node of at least one access node cluster in the plurality of access node clusters is disposed on a mobile platform. 7. The system of claim 1, wherein a first set of forward uplink signals from a first access node cluster in the plurality of access node clusters is carried via a first set of the plurality of receive/transmit signal paths, and a second set of forward uplink signals from a second access node cluster in the plurality of access node clusters is carried via a second set of the plurality of receive/transmit signal paths. 8. The system of claim 7, wherein both the first set of forward uplink signals and the second set of forward uplink signals contribute to forming at least one forward user beam associated with at least one forward user beam coverage area among the plurality of forward user beam coverage areas. 9. The system of claim 7, wherein the first set of the plurality of receive/transmit signal paths is coupled to a first plurality of antenna elements of the user link antenna subsystem of the end-to-end repeater, and the second set of the plurality of receive/transmit signal paths is coupled to a second plurality of antenna elements of the user link antenna subsystem. 10. The system of claim 9, wherein the first plurality of antenna elements is a first subset of antenna elements that cooperate with the user link to form an antenna element array, and the second plurality of antenna elements is a second subset of antenna elements that cooperate with the user link to form an antenna element array. 11. The system of claim 10, wherein the first plurality of antenna elements and the second plurality of antenna elements are arranged in an interleaved feeding mode within the antenna element array comprising the cooperating user link. 12. The system of claim 9, wherein the first plurality of antenna elements is a first antenna element array composed of a user link, and the second plurality of antenna elements is a second antenna element array composed of a user link. 13. The system of claim 12, wherein the user coverage area includes a first user coverage area and a second user coverage area, the first cooperating user link constituting an antenna element array is associated with the first user coverage area, and the second cooperating user link constituting an antenna element array is associated with the second user coverage area. 14. The system of claim 13, wherein the corresponding access node region of the first access node cluster is within the first user coverage area, and the corresponding access node region of the second access node cluster is within the second user coverage area. 15. The system of claim 13, wherein the corresponding access node region of the first access node cluster is outside the first user coverage area, and the corresponding access node region of the second access node cluster is outside the second user coverage area. 16. The system according to any one of claims 14 to 15, wherein the corresponding access node area of the first access node cluster is within the second user coverage area. 17. The system of claim 1, wherein the plurality of receive/transmit signal paths are selectively coupled via a first set of switches to either a first cooperating feed link constituting an antenna element array associated with a first access node cluster in the plurality of access node clusters, or a second cooperating feed link constituting an antenna element array associated with a second access node cluster in the plurality of access node clusters. 18. The system of claim 17, wherein the user coverage area includes a first user coverage area and a second user coverage area, and wherein the plurality of receive/transmit signal paths are selectively coupled via a second set of switches to one of a first cooperating user link constituting an antenna element array associated with the first user coverage area or a second cooperating user link constituting an antenna element array associated with the second user coverage area. 19. The system of claim 18, wherein the first access node cluster is associated with the first user coverage area, and the second access node cluster is associated with the second user coverage area. 20. The system of claim 18, wherein the first set of switches and the second set of switches include a first switch mode and a second switch mode, the first switch mode coupling the first cooperating feed link antenna element array to the first cooperating user link antenna element array via the plurality of receive/transmit signal paths, and the second switch mode coupling the second cooperating feed link antenna element array to the second cooperating user link antenna element array via the plurality of receive/transmit signal paths. 21. The system of claim 18, wherein the first user coverage area does not overlap with the corresponding access node area of the first access node cluster, and the second user coverage area does not overlap with the corresponding access node area of the second access node cluster. 22. The system of claim 21, wherein the corresponding access node region of the first access node cluster is within the second user coverage area, and the corresponding access node region of the second access node cluster is within the first user coverage area. 23. The system according to claim 1, wherein: Each of the plurality of access nodes includes a receiver that receives a corresponding return downlink signal from the end-to-end repeater via an antenna. Each of the corresponding return downlink signals includes a composite of return uplink signals that are transmitted from the plurality of user terminals and relayed by at least a subset of the plurality of receive/transmit signal paths of the end-to-end repeater to form a composite return signal. The beam weight generator generates a return beam weight matrix, which is used for end-to-end beamforming of transmissions from multiple return user beam coverage areas to the multiple access node clusters via the end-to-end repeater; and The beamformer includes a return matrix multiplier that obtains a corresponding return beam signal for the coverage area of the plurality of return user beams based on the matrix product of the return beam weight matrix and the vector of the corresponding synthesized return signal, wherein the timing and phase of the corresponding synthesized return signal are corrected for the corresponding path delay and phase offset between the end-to-end repeater and the plurality of access nodes. 24. The system according to claim 1, further comprising: A distribution network that distributes the plurality of access node-specific forward signals to the plurality of access nodes for each of the plurality of access node clusters. 25. A method for providing communication services to user terminals geographically distributed within a user coverage area via an end-to-end repeater comprising multiple receive/transmit signal paths, comprising: Multiple forward beam signals are obtained, including forward user data streams for transmission to multiple user terminals grouped by multiple forward user beam coverage areas; Identify a forward beam weight matrix for end-to-end beamforming for transmission via the end-to-end repeater from a set of access nodes to the plurality of forward user beam coverage areas, the set of access nodes including access nodes of at least one of a plurality of access node clusters, wherein each of the plurality of access node clusters includes a plurality of access nodes located at geographically distributed locations within a corresponding one of the plurality of access node areas. Generate corresponding access node-specific forward signals for transmission by the set of access nodes, each of the corresponding access node-specific forward signals comprising a synthesis of a corresponding forward beam signal weighted by a corresponding forward beamforming weight of the forward beam weight matrix; and Based on the corresponding access node-specific forward signals, corresponding forward uplink signals are transmitted from the group of access nodes, wherein the corresponding forward uplink signals are pre-corrected to compensate for corresponding path delays and phase offsets between the plurality of access nodes and the end-to-end repeater. 26. The method of claim 25, wherein each of the plurality of access node regions does not overlap with the other access node regions of the plurality of access node regions. 27. The method of claim 25, wherein at least one access node region among the plurality of access node regions partially overlaps with at least one other access node region among the plurality of access node regions. 28. The method of claim 25, wherein at least one of the plurality of access node regions at least partially overlaps with the user coverage area. 29. The method of claim 25, wherein at least one of the plurality of access node regions does not overlap with the user coverage area. 30. The method of claim 25, wherein at least one access node of at least one access node cluster in the plurality of access node clusters is configured on a mobile platform. 31. The method of claim 25, wherein the transmission comprises: A first set of forward uplink signals is transmitted from a first access node cluster in the plurality of access node clusters to the end-to-end repeater for carrying via a first set of the plurality of receive/transmit signal paths; and A second set of forward uplink signals is transmitted from the second access node cluster in the plurality of access node clusters to the end-to-end repeater for carrying via a second set of the plurality of receive/transmit signal paths. 32. The method of claim 31, further comprising: At least one subset of the first set of forward uplink signals and at least one subset of the second set of forward uplink signals are used to form at least one forward user beam for providing the communication service in at least one coverage area of the plurality of forward user beam coverage areas. 33. The method according to any one of claims 31 to 32, wherein the user coverage area includes a first user coverage area and a second user coverage area, and the method further includes forming a first set of user beams from the first set of forward uplink signals for providing the communication service in the first user coverage area, and forming a second set of user beams from the second set of forward uplink signals for providing the communication service in the second user coverage area. 34. The method of claim 33, wherein the corresponding access node region of the first access node cluster is at least partially within the first user coverage area, and the corresponding access node region of the second access node cluster is at least partially within the second user coverage area. 35. The method of claim 33, wherein the corresponding access node region of the first access node cluster is outside the first user coverage area, and the corresponding access node region of the second access node cluster is outside the second user coverage area. 36. The method of claim 35, wherein the corresponding access node region of the first access node cluster is at least partially within the second user coverage area. 37. The method of claim 25, further comprising: During a first time period, the inputs of the plurality of receive/transmit signal paths are selectively coupled to an antenna element array formed by a first cooperating feed link associated with a first access node cluster in the plurality of access node clusters; and During the second time period, the inputs of the plurality of receive/transmit signal paths are selectively coupled to a second cooperating feed link associated with a second access node cluster in the plurality of access node clusters to form an antenna element array. 38. The method of claim 37, wherein the transmission comprises: During the first time period, a first set of forward uplink signals is transmitted from the first access node cluster to form a first set of forward user beams for providing the communication service within the user coverage area during the first time period; and During the second time period, a second set of forward uplink signals is transmitted from the second access node cluster to form a second set of forward user beams for providing the communication service within the user coverage area during the second time period. 39. The method of claim 37, wherein the user coverage area includes a first user coverage area and a second user coverage area, and the method further includes: During the first time period, the outputs of the plurality of receive/transmit signal paths are selectively coupled to an antenna element array composed of a first cooperating user link associated with the first user coverage area; and During the second time period, the outputs of the plurality of receive/transmit signal paths are selectively coupled to a second cooperating user link associated with the second user coverage area to form an antenna element array. 40. The method of claim 39 further includes a first switching mode and a second switching mode, wherein the first switching mode couples the first cooperating feed link antenna element array to the first cooperating user link antenna element array via the plurality of receive/transmit signal paths, and the second switching mode couples the second cooperating feed link antenna element array to the second cooperating user link antenna element array via the plurality of receive/transmit signal paths. 41. The method of claim 39, wherein the transmission comprises: During the first time period, a first set of forward uplink signals is transmitted from the first access node cluster to form a first set of forward user beams for providing the communication service within the first user coverage area during the first time period; and During the second time period, a second set of forward uplink signals is transmitted from the second access node cluster to form a second set of forward user beams for providing the communication service within the second user coverage area during the second time period. 42. The method of claim 39, wherein the first user coverage area does not overlap with the corresponding access node area of the first access node cluster, and the second user coverage area does not overlap with the corresponding access node area of the second access node cluster. 43. The method of claim 39, wherein the corresponding access node region of the first access node cluster is at least partially within the second user coverage area, and the corresponding access node region of the second access node cluster is at least partially within the first user coverage area. 44. The method according to any one of claims 39 to 43, further comprising: During the first time period, a first set of forward uplink signals is transmitted from the plurality of access nodes in the first access node cluster within a first bandwidth range; and The antenna element array, composed of the first cooperating user links, relays the first group of forward uplink signals to user terminals within the first user coverage area within the first bandwidth range. 45. The method of claim 25, further comprising: Each of the plurality of access nodes receives a corresponding return downlink signal from the end-to-end repeater, each of the corresponding return downlink signals comprising a composite of a return uplink signal transmitted from the plurality of user terminals and relayed by at least a subset of the plurality of receive/transmit signal paths of the end-to-end repeater to form a composite return signal; Generate a return beam weight matrix for end-to-end beamforming for transmission via the end-to-end repeater from the multiple return user beam coverage areas to the multiple access node clusters; and The corresponding return beam signal for the coverage area of the plurality of return user beams is obtained by matrix product of the return beam weight matrix and the vector of the corresponding synthetic return signal, wherein the timing and phase of the corresponding synthetic return signal are corrected for the corresponding path delay and phase offset between the end-to-end repeater and the plurality of access nodes. 46. The method of claim 25, further comprising: The plurality of access node-specific forward signals are distributed to the plurality of access nodes for each of the plurality of access node clusters. 47. A system for providing communication services to user terminals geographically distributed within a user coverage area via an end-to-end repeater comprising multiple receive/transmit signal paths, comprising: A means for generating a forward beam weight matrix for end-to-end beamforming for transmission via the end-to-end repeater from a set of access nodes to multiple forward user beam coverage areas of the user coverage area, the set of access nodes including access nodes of at least one of a plurality of access node clusters, wherein each of the plurality of access node clusters includes multiple access nodes located at geographically distributed locations within a corresponding one of the plurality of access node areas. Means for generating access node-specific forward signals based on a plurality of forward beam signals, the plurality of forward beam signals including forward user data streams for transmission to a plurality of user terminals grouped by the plurality of forward user beam coverage areas, the respective access node-specific forward signals being transmitted from the group of access nodes to the plurality of forward user beam coverage areas via the end-to-end repeater, each of the respective access node-specific forward signals comprising a synthesis of at least a subset of the forward beam signals weighted by a respective forward beamforming weight of the forward beam weight matrix; and A means for transmitting a corresponding forward uplink signal from the group of access nodes based on the corresponding access node-specific forward signal, wherein the corresponding forward uplink signal is pre-corrected to compensate for corresponding path delays and phase offsets between the geographically distributed locations and the end-to-end repeaters. 48. The system of claim 47, wherein each access node region in the plurality of access node regions does not overlap with other access node regions in the plurality of access node regions. 49. The system of claim 47, wherein at least one access node region of the plurality of access node regions at least partially overlaps with at least one other access node region of the plurality of access node regions. 50. The system of claim 47, wherein at least one of the plurality of access node regions at least partially overlaps with the user coverage area. 51. The system of claim 47, wherein at least one of the plurality of access node regions does not overlap with the user coverage area. 52. The system of claim 47, wherein at least one access node of at least one access node cluster in the plurality of access node clusters is disposed on a mobile platform. 53. The system according to any one of claims 47 to 52, wherein the means for transmission: A first set of forward uplink signals is transmitted from a first access node cluster in the plurality of access node clusters to the end-to-end repeater for carrying via a first set of the plurality of receive/transmit signal paths; and A second set of forward uplink signals is transmitted from the second access node cluster in the plurality of access node clusters to the end-to-end repeater for carrying via a second set of the plurality of receive/transmit signal paths. 54. The system of claim 53, wherein the means for generating the respective access node-specific forward signal generates the respective access node-specific forward signal to form at least one forward user beam for providing the communication service in at least one forward user beam coverage area in at least one of the plurality of forward user beam coverage areas using at least one subset of the first set of forward uplink signals and at least one subset of the second set of forward uplink signals. 55. The system of claim 54, wherein the user coverage area includes a first user coverage area and a second user coverage area, and wherein the means for generating the respective access node-specific forward signals generates the respective access node-specific forward signals to form a first set of user beams from the first set of forward uplink signals and a second set of user beams from the second set of forward uplink signals, and wherein the respective set of user beams provides the communication service in the respective user coverage area. 56. The system of claim 55, wherein the corresponding access node region of the first access node cluster is at least partially within the first user coverage area, and the corresponding access node region of the second access node cluster is at least partially within the second user coverage area. 57. The system of claim 56, wherein the corresponding access node region of the first access node cluster is outside the first user coverage area, and the corresponding access node region of the second access node cluster is outside the second user coverage area. 58. The system of claim 57, wherein the corresponding access node region of the first access node cluster is at least partially within the second user coverage area. 59. The system of claim 47, further comprising: A first selective coupling device is used to selectively couple the inputs of the plurality of receive/transmit signal paths to one of either a first cooperating feed link antenna element array that receives a first set of forward uplink signals from a first access node cluster in the plurality of access node clusters, or a second cooperating feed link antenna element array that receives a second set of forward uplink signals from a second access node cluster in the plurality of access node clusters. 60. The system of claim 59, wherein the user coverage area includes a first user coverage area and a second user coverage area, and the system further includes: The second selective coupling device is used to selectively couple the plurality of receive/transmit signal paths to one of either a first cooperating user link constituting an antenna element array associated with the first user coverage area or a second cooperating user link constituting an antenna element array associated with the second user coverage area. 61. The system of claim 60, wherein the first selective coupling device and the second selective coupling device: During the first time period, the plurality of receive/transmit signal paths are selectively coupled between the antenna element array consisting of the first cooperating feed link and the antenna element array consisting of the first cooperating user link; and During the second time period, the plurality of receive/transmit signal paths are selectively coupled between the second cooperative feed link constituting the antenna element array and the second cooperative user link constituting the antenna element array. 62. The system of claim 61, wherein the first selective coupling device and the second selective coupling device include a first switching mode and a second switching mode, wherein the first switching mode couples the first cooperating feed link antenna element array to the first cooperating user link antenna element array via the plurality of receive/transmit signal paths, and the second switching mode couples the second cooperating feed link antenna element array to the second cooperating user link antenna element array via the plurality of receive/transmit signal paths. 63. The system of claim 62, wherein the first user coverage area does not overlap with the corresponding access node area of the first access node cluster, and the second user coverage area does not overlap with the corresponding access node area of the second access node cluster. 64. The system according to claim 61, wherein: The means for transmission transmits the first set of forward uplink signals from the plurality of access nodes of the first access node cluster within a first bandwidth range during the first time period; and The first cooperating user link forms an antenna element array that relays the first group of forward uplink signals to terminals within the first user coverage area within the first bandwidth range. 65. The system of claim 47, further comprising: Means for receiving a corresponding return downlink signal from the end-to-end repeater at each of the plurality of access nodes, each of the corresponding return downlink signals comprising a composite of a return uplink signal transmitted from the plurality of user terminals and relayed by at least a subset of the plurality of receive/transmit signal paths of the end-to-end repeater to form a composite return signal; A means for generating a return beam weight matrix for end-to-end beamforming of transmissions via the end-to-end repeater from multiple return user beam coverage areas to the multiple access node clusters; and A means for obtaining a corresponding return beam signal for the coverage area of the plurality of return user beams based on the matrix product of the return beam weight matrix and the vector of the corresponding synthesized return signal, wherein the timing and phase of the corresponding synthesized return signal are corrected for the corresponding path delay and phase offset between the end-to-end repeater and the plurality of access nodes. 66. The system of claim 47, further comprising: A means for distributing the plurality of access node-specific forward signals to the plurality of access nodes for each of the plurality of access node clusters. 67. A system for providing communication services to user terminals geographically distributed within a user coverage area via an end-to-end repeater comprising multiple receive/transmit signal paths, comprising: Multiple access node clusters, wherein each access node cluster is associated with a corresponding access node region among multiple access node regions, and wherein each of the multiple access node clusters includes: Multiple access nodes are geographically distributed within the corresponding access node area. Each of the multiple access nodes includes a receiver that receives a corresponding return downlink signal from the end-to-end repeater. Each of the corresponding return downlink signals includes a composite of a return uplink signal that is transmitted from multiple user terminals and relayed by at least a subset of the multiple receive/transmit signal paths of the end-to-end repeater to form a composite return signal. A beamweight generator that generates a return beamweight matrix for end-to-end beamforming for transmissions via the end-to-end repeater from multiple return user beam coverage areas to the multiple access node clusters; and A return beamformer, coupled to the beam weight generator, includes a matrix multiplier that obtains a corresponding return beam signal for the coverage area of the plurality of return user beams based on the matrix product of the return beam weight matrix and the vector of the corresponding synthesized return signal, wherein the timing and phase of the corresponding synthesized return signal are corrected for the corresponding path delay and phase offset between the end-to-end repeater and the plurality of access nodes. 68. The system of claim 67, wherein each of the plurality of access node regions does not overlap with other access node regions in the plurality of access node regions. 69. The system of claim 67, wherein at least one access node region of the plurality of access node regions at least partially overlaps with at least one other access node region of the plurality of access node regions. 70. The system of claim 67, wherein at least one of the plurality of access node regions at least partially overlaps with the user coverage area. 71. The system of claim 67, wherein at least one of the plurality of access node regions does not overlap with the user coverage area. 72. The system according to any one of claims 67 to 71, wherein at least one access node of at least one access node cluster in the plurality of access node clusters is disposed on a mobile platform. 73. The system of claim 67, wherein a first access node cluster in the plurality of access node clusters receives a first set of return downlink signals corresponding to the return uplink signal carried via a first set of the plurality of receive/transmit signal paths, and a second access node cluster in the plurality of access node clusters receives a second set of return downlink signals corresponding to the return uplink signal carried via a second set of the plurality of receive/transmit signal paths. 74. The system of claim 73, wherein both the first set of return downlink signals and the second set of return downlink signals contribute to forming at least one return user beam associated with at least one return user beam coverage area among the plurality of return user beam coverage areas. 75. The system of claim 74, wherein the inputs of the first set of the plurality of receive/transmit signal paths are coupled to a first plurality of antenna elements of the user link antenna subsystem of the end-to-end repeater, and the inputs of the second set of the plurality of receive/transmit signal paths are coupled to a second plurality of antenna elements of the user link antenna subsystem. 76. The system of claim 75, wherein the first plurality of antenna elements is a first subset of antenna elements that cooperate with the user link to form an antenna element array, and the second plurality of antenna elements is a second subset of antenna elements that cooperate with the user link to form an antenna element array. 77. The system of claim 76, wherein the first plurality of antenna elements and the second plurality of antenna elements are arranged in an interleaved feeding mode within the antenna element array comprising the cooperating user link. 78. The system of claim 75, wherein the first plurality of antenna elements is a first antenna element array composed of user links, and the second plurality of antenna elements is a second antenna element array composed of user links. 79. The system of claim 78, wherein the user coverage area includes a first user coverage area and a second user coverage area, the first cooperating user link constituting an antenna element array is associated with the first user coverage area, and the second cooperating user link constituting an antenna element array is associated with the second user coverage area. 80. The system of claim 79, wherein the corresponding access node region of the first access node cluster is within the first user coverage area, and the corresponding access node region of the second access node cluster is within the second user coverage area. 81. The system of claim 79, wherein the corresponding access node region of the first access node cluster is outside the first user coverage area, and the corresponding access node region of the second access node cluster is outside the second user coverage area. 82. The system according to any one of claims 80 to 81, wherein the corresponding access node area of the first access node cluster is within the second user coverage area. 83. The system of claim 67, wherein the plurality of receive/transmit signal paths are selectively coupled via a first set of switches to either a first cooperating feed link antenna element array for transmitting a first set of return downlink signals to a first access node cluster in the plurality of access node clusters, or a second cooperating feed link antenna element array for transmitting a second set of return downlink signals to a second access node cluster in the plurality of access node clusters. 84. The system of claim 83, wherein the user coverage area includes a first user coverage area and a second user coverage area, and wherein the plurality of receive/transmit signal paths are selectively coupled via a second set of switches to one of a first cooperating user link constituting an antenna element array associated with the first user coverage area or a second cooperating user link constituting an antenna element array associated with the second user coverage area. 85. The system of claim 84, wherein the first access node cluster is associated with the first user coverage area, and the second access node cluster is associated with the second user coverage area. 86. The system of claim 84, wherein the first set of switches and the second set of switches include a first switch mode and a second switch mode, the first switch mode coupling the first cooperating feed link antenna element array to the first cooperating user link antenna element array via the plurality of receive/transmit signal paths, and the second switch mode coupling the second cooperating feed link antenna element array to the second cooperating user link antenna element array via the plurality of receive/transmit signal paths. 87. The system of claim 84, wherein the first user coverage area does not overlap with the corresponding access node area of the first access node cluster, and the second user coverage area does not overlap with the corresponding access node area of the second access node cluster. 88. The system according to any one of claims 84 to 87, wherein the corresponding access node area of the first access node cluster is within the second user coverage area, and the corresponding access node area of the second access node cluster is within the first user coverage area. 89. The system of claim 67, further comprising: An allocation network obtains the corresponding synthesized return signal from each of the plurality of access nodes in the plurality of access node clusters. 90. A method for providing communication services to user terminals geographically distributed within a user coverage area via an end-to-end repeater comprising multiple receive/transmit signal paths, the method comprising: At a set of access nodes, corresponding return downlink signals are received from the end-to-end repeater, each of the corresponding return downlink signals comprising a return user data stream transmitted from a plurality of user terminals and relayed by the end-to-end repeater to form a composite return signal, the set of access nodes comprising access nodes of at least one of a plurality of access node clusters, wherein each of the plurality of access node clusters comprises a plurality of access nodes located at a geographically distributed location within a corresponding one of a plurality of access node regions; Identify the return beam weight matrix for end-to-end beamforming used for transmissions via the end-to-end repeaters from multiple return user beam coverage areas to the set of access nodes. Apply the corresponding beamforming weights of the return beam weight matrix to each of the corresponding synthesized return signals to obtain corresponding weighted synthesized return signals associated with each of the plurality of return user beam coverage areas; and The corresponding plurality of weighted composite return signals are combined for each coverage area in the plurality of return user beam coverage areas to obtain a return beam signal associated with each coverage area in the plurality of return user beam coverage areas, wherein the corresponding plurality of weighted composite return signals are corrected before the combination to compensate for corresponding path delays and phase offsets between the end-to-end repeater and the set of access nodes. 91. The method of claim 90, wherein each access node region in the plurality of access node regions does not overlap with other access node regions in the plurality of access node regions. 92. The method of claim 90, wherein at least one access node region among the plurality of access node regions at least partially overlaps with at least one other access node region among the plurality of access node regions. 93. The method of claim 90, wherein at least one of the plurality of access node regions at least partially overlaps with the user coverage area. 94. The method of claim 90, wherein at least one of the plurality of access node regions does not overlap with the user coverage area. 95. The method according to any one of claims 90 to 94, wherein at least one access node of at least one access node cluster in the plurality of access node clusters is disposed on a mobile platform. 96. The method of claim 90, wherein receiving comprises: At the first access node cluster in the plurality of access node clusters, a first set of return downlink signals corresponding to the return uplink signals, carried via a first set of the plurality of receive/transmit signal paths, is received; and At the second access node cluster in the plurality of access node clusters, a second set of return downlink signals corresponding to the return uplink signals are received via a second set of the plurality of receive/transmit signal paths. 97. The method of claim 96, further comprising: Using at least one subset of the first set of returned downlink signals and at least one subset of the second set of returned downlink signals, at least one returned user beam is formed that is associated with at least one returned user beam coverage area among the plurality of returned user beam coverage areas. 98. The method of claim 97, wherein the user coverage area includes a first user coverage area and a second user coverage area, the method further comprising: The first set of returned downlink signals forms a first set of returned user beams associated with the first user coverage area, and the second set of returned downlink signals forms a second set of returned user beams associated with the second user coverage area. 99. The method of claim 98, wherein the corresponding access node region of the first access node cluster is at least partially within the first user coverage area, and the corresponding access node region of the second access node cluster is at least partially within the second user coverage area. 100. The method of claim 98, wherein the corresponding access node region of the first access node cluster is outside the first user coverage area, and the corresponding access node region of the second access node cluster is outside the second user coverage area. 101. The method according to any one of claims 99 to 100, wherein the corresponding access node region of the first access node cluster is at least partially within the second user coverage area. 102. The method of claim 90, wherein the user coverage area includes a first user coverage area and a second user coverage area, and the method further includes: During the first time period, the inputs of the plurality of receive/transmit signal paths are selectively coupled to an antenna element array composed of a first cooperating user link associated with the first user coverage area; and During the second time period, the plurality of receive/transmit signal paths are selectively coupled to a second cooperating user link associated with the second user coverage area to form an antenna element array. 103. The method of claim 102, wherein receiving comprises: During the first time period, a first set of return downlink signals carried via the multiple receive/transmit signal paths is received at a first access node cluster in the plurality of access node clusters; and During the second time period, a second set of return downlink signals carried via the multiple receive/transmit signal paths is received at the second access node cluster in the plurality of access node clusters. 104. The method of claim 102, further comprising: During the first time period, the outputs of the plurality of receive/transmit signal paths are selectively coupled to a first cooperating feed link associated with a first access node cluster in the plurality of access node clusters to form an antenna element array; and During the second time period, the outputs of the plurality of receive/transmit signal paths are selectively coupled to a second cooperating feed link associated with a second access node cluster in the plurality of access node clusters to form an antenna element array. 105. The method of claim 104, further comprising a first switching mode and a second switching mode, wherein the first switching mode couples the first cooperating feed link antenna element array to the first cooperating user link antenna element array via the plurality of receive/transmit signal paths, and the second switching mode couples the second cooperating feed link antenna element array to the second cooperating user link antenna element array via the plurality of receive/transmit signal paths. 106. The method of claim 104, wherein receiving comprises: During the first time period, a first set of return downlink signals is received at the first access node cluster to form a first set of return user beams associated with the first user coverage area during the first time period; and During the second time period, a second set of return signals is received from the second access node cluster to form a second set of return user beams associated with the second user coverage area during the second time period. 107. The method of claim 104, wherein the first user coverage area does not overlap with the corresponding access node area of the first access node cluster, and the second user coverage area does not overlap with the corresponding access node area of the second access node cluster. 108. The method of claim 104, wherein the corresponding access node region of the first access node cluster is within the second user coverage area, and the corresponding access node region of the second access node cluster is within the first user coverage area. 109. The method according to any one of claims 102 to 108, further comprising: During the first time period, the first group of return uplink signals are relayed from a first subset of the plurality of user terminals in the first user coverage area within a first frequency range. The receiving also includes receiving the first set of returned downlink signals at the first access node cluster within the first frequency range during the first time period. 110. The method of claim 90, further comprising: The corresponding synthesized return signal is obtained from each of the plurality of access nodes in the plurality of access node clusters. 111. A system for providing communication services to user terminals geographically distributed within a user coverage area via an end-to-end repeater comprising multiple receive/transmit signal paths, comprising: Means for receiving corresponding composite return signals from the end-to-end repeater at a set of access nodes, each of the corresponding return downlink signals comprising a return uplink signal transmitted from a plurality of user terminals and relayed by the end-to-end repeater to form a composite return signal, the set of access nodes comprising access nodes of at least one of a plurality of access node clusters, wherein each of the plurality of access node clusters comprises a plurality of access nodes located at geographically distributed locations within a corresponding one of a plurality of access node regions. A means for applying a corresponding beamforming weight to each of the corresponding synthesized return signals to obtain corresponding weighted synthesized return signals associated with each of the plurality of return user beam coverage areas, the return beamweight matrix being used for end-to-end beamforming of transmissions from the plurality of return user beam coverage areas to the set of access nodes via the end-to-end repeater; and An apparatus for combining the respective plurality of weighted composite return signals for each of the plurality of return user beam coverage areas to obtain a return beam signal associated with each of the plurality of return user beam coverage areas, wherein the respective plurality of weighted composite return signals are corrected before the combination to compensate for corresponding path delays and phase offsets between the end-to-end repeater and the set of access nodes. 112. The system of claim 111, wherein each access node region in the plurality of access node regions does not overlap with other access node regions in the plurality of access node regions. 113. The system of claim 111, wherein at least one access node region among the plurality of access node regions at least partially overlaps with at least one other access node region among the plurality of access node regions. 114. The system of claim 111, wherein at least one of the plurality of access node regions overlaps at least partially with the user coverage area. 115. The system of claim 111, wherein at least one of the plurality of access node regions does not overlap with the user coverage area. 116. The system according to any one of claims 111 to 115, wherein at least one access node of at least one access node cluster in the plurality of access node clusters is disposed on a mobile platform. 117. The system of claim 111, wherein the means for receiving: At the first access node cluster in the plurality of access node clusters, a first set of return downlink signals corresponding to the return uplink signals, carried via a first set of the plurality of receive/transmit signal paths, is received; and At the second access node cluster in the plurality of access node clusters, a second set of return downlink signals corresponding to the return uplink signals are received via a second set of the plurality of receive/transmit signal paths. 118. The system of claim 117, wherein the means for application and the means for combination use at least one subset of the first set of returned downlink signals and at least one subset of the second set of returned downlink signals to form at least one returned user beam associated with at least one of the plurality of returned user beam coverage areas. 119. The system of claim 117, wherein the user coverage area includes a first user coverage area and a second user coverage area, and the means for application and the means for combination return downlink signals from the first set to form a first set of user beams associated with the first user coverage area, and return downlink signals from the second set to form a second set of user beams associated with the second user coverage area. 120. The system of claim 119, wherein the corresponding access node region of the first access node cluster is at least partially within the first user coverage area, and the corresponding access node region of the second access node cluster is at least partially within the second user coverage area. 121. The system of claim 119, wherein the corresponding access node region of the first access node cluster is outside the first user coverage area, and the corresponding access node region of the second access node cluster is outside the second user coverage area. 122. The system of claim 121, wherein the corresponding access node region of the first access node cluster is at least partially within the second user coverage area. 123. The system according to any one of claims 117 to 122, wherein the first set of the plurality of receive/transmit signal paths is coupled to a first subset of antenna elements forming an antenna element array in cooperation with user links, and the second set of the plurality of receive/transmit signal paths is coupled to a second subset of antenna elements forming an antenna element array in cooperation with user links. 124. The system of claim 111, further comprising: A first selective coupling device is used to selectively couple the outputs of the plurality of receive/transmit signal paths to one of either a first cooperating feed link antenna element array for transmitting a first set of return downlink signals to a first access node cluster in the plurality of access node clusters, or a second cooperating feed link antenna element array for transmitting a second set of return downlink signals to a second access node cluster in the plurality of access node clusters. 125. The system of claim 124, wherein the user coverage area includes a first user coverage area and a second user coverage area, and the system further includes: The second selective coupling device is used to selectively couple the inputs of the plurality of receive/transmit signal paths to one of a first cooperating user link constituting an antenna element array associated with the first user coverage area or a second cooperating user link constituting an antenna element array associated with the second user coverage area. 126. The system of claim 125, wherein the first selective coupling device and the second selective coupling device: During the first time period, the plurality of receive/transmit signal paths are selectively coupled between the antenna element array consisting of the first cooperating user link and the antenna element array consisting of the first cooperating feed link; and During the second time period, the plurality of receive/transmit signal paths are selectively coupled between the second cooperating user link antenna element array and the second cooperating feed link antenna element array. 127. The system of claim 126, wherein the first selective coupling device and the second selective coupling device include a first switching mode and a second switching mode, the first switching mode coupling the first cooperating feed link antenna element array to the first cooperating user link antenna element array via the plurality of receive/transmit signal paths, and the second switching mode coupling the second cooperating feed link antenna element array to the second cooperating user link antenna element array via the plurality of receive/transmit signal paths. 128. The system according to any one of claims 125 to 127, wherein the first user coverage area does not overlap with the corresponding access node area of the first access node cluster, and the second user coverage area does not overlap with the corresponding access node area of the second access node cluster. 129. The system of claim 111, further comprising: A means for obtaining a corresponding synthetic return signal from each of the plurality of access node clusters.