RU2844326C2 - Method and device for communication using massive-beam mimo phased array - Google Patents

Abstract

FIELD: communication technique.

SUBSTANCE: invention relates to the field of long distance wireless communication, for example, between ground devices and satellites, such as low earth orbit (LEO) satellites, in particular to phased antenna arrays (PAA) for multiple input multiple output (MIMO) communication. Method and a device for long-range wireless communication, e.g. satellite-earth, are provided. Two-dimensional antenna arrays operate in pairs to form alternating groups of beams which are elongated in one direction and aligned in the other direction. These groups of beams may be provided by means of fixed analogue arrays of beam formation. Active beam former can be used to generate beams directed within each group of beams. Different ports of the analogue beam-forming arrays can be used to form beams in different groups or different two-sector beams in the same group. Simplified parametric precoding of channel state information using a direction of arrival for MIMO processing is also provided.

EFFECT: high throughput using massive-beam MIMO phased antenna array installed on a LEO satellite.

18 cl, 21 dwg

Description

CROSS REFERENCE

[0001] This application claims the benefit of and priority to non-provisional U.S. Patent Application No. 17/195,089, entitled "Method and Apparatus for Communication Using a Massive-Beam MIMO Phased Array," filed March 8, 2021, the contents of which are incorporated herein by reference in their entirety.

AREA OF TECHNOLOGY

[0002] The present invention relates generally to long-range wireless communications, such as between terrestrial devices and satellites, such as low-earth orbit (LEO) satellites, and in particular to MIMO phased array antennas and related methods and devices, such as those installed on such satellites.

LEVEL OF TECHNOLOGY

[0003] Various constellations of low-Earth orbit satellites are planned or launched to support a variety of applications, such as improved global communications, high-speed and secure communications, and global Internet access. Of particular interest are high-throughput satellite systems (HTS), which are capable of delivering significantly higher data rates than conventional satellite services. These systems typically employ multiple spot beams directed at targets to improve data capacity using high-gain transmit/receive antennas, allowing for better frequency reuse. However, conventional approaches to creating these steerable high-gain beams require large, complex, and expensive phased array antennas. Thus, the large phased array approach has financial and physical limitations.

[0004] Recently, high-speed cellular communications (between ground units) have developed using large phased arrays and pre-coding processing. Such developments include technologies such as massive multiple-input multiple-output (MIMO) communications. Using this technique, a ground station can create multiple, steerable, and independent high-gain beams using a large number of antenna elements (electromagnetic radiators). Current developments in massive MIMO are well suited for high-capacity terrestrial cellular systems in which transmitters and receivers are located relatively close to each other.

[0005] One of the most important components of modern massive MIMO systems is the use of pilot signals, which are necessary for complex signal processing for each specific target device. Pilot signals are transmitted from the transmitter to the receiver, the receiver provides feedback to the transmitter, thereby maintaining channel estimation, which is important for the correct MIMO configuration. For terrestrial communications with target devices contained in a cell of relatively small size (e.g., a few kilometers), a relatively successful approach using pilot signals has been developed. However, for space-to-ground communications or networks over significantly longer distances, the same approach will likely not have sufficient signal power to achieve the required processing performance. In addition, propagation delays over long distances relative to the channel coherence time and other factors specific to satellite networks, such as high relative satellite velocities, make the use of such pilot signals problematic. In addition, antenna arrays specially adapted for use over long distances are subject to improvement.

[0006] There is therefore a need to provide a communication method and apparatus that overcomes or mitigates one or more limitations of the prior art.

[0007] This background information is provided to disclose information that applicant believes may be relevant to the present invention. No admission is necessarily intended or should be construed that any of the prior information constitutes prior art with respect to the present invention.

ESSENCE OF THE INVENTION

[0008] An object of embodiments of the present invention is to provide a method, device and system for communication using massive-beam MIMO phased arrays, such as those installed on a satellite, such as a LEO satellite. Although the present invention has been described primarily with respect to a satellite implementation, it should be noted that embodiments of the invention may be included in other communication devices, such as terrestrial, airborne, orbital or space devices. Various aspects of the invention are described below. It should also be noted that embodiments of the present invention may be implemented using synergistic combinations of multiple aspects of the invention, as described herein. For example, embodiments of the present invention may include a plurality of antenna arrays, a plurality of beamformer arrays and an active beamformer, where the plurality of beamformer arrays create narrow, interleaved groups of beams, and the active beamformer is used to direct the beams using the beams of a given group. In some embodiments, a simplified CSI operation may also be used in combination with the above.

[0009] Embodiments of the present invention provide a method and device with multiple antennas (e.g., MIMO or massive MIMO), which include both analog and digital pre-coding (e.g., with respect to beamforming). This makes the method and device more suitable for long-range communications, such as when applied to LTS, high-throughput satellite (HTS) communications. A simplified approach to processing channel state information (CSI) can be used, which can facilitate simpler and faster processing compared to a conventional massive MIMO phased array approach.

[0010] According to some embodiments, a communication device is provided that includes one, two or more sets of antenna arrays. Each set of antenna arrays may be a pair of antenna arrays. The antenna arrays may be located in close proximity with a distance between elements less than or equal to half the operating wavelength. Each of each set of antenna arrays is configured and operates to create several groups of beams. Each group of beams may collectively have a cross-section that takes an elongated (e.g., elliptical) shape. This elongated shape may be significantly narrower than the long one. The shape may be elongated in the main direction of movement of the communication device (e.g., in the orbital direction of the satellite). Different groups of beams of a given antenna array are spaced apart, and groups of different antenna arrays of the same set (e.g., a pair) alternate with each other. Thus, each set of antenna arrays is configured to create a plurality of beam groups that may be substantially adjacent and that have the property that adjacent beam groups are created by different antenna arrays in the same set of antenna arrays. This property may be applied to all pairs of adjacent beam groups.

[0011] According to additional or any previous embodiments, a communication device with a two-sector phased array massive MIMO in beam-space massive MIMO is provided. The communication device includes a two-dimensional phased antenna array, for example, having N sets of N antenna elements each, for a total of N ² elements. Several panels may be provided, each of which has such a phased antenna array. For ease of presentation, the array can be described as having N rows and N columns. N can be equal to, for example, 8 or 16. In addition, a plurality of beamformer networks are provided, connected to the array elements. The beamformer networks together form part of the beamformer arrays. Each beamformer network can be implemented using an analog radio frequency (RF) circuit and can operate in a fixed configuration. Each network of beamformers may be configured to create N orthogonal beams, different of which are directed in different (e.g., azimuthal) directions. A subset M < N of such beams may be selected and used for communication. Sets of two or more antenna arrays (as described above) may operate together to create a plurality of substantially orthogonal extended beam groups. Several sets of antenna arrays may operate together using an additional active beamformer. Pairs or more antenna arrays may operate together to create smaller tracking beams by combining beams from a given group or beams from several jointly directed groups. The tracking beams may be steered in a given direction (e.g., in elevation). In various embodiments, beam steering and tracking along the main axis of the extended beams may be implemented using linear massive MIMO processing.

[0012] According to additional or any previous embodiments, the beamformer array includes N beamformer networks and a plurality (e.g., N/2 rows) of hybrid couplers, where N is the number of rows of antenna elements in the array. Each beamformer network may be a Butler matrix or similar beamformer. In such embodiments, each beamformer network may have N beam ports and N antenna ports that are operatively connected to a corresponding row of antenna elements of a phased array. The N beamformer networks may be implemented in parallel, each of which is connected to different rows of antenna elements. Pairs of beamformer networks may be connected together via rows of hybrid couplers and operate together to create N forward beams and N backward beams in a two-sector mode.

[0013] According to additional or any previous embodiments, the beamformer array includes N/2 tuned beamformer networks, where N is the number of rows of antenna elements in the array. Each beamformer network is connected to two (e.g., adjacent) rows of antenna elements. Each beamformer network includes a plurality of beam ports, the number of which is less than the total number of antenna elements (and corresponding antenna ports) in the two rows. For example, the number of beam ports can be approximately a quarter of the total number of antenna ports. The beamformer networks of a given array can be the same or substantially identical. However, two different configurations of beamformer networks (e.g., with different phase shifter settings) can be provided and used in two different additional antenna arrays to create different sets of beams to be interleaved together. In such embodiments, hybrid couplers configured and operative to form forward and backward (bi-sector) beams may also be used.

[0014] According to additional or any previous embodiments, a communication device is provided, configured to create (at least) two orthogonal and independently controllable dual-sector beams. The beams are dual-sector in the sense that one of the beams is directed toward the front of a given region, and the other of the beams is directed toward the back of the same given region. The two beams may overlap in the sense that the front and back may overlap. In some embodiments, the dual-sector beams are created using hybrid couplers, as described above. The hybrid couplers may be 90° hybrid couplers. Arbitrary amplitude and phase roll-offs may also be used in the beam formers. The two dual-sector beams may have forward and backward pre-tilt angles of 30°, respectively, at the operating frequency. The pre-tilt angles are relative to an axis that is perpendicular to the plane of the array. This is the effective spacing between elements on a half-wave. In some embodiments, each of the two two-sector beams can be controlled from 0° to 45° with a radiation efficiency of at least 85%. Coverage in directions angularly close to the axis perpendicular to the plane of the array, within the half-power beam width (HPBW) can be achieved using a combination of two beams.

[0015] According to additional or any previous embodiments, a communication device is provided that includes two independent Nx2N (e.g., N=8) orthogonal beamforming networks having low sidelobes and a low beam coupling factor (BCF).

[0016] According to additional or any previous embodiments, a simplified channel state information (CSI) precoder based on parametric parameters and an associated method are provided that utilize the direction of arrival of signals from target devices for processing massive MIMO.

[0017] According to embodiments of the present invention, a wireless communication device is proposed. The device includes first and second separate two-dimensional arrays, each of which has a plurality of antenna elements, as well as first and second arrays of beam formers (e.g., fixed analog arrays). The first array of beam formers is operatively connected to the first antenna array and is configured to form a first plurality of beams by operating the first antenna array as a phased array. The first plurality of beams are divided into a plurality of spaced groups of beams, for example, spaced in the azimuthal direction. Similarly, the second array of beam formers is operatively connected to the second antenna array and is configured to form a second plurality of beams by operating the second antenna array as a second phased array. The second plurality of beams are divided into a plurality of additional spaced groups of beams, which alternate with the plurality of spaced groups of beams from the first array. Each group of beams typically includes a corresponding plurality of overlapping beams that can be controlled together for further beam formation. In various embodiments, each array of beam formers includes a plurality of networks of beam formers arranged in parallel. In such embodiments, the array of beam formers is configured to provide a set of beam ports. Each of the beam ports is operatively connected through one of the networks of beam formers or through a connected pair of networks of beam formers to a pair of adjacent rows of antenna elements.

[0018] According to additional or any previous embodiments, each of the beamformer networks is connected to another corresponding row of antenna elements, and each beamformer array includes one or more rows of hybrid couplers. Each row of hybrid couplers is connected to a corresponding pair of the plurality of beamformer networks, wherein said beam ports are ports of hybrid couplers. In some additional embodiments, different hybrid couplers control beams in different beam groups, and each hybrid coupler comprises a pair of ports. Each of the pair of ports controls different two-sector beams in the same beam group.

[0019] According to additional or any previous embodiments, each of the beamformer networks is connected to another respective pair of adjacent rows of said antenna elements and includes a subset of the set of beam ports. The number of beam ports in the subset is less than the number of antenna elements in said pair of adjacent rows. In additional embodiments, each of the beamformer networks includes a plurality of hybrid couplers arranged in a series-parallel configuration, a plurality of power dividers, each of which is connected to a pair of antenna elements comprising one antenna element in each of said pair of adjacent rows, and a plurality of phase shifters, at least some of the phase shifters are located between said power dividers and said antenna elements.

[0020] According to further or any previous embodiments, in particular in combination with the case where each network of beam formers is connected to another respective pair of adjacent rows of said antenna elements, the plurality of antenna elements and the plurality of further elements are respectively arranged with a distance between the elements less than or equal to half the operating wavelength, so as to provide a fine pitch array.

[0021] According to additional or any previous embodiments, each beam group consists of individual beams that together have a corresponding combined cross-section extended in a first (e.g., elevation) direction, and different beam groups are aligned opposite to each other in a second (e.g., azimuthal) direction that is perpendicular to the first direction. In some additional embodiments, the device is mounted on a satellite that moves relative to the Earth, and the first direction is oriented so that each corresponding combined cross-section is a portion of the Earth's surface extended parallel to the direction of motion of the satellite. In some embodiments, each beam group is a two-sector beam group that includes one, two or more forward beams and one, two or more rear beams. The forward beams together form a first portion of said combined cross-section. The first portion is located closer to the first end of the combined cross-section. The rear beams together form a second portion of the combined cross-section. The second portion is located closer to the second end of the combined cross-section. The first end and the second end are located opposite each other in the first direction, and the first part and the second part may (partially) overlap or, alternatively, not overlap. The front rays may be orthogonal to the back rays. The front rays may be directed at a different angle relative to the back rays.

[0022] According to additional or any previous embodiments, an active beam former is provided, for example as part of the device described above. The active beam former can be operatively connected to a first array of beam formers. The active beam former is configured to form, using digital pre-coding, one or more tracking beams, at least in part, by combining several beams belonging to one of the beam groups, from a plurality of spaced beam groups. In some additional embodiments, each beam group consists of individual beams that together have a corresponding combined cross-section elongated in a first direction, and the active beam former is configured to steer the tracking beams in the first direction. In some additional embodiments, the device includes, in addition to the first and second arrays, one or more additional antenna arrays and one or more additional beam former arrays, each of which is operatively connected to a corresponding one of the additional antenna arrays. Each of the additional beamformer arrays is configured to create additional copies of the first plurality of beams by operating a corresponding one of the additional antenna arrays as an additional phased array. Each of these additional copies overlaps with the first plurality of beams. In such embodiments, the active beamformer is additionally operatively connected to each of the additional beamformer arrays, and the active beamformer is configured to form said one or more tracking beams additionally by combining said plurality of beams with one or more additional beams belonging to said additional copies of the first plurality of beams.

[0023] According to additional or any previous embodiments, each group of beams consists of individual beams that collectively have a corresponding combined cross-section that is elongated in the first direction. Different groups of beams are aligned next to each other in a second direction that is perpendicular to the first direction. In addition, the rows of antenna elements extend parallel to each other in the second direction and are spaced apart in the first direction.

[0024] According to additional or any previous embodiments, a channel state estimator is provided, for example (but not necessarily) as part of the device described above. The channel state estimator is configured to estimate the state of the wireless communication channel primarily within the line of sight between the host device and the remote wireless communication device. The estimation is based on the direction of arrival of the signal transmitted by the remote wireless communication device. The estimation is further based on the geometry of the antenna array (for example, the first antenna array and the second antenna array) using statistical information about the channel state and a parametric channel model. In some embodiments, when the channel state estimator forms part of the above-described device, the beam groups are orthogonal to each other, and estimating the state of the wireless communication channel includes performing a plurality of separate linear precoding operations.

[0025] According to embodiments of the present invention, a system is provided that includes two or more devices, including one or more devices as described above, one or more target devices, or a combination thereof.

[0026] According to embodiments of the present invention, a method of wireless communication is provided that includes operating a device or system as described above or elsewhere herein.

[0027] The embodiments have been described above in connection with the aspects of the present invention on which they can be implemented. Those skilled in the art will understand that the embodiments can be implemented in combination with the aspect for which they are described, but can also be implemented with other embodiments of this aspect. When embodiments are mutually exclusive or otherwise incompatible with each other, this will be apparent to those skilled in the art. Some embodiments may be described with respect to one aspect, but may also be applicable to other aspects, as will be apparent to those skilled in the art.

BRIEF DESCRIPTION OF DRAWINGS

[0028] Additional features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0029] Fig. 1a illustrates a steerable two-sector (N×N) massive-MIMO array in beam space according to an embodiment.

[0030] Fig. 1b illustrates a steerable two-sector (N×N) massive-MIMO array in beam space according to another embodiment.

[0031] Fig. 2 is a graph showing typical orthogonal beam patterns created using a Butler matrix, according to an embodiment.

[0032] Fig. 3 is a graph showing composite beam patterns by superimposing N×N orthogonal Butler beams according to an embodiment.

[0033] Fig. 4 is a graph showing the radiation patterns of a first orthogonal composite spatially phased array, referred to herein as array A, according to an embodiment.

[0034] Fig. 5 is a graph showing the radiation patterns of a second orthogonal composite spatially phased array, referred to herein as array B, according to an embodiment.

[0035] Fig. 6a illustrates an 8x16 orthogonal analog beamformer for phased array embodiment A.

[0036] Fig. 6b is a table showing the phase shift values for the various phase shifters of Fig. 6a.

[0037] Fig. 7a illustrates an 8x16 orthogonal analog beamformer for phased array embodiment B.

[0038] Fig. 7b is a table showing the phase shift values for the various phase shifters of Fig. 7a.

[0039] Fig. 8a is a graph showing 12 of 16 orthogonal beams having a low beam interaction coefficient for a phased array combining phased array A and phased array B (A+B) for coverage of up to ±40 degrees along the azimuthal axis Az, according to an embodiment.

[0040] Fig. 8b is a table showing the effective amplitude and phase roll-off of the excitation for an 8x16 beamforming network according to the embodiment shown in Fig. 8a, where the beams are designated L1-L6.

[0041] Fig. 8c is a table showing the effective amplitude and phase roll-off of the excitation for an 8x16 beamforming network according to the embodiment shown in Fig. 8a, where the beams are designated R1-R6.

[0042] Fig. 9 illustrates a general coordinate system for a two-dimensional massive MIMO phased array according to an embodiment.

[0043] Fig. 10 is a conceptual illustration of a low-orbit massive-MIMO VHTS array according to an embodiment.

[0044] Fig. 11 illustrates a two-panel orthogonal phased array with massive-MIMO in beam space according to an embodiment.

[0045] Fig. 12 is a graph showing the forward radiation pattern and the backward radiation pattern resulting from a 90 degree hybrid that effectively splits the radiation pattern of one element into two sector orthogonal beams.

[0046] Fig. 13 is a graph showing the array patterns of the output signals of two-sector orthogonal steerable beams over a range of ±45° in the elevation plane, except for angles close to 0° elevation, according to an embodiment.

[0047] Fig. 14 is a graph showing a combined radiation pattern for two dual-sector steerable beams near an elevation angle of 0°, according to an embodiment in which the low-orbit satellite operates at 30 GHz at an altitude of 350 km.

[0048] Fig. 15a is a table showing m-MIMO performance data for a pilot signal using two 320 mm2 grating panels according to an embodiment.

[0049] Fig. 15b is a table showing actual m-MIMO performance data for a pilot signal using 2 grating panels of 320 mm2, where m-MIMO processing has a wider bandwidth and a larger number of grating panels, such as 2x5, according to an embodiment.

[0050] It should be noted that in all the accompanying drawings, the same elements are designated by the same reference designations.

DETAILED DESCRIPTION

[0051] The term "approximately"/"about" as used herein shall be understood to include a deviation from the nominal value, such as a deviation of +/- 10% from the nominal value. It shall be understood that such a variation is always included in the value presented herein, whether or not it is specifically mentioned.

[0052] Embodiments of the present invention provide methods and apparatus related to a massive MIMO phased array antenna in beam space. The phased array may have a high gain and be steerable. Massive MIMO technology has not been previously applied to satellite communications. This is due, for example, to the long transmission distances (and long delays) and high transmission losses. Such factors make it difficult to obtain CSI feedback for use in channel estimation, which is typically used in MIMO systems. Embodiments of the present invention include using a large phased array using massive-MIMO processing for long-range communications using a combination of analog and digital precoding. This potentially results in stronger pilot signals for CSI processing and a significant simplification of CSI processing. The simplification may include reducing the two-dimensional digital precoding operation to a combination of separate, simpler linear processing operations. This may be particularly well suited for use in low-orbit high-throughput satellite (HTS) communications.

[0053] Fig. 1a illustrates a single antenna array 102 provided in accordance with an embodiment of the present invention. This may be referred to as an M-steered dual-sector (N×N) massive-MIMO array. The illustrated antenna array is applicable, for example, in a single-polarized application, for example, using single-polarized antennas (radiators). However, it should be understood that the present invention can be easily extended to a dual-polarized application by using dual-polarized radiators. The antenna array is a two-dimensional array having a plurality of elements 110, for example, arranged in N rows (for example, row 105) with N radiators in each. For purposes of explanation and in various embodiments of the present invention, each row (vertically oriented in Fig. 1a) extends in the azimuthal direction, and the rows are parallel to each other and spaced apart in the elevation direction. However, it should be understood that other directions and orientations may also be used. The antenna array may be a flat array or the array may be located on a curved surface. In operation, a beam space may be formed from M (out of possible N) orthogonal beams (or beam groups), where each of the M beams is directed differently in the azimuthal direction. In the embodiment illustrated here, these beams or beam groups are created in part using a plurality of beamformer networks 120, each of which has N antenna ports and N beam ports (called N×N beamformers). Although N beam ports are available, which implies N beams, in various embodiments only M<N beams are used, where the number M is selected, for example, based on the requirements for the scan angle in the azimuthal direction.

[0054] According to various embodiments, the distance between the elements of the antenna array 102, as well as the distance between the elements of other antenna arrays of the device, is less than or equal to half the operating wavelength of the antenna array. In essence, the antenna array can be a fine-pitch array. The array can also be implemented as a non-resonant array. Such embodiments are particularly useful, for example, when implementing the beamformer networks shown in Figs. 6a and 7a.

[0055] An element spacing less than or equal to half a wavelength typically results in high mutual coupling between the antenna elements. A tightly coupled phased array is designed and operated taking into account such high mutual coupling. An example is the tightly coupled dipole array (TCDA), which has been recently presented in the literature. See, for example, J.T. Logan, R.W. Kindt, M.Y. Lee, M.N. Vouvakis, "A new class of planar ultrawideband modular antenna arrays with improved bandwidth," IEEE Trans. On Antennas and Prop., vol. 66, no. 2, Feb. 2018, pp. 692–701, and J.J.H. Wang, "Traveling-wave antenna array (TWAA) with multioctave scan-gain-banwdith," 2016 IEEE International Symposium on Phased Array Systems and Technology (PAST), 2016.

[0056] A typical phased array is designed using independently resonating radiators. These radiators resonate in specific frequency ranges or are narrow-band resonators. In a tightly coupled phased array, the entire array operates essentially unitarily. However, each radiator does not necessarily operate as a resonator in the operating frequency range.

[0057] In more detail, each network 120 of beamformers is connected to another corresponding set (e.g., a row or a pair of rows with a small pitch) of N antenna elements 110 of the same antenna array 102. The networks of beamformers may be Butler matrices or structures similar to Butler matrices. In an alternative embodiment, the networks use beamformers as described with reference to Figs. 6a and 7a. In such cases, hybrid couplers 155 may also be included, which can be used to form two-sector beams, for example, in the direction of the elevation angle. Such embodiments are described in more detail elsewhere in this document.

[0058] Beamformer networks are typically constructed using analog components and have fixed behavior, such as phase shifts that are essentially uncontrollable or at least controllable only during calibration. Beamformer networks may use, for example, power splitters/combiners, phase shifters, and hybrid couplers. Since the beamformer network components are fixed, i.e., uncontrollable, beam steering is typically accomplished using an additional active beamformer, which is described elsewhere in this document.

[0059] The beam ports of the beamformer networks are operatively connected to rows 152 of hybrid (e.g., 3 dB) couplers 155, which may be 90-degree hybrid couplers, also referred to as quadrature hybrids or simply hybrids. For clarity, in Fig. 1a, each row of hybrids is shown extended in the direction of the elevation angle, although this is done only for ease of illustration. The hybrid couplers are directional couplers with four ports that provide equal power splitting/combining between the input and output ports. In some embodiments, the 90° hybrid coupler operates with a resulting phase shift of 90° between the output ports. As shown, each hybrid has a first pair of ports facing the antennas and beamformer networks and a second pair of ports facing away from the beamformer networks. The second pairs of ports may be connected to a separate active beamformer. Each row of hybrids is connected to a pair of two different beamformer networks by connecting the first pair of ports of the hybrids to the beam ports of the beamformer networks. In various embodiments, two different beamformer networks that are connected to the same row of hybrids are adjacent to each other, for example, in the sense that they are associated with adjacent rows of antenna elements in the array.

[0060] Accordingly, a plurality of beamformer networks are arranged in parallel and connected to different corresponding sets of antenna elements. Rows 152 of hybrid couplers are connected to corresponding (adjacent) pairs of beamformer networks. Different beam ports of the beamformer networks 120 and, therefore, different ports of the hybrid couplers 155 control beams in different beam groups. Different beam ports of the same hybrid coupler control different two-sector beams in the same beam group due to the fact that such different ports direct radio frequency energy differently to or from pairs of beamformer networks.

[0061] Multiple beamformer networks 120 connected to the same antenna array, together with hybrid couplers 155 connected to the multiple beamformer networks, form parts of a common beamformer array. Each antenna array can be operatively connected to its own corresponding beamformer array.

[0062] The array of beam formers, which is operatively connected to the antenna array 102, is configured to create a first plurality of beams by operating the antenna array 102 as a phased array. The beams may be transmit beams, receive beams, or a combination of both. As will be described in more detail below, the first plurality of beams is divided into a plurality of spaced groups of beams. That is, adjacent groupings may be separated by gaps of a given width. Each group of beams includes a corresponding plurality of overlapping beams.

[0063] The second antenna array and the second beamformer array are provided and configured similarly, but not identically, to the antenna array and the beamformer array as described above. In particular, the second beamformer array is operatively connected to the second antenna array. The second antenna array includes a plurality of additional antenna elements and is typically separated from the first antenna array. For example, the first and second antenna arrays can be spaced apart. The first and second arrays can be substantially identical in terms of the design and arrangement of the elements. The second beamformer array is configured to form a second plurality of beams by operating the second antenna array as a second phased array. The second plurality of beams are divided into a plurality of additional, spaced apart groups of beams. Notably, the plurality of additional spaced apart groups of beams alternate with the plurality of spaced apart groups of beams of the first antenna array and the first beamformer. In various embodiments, the two groups of beams alternate. However, three or more beam groups could theoretically be interleaved, provided that the beamformer structure is designed to accommodate this configuration. Using multiple individual arrays can facilitate beam orthogonality.

[0064] Additional antenna arrays and corresponding additional beamformer arrays may also be provided, each of which is operatively connected to a corresponding one of the additional antenna arrays. Each of the additional beamformer arrays is configured to create additional copies of the first plurality of beams or the second plurality of beams. This is achieved by operating the additional array as an additional phased array in the same manner as described above with respect to the first and second beamformer arrays and the corresponding arrays. The additional arrays may be substantially identical to the arrays already described above. Each of the additional copies overlaps (e.g., coincides or is co-directional) with the first plurality of beams or the second plurality of beams. As will be explained elsewhere herein, multiple beamformer arrays, such as a first beamformer array and one, two or more additional beamformer arrays having overlapping/coincident copies of beams, may operate together using an active beamformer to create steerable tracking beams. These steerable tracking beams can be more precisely focused and controlled to direct RF energy to communicate with specific target devices.

[0065] In various embodiments, each group of beams consists of individual beams that, in combination, have a corresponding combined cross-section that extends in a first direction, which may be an elevation direction. The different groups of beams are aligned next to each other in a second direction, which may be perpendicular to the first direction and which may be an azimuthal direction. In some embodiments, for example, when the device is located on a satellite that moves relative to the Earth, the first direction is oriented such that each corresponding combined cross-section represents a portion of the Earth's surface, and this cross-section extends parallel to the direction of orbital motion of the satellite.

[0066] The beam groups of the second beamformer array may be wide enough to substantially fill the spaces between the beam groups of the first beamformer array. Accordingly, in various embodiments, the beams of the first and second beamformer arrays (i.e., the plurality of beam groups and the plurality of additional beam groups) may together form a substantially continuous common set of beams that are aligned next to each other.

[0067] Fig. 11 shows an example of two alternating sets of a plurality of beam groups that are elongated in a first (e.g., elevation) direction and aligned next to each other in a second (e.g., azimuthal) direction. The elongated cross-section may have the shape of an ellipse, as shown, or another shape. Each ellipse 1120, 1130 corresponds to a beam group. The unshaded ellipses 1120 correspond to a plurality of spaced beam groups of one of the arrays, such as array A1, while the shaded ellipses 1120 correspond to a plurality of spaced beam groupings of another, complementary one of the arrays, such as array B1. The lattices A2 through Am can also create ray groups that correspond to the unshaded ellipses 1120, and the lattices A2 through Am can also create ray groups that correspond to the shaded ellipses 1130.

[0068] In various embodiments, each group of rays includes at least two different two-sector rays. The first of the two-sector rays is directed toward a first (e.g., front) portion of the combined cross-section (e.g., toward the bottom of the ellipse 1120 or 1130 in Fig. 11), and the second of the two-sector rays is directed toward a second (e.g., back) portion of the combined cross-section (e.g., toward the top of the ellipse 1120 or 1130 in Fig. 11). Thus, the two-sector rays are directed differently, but typically overlap. Each group may include multiple copies of each of the two-sector rays.

[0069] Accordingly, each group of rays may be a two-sector group of rays having one, two or more front rays and one, two or more rear rays. The front rays may be substantially identical to each other, and the rear rays may be substantially identical to each other. The front rays together form a first portion of the combined cross-section of the group. This first portion is located closer to the first end of the combined cross-section. Similarly, the rear rays together form a second portion of said combined cross-section. This second portion is directed toward the second end of the combined cross-section. The first end and the second end are located opposite each other in the first direction, and the first portion and the second portion may overlap. Alternatively, the first and second portions may be non-overlapping, however, this may affect the beam forming options when it is desirable to form a beam (for example, using an active beam former) directed toward the central portion of the combined cross-section. Since all the rays come from almost the same place (as seen from a distant target), the rays are directed in different ways and to different places by different angles of the rays. For example, the front rays are directed at a different angle relative to the back rays.

[0070] In various embodiments, different beams are orthogonal. For example, the front beams may be orthogonal to the back beams. Additionally or alternatively, different groups of beams may be orthogonal to each other. Orthogonality is used to describe spatial orthogonality in beamforming, for example, as follows. For advanced communication using multipath transmission, the excitation of a phased array must satisfy the following conditions for optimal performance:

[0071] Equation (1) above ensures the orthogonality of the ports between the two beams, where Li and Ri represent two complex beam excitations. The sum is zero when the two ports are perfectly orthogonal. It is usually desirable to keep this effect below -20 dB. Equation (2) above represents the beam coupling factor (BCF) between the two beams. This further minimizes complex excitations such as interactions across radiation patterns, E _R and E _L . Typically the BCF should be below -15 dB.

[0072] Fig. 1b illustrates an embodiment similar to Fig. 1a. The device 170 has six grating panels operatively connected thereto, which corresponds to M=3 pairs of panels. One such panel 175 is shown in more detail. The panel 175 forms several spaced groups of beams, for example, group 177. Another panel 185 creates a plurality of additional spaced groups of beams, for example, group 187 (dashed lines), which alternate with the groups 177.

[0073] Digital beamforming is performed on rows of beam ports, for example row 157, to perform active beamforming in the direction of the angle of elevation. There are three groups (pairs of rows) of antenna elements 190, each of which forms one group of beams, including a front beam 192 and a rear beam 194. The groups overlap each other. Active beamforming in the direction of the angle of elevation is performed, at least in part, using a combination of these three groups of beams. Beamforming may also include additional overlapping groups of beams from other panels. Different rows of beam ports, for example rows 157 and 159, can be used to create beams directed differently in the azimuth direction. Different ports of the same hybrid, for example ports 162, 164, can be used to create different ports of the front and rear beams 192, 194 of the same group of beams.

[0074] Typically, an N×N beamformer, such as a Butler matrix, produces N orthogonal radiation patterns with a relatively high side lobe, which may be -13 dB. Figure 2 shows typical orthogonal radiation patterns that may be produced, for example, by a 16×16 Butler matrix. The N orthogonal radiation patterns may have high side lobes. The beams are labeled 1R through 6R for beams that are gradually tilted outward to the right, and 1L through 6L for beams that are gradually tilted outward to the left.

[0075] Although the resulting beams of such an N×N beamformer are typically orthogonal to each other, the beam space patterns may have a high beam coupling factor (BCF). This may increase interference between adjacent beams and reduce the overall system capacity. In Fig. 2, the beams are orthogonal with an intersection of -4 dB. However, the sidelobe levels (SLL) are only -13 dB. Therefore, the beam coupling factor between all beams exceeds -10 dB, and the correlation coefficient exceeds 0.3. This problem can be solved by superimposing two or three N×N orthogonal beams to form a set of new orthogonal beams. In this case, the sidelobe levels can be reduced to below -15 dB, which is more acceptable from the BCF point of view.

[0076] Fig. 3 shows the patterns of composite beams formed by superimposing N×N orthogonal beams created by the Butler matrix of the beamforming network. Only a limited number of beams are shown, and these beams fall within the angular range of interest. The beams of Fig. 3 can be obtained by superimposing pairs of beams of Fig. 2. For example, the two leftmost beams 6R and 5R in Fig. 2 can be superimposed to form the leftmost beam 6R-5R in Fig. 3. The composite beams are labeled as 1R-1L through 6L-5L to indicate from which combination of beams in Fig. 2 each composite beam is formed. The composite beams can be formed by combining multiple output beams with appropriate amplitudes and phases using an RF signal combining scheme. In Fig. 3, The SLL of composite beams can be less than -15dB, and the correlation coefficient can be less than 0.3 with an intersection less than 2dB.

[0077] However, such composite beams are orthogonal only to beams that are more than one beam space apart. Accordingly, in embodiments of the present invention, two separate and/or independent phased arrays, which may be referred to as array A and array B, may be used to cover the entire beam space in the azimuth direction, with each array creating beam patterns for alternating beams (as in Fig. 11). That is, array A may create a first diversity group of beams, and array B may create a second diversity group of beams that alternates with the first diversity group of beams. Array A may correspond to a first antenna array and a first array of beam formers, and array B may correspond to a second antenna array and a second array of beam formers.

[0078] Fig. 4 is a graph showing the radiation patterns of a first orthogonal composite phased array of beams in space, referred to herein as array A, according to an embodiment. The composite beams are the same as the corresponding beams in Fig. 3, however, only those beams that are actually formed by array A are shown.

[0079] Fig. 5 is a graph showing the radiation patterns of a second orthogonal composite phased array of beams in space, referred to herein as array B, according to an embodiment. The composite beams are the same as the corresponding beams in Fig. 3, however, only those beams that are actually formed by array B are shown.

[0080] Together, array A and array B can form a full set of 16×16 orthogonal radiation patterns in a low BCF beam space in the azimuth direction. Unlike a conventional massive-MIMO array, the output signal of each transmit/receive (Tx/Rx) port of the array according to an embodiment can have significantly higher signal power due to the high-gain radiation patterns. As a result, the array can handle a significantly larger range, since each pilot signal from a beam port can have a much better signal-to-noise ratio (SNR) at individual beam ports.

[0081] Fig. 6a illustrates an 8x16 network of orthogonal analog beamformers for embodiment A of phased array. At the bottom, there are 8 beam ports, labeled 1L through 8R. At the top, there are two subsets of 15 antennas each, labeled A2 through B16 (A1 and B1 are optional in this implementation). Antenna elements A2 through A16 may correspond to elements in the first row of the antenna array, and antenna elements B2 through B16 may correspond to elements in the second row of the same antenna array, with the second row typically located near the first row. Rectangles (e.g., 610) represent hybrid couplers, and circles (e.g., 615) represent phase shifters. Y-shaped couplers (e.g., 620) may be power splitters. The various phase shifts are given in multiples of ϕ, which can be approximately -11.25o. The phase shifts from α2 to α16 and from β2 to β16 are shown in Fig. 6b.

[0082] Fig. 7a illustrates a network of 8x16 orthogonal analog beamformers for embodiment B of phased array. The structure and phase shifts are similar to Fig. 6a. The phase shifts from α2 to α16 and from β2 to β16 are shown in Fig. 7b.

[0083] The beamformer networks of Fig. 6a and 7a (with the associated phase shifts as in Fig. 6b and 7b) are implemented with a 7 dB amplitude roll-off, although this may be changed in other embodiments. The beamformer networks of Fig. 6a and 7a (with the associated phase shifts as in Fig. 6b and 7b) are simplified compared to a conventional Butler beamformer network (or a pair of Butler beamformer networks connected together using a number of hybrids). For example, each of the beamformer networks of Fig. 6a and 7a requires 12 hybrid couplers each (24 total), whereas a 16-beam Butler beamformer network would require interleaving a total of 4×8=32 hybrid couplers. Thus, a reduction of at least 8 hybrid couplers is realized. The reduction in complexity and the number of components also provides a corresponding reduction in losses. In addition, the use of two beamformer networks shown in Fig. 6a and 7a to create interleaved beam patterns (e.g., in the azimuth direction) results in beams that are orthogonal and also have low correlation due to small sidelobes. This situation is not easily achieved with a conventional Butler beamformer network.

[0084] The beamformer networks of Fig. 6a and 7a may be used as beamformer networks in a given beamformer array. Each beamformer network is connected to two different, typically adjacent, rows of antennas. The antennas in this case have an element spacing of less than or equal to half the operating wavelength. The beamformer networks may include or be used with hybrids to create two-sector beams (e.g., forward and backward beams in the elevation direction), similar to those shown in Fig. 1a. The beamformer networks of Fig. 6a and 7a may be used with antenna arrays having an element spacing of less than or equal to half the operating wavelength.

[0085] For example, two adjacent beamformer networks in Fig. 6a or 7a may be connected to a series of hybrid couplers similar to the circuit shown in Fig. 1a. In this case, the spacing between the array elements may be required to be less than or equal to one quarter of the operating wavelength. As a result, the effective spacing between adjacent beamformer networks remains less than or equal to one half wavelength. Therefore, in some embodiments, only N/4 hybrids are required to form the beam of a two-sector array. Note that in some embodiments, only N/2 azimuthal beamformers may be required.

[0086] Accordingly, in some embodiments, as shown, for example, in Fig. 1a, each of the pair of rows of antenna elements is connected to the other of two corresponding beamformer networks, and the two beamformer networks are interconnected using a plurality of hybrid couplers. In other embodiments, as shown, for example, in Fig. 6a and 7a, each of the pair of rows of antenna elements is connected to a single interconnected beamformer network, which is used to control both rows of antenna elements. In both cases, the two rows of antenna elements are jointly controlled to form a beam. Two different sets of antenna elements that are connected to a pair of interconnected beamformer networks or to a single interconnected beamformer network may be two different rows of antenna elements. These rows may be rows of the same corresponding antenna array. These rows may extend parallel to each other in one direction (for example, in the azimuth direction) and be spaced apart from each other in another direction (for example, in the elevation direction).

[0087] All embodiments shown in Fig. 1a, 6a and 7a can be described as follows. Each beamformer array includes a plurality of beamformer networks arranged in parallel. In the case of Fig. 1a, each beamformer network is connected to one row of antenna elements, and pairs of beamformer networks are connected together using rows of hybrid couplers. In the case of Fig. 6a and 7a, each beamformer network is connected to a pair of rows of antenna elements. The beamformer array in each case is configured to provide a set of beam ports. Each of the beam ports is operatively connected via one of the beamformer networks or via a connected pair of beamformer networks to a pair of adjacent rows of antenna elements. In the case of Fig. 1a, the beam ports are hybrid coupler ports facing away from the antenna array. In the case of Fig. 6a and 7a beam ports are directly integrated into the beamformer networks.

[0088] In more detail, in the case of Fig. 1a, each of the beamformer networks is connected to another respective row of antenna elements, and each beamformer array includes one or more rows of hybrid couplers. Each row of hybrid couplers is connected to a respective pair of beamformer networks, and, as mentioned above, the nominal beam ports of the array are ports of the hybrid couplers. In further embodiments, different hybrid couplers control beams in different beam groups, and each hybrid coupler has a pair of ports. As described elsewhere herein, each of the pair of ports controls a different two-sector beam in the same beam group.

[0089] In more detail, in the case of Fig. 6a and 7a, each of the beamformer networks is connected to another respective pair of adjacent rows of antenna elements. Each beamformer network includes a subset of a set of beam ports, where the number of beam ports in the subset is less than the number of antenna elements in said pair of adjacent rows. For example, in Fig. 6a and 7a, there are up to 8 beam ports (e.g., 1L, 2L, ... 8R), and the antenna elements are 30 (or 32). In fact, the number of beam ports is less (e.g., about half) the number of antenna elements in one row.

[0090] In even more detail, in the case of Figs. 6a and 7a, each of the beamformer networks can be characterized as follows. Each of the beamformer networks includes a plurality of hybrid couplers arranged in a series-parallel configuration. In the illustrated example, there are three rows of four hybrids each with phase shifters between the rows of hybrids. Each of the beamformer networks includes a plurality of power splitters, each of which is connected to a pair of antenna elements, including one antenna element from each pair of rows. That is, each power splitter is connected to a pair of antenna elements, one antenna element in each row. The uppermost row of hybrid couplers is connected to the antenna elements via power splitters. The beamformer network also includes a plurality of phase shifters. At least some of the phase shifters are located between the power splitters and the antenna elements. The phase shifters have different phase settings. There may be multiple cascaded sets of power dividers, and there may also be phase shifters connected between hybrid couplers and power dividers, and between different cascaded sets of power dividers.

[0091] In embodiments such as those corresponding to the beamforming network implementation of Figs. 6a-7b, 12 of the 16 orthogonal beams with low BCF may be created by the joint operation of array A and array B. This may provide azimuth coverage of up to ±40 degrees. The beams may create low sidelobes (less than -15 dB) with low beam intersections of > 10 dB. This may result in a significantly low BCF for each set of phased arrays. In such a beamforming network (BFN), a total of only 24 hybrids are required for the two arrays instead of 32 hybrids for each of the conventional 16x16 BFNs. In addition, only 15 radiating elements are required instead of the conventional 16, since the arrays have an effective amplitude roll-off.

[0092] Fig. 8a is a graph showing 12 of 16 orthogonal low BCF beams of a phased array combining phased array A and phased array B (A+B) for coverage of up to ±40 degrees along the azimuth (Az) axis, according to an embodiment. Solid lines represent beams of phased array A, such as with beam R2 accessible through port 2R in Fig. 6a, etc. Dashed lines represent beams of phased array B, such as with beam R1 accessible through port 1R in Fig. 7a, etc.

[0093] In embodiments, each of the arrays A and B may require two rows of identical arrays having different phase distributions in the final stage of the beam forming network (BFN). This is shown in both Fig. 6a and Fig. 7a. Due to the effective amplitude and phase roll-off (e.g., as in Figs. 8b and 8c), such array architectures can create orthogonal beams having low sidelobes.

[0094] Fig. 8b is a table showing the effective amplitude roll-off and excitation phase for an 8x16 beamforming network according to an embodiment, where the beams are labeled L1-L6 and correspond to the beams in Fig. 8a. The magnitudes and phases for various antenna combinations (shown as in Figs. 6a, 7a) are shown for the various beams.

[0095] Fig. 8c is a table showing the effective amplitude roll-off and excitation phase for an 8x16 beamforming network according to an embodiment, where the beams are designated R1-R6 and correspond to the other beams in Fig. 8a. The magnitudes and phases for various antenna combinations (shown as in Figs. 6a, 7a) are shown for the various beams.

[0096] Having described various aspects of analog beamforming arrays and antenna arrays, methods for active (e.g., digital) beamforming and channel state information estimation according to embodiments of the present invention will now be described.

[0097] In embodiments, analog (e.g., 8x16) BFNs can effectively divide the azimuth coverage space into multiple orthogonal beam spaces with high-gain beam grouping. The directions of these beams can be fixed and can be selected to be orthogonal to the flight direction of the satellite on which the equipment is installed. Thus, target devices can be allocated based on the location of the beam in the azimuth direction. However, target devices for each beam can be tracked along the flight path using digital beamforming methods.

[0098] Channel estimation in a massive MIMO system can be achieved by estimating the channel transfer function using available channel state information (CSI). However, due to large propagation delays (e.g., between target devices and satellites), which can typically be several milliseconds, and due to the high mobility of satellites and target devices, obtaining instantaneous CSI at the transmitting side of the satellite system is not feasible. In embodiments, channel estimation can be performed based on parametric channel models using the direction-of-arrival (DOA) of the signals. Basically, for line-of-sight transmission, which can be assumed in many cases, the relative excitation phases of the emitters in a two-dimensional phased array can be approximated after determining the DOA of the incident signal. In embodiments, this approach can be based on determining the response vectors of the phased array. In embodiments, a simple linear precoding processing can be obtained for 2D massive MIMO based on the overall array configuration.

[0099] Fig. 9 illustrates a general coordinate system for a two-dimensional massive MIMO phased array according to an embodiment. An XYZ coordinate system is shown, where the X axis may pass, for example, in the azimuth direction of the antenna array, and the Y axis may pass, for example, in the direction of the elevation angle of the antenna array. The two-dimensional antenna array is located in the XY plane, the pointing angle of the reference antenna is shown in the direction (U _o , V _o ), and the direction 910 of the target device i is shown as having a component projected onto the XY plane, (Ui, Vi). The angles θ _i and ϕ _i are related to the direction 910 of the target device i using spherical coordinates.

[00100] For line-of-sight (LOS) transmission, the signals received by the satellite's two-dimensional phased array antennas from a number P of target devices on the ground can be expressed as:

Where:

β _i (t) is the channel gain for the target device i,

- time coefficient of the satellite phased array,

- transmission signal from target device i with delay , And

N(t) is noise, for example additive white Gaussian noise (AWGN).

[00101] Frequency response corresponding to , is equal to:

Where:

- complex channel amplification,

- complex coefficient of a two-dimensional lattice,

- transmitted signal with phase delay , And

W - AWGN noise.

[00102] Based on Fig. 9, the general form of the array coefficient for a homogeneous two-dimensional phased array can be expressed as:

Where:

x and y are the axes of a two-dimensional lattice,

k ₀ - propagation constant

m - lattice element number

dx and dy are the distance between elements in the x and y directions.

u and v are the scanning axes,

( - the pointing angle of the reference antenna and

( - the location of the target device i, given as follows:

[00103] By performing analog beamforming in the scan axis direction u, a set of orthogonal beams can be obtained with the following overall radiation pattern (1/x)sin(x) (ray space in the u direction):

[00104] The above equation can be represented as a set of N orthogonal beams in the u direction, where the value for each beam depends only on the location of the target device i and the beam number m. Therefore, the signal received by the two-dimensional phased array can be expressed as:

[00105] Since the N beams in the direction of the scan axis u are orthogonal and have little beam interaction, they can be considered as a spatially separated sector. Therefore, the total received signal can be considered separately in each beam space m:

[00106] In embodiments where the satellite moves at a constant high speed , and the terminals move at a relatively much slower speed, the Doppler shift can be included in the formulation as a coefficient phase shift with Doppler radian angle defined as:

[00107] Each received beam signal becomes equal to:

[00108] The beam steering vector can be defined as:

(1,

[00109] Here, {A⋅S(t)} _n is an n-dimensional linear precoder, which can be easily implemented using one of a variety of processing methods, including Digital Fourier Transform (DFT), Multiple Signal Classification (MUSIC), and Estimation Signal Parameter via a Rotational Invariant Technique (ESPRIT). Accordingly, for each target device i, the complex massive-MIMO processing can be reduced to linear precoding of n dimensions.

[00110] According to the above, a channel state estimator may be provided in the device disclosed here. The channel state estimator is configured to estimate the state of a wireless communication channel (primarily line of sight) between the device and a remote wireless communication device. This estimate may be based on the direction of arrival of a signal (e.g., a pilot signal) transmitted by the remote wireless communication device, and, in addition, on the basis of the geometry of the first antenna array and the second antenna array. This estimate may be obtained using statistical information about the channel state and a parametric channel model. The estimate may be performed as described above with respect to Fig. 9 and the disclosed equations.

[00111] Channel state estimation can be described as using statistical information about the channel state, for example, using a parametric model. In this approach, the processing of a two-dimensional pilot signal (which would be required for a conventional two-dimensional antenna array) is replaced by a plurality of linear processing operations. The processing operations are based on the direction of arrival (e.g., of the pilot) signals in a calculation that is configured based on the geometry of the array (as represented by the array coefficient). The direction of arrival is specified for one direction, for example, in the direction of the elevation angle. This leads to an increase in speed and a decrease in simplicity. Since the pilot signals are received via beams and not at the level of a single antenna element, the power of the pilot signals is significantly increased compared to conventional methods. Since there are many separate beam groups that are essentially separated, the processing is simplified to a set of one-dimensional linear processing operations. In particular, the pilot signal processing is reduced to N parallel linear precoding operations using statistical CSI.

[00112] In some embodiments, estimating the state of a wireless communication channel comprises performing a plurality of separate linear precoding operations, as described above.

[00113] Also according to the above, an active (e.g. digital) beam former can be provided, which is connected to one, two or more beam forming arrays. The active beam former can be configured to form, using digital pre-coding, one or more tracking beams, at least in part, by combining a plurality of beams belonging to one of the beam groups, from a plurality of spaced beam groups, which are created by an antenna array or arrays in combination with the beam forming array or arrays. The active beam former can combine, using different phasing, the beams of a given beam group or a set of overlapping beam groups to create steerable beams.

[00114] Since the beam groups may have a narrow cross-section and be elongated in a first direction (e.g., the direction of the elevation angle), the beam steering may be substantially one-dimensional, i.e., the direction in the first direction. This may simplify the operation. Accordingly, in various embodiments, each beam group (beamformer arrays and antenna arrays) consists of individual beams that, in combination, have a corresponding combined cross-section elongated in the first direction. Then, the tracking beams of the active beamformer become steerable in the first direction.

[00115] Fig. 10 is a conceptual view of a low-orbit phased array VHTS with massive-MIMO on board a satellite 1000, shown in three different positions, according to an embodiment. The satellite can form a plurality of orthogonal elliptical high-gain beams (or beam sets) 1010a, 1010b, 1010c, 1010d, 1010e, 1010f, 1010g, 1010h in an azimuthal direction 1030. This is shown in more detail in Fig. 11. Beams 1010a, 1010c, 1010e, 1010g may be created by one array or a set of arrays, and beams 1010b, 1010d, 1010f, 1010h may be created by another array or a set of arrays. The target device on the ground may then be tracked by the satellite using massive-MIMO processing during each pass. As illustrated by way of example, the cross-sections of the beam (or group of beams) when crossing the Earth may have, for example, a length of 900 km (corresponding to the direction of the 1020 elevation angle) and a width of 24 km (corresponding to the azimuth direction). Thus, the beams or groups of beams are such that this cross-section is significantly longer (for example, at least ten times longer in some embodiments and 30-50 times longer in some additional embodiments than its width).

[00116] In an embodiment, the phased array may be implemented with a two-panel orthogonal massive-MIMO in beam space. A set of two complementary grid panels, grid A and grid B, may be used, and they may create alternating beams that are orthogonal to each other. Several sets of two such additional grid panels may be provided. A total of M pairs of panels may be used to achieve a high data rate due to massive-MIMO processing. Each grid panel includes an antenna array and, optionally, a corresponding beamforming array. Alternatively, the beamforming arrays may be separated from the panels, provided that sufficient coupling can be performed between the beamforming arrays and the antenna arrays.

[00117] Fig. 11 illustrates a dual-panel orthogonal phased array with massive-MIMO in beam space according to an embodiment. A brief explanation of Fig. 11 was presented earlier. However, it should be noted here that Fig. 11 illustrates a device having a chassis 1100 and a first set of antennas and beam-forming arrays A1, A2, A3, A4, ... Am, and a second set of antennas and beam-forming arrays B1, B2, B3, B4, ... Bm. In general, m can be any number greater than or equal to one or two. Each of the first set of antennas and beam-forming arrays is configured to create a copy of the diverse groups of beams 1120, while each of the second set of antennas and beam-forming arrays is configured to create a copy of the diverse groups of beams 1130. Notably, the beam groups are extended in the first direction and each typically includes several beams. Furthermore, multiple copies of the constellations provide multiple overlapping beams. All overlapping beams corresponding to a given constellation can be operated together using an active beamformer to create composite beams steerable in the first direction. Beam steerability in the second direction can be achieved by using different constellations.

[00118] According to an exemplary embodiment corresponding to FIG. 11, several (e.g., 16) elliptical beam groups may be provided per satellite. Beam steering or tracking may be performed along the main axis of each ellipse, Massive-MIMO (M-MIMO) operation may be performed, or both. Such a configuration may potentially improve the complexity of handover. In various embodiments, 8-16 parallel elliptical beams or beam groups may be provided per satellite via beamforming. 50 ports (800/satellite) may be provided per beam for HPBW = 2 degrees. M grid panels per satellite may be used for M-MIMO or tracking processing to achieve an effective beam with HPBW < 1 degree (along the path). This may include ultra-wideband active phased arrays with a bandwidth of more than 5 GHz, dual polarization and a wide scan angle > ± 45. A phased array with an element pitch < λ/2 and good active resistance can be provided for a scan angle of up to 45°.

[00119] A low earth orbit satellite may typically move at a relatively high speed along a constant trajectory at an altitude of several hundred to one thousand kilometers above the earth. For a user (target device) on the ground, the low earth orbit satellite appears in the field of view for only a short period of time (several minutes) and may move at a constant speed along a predictable linear direction. Thus, a satellite beam may be required to track a target device on the ground as it moves. This may require wide-angle beam steering capability in the elevation direction. Since the satellite's field of view is expected to be approximately ±40°, the antenna array beam must be able to steer through an angle greater than ±45°. To achieve this goal using massive-MIMO precoding in elevation, each individual output azimuth beam may need to have a coverage angle of ±45° and produce a pilot signal with sufficient strength to achieve the minimum signal-to-noise ratio for massive-MIMO processing. The output signals of each orthogonal beam at a given azimuth angle can then be combined to form a typical phased array steerable beam. However, due to the large beam elevation angle (±45°), this may not provide sufficient signal strength at each azimuth beamformer.

[00120] In order to improve the pilot signal power and to form two orthogonally controlled elevation angles with a high gain, embodiments of the present invention use a 90° hybrid coupler (also called a hybrid) at the output of each orthogonal azimuth beam. An embodiment including hybrids with a 90° rotation angle is shown in Fig. 1a. Each 90-degree hybrid can effectively divide the radiation pattern of one element into two sectors: a forward radiation sector and a rear radiation sector.

[00121] Fig. 12 is a graph showing a forward radiation pattern and a backward radiation pattern resulting from a 90-degree hybrid that effectively splits the radiation pattern of one element into two-sector orthogonal beams. The forward radiation pattern 1210 and the rear radiation beam 1220 are orthogonal to each other, and they can be steered with a pre-tilt angle of approximately or exactly 30° at an operating frequency at which the spacing between the arrays is exactly half a wavelength. These two radiation patterns can have a suitable (e.g., correct) half-power beamwidth (HPBW) to provide beam steering using array processing from 0° to 45° with a minimum radiation efficiency of 85%. Since the coverage angle of each beam can be halved, the overall gain of each steered beam can be increased by a factor of 2 (3 dB).

[00122] Fig. 13 is a graph showing the output pattern of two-sector orthogonal steerable beams over a range of ±45° in the elevation plane, except for angles close to 0° elevation. The beams are two-sectored: the back beams (labeled NDIR) and the front beams (labeled PDIR) are separated at an angle.

[00123] Accordingly, when dual-sector front and rear beams are used, each beam can be used alone (or together with other front or rear beams, respectively) to steer the beam toward the front or rear portion of a given region, such as toward one end of the ellipse in Fig. 11. The front and rear beams can be combined to steer the beam toward the center portion of a given region, such as toward the center of the ellipse in Fig. 11.

[00124] Fig. 14 is a graph showing a combined radiation pattern for two two-sector steerable beams with an elevation angle of about 0°, according to an embodiment in which a low-orbit satellite operates at a frequency of 30 GHz at an altitude of 350 km. At a low elevation angle (less than one HPBW), the two beams may overlap. As a result, the radiation efficiency of each beam may be reduced due to high coupling. Although the two beams may have a large beam interaction at an elevation angle of about 0°, they can be excited individually without loss of coupling, since the two beams remain orthogonal. Combining the two beams can lead to almost complete recovery of the efficiency losses in each individual beam.

[00125] In an embodiment, m-MIMO performance may be achieved using a pilot signal using two 320 mm2 grating panels.

[00126] Fig. 15a is a table showing actual m-MIMO performance data for a pilot signal using two 320 mm2 grating panels.

[00127] The performance can then be significantly improved using m-MIMO processing with significantly wider bandwidth and more grid panels.

[00128] Fig. 15b is a table showing actual m-MIMO performance data for a pilot signal using two 320 mm2 grating panels, where m-MIMO processing has a wider bandwidth and a larger number of grating panels, five panel pairs.

[00129] In view of the above, a long-range wireless communication device is proposed that can be adapted for use in satellite systems. For example, the device can be used to provide a massive-MIMO array based on a VLEO satellite for a direct handset-to-satellite communication link, for example, using Ku/Ka/V/Q-band transmission. For a very low altitude satellite constellation at an altitude of 350 km, embodiments of the present invention can be used to provide direct communication between telephone devices to a satellite using massive-MIMO in beam space, for example with a BER=1e-05.

[00130] In various embodiments, pilot signals from target devices that use a low modulation code such as BPSK/QPSK may be used, while higher order modulation may be used during data transmission. A method for parametric channel estimation based on DOA for fast linear precoding was developed here.

[00131] Embodiments of the present invention provide a multi-beam M-MIMO device that potentially reduces the complexity of the antenna and beamforming array and potentially provides flexibility in improving overall performance.

[00132] Embodiments of the present invention can potentially be used in a communication system providing a total throughput of more than 30 Gbps/satellite/beam, using massive-MIMO phased arrays of dimensions on the order of 1.6 x 0.64 m and an available spectrum bandwidth of 5 GHz, with a transmit power of 200 mW/panel.

[00133] In some cases, in contrast to the conventional m-MIMO spot beam phased array, embodiments of the present invention use parametric channel estimation for fast signal processing. An advantageous linear precoding method for parametric channel estimation based on the DOA of a user is disclosed here. This channel estimation method is applicable to both TDD and FDD transmission.

[00134] In some cases, compared to a conventional massive-MIMO system, embodiments of the present invention provide significantly improved pilot signal power, which improves service quality and allows for an increase in service range. Pilot signals are monitored on a beam-by-beam basis rather than on an antenna element-by-antenna basis.

[00135] In some embodiments related to low-orbit satellite applications, if the beam steering direction of the array (e.g., the elevation direction) is set to the same as the rotation direction of the satellite, then beam tracking for a given user is reduced to a simple linear one-dimensional precoding processing after selecting the appropriate azimuth beam. Compared to a full two-dimensional phased array with a spot beam, this allows for significantly simpler and more energy-efficient multi-user operations.

[00136] Embodiments of the present invention are easily scalable. The capacity of the system can be increased by adding additional grid panels without significantly increasing the complexity and processing time. Adding panels increases the degree of freedom available for beamforming using an active beamformer and M-MIMO processing in at least one direction (e.g., in the elevation direction). This can help to reduce the beamwidth, increase the gain, or both, wherein the beamwidth is reduced proportionally to the number of panels used. In one embodiment, the HPBW can be approximately 0.2° in the direction of constellation elongation (e.g., in the elevation direction).

[00137] Although the present invention describes the beams as being created, it should be noted that the beams may be implemented for use in transmission, reception, or both, through the principle of antenna reciprocity.

[00138] Although the present invention has been described with reference to specific features and embodiments thereof, it will be apparent that various modifications and combinations may be made therein without departing from the scope of the invention. Accordingly, the description and drawings are to be regarded merely as illustrative of the invention as defined by the appended claims, and are intended to cover any and all modifications, variations, combinations or equivalents that fall within the scope of the present invention.

Claims (30)

1. A wireless communication device comprising: a first two-dimensional antenna array comprising a plurality of antenna elements; a second two-dimensional antenna array, wherein the second antenna array comprises a plurality of additional antenna elements and is separated from the first antenna array; a first array of beam formers operatively connected to the first antenna array and configured to form a first plurality of beams by operating the first antenna array as a phased array, wherein the first plurality of beams are divided into a plurality of spaced groups of beams; and a second array of beam formers operatively connected to the second antenna array and configured to form a second plurality of beams by operating the second antenna array as a second phased array, wherein the second plurality of beams is divided into a plurality of additional spaced groups of beams that alternate with said plurality of spaced groups of beams, where each group of rays contains a corresponding set of overlapping rays; and wherein each array of beam formers comprises a plurality of networks of beam formers arranged in parallel, and wherein the array of beam formers is configured to provide a set of beam ports, wherein each of the beam ports is functionally connected through one of the networks of beam formers or through a connected pair of a network of beam formers to a pair of adjacent rows of said antenna elements. 2. The device of claim 1, wherein each of the beamformer networks is connected to another corresponding row of antenna elements and each array of beamformers further comprises one or more rows of hybrid couplers, wherein each row of hybrid couplers is connected to a corresponding pair of the plurality of beamformer networks, and wherein said beam ports are hybrid coupler ports. 3. The device of claim 2, wherein different hybrid couplers control beams in different beam groups, and wherein each hybrid coupler comprises a pair of ports, wherein each of the pair of ports controls different two-sector beams in the same one of the beam groupings. 4. The device according to any one of claims 1-3, in which each of the beamformer networks is connected to another corresponding pair of adjacent rows of said antenna elements and comprises a subset of the set of beam ports, wherein the number of beam ports in said subset is less than the number of antenna elements in said pair of adjacent rows. 5. The device of claim 4, wherein each of the beamformer networks comprises a plurality of hybrid couplers arranged in a series-parallel configuration, a plurality of power dividers, each of which is connected to a pair of antenna elements comprising one antenna element in each of said pair of adjacent rows, and a plurality of phase shifters, at least some of the phase shifters being arranged between said power dividers and said antenna elements. 6. A device according to any one of paragraphs 1-5, in which the plurality of antenna elements and the plurality of additional elements are respectively arranged with a distance between the elements less than or equal to half the operating wavelength. 7. A device according to any one of claims 1 to 6, wherein each group of rays consists of individual rays which, taken together, have a corresponding combined cross-section elongated in a first direction, and wherein the different groups of rays are aligned next to each other in a second direction perpendicular to the first direction. 8. The device according to claim 7, wherein the device is installed on a satellite that moves relative to the Earth, and wherein the first direction is oriented so that each corresponding combined cross-section represents a portion of the Earth's surface extended parallel to the direction of motion of the satellite. 9. The device according to claim 7 or 8, wherein each group of rays is a two-sector group of rays comprising one, two or more forward rays which together form a first part of said combined cross-section, wherein said first part is located toward a first end of the combined cross-section, wherein each group of rays further comprises one, two or more backward rays which together form a second part of said combined cross-section, wherein said second part is located closer to the second end of the combined cross-section, wherein the first end and the second end are located opposite each other in a first direction, wherein the first part and the second part overlap or do not overlap. 10. The device according to claim 9, wherein said front rays are orthogonal to said rear rays and wherein said front rays are directed at a different angle relative to said rear rays. 11. The device according to any one of claims 1-10, further comprising an active beam former operatively connected to the first array of beam formers, wherein the active beam former is configured to form, using digital pre-coding, one or more tracking beams, at least in part, by combining several beams belonging to one of the beam groups from a plurality of spaced beam groups. 12. The device of claim 11, wherein each group of beams consists of individual beams that together have a corresponding combined cross-section elongated in the first direction, and wherein the active beam former is configured to control the tracking beams in the first direction. 13. The device according to claim 11 or 12, further comprising one or more additional antenna arrays and one or more additional beamformer arrays, each of which is operatively connected to a corresponding one of the additional antenna arrays, wherein each of the additional beamformer arrays is configured to create additional copies of the first plurality of beams by driving a corresponding one of the additional antenna arrays as an additional phased array, wherein each of said additional copies overlaps with the first plurality of beams, wherein the active beamformer is further operatively connected to each of the additional beamformer arrays, and wherein the active beamformer is configured to form said one or more tracking beams further by combining said plurality of beams with one or more additional beams belonging to said additional copies of the first plurality of beams. 14. A device according to any one of claims 1 to 13, wherein each group of beams consists of individual beams which together have a respective combined cross-section elongated in a first direction, and wherein the different groups of beams are aligned next to each other in a second direction which is perpendicular to the first direction, and wherein said rows of antenna elements extend parallel to each other in the second direction and are spaced apart in the first direction. 15. The device according to any one of claims 1-14, further comprising a channel state estimation means configured to estimate the state of a wireless communication channel primarily within the line of sight between the device and a remote wireless communication device based on the direction of arrival of a signal transmitted to the remote wireless communication device, and further based on the geometry of the first antenna array and the second antenna array using statistical information about the channel state and a parametric channel model. 16. The apparatus of claim 15, wherein said beam groups are orthogonal to each other and wherein estimating the state of the wireless communication channel comprises performing a plurality of separate linear pre-coding operations. 17. The device of any one of claims 1 to 16, wherein the first beamforming array and the second beamforming array are fixed analog beamforming arrays. 18. A method for wireless communication, comprising: operation of a first two-dimensional antenna array comprising a plurality of antenna elements arranged with a distance between the elements less than or equal to half the operating wavelength; operation of a second two-dimensional antenna array, wherein the second antenna array comprises a plurality of additional antenna elements arranged with a distance between the elements less than or equal to half the operating wavelength and separated from the first antenna array; operating a first array of beam formers operatively connected to the first antenna array and configured to form a first plurality of beams by operating the first antenna array as a phased array, wherein the first plurality of beams are divided into a plurality of spaced groups of beams; and the operation of a second array of beam formers, operatively connected to the second antenna array and configured to form a second plurality of beams, by operating the second antenna array as a second phased array, wherein the second plurality of beams is divided into a plurality of additional spaced groups of beams that alternate with said plurality of spaced groups of beams, where each group of rays contains a corresponding set of overlapping rays; and wherein each array of beam formers comprises a plurality of networks of beam formers arranged in parallel, and wherein the array of beam formers is configured to provide a set of beam ports, wherein each of the beam ports is functionally connected through one of the networks of beam formers or through a connected pair of a network of beam formers to a pair of adjacent rows of said antenna elements.