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WO2016210439A1 - Système d'antennes distribuées ayant des unités éloignées à récepteurs de balayage - Google Patents

Système d'antennes distribuées ayant des unités éloignées à récepteurs de balayage Download PDF

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Publication number
WO2016210439A1
WO2016210439A1 PCT/US2016/039653 US2016039653W WO2016210439A1 WO 2016210439 A1 WO2016210439 A1 WO 2016210439A1 US 2016039653 W US2016039653 W US 2016039653W WO 2016210439 A1 WO2016210439 A1 WO 2016210439A1
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signal
band
sub
das
digital
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William J. CRILLY
David J. Schwartz
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Westell Inc
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Westell Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/08—Access point devices
    • H04W88/085—Access point devices with remote components

Definitions

  • the present invention relates to distributed antenna systems, and, more particularly, to distributed antenna systems utilizing digital filters to establish high near-far performance.
  • the present invention is a system comprising a DAS with one or more digital filters to reduce unwanted signals from being applied to the LASER and to reject broadband noise from the LASER from being transmitted to and interfering with User Equipment (“UE”) thereby enhancing the uplink and downlink dynamic ranges of the DAS.
  • DAS distributed antenna system
  • One aspect of the present invention is a distributed antenna system comprising one or more interfaces to one or more base stations; one or more optical paths; one or more analog to digital and/or digital to analog converters; one or more remote units, having a plurality of sub-bands and digital signal processing; a photodiode; a LASER; one or more server antennas; and uplink and/or downlink digital filtering, wherein the digital filtering is in one or more remote units thereby improving the uplink and/or downlink Near Far performance of the distributed antenna system.
  • One embodiment of the system is wherein selective uplink and downlink filtering occurs at a first remote unit to allow the selective transmission and reception of a selected sub- band within the first remote unit.
  • One embodiment of the system is wherein a downlink combined signal is carried by an optical path to a second remote unit, transmitting the downlink combined signal, wherein the downlink combined signal is filtered by the first remote unit, thereby reducing the
  • One embodiment of the system further comprises a total power detector to prevent unwanted signals from overloading stages in front of the LASER.
  • One embodiment of the system further comprises a sub-band specific uplink automatic gain control feature within the digital signal processing in the remote unit.
  • One embodiment of the system further comprises one or more detectors operating within the digital signal processing, and in front of the analog to digital converter, to protect the analog to digital converter from overload.
  • One embodiment of the system is wherein the digital filtering within a remote can be eliminated when Near Far performance degradation does not occur.
  • One embodiment of the system is wherein uplink attacks and decay times operating in the automatic gain control feature are dependent on the technology used for the downlink of the same sub-band.
  • One embodiment of the system is wherein the selection of the delay of a digital filter in the uplink and/or downlink paths is used to equalize the delay of the transmission time of signals from multiple remote units, while simultaneously meeting the rejection requirements of the digital filter.
  • One embodiment of the system is wherein flexible signal selection is
  • Figure 1 shows a conventional prior art DAS system, describing the uplink and downlink path.
  • Figure 2A shows a schematic of one embodiment of the remote selection of sectors and sub-bands of the DAS system of the present invention in the uplink direction.
  • Figure 2B shows a schematic of one embodiment of the remote selection of sectors and sub-bands of the DAS system of the present invention in the downlink direction.
  • FIG. 3 shows a schematic of one embodiment of the DAS system of the present invention.
  • FIG 4 shows a schematic of one embodiment of the DAS system of the present invention with remote units that carry the uplink and downlink signals of different wireless service provider (“WSP") sectors and sub-bands.
  • WSP wireless service provider
  • Figure 5 shows a schematic of one embodiment of configuring the DAS system of the present invention.
  • Figure 6 shows a schematic of one embodiment of the DAS system of the present invention as shown in Figure 5.
  • Figure 7 shows a schematic of several embodiments of the DAS system of the present invention with alternative splitting and combining methods.
  • Figure 8 shows a schematic of several embodiments of the DAS system of the present invention with alternative splitting and combining methods.
  • Figure 9 shows a schematic of one embodiment of the DAS system of the present invention where hybrid combiners may be used to allow multi-WSP signal sets to be serviced by multiple remote units ("RU").
  • RU remote units
  • Figure 10 is a graph illustrating a number of wireless signals being measured by a scanning receiver.
  • Figure 11 is a block diagram showing example scanning receivers of an RU that may be implemented via digital signal processing. DETAILED DESCRIPTION OF THE PREFERRED EMB ODFMENT S
  • Wireless coverage inside buildings is generally reduced due to the attenuation caused by building materials and blockages. Wireless signals from macro cell sites experience reduced levels resulting in low speed data connections and potentially lost voice connections.
  • the solution to this problem is the use of a Distributed Antenna System (DAS).
  • DAS Distributed Antenna System
  • the DAS is passive, it may be comprised of coaxial cable, splitters and antennas, generally called server antennas, and the like.
  • the DAS is active, it uses one or more amplifiers, combined with systems to efficiently carry the wireless signals from the source of the signals to the server antennas for propagation to User Equipment (“UE").
  • UEs include, but are not limited to, cellphones, smartphones, wireless modems, tablets, and the like.
  • Media conversion is often done between coaxial cable and fiber optic cable. Generally, fiber is preferred because it is lightweight and has low loss at high distance.
  • the conversion of RF signals to be carried over the fiber optic cable usually involves the use of a LASER to produce modulated light. Conversion from light to modulation to RF signals is usually done with a photodiode.
  • a cellular base station referred to as an eNodeB for LTE signals
  • an off-air repeater or a small cell, which is a type of base station that has reduced capacity compared to a full eNodeB with multiple sectors, and the like.
  • One objective of the DAS transport system is to transport the source RF signals to one or more server antennas with a minimum loss of signal purity and fidelity.
  • Signal purity and fidelity are generally quantified in one or more of the following measures: Adjacent Channel Power, Alternate Channel Power, Broadband Noise, Spurious Signals, Intermodulation Products, and in-channel Signal to Noise Ratio to name a few. Each of these measures is affected to some degree by the performance of the LASER and photodiode that are used to transport the RF signals.
  • RF signals may be transported in a variety of ways. It is common that RF signals are carried directly by amplitude modulating the optical power. Signals may also be carried by frequency modulating a subcarrier with a base band version of the RF signal. Signals may also be carried by modulating the optical power with a low frequency, or the base band components of the RF signal. The RF signal may be down-converted, digitized, and transmitted over the fiber using Pulse Code Modulation ("PCM").
  • PCM Pulse Code Modulation
  • the digital filter of one embodiment of the DAS system of the present invention is used on the uplink to reduce unwanted signals from being applied to the LASER, thus "enhancing" the overall DAS uplink dynamic range, above the dynamic range of the uplink LASER.
  • the LASER emits broadband noise.
  • the digital filter of one embodiment of the DAS system of the present invention is in the remote unit and rejects almost all of this broadband noise from transmission to and subsequent interference with UE, therefore enhancing the downlink dynamic range of the DAS.
  • the downlink signals are applied to the LASER, through conditioning, from Base Stations, eNodeBs, repeaters and other RF sources and are not necessarily digitally filtered before application to the downlink LASER. There is no need to apply digital filtering at the DAS head end, in the downlink direction, because the signals that are applied to the downlink LASER are intended to be transmitted, or selectively rejected by the digital filter. In certain embodiments, downlink signals that are applied to the LASER are selectively rejected in the remote unit, simplifying switching arrangements. In certain
  • the DAS provides electronically-switched selective choice of downlink transmitted signals, on a remote unit by remote unit basis. If a particular downlink signal is selectively not transmitted then its uplink is also rejected in the digital filter.
  • Uplink and Downlink signals are carried using Frequency Division Duplex on one or more fibers.
  • the characteristics of optical systems described in certain embodiments of the present invention applies to signals carried in either direction.
  • the degradation of performance described herein results from the use of conventional methods to improve dynamic range. It is one object of this invention to use unconventional techniques to improve the dynamic range performance of an optical fiber transport RF link.
  • Near-Far refers to the performance of a UE that is far from a server antenna, while interfering signals are transmitted from a UE that is near a server antenna.
  • the User Equipment that is far from the server antenna may lose uplink performance if attenuation is added to protect the LASER modulator from overload due to the close-in Near Signal.
  • User Equipment that is not served by the DAS may receive a high level of broadband noise, when near a server antenna.
  • the LASER modulator is driven to a low level of modulation, while the signal is amplified for transmission by the server antenna.
  • the broadband noise, caused by RIN is also amplified.
  • the effective input noise is carried by the various stages within the DAS to eventually be transmitted within an entire wireless band.
  • a particular WSP usually only utilizes a portion of the band.
  • the broadband noise is transmitted over the entire band.
  • Some of the unwanted noise energy from the LASER, in this band falls within a sub-band in the band that is allocated to another WSP.
  • the UE that is near a server antenna is often de-sensed by this noise.
  • WSPs do not always ensure that their signals are present on all DASs. Therefore, the use of a DAS by one WSP reduces the performance of the UE of the non-DAS carried WSP. It is an objective of this invention to ameliorate the downlink and uplink Near-Far issues caused by RF over fiber links.
  • Some of the scenarios addressed by this invention involve the following: UEs that have service provided by the DAS that are far from a server antenna while other strong sources are near a server antenna, and UEs that do not have service provided by the DAS, that are close to a server antenna, reducing the throughput from a UE that is on the DAS, and far from a server antenna. See, for example, Figure 1.
  • FIG. 1 Still referring to Figure 1, a prior art, conventional, DAS system 100, describing the uplink and downlink path is shown.
  • the UEs shown as WSP A (105a, b), are located far from a server antenna 110.
  • the power applied to the server antenna 110 must be moderately high. Values typically range between 0 and +20 dBm per channel, depending on coverage requirements within a building, wall attenuation, and desired throughput at a distance.
  • the broadband noise caused by LASER RIN (A) 122 sets a broadband noise floor that degrades the performance of the UEs of WSP B (115a, b), served by the macro cell site of WSP B 120. Problems arise due to strong signals from WSP B UEs (115a, b) close to a server antenna 110, and broadband noise to WSP B UEs (115a, b).
  • FIG. 1 shows bidirectional uplink and downlink operation of a prior art DAS system 100.
  • Each electrical to optical block (e.g., 125, 127) comprises a LASER and a photodiode for sending or receiving optical signals along optical path 129.
  • the LASER in the RU 127 is used to carry the uplink signals.
  • Strong UE signals from the near WSP B UE (115a, b) can overdrive the uplink LASER and require attenuation 130, shown between LASER and antenna 110, to be increased. The increase of this uplink attenuation degrades the desired coverage area of the DAS 100 by WSP A.
  • the present invention adds down conversion, digital filters, and up conversion, and other stages listed above.
  • Figure 3 additionally describes some of the nomenclature used for the flexibility of the DAS of the present invention.
  • Capital letters, numbers, subscripts and Greek letters are used to identify WSPs, bands, sub-bands and sectors respectively.
  • the added items contained within the system are found between the downlink photodiode and the remote unit downlink output; and the remote unit antenna uplink input and the uplink LASER.
  • Near-Far performance is often measured using the parameters of adjacent channel selectivity for a receiver, and adjacent channel power for a transmitter. These parameters are important because the WSP A and WSP B do not use the same frequency spectrum. Adjacent channels are those in closest proximity in frequency to a desired channel. In addition to adjacent channels, there are multiple alternate channels that extend on both sides of the desired channel beyond the adjacent channels.
  • the performance of a radio link may be determined by the adjacent channel power of a transmitter together with the adjacent channel selectivity of a receiver.
  • the limitation in performance may be caused by either parameter, or together in combination. It is an objective of this invention to provide a system that reduces cost and complexity while using the approximately known performance of the devices, UEs, adjacent, alternate channel selectivity, and power. For example, a UE that has very high adjacent channel power, and is located close to a sever antenna, will limit the uplink performance due to noise transmitted in the desired channel carried by the DAS.
  • the DAS uplink be able to operate without performance degradation in the presence of this near strong signal.
  • a mechanism is provided to ameliorate the effect of the close-in UE, up to a point that the UE itself limits the performance.
  • the mechanism provided is a digital filter used in front of the LASER modulator being applied to the LASER.
  • Digital filters may be designed to have a particular level of dynamic range.
  • ADC Analog to Digital Converter
  • S R signal to noise ratio
  • ADC dynamic range is related to the SNR, providing that the ADC has sufficient intermodulation performance to not degrade low level unwanted power above the noise, before the ADC full scale power is reached.
  • the dynamic range of a digital filter is affected generally by several effects: analog to digital conversion, quantization noise in filtering, limited out of band rejection of the digital filter, and digital to analog conversion.
  • the cost and complexity of the devices used are chosen such that the best balance of dynamic range is achieved.
  • these parameters are also traded off to provide the best balance for the UE performance. For example, the level of out of band attenuation and the slope of rejection are traded off to provide a level near-signal performance that is not greatly more than the performance of the UE itself.
  • the degree of filtering of adjacent signals may be adjusted to cause out of band signals to be close to -20 dBm composite power, but not -60 dBm, for example.
  • the filter may be made to have a smaller transition band. This provides rejection of unwanted signals that are close by in frequency to the desired channel, and also can reduce the cost and complexity of the digital filter.
  • the complexity and delay of a digital filter is strongly dependent on the degree of stop band attenuation required. This stop band attenuation is chosen to provide a tradeoff between the rejection of LASER noise and adjacent channel rejection, and the delay and complexity of the filter.
  • Delay in a DAS is an important design criteria, and may be implemented to be greater than the minimum delay of a filter that meets rejection requirements. This greater delay is useful when, for example, signals must be transmitted at the same time from multiple antennas connected to multiple remote units.
  • a digital filter may meet the rejection requirements, using 400 FIR taps, while an additional 300 delay taps may be effectively added to equalize the transmission time of two digital filters in different remote units, located at an antenna separation equivalent to the additional 300 tap delay.
  • the LASER RIN de-senses close-in UEs that are not served by the DAS. These close-in UEs have adjacent channel selectivity, and alternate channel selectivity to reject unwanted signals.
  • the LASER RIN will be received by the UE in the pass band of the UE. If the adjacent channel selectivity of a UE is sufficient to reject the downlink signal transmitted by the server ante 1 ma, the UE may still be desensed by the broadband RIN of the LASER.
  • the downlink signal is digitally filtered to reduce the LASER RIN that is transmitted, to a point that provides ultimate performance determined primarily by the UE adjacent channel selectivity.
  • the DAS used at the output of the digital filter may be chosen to have a bandwidth and noise floor that will not de-sense a close in UE. In this way, overall cost is reduced.
  • a UE served by a macro cell site, may be blocked and first desensed by an alternate channel signal on the DAS, at or above -20 dBm, referred to the UE antenna input.
  • the UE in this example uses a 10 MHz bandwidth, has a Noise Figure of 4 dB, and is located a distance that corresponds to 50 dB path loss from the server antenna.
  • the downlink effective noise of the UE, due to its Noise Figure performance and bandwidth is -100 dBm/10 MHz, using a 70 dB (10 MHz/1 Hz) bandwidth factor, and -174 dBm/Hz matched load noise at 290 K.
  • the unwanted signal from the DAS, at the UE is -30 dBm, due to path loss. This value is 10 dB below the blocking level of the UE, and therefore generally has little effect on UE downlink performance.
  • the remote unit in the DAS transmits a LASER-caused broadband noise power of -30 dBm/10 MHz, then the resulting broadband noise at the antenna of the UE is -80 dBm/10 MHz, due to path loss. This unwanted noise level is 20 dB higher than the inherent effective input noise of the UE.
  • a 20 dB degradation in in-band SNR usually will cause a UE to decrease performance from its maximum downlink speed to close to, or at, a lost connection.
  • the DAS broadband noise level is present at all times, while the blocking signal is only present when the WSP is transmitting on the DAS. Therefore, the effect of continuously transmitted broadband noise caused by the LASER is significantly worse than the intermittent blocking signal transmitted by the DAS.
  • this invention also total power detector at its input to prevent unwanted signals from overloading stages in front of the LASER.
  • a down converter and ADC are used to sample the RF for digital filtering. These stages are subject to overload and therefore have a mechanism to reduce gain when one or more UEs are near a server antenna.
  • the attack and decay time characteristics of the Automatic Gain Control (“AGC”) that is used to protect the RU front end is optimized given the scenario and physical layer technology used for near and far user equipment.
  • an AGC mechanism ensures that the maximum power is not exceeded, and that the total power transmitted does not degrade the adjacent and alternate power due to intermodulation. This may be accomplished by placing a detector diode or power measuring system at the downlink output of the server port, and controlling the transmit gain to reduce out of channel spectral emissions. Alternatively, measurements may be made within the digital domain to determine the level of attenuation required in the downlink. Similarly, measurements may be made after the ADC, in the uplink path, to determine if strong signals may overload the ADC.
  • Digital processing is not required at the end of the link served by the eNodeB or off-air repeater. This is because the eNodeB and repeater are able to handle the signals pre- filtered by the digital filter within the DAS, and do not need to be filtered in the downlink path.
  • the part of the system on the eNodeB side of the optical link is often referred to as the head-end unit, while the part of the system at the server end is often referred to as a remote unit ("RU").
  • the head-end will generally have lower cost and complexity than a PCM optical system because no digital processing is required in the head-end unit.
  • RUs may serve areas that have a combination of coax splitters and antennas that mitigate the Near-Far problem.
  • digital filtering in a RU may not be needed.
  • a RU may be configured with, or without, digital filtering to accommodate a deployment that does not experience Near-Far issues.
  • Digital filtering capability in the RU may be configured in the RU through modules installed, or a factory-shipped fixed capability. In general, a modular approach is preferred, as it can ameliorate a Near-Far problem that was not anticipated during the design and purchasing of the original DAS components.
  • the system encompasses the use of digital filtering in the RU of a DAS to reduce the required dynamic range of the LASER used in the uplink direction.
  • the digital filter ensures that only those uplink signals that must be carried by the DAS are actually applied to the LASER. See, for example, Figure 2A.
  • the RUs of a DAS may include scanning receivers configured to measure the power being received by the RU in a specified bandwidth. Typically this bandwidth is equivalent to the channel width of the communication system.
  • the scanning receiver of the RU will measure power received over a set of channels where the measurement bandwidth of the scanning receiver of the RU is centered on each of the channels of interest. By scanning the received power in the set of channels of interest, the scanning receiver can be utilized for the commissioning and optimization of the DAS.
  • an operator may need to survey the existing conditions on the various uplink channels that will be served by the DAS in order to set uplink configuration parameters (e.g., gain or attenuation) appropriately, or to validate that an appropriate number and arrangement of RUs have been included in the design and implementation of a particular DAS deployment.
  • uplink configuration parameters e.g., gain or attenuation
  • the DAS or its operators can utilize the scanning receivers in the RUs to evaluate the current operating conditions for the DAS and the operational trends in order to optimize the system's settings for the current conditions and to determine when and where system enhancements might be desirable.
  • Examples of operating conditions of a DAS include gain distribution and passband filtering.
  • DAS elements have their gain adjusted to meet DAS noise, overload, and dynamic range performance levels.
  • An indication of low uplink measured power, detected using the scanning receivers, may be used by an operator, using a manual or automatic algorithm, to raise the gain of stages that yield improved DAS uplink Noise Figure.
  • a detection of high uplink measured power may be used to adjust for high power levels to be handled without distortion. These functions may be performed on a passband specific basis. During major events at a venue having a DAS, it is likely that UEs will be located in different places at different times. Trends can be determined and the DAS may be optimized to handle an anticipated large number of UEs in certain coverage zones of the DAS. Filtering may be adjusted to reduce interfering signals, on a passband-specific and RU-specific basis.
  • An example of passband filter changes includes the adjustment of the edge attenuation of a digital filter.
  • Scanning receivers according to the invention may be implemented at any point where the full-band uplink signal may be tapped, for example, prior to ADC 207, which is described more fully below with respect to Fig. 2A.
  • Figure 10 is a graph illustrating a number of wireless signals being measured by a scanning receiver that may be implemented within an RU of the present disclosure.
  • the horizontal axis of the graph represents frequency or channel number, while the vertical axis represents signal power.
  • Each wireless signal 1000 is constrained to a particular bandwidth or channel along the horizontal axis.
  • the scanning receiver monitors a defined measurement bandwidth (indicated by bracket 1002) that is centered over a central frequency of the channel being monitored.
  • DSP -based scanning receiver capabilities are provided in the individual RUs enabling individual filtering and measurement of received signal power for each WSP's block of channels, which may alternatively be referred to as a sub band.
  • the inclusion of these DSP capabilities in the RUs allows for a more flexible and capable arrangement of multiple scanning receivers to be implemented.
  • the DSPs of each RU may be configured to provide unique scanning receivers for each WSP's block of channels.
  • DSP-implemented scanning receivers When performing received signal power measurements for each channel, the use of DSP-implemented scanning receivers allows many of the parameters of the receiver, such as measurement bandwidth and averaging method among others, to be readily configured to suit different system types and user applications.
  • the use of DSP implemented scanning receivers further allows each WSP to be provided with a scanning receiver in each RU that can be configured and operated independently of those provided to the other WSPs.
  • measurement bandwith or channel type, scanning sequence, scanning rate, alarm thresholds, and other parameters of each scanning receiver in each RU can be specified by the given WSP independently of the choices made by other WSPs. If desired, the scanning locations available to each scanning receiver can be limited to a given WSPs block.
  • the scanning receiver of a particular RU may be configured to scan through the entirety of any wireless bands supported by the given RU.
  • Such an implementation may be used by, for example, a system installer or troubleshooter and can be made available on a shared basis to the various WSPs utilizing the system or be restricted to use only by such authorized service personnel.
  • Figure 11 is a block diagram showing example scanning receivers of an RU that may be implemented via digital signal processing.
  • RU 1100 is configured to receive input signals 1102 over a wireless band. Those signals, once received, can then be filtered via one or more DSP-implemented scanning receivers.
  • RU 1100 includes one or more WSP-specific scanning receivers 1104. As described above, the WSP-specific scanning receivers 1104 may be configured to individually filter and measure received signal power for a particular WSP's block of channels or sub band.
  • RU 1100 also includes a shared full band scanning receiver 1106.
  • Shared full band scanning receiver 1106 may, like WSP-specific scanning receivers 1104, be implemented via a DSP. Shared full band scanning receiver 1106 may be configured to scan through the entirety of any wireless bands supported by RU 1100 and, in that manner, may be used, for example, to troubleshoot RU 1100.
  • FIG. 2A a schematic of one embodiment of the remote selection of sectors and sub-bands of the DAS system of the present invention in the uplink direction is shown.
  • the digital attenuators @ A, B, C (205a, b, c) arranged between analog to digital converter 207 and digital to analog converter 209 are used on a sub-band selective basis to reduce the level of signals applied to the LASER 210.
  • UEs 215, 220 are power controlled to a low level to reduce their power, as received at the eNodeB.
  • a high power level may still be present including, but not limited to 1) set up activities where handsets typically transmit at full power; 2) the presence of a large number of UE devices in a particular sub-band; and 3) UEs that operate outside of the power control loop of the UE.
  • This can be done using an AGC mechanism using the "det" or detector devices before or after the digital signal processing, e.g., detectors such as 225a, which provide an output used to set the attenuation of variable attenuators such as corresponding attenuator 205a.
  • Condition 3 described above, will generally occur when UEs are very close to server antennas. In this situation, protection of the LASER is accomplished. In certain embodiments, protection of the ADC is performed.
  • Attenuators, gain automatic gain control, filters, test tones, and detectors are added to the system.
  • Certain embodiments of the downlink path comprise: a wireless provider base station; base station conditioning, filtering; combiners and splitters, optional signal switching; electrical to optical conversion; fiber, interface between Head End and Remote Unit; optical to electrical conversion; down conversion; analog to digital conversion; DSP including, filtering, level control, and the like; digital to analog conversion; up conversion, a power amplifier, or the like.
  • Certain embodiments of the uplink path comprise: low noise Amplifiers; uplink overload protection; down conversion; analog to digital conversion; DSP including filtering, level control per sub-band; digital to analog conversion; up conversion; electrical to optical conversion; fiber, interface between Remote Unit and Head End; optical to electrical conversion; combiners from other RUs; optional signal switching; base station conditioning; filtering or the like.
  • a remote unit includes a full band capture buffer 230, which has sufficient capability to store the combined (i.e., the multiple WSP) signal received from the ADC prior to the individual, WSP sub-band signal components being subject to filtering and attenuation. Additionally or alternatively, individual sub-band signals, corresponding to individual WSPs, are stored in one or more sub-band capture buffers, e.g., 235. The stored signals from any or all of the buffers are subject to analysis by a programmable processor 240, which would perform advanced analytics such as spectrum analysis, interference detection, or signal quality measurements, in some cases, in conjunction with logic implemented in the FPGA.
  • a programmable processor 240 which would perform advanced analytics such as spectrum analysis, interference detection, or signal quality measurements, in some cases, in conjunction with logic implemented in the FPGA.
  • FIG. 2B a schematic of one embodiment of the remote selection of sectors and sub-bands of the DAS system of the present invention in the downlink direction is shown.
  • an algorithm is used to ensure that the adjacent and alternate channel power of signals applied to the LASER do not affect the performance of other WSP sub-bands.
  • this algorithm may predict the expected adjacent channel power, given know LASER performance, and known in-band power, and adjust the attenuator at the corresponding location A, B and/or C to reduce the power applied to the LASER.
  • the criteria for adjustment of power may be that the LASER noise to be degraded by more than 3 dB, for example.
  • an algorithm is used for each WSP with known values of power applied in each sub-band.
  • bands or sub-bands may be removed from particular RUs.
  • WSP B is not supplying sub-band 2b through remote N.
  • Remote N uses a digital filter that does not pass sub-band 2b.
  • Sub-bands la, 2a and Id are passed by the digital filter.
  • Figure 3 additionally describes the nomenclature used for the flexibility of the DAS.
  • Capital letters, numbers, subscripts and Greek letters are used to identify WSPs, bands, sub-bands and sectors respectively.
  • WSP on the DAS of the present invention are shown. More particularly, in certain embodiments WSP B desires not to use the same sectors that WSP A uses. This could be because the physical layer technologies used in the sectors may be different and require different sectorization. Soft hand off and co-channel interference may also be an issue. In addition, WSP B may desire to bring three sectors of capacity to the venue's DAS, while WSP A may wish to use its Al a a to serve capacity to a different area than the DAS. Still referring to Figure 4, the R numbers represent RUs that carry the uplink and downlink signals of particular WSP sectors and sub- bands.
  • the diagram shows how three sectors each of two WSPs are summed and routed to ten RUs.
  • a dedicated optical path to R6 is required in order to develop the sector split requirements shown.
  • Certain embodiments will implement the desired sectorization, except for RU #6, in this example.
  • this RU is in the set dedicated to B's ⁇ sector, and therefore is simulcasting across R4, R5, R6.
  • a dedicated single input module is installed to provide only R6.
  • FIG. 6 the dedicated R6 path required for the sector split requirements as shown in Fig 5 is shown. More particularly, the diagram shows that configuring the head-end on an exception basis is effective because the head-end is an analog only solution that is relatively low cost.
  • the R6 associated head-end uses a LASER diode, a photodiode, signal conditioning, control and management functions, and the like. These functions can be
  • head-end LASER/photodiode module is required when a combination of sectorization is unique across RUs.
  • head-end modules can be designed having appropriate numbers of Ni inputs and No outputs. Inputs are Ni WSP input signals to be simulcasted across No.
  • Figure 7 typical alternative splitting and combining methods that allow for different numbers of LASER/photodiode optical paths per WSP signal set, and different numbers of WSP signal sets driving different numbers of
  • FIG. 8 Another alternative is to make the LASER slices small enough that all systems are implemented using single LASER modules. See, for example, Figure 8. Still referring to Figure 8, the system eliminates unused LASERs and photodiodes. Figure 8 shows typical alternative splitting and combining methods that allow for different numbers of WSP signal sets driving a LASER/photodiode optical path.
  • LASER slices See, for example, Figure 9. Still referring to Figure 9, one embodiment of the system of the present invention may use a quadrature hybrid allowing multiple WSPs to be combined and split in one module. If 4 x 1 slices are used, the combining of WSPs is
  • Figure 9 describes how a single 4x4 hybrid combiner may be used to allow multi-WSP signal sets to be serviced by multiple RUs.
  • Each RU has the capability, using DSP, to selectively control the level of each WSP sub-band, therefore allowing fully flexible routing of any signal through any RU to a server antenna, providing that no co-channel signals exist within this particular signal set of the DAS.
  • the paths in the figures generally show the downlink paths. Similar choices of sectorization and selective filtering of signals occurs in the uplink path as well. Uplink paths are combined from multiple RUs, at the head end, while downlink paths are split at the head end to drive multiple RUs. In uplink and downlink directions, bidirectional digital filtering in the remote units allows the selective use of a given RU in a given sub-band, by a given WSP. The use of digital filtering in the RU reduces the need for hardware RF switching at the head end to accomplish the same objective of signal flexibility, by one of more WSPs, providing one or more sectors exists within the DAS.
  • MTMO for example, is equivalent in signal switching to providing a second sector, because MTMO signals are co-channel to each other. Unlike sectors, the MIMO signals are transmitted to the same RU, on a second fiber, or wavelength, as examples. A switch path in the head end switch is duplicated to provide the second MFMO path to the same RU.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

L'invention concerne un système et un procédé pour améliorer l'effet d'équipement utilisateur proche jusqu'à un certain point où l'équipement utilisateur lui-même limite le fonctionnement. Le système et le procédé utilisent un filtre numérique à l'avant du modulateur LASER appliqué au LASER. De plus, des détecteurs de puissance totale peuvent être utilisés au niveau d'une entrée pour empêcher des signaux indésirables de surcharger des étages à l'avant du LASER. Le système comprend en outre un récepteur de balayage capable de balayer et d'analyser le signal de large bande reçu de l'équipement utilisateur dans la direction de liaison montante.
PCT/US2016/039653 2015-06-25 2016-06-27 Système d'antennes distribuées ayant des unités éloignées à récepteurs de balayage Ceased WO2016210439A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5642405A (en) * 1992-09-17 1997-06-24 Adc Telecommunications, Inc. Cellular communications system with centralized base stations and distributed antenna units
US20110210843A1 (en) * 2010-03-01 2011-09-01 Andrew Llc System and method for location of mobile devices in confined environments
US20140248050A1 (en) * 2013-03-02 2014-09-04 Cellular Specialties, Inc. Distributed antenna system having high near far performance
US20150119079A1 (en) * 2010-03-01 2015-04-30 Andrew Llc System and method for location of mobile devices in confined environments
WO2015095574A1 (fr) * 2013-12-19 2015-06-25 Dali Systems Co. Ltd Transport numérique de données sur un réseau d'antennes distribuées

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5642405A (en) * 1992-09-17 1997-06-24 Adc Telecommunications, Inc. Cellular communications system with centralized base stations and distributed antenna units
US20110210843A1 (en) * 2010-03-01 2011-09-01 Andrew Llc System and method for location of mobile devices in confined environments
US20150119079A1 (en) * 2010-03-01 2015-04-30 Andrew Llc System and method for location of mobile devices in confined environments
US20140248050A1 (en) * 2013-03-02 2014-09-04 Cellular Specialties, Inc. Distributed antenna system having high near far performance
WO2015095574A1 (fr) * 2013-12-19 2015-06-25 Dali Systems Co. Ltd Transport numérique de données sur un réseau d'antennes distribuées

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