End-to-end beamforming system and satellite

Abstract

To provide systems, methods, and apparatuses capable of increasing the amount of data that may be transmitted through a satellite.SOLUTION: An end-to-end beamforming system 500 includes an end-to-end relay 503 and a ground segment 502, for communicating with user terminals 517. Return uplink signals 525 transmitted from the user terminals have multipaths induced by a plurality of receive / transmit signal paths in the end-to-end relay, and are relayed to the ground segment. The ground segment, using a beamformer 513, recovers user data streams from return downlink signals 527, and, using the beamformer 513, generates forward link signals 521 from appropriately weighted combinations of user data streams that, after relay, produce forward downlink signals 522 that combine to form user beams.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The disclosed systems, methods, and apparatus relate to end-to-end beamforming in systems using end-to-end relays. [Background technology]

[0002] Wireless communication systems, such as satellite communication systems, provide a means by which data, including audio, video, and other types of data, can be communicated from one location to another. Information originates at a first station, such as a first ground station, and is transmitted to a radio relay, such as a communication satellite. Information received by the radio relay is retransmitted to a second station, such as a second ground station. In some radio relay communication systems, either the first or second station (or both) are mounted on a craft, such as an aircraft, ship, or ground vehicle. Information can be transmitted in only one direction (e.g., from the first ground station to the second ground station) or in both directions (e.g., from the second ground station to the first ground station as well).

[0003] In radio relay communication systems in which the radio relays are satellites, the satellites may be geostationary satellites, in which case the satellite's orbit is synchronized with the Earth's rotation, keeping the satellite's coverage area essentially fixed relative to the Earth. In other cases, the satellites are in orbit around the Earth, causing the satellite's coverage area to move above the Earth's surface as the satellite traverses its orbit.

[0004] Signals destined for or from the first station can be directed by using an antenna shaped to focus the signal into a narrow beam. Such antennas typically include a parabolic reflector to focus the beam.

[0005] In some cases, beams can be formed electronically by adjusting the gain and phase (or time delay) of signals transmitted, received, or both from several elements of a phased array antenna. By appropriately selecting the relative phase and gain transmitted and / or received by each element of the phased array antenna, the beam can be steered. In most cases, all of the energy being transmitted from a ground station is intended to be received by one radio relay. Similarly, information received by a second station is typically received from one radio relay at a time. Therefore, transmit beams formed to transmit information to a radio relay (whether using electronic beamforming or an antenna with a shaped reflector) are typically relatively narrow to allow as much of the transmitted energy as possible to be directed to the radio relay. Similarly, receive beams formed to receive information from a radio relay are typically narrow to collect energy from the direction of the radio relay while minimizing interference from other sources.

[0006] In many cases of interest, the signals transmitted from the wireless relay to the first and second stations are not directed to a single station. Rather, the wireless relay may transmit signals over a relatively large geographic area. For example, in one satellite communications system, a satellite may provide service to the entire United States. In such a case, the satellite is said to have a satellite coverage area that includes the entire United States. Nevertheless, to increase the amount of data that can be transmitted through the satellite, the energy transmitted by the satellite is focused into a beam. This beam may be directed to a geographic area on Earth. [Brief explanation of the drawings]

[0007] The drawings are provided for illustrative purposes only and represent examples only. These drawings are provided to facilitate the reader's understanding of the disclosed methods and apparatus. These drawings do not limit the breadth, scope, or applicability of the claimed invention. For clarity and ease of illustration, these drawings are not necessarily to scale.

[0008] [Figure 1] FIG. 1 is an explanatory diagram of an embodiment of a satellite communication system.

[0009] [Figure 2] FIG. 1 illustrates an exemplary pattern of a beam covering the continental United States.

[0010] [Figure 3] FIG. 1 is an illustration of an embodiment of an outbound link of a satellite communications system in which the satellite has on-board beamforming capability for multiple feeds per beam of a phased array.

[0011] [Figure 4] FIG. 1 is an illustration of an embodiment of an inbound link of a satellite communication system with terrestrial beamforming.

[0012] [Figure 5] FIG. 1 is an illustration of an example end-to-end beamforming system.

[0013] [Figure 6] FIG. 2 is an illustration of an exemplary signal path for a signal in the return direction.

[0014] [Figure 7] FIG. 2 is an illustration of an exemplary signal path in the return direction from a user terminal.

[0015] [Figure 8] FIG. 2 is a simplified illustration of an exemplary end-to-end return channel matrix model.

[0016] [Figure 9] FIG. 2 is an illustration of an exemplary signal path in the forward direction.

[0017] [Figure 10] An illustrative diagram of an exemplary signal path in the forward direction to a user terminal located within a user beam coverage area.

[0018] [Figure 11] FIG. 2 is a simplified illustration of an exemplary end-to-end outbound channel matrix model.

[0019] [Figure 12] FIG. 1 is an illustration of an exemplary end-to-end relay satellite supporting outbound and return data.

[0020] [Figure 13] FIG. 2 is an illustration of an embodiment of an uplink frequency range divided into two parts.

[0021] [Figure 14] FIG. 1 is an illustration of an exemplary end-to-end relay that is time multiplexed between forward and return data.

[0022] [Figure 15] FIG. 1 is a block diagram of components of an exemplary end-to-end relay implemented as a satellite.

[0023] [Figure 16] FIG. 2 is a block diagram of an exemplary transponder including a phase shifter.

[0024] [Figure 17] 4 is a graph of exemplary signal strength patterns for several antenna elements.

[0025] [Figure 18] FIG. 1 is an illustration of exemplary 3 dB signal strength contours for several antenna elements.

[0026] [Figure 19] FIG. 2 is an illustration of exemplary overlapping signal intensity patterns of several antenna elements.

[0027] [Figure 20A] FIG. 1 is an illustration of exemplary overlapping 3 dB signal strength contours of several antenna elements. [Figure 20B] FIG. 1 is an illustration of exemplary overlapping 3 dB signal strength contours of several antenna elements. [Figure 20C] FIG. 1 is an illustration of exemplary overlapping 3 dB signal strength contours of several antenna elements. [Figure 20D] FIG. 1 is an illustration of exemplary overlapping 3 dB signal strength contours of several antenna elements. [Figure 20E] FIG. 1 is an illustration of exemplary overlapping 3 dB signal strength contours of several antenna elements.

[0028] [Figure 21] FIG. 1 is an illustration of an exemplary enumeration of 16 antenna elements and their overlapping 3 dB signal strength contours.

[0029] [Figure 22] 10 is a table illustrating an exemplary mapping of receive antenna elements to transmit antenna elements through 16 transponders.

[0030] [Figure 23] FIG. 1 is an illustration of a cross section of a parabolic antenna reflector and an array of elements centered at the focus of the parabola.

[0031] [Figure 24] FIG. 1 is an illustration of a cross section of a parabolic antenna reflector and an array of elements positioned away from the focus of the parabola.

[0032] [Figure 25]FIG. 1 is an illustration of an exemplary relay coverage area (shown with a single crosshatch) and the area defined by points within the relay coverage area that are also included within six antenna element coverage areas (shown with double crosshatching).

[0033] [Figure 26] FIG. 10 is an illustration of an exemplary relay antenna pattern in which all points within the relay coverage area are also included within at least four antenna element coverage areas.

[0034] [Figure 27] An illustration of an exemplary distribution of access nodes (ANs) and user beam coverage areas.

[0035] [Figure 28] 1 is an exemplary graph of normalized forward and return link capacity as a function of the number of deployed ANs.

[0036] [Figure 29] FIG. 5 is a block diagram of an example ground segment 502 of an end-to-end beamforming system.

[0037] [Figure 30] FIG. 2 is a block diagram of an exemplary forward / return beamformer.

[0038] [Figure 31] FIG. 1 is a block diagram of an exemplary forward beamformer comprising multiple return time-sliced ​​beamformers with time domain demultiplexing and multiplexing.

[0039] [Figure 32] FIG. 1 is a simplified exemplary ground segment diagram illustrating the operation of a forward time-slice beamformer.

[0040] [Figure 33]FIG. 10 is a block diagram of an exemplary return beamformer comprising a time-sliced ​​beamformer with time-domain demultiplexing and multiplexing.

[0041] [Figure 34] FIG. 1 is a simplified exemplary ground segment diagram illustrating the operation of a return beamformer with time domain multiplexing.

[0042] [Figure 35] FIG. 10 is a block diagram of an exemplary multi-band forward / return beamformer with sub-band demultiplexing and multiplexing.

[0043] [Figure 36] FIG. 10 is an illustration of an exemplary timing alignment for an initiating link. [Figure 37] FIG. 10 is an illustration of an exemplary timing alignment for an initiating link.

[0044] [Figure 38] FIG. 1 is a block diagram of an exemplary AN.

[0045] [Figure 39] FIG. 1 is a block diagram of a portion of an embodiment of an AN.

[0046] [Figure 40] FIG. 1 is a block diagram of an example AN515 in which multiple frequency sub-bands are processed separately.

[0047] [Figure 41] FIG. 1 is an illustration of an exemplary end-to-end beamforming system for enabling different user link and feeder link coverage areas.

[0048] [Figure 42] FIG. 2 is an illustration of an exemplary model of the signal path of a signal carrying backhaul data on an end-to-end backhaul link.

[0049] [Figure 43]FIG. 2 is an illustration of an exemplary model of the signal path of a signal carrying forward data on an end-to-end forward link.

[0050] [Figure 44A] 1A and 1B are illustrations of exemplary forward and return signal paths, respectively. [Figure 44B] 1A and 1B are illustrations of exemplary forward and return signal paths, respectively.

[0051] [Figure 45] FIG. 1 is an illustration of an embodiment of the visible terrestrial coverage area of ​​an end-to-end relay.

[0052] [Figure 46] FIG. 1 is an illustration of an example of a North American coverage area for end-to-end relay.

[0053] [Figure 47A] 1A and 1B are block diagrams of exemplary forward and return signal paths, respectively, each having selective activation of multiple user link antenna subsystems. [Figure 47B] 1A and 1B are block diagrams of exemplary forward and return signal paths, respectively, each having selective activation of multiple user link antenna subsystems.

[0054] [Figure 48A] FIG. 1 is an illustration of an embodiment of an end-to-end relay coverage area including multiple selectively activated user coverage areas. [Figure 48B] FIG. 1 is an illustration of an embodiment of an end-to-end relay coverage area including multiple selectively activated user coverage areas.

[0055] [Figure 49] FIG. 1 is a block diagram of an exemplary forward signal path having selective activation of multiple user link antenna subsystems and multiple feeder link antenna subsystems.

[0056] Reference numerals (e.g., 100) are used herein to refer to embodiments in the drawings. Similar or identical embodiments are generally indicated using the same numeral. A group of similar or identical elements may be collectively referred to by a single reference numeral (e.g., 200), while individual elements of the group may be referred to by a reference numeral with an appended letter (e.g., 200a, 200b).

[0057] The drawings are not intended to be exhaustive or to limit the claimed invention to the particular forms disclosed. The disclosed methods and apparatus are subject to modification and variation, and the present invention is limited only by the claims and their equivalents. DETAILED DESCRIPTION OF THE INVENTION

[0058] This detailed description is organized as follows: First, an introduction to satellite communications and wireless relay communication systems using beamforming is provided. Second, end-to-end beamforming is described generally and at the system level using satellite end-to-end beamforming as an example, although the application of end-to-end beamforming is not limited to satellite communications. Third, the operation of forward and return path data in the context of end-to-end beamforming is described. Fourth, end-to-end relays and their antennas using communications satellites as an example are described. Next, a terrestrial network for end-to-end beamforming is described, including related aspects such as delay equalization, removal of feeder link impairments, and calculation of beam weights. Finally, end-to-end beamforming with different user link and feeder link coverage areas, as well as systems with multiple coverage areas, is described. satellite communications

[0059] FIG. 1 is an illustration of an embodiment of a hub-and-spoke satellite communications system 100. A satellite serves as one example of a wireless relay. While many embodiments are described throughout this disclosure in the context of a satellite or satellite communications system, such embodiments are not intended to be limited to satellites; any other suitable wireless relay may be used and operated in a similar manner. The system 100 includes a terrestrial earth station 101, a communications satellite 103, and a terrestrial transmission source, such as a user terminal 105. A satellite coverage area can be broadly defined as an area in which communication can be made through the satellite to and / or from either a terrestrial transmission source or a terrestrial receiver, such as a terrestrial earth station or a user terminal. In some systems, the coverage area of ​​each link (e.g., forward uplink coverage area, forward downlink coverage area, return uplink coverage area, and return downlink coverage area) may be different. The forward uplink coverage area and return uplink coverage area are collectively referred to as the uplink satellite coverage area. Similarly, the outbound downlink coverage area and the return downlink coverage area are collectively referred to as the downlink satellite coverage area. Although the satellite coverage area is active only for the satellite providing the service (e.g., in a serving orbit), the satellite can be considered to have (e.g., can be designed to have) a satellite antenna pattern that is independent of the satellite's relative location with respect to the Earth. That is, the satellite antenna pattern is the distribution pattern of energy transmitted from (transmitted from or received by) the satellite's antenna. When the satellite is in a serving orbit, it irradiates (transmits to or receives from) a specific satellite coverage area. The satellite coverage area is defined by the satellite antenna pattern, the orbital position and attitude designed for the satellite, and a given antenna gain threshold. Generally, the intersection of the antenna pattern (at a particular effective antenna gain, e.g., 3 dB, 4 dB, 6 dB, or 10 dB from peak gain) with a particular physical target area defines the coverage area of ​​that antenna.Antennas can be designed to provide particular antenna patterns (and / or coverage areas), and such antenna patterns can be computationally determined (e.g., by analysis or simulation) and / or experimentally measured (e.g., at an antenna test range or in actual use).

[0060] For simplicity, only one user terminal 105 is shown in the figure, although typically there are many user terminals 105 in the system. The satellite communications system 100 operates as a point-to-multipoint system. That is, an earth station 101 within the satellite coverage area can transmit information to and receive information from any of the user terminals 105 within the satellite coverage area. However, the user terminals 105 communicate only with the earth station 101. The earth station 101 receives outbound data from the communications network 107, conditions the data using a feeder link modem 109, and transmits the data to the satellite 103 on an outbound feeder uplink 111. The satellite 103 relays this outbound data to the user terminals 105 on an outbound user downlink (also called an outbound service downlink) 113. In some cases, outbound communications from the earth station 101 are intended for several of the user terminals 105 (e.g., information is multicast to the user terminals 105). In some cases, outbound communications from the earth station 101 are intended for only one user terminal 105 (e.g., unicast to a specific user terminal 105). The user terminal 105 transmits backhaul data to the satellite 103 on a backhaul user uplink (also called a backhaul service uplink) 115. The satellite 103 relays the backhaul data to the earth station 101 on a backhaul feeder downlink 117. A feeder link modem 109 demodulates the backhaul data, which is forwarded to the communications network 107. This backhaul link capability is typically shared by several user terminals 105.

[0061] FIG. 2 illustrates an example configuration of one beam coverage area for a satellite serving the continental United States. 70 beams are shown in the exemplary configuration. A first beam 201 covers approximately two-thirds of Washington state. A second beam 203, adjacent to the first beam 201, covers the area immediately east of the first beam 201. A third beam 205 covers approximately Oregon south of the first beam 201. A fourth beam 207 covers an area approximately southeast of the first beam 201. Typically, there is some overlap between adjacent beams. In some instances, multiple colors (e.g., two-, three-, or four-color reuse patterns) are used. In one example of a four-color pattern, beams 201, 203, 205, and 207 are individually assigned, unique combinations of frequencies (e.g., one or more frequency ranges or one or more channels) and / or antenna polarizations (e.g., in some cases, antennas may be configured to transmit signals with right-hand circular polarization (RHCP) or left-hand circular polarization (LHCP), and other polarization techniques may be utilized). Thus, there may be relatively little interference between signals transmitted on different beams 201, 203, 205, and 207. These combinations of frequencies and antenna polarizations may then be reused in a recursive, non-overlapping "four-color" reuse pattern. In some situations, desired communication capacity may be achieved using a single color. In some cases, time division among the beams and / or other interference mitigation techniques may be used.

[0062] Within some limits, focusing the beams into a smaller area and therefore increasing the number of beams increases the data capacity of the satellite by allowing more frequency reuse opportunities, however, increasing the number of beams can increase the complexity of the system and, in many cases, the complexity of the satellite.

[0063] Complexity in satellite design generally results in larger size, more weight, and more power consumption. Satellites are expensive to launch into orbit. The cost of launching a satellite is determined in part by the weight and size of the satellite. In addition, if a satellite is to be launched using currently available rocket technology, there are absolute limits on the weight and size of the satellite. This leads to trade-offs between the features that can be designed into the satellite. Furthermore, the amount of power that can be provided to the satellite's components is limited. Therefore, weight, size, and power consumption are parameters that must be considered in the design of a satellite.

[0064] Throughout this disclosure, the term receive antenna element refers to a physical transducer that converts an electromagnetic signal into an electrical signal, and the term transmit antenna element refers to a physical transducer that emits an electromagnetic signal when excited by an electrical signal. Antenna elements include horns, septum-polarized horns (e.g., that can function as two combined elements with different polarizations), multi-port multi-band horns (e.g., dual-band 20 GHz / 30 GHz with dual-polarized LHCP / RHCP), cavity-backed slots, inverted-F, slotted waveguides, Vivaldi, helical, loops, patches, or any other antenna element configuration or combination of interconnected sub-elements. Antenna elements have a corresponding antenna pattern that describes how the antenna gain varies as a function of direction (or angle). An antenna element also has a coverage area, which corresponds to an area (e.g., a portion of the Earth's surface) or volume (e.g., a portion of the Earth's surface plus the space above that surface) over which the antenna element provides a desired level of gain (e.g., within 3 dB, 6 dB, 10 dB, or other value of the antenna element's peak gain). The coverage area of ​​an antenna element can be modified by various structures, such as reflectors, frequency-selective surfaces, lenses, radomes, and the like. Some satellites, including those described herein, can have multiple transponders, each capable of independently receiving and transmitting signals. Each transponder is coupled to an antenna element (e.g., a receiving element and a transmitting element) to form a receive / transmit signal path with a different radiation pattern (antenna pattern) from the other receive / transmit signal paths, creating a unique beam that can be assigned to different beam coverage areas. It is common for a single receive / transmit signal path to be shared across multiple beams using inputs and / or multiplexing devices. In either case, the number of simultaneous beams that can be formed is generally limited by the number of receive / transmit signal paths deployed on the satellite. Beamforming

[0065] Beamforming for a communication link can be achieved by adjusting the signal phase (or time delay) and sometimes the signal amplitude of signals transmitted and / or received by multiple elements of one or more antenna arrays having overlapping coverage areas. In some cases, some or all of the antenna elements are arranged as an array of constituent receive and / or transmit elements that cooperate to enable end-to-end beamforming, as described below. In the case of transmission (from the transmit elements of one or more antenna arrays), the relative phase and sometimes the amplitude of the transmit signals are adjusted so that the energy transmitted by the transmit antenna elements constructively overlaps at the desired location. This phase / amplitude adjustment is generally referred to as "applying beam weights" to the transmit signals. In the case of reception (by the receive elements of one or more antenna arrays), the relative phase and sometimes the amplitude of the receive signals are adjusted (i.e., the same or different beam weights are applied) so that the energy received by the receive antenna elements from the desired location constructively overlaps at those receive antenna elements. In some cases, the beamformer calculates the desired antenna element beam weights. The term beamforming can refer to the application of beam weights in some instances. An adaptive beamformer includes the capability to dynamically calculate beam weights. Calculating beam weights may require direct or indirect discovery of communication channel characteristics. The processes of calculating beam weights and applying beam weights can occur in the same or different system elements.

[0066] Antenna beams can be steered, selectively formed, and / or otherwise reconfigured by applying different beam weights. For example, the number of active beams, the beam's coverage area, the beam's size, the beam's relative gain, and other parameters can be varied over time. Such flexibility is desirable in certain situations. Beam-forming antennas are typically capable of forming relatively narrow beams. Narrow beams can enable signals transmitted in one beam to be distinguished from signals transmitted in another beam (e.g., to avoid interference). Thus, narrow beams can enable frequency and polarization reuse to a greater extent than when wider beams are formed. For example, narrowly formed beams can serve two non-overlapping, non-adjacent coverage areas. Each beam can use right- and left-hand polarization. Greater reuse can increase the amount of data transmitted and / or received.

[0067] Some satellites use on-board beamforming (OBBF) to electronically steer an array of antenna elements. Figure 3 is an illustration of a satellite system 300 in which a satellite 302 has on-board beamforming capability for multiple feeds per beam (MFPB) of a phased array. In this example, beam weights are calculated at a terrestrial computing center and then transmitted to the satellite for application or pre-stored on the satellite (not shown). While the forward link is shown in Figure 3, this architecture can be used for the forward link, the return link, or both the forward and return links. Beamforming can be utilized on the user link, the feeder link, or both. The illustrated forward link is a signal path from one of multiple gateways (GWs) 304 to one or more of multiple user terminals within one or more spot beam coverage areas 306. The satellite 302 includes a receive antenna array 307, a transmit antenna array 309, a downconverter (D / C) and gain module 311, a receive beamformer 313, and a transmit beamformer 315. The satellite 302 can form beams on the feeder link 308 and the user link 310. Each of the L elements of the receive array 307 receives K signals from K GWs 304. For each of the K feeder link beams created (e.g., one beam per GW 304), a different beam weight value is applied (e.g., phase / amplitude adjustments are made) by the receive beamformer 313 to each signal received by each of the L receive antenna array elements (of the receive antenna array 307). Thus, for K beams formed using the receive antenna array 307 with L receive antenna elements, K beam weight vectors of different lengths L are applied to the L signals received by the L receive antenna array elements. The receive beamformer 313 in the satellite 302 adjusts the phase / amplitude of the signals received by the L receive antenna array elements to create K receive beam signals. Each of the K receive beams is focused to receive signals from one GW 304. Thus, the receive beamformer 313 outputs the K receive beam signals to the D / C and gain module 311.One such receive beam signal is formed for signals received from each transmit GW 304 .

[0068] The D / C and gain module 311 downconverts each of the K receive beam signals and adjusts the gain appropriately. The K signals are output from the D / C and gain module 311 and coupled to the transmit beamformer 315. The transmit beamformer 315 applies a vector of L weights to each of the K signals, for a total of L×K transmit beam weights, to form K beams for the user downlink 310.

[0069] In some cases, significant processing power may be required within the satellite to control the phase and gain of each antenna element used to form the beam. Such processing power increases the complexity of the satellite. In some cases, the satellite can operate with ground-based beamforming (GBBF) to reduce the complexity of the satellite, while still offering the benefits of electronically forming narrow beams.

[0070] 4 is an illustration of one embodiment of a satellite communications system 400 with forward GBBF. GBBF is performed on the forward user link 317 via an L-element array similar to that described above. The phase / amplitude of signals transmitted on the user link 317 are weighted to form a beam. The feeder link 319 uses a single feed per beam (SFPB) scheme, where each receive and transmit antenna element of antenna 324 is dedicated to one feeder link beam.

[0071] For each of the K forward feeder link beams, a transmit beamformer 321 applies a respective one of K beam weight vectors, each of length L, to each of the K signals to be transmitted prior to transmission from one or more GWs 304. Determining K vectors of L weights and applying the vectors to the signals allows K forward beams to be formed on the ground for the forward user downlink 317. On the feeder uplink 319, each of the L different signals is multiplexed into a frequency division multiplexed (FDM) signal by a multiplexer 323 (or the like). Each FDM signal is transmitted by the GW 304 to one of the receive antenna elements of an antenna 324 on the feeder link 319. An FDM receiver 325 on the satellite 327 receives the signals from the antenna 324. An analog-to-digital converter (A / D) 326 converts the received analog signals to digital signals. The digital channel processor 328 demultiplexes the FDM signals, each of which has been appropriately weighted by the beamformer 321 for transmission through one of the L elements of the array of transmit antenna elements of the transmit antenna 329. The digital channel processor 328 outputs the signals to a digital-to-analog converter (D / A) 331 for conversion back to analog form. The analog output of the D / A 331 is upconverted, amplified by an upconverter (U / C) and gain stage 330, and transmitted by the associated element of the transmit antenna 329. For the return beam, the process of conversion occurs in reverse. Note that in this type of system, the FDM feeder link requires as much as L times the bandwidth of the user beam, making it impractical for systems with wide data bandwidths or a large number of elements L. End-to-End Beamforming System

[0072] The end-to-end beamforming system described herein forms end-to-end beams through end-to-end relays. The end-to-end beamforming system can connect user terminals with data sources / sinks. In contrast to the beamforming systems discussed above, in an end-to-end beamforming system, beam weights are calculated in a central processing system (CPS), and the end-to-end beam weights are applied in a terrestrial network (rather than in a satellite). Signals in the end-to-end beams are transmitted and received at an array of access nodes (ANs), which may be satellite access nodes (SANs). As described above, any suitable type of end-to-end relay can be used in an end-to-end beamforming system, and different types of ANs can be used to communicate with different types of end-to-end relays. The term "central" refers to the fact that the CPS has access to the ANs involved in transmitting and / or receiving signals, and does not refer to a particular geographic location where the CPS resides. The beamformer in the CPS calculates a set of end-to-end beam weights corresponding to (1) the wireless signal uplink path to the end-to-end relay, (2) the receive / transmit signal path through the end-to-end relay, and (3) the wireless signal downlink path from the end-to-end relay. The beam weights can be mathematically represented as a matrix. As discussed above, OBBF and GBBF satellite systems have a beam weight vector dimension set by the number of antenna elements on the satellite. In contrast, the end-to-end beam weight vector has a dimension set by the number of ANs, not the number of elements on the end-to-end relay. In general, the number of ANs is not the same as the number of antenna elements on the end-to-end relay. Furthermore, the formed end-to-end beam is not terminated at either the transmit or receive antenna element of the end-to-end relay. Rather, the formed end-to-end beam is effectively relayed because the end-to-end beam has an uplink signal path, a relay signal path (via the satellite or other suitable end-to-end relay), and a downlink signal path.

[0073] Because end-to-end beamforming considers the user link and feeder link (as well as the end-to-end relay), only a single set of beam weights is required to form a desired end-to-end user beam (e.g., an outgoing user beam or a return user beam) in a particular direction. Thus, a set of end-to-end outgoing beam weights (hereinafter referred to as outgoing beam weights) is transmitted from the AN through the outgoing uplink, the end-to-end relay, and the outgoing downlink, and combined to form an end-to-end outgoing user beam (hereinafter referred to as an outgoing user beam). Conversely, signals transmitted from the return user through the return uplink, the end-to-end relay, and the return downlink have end-to-end return beam weights (hereinafter referred to as return beam weights) to form an end-to-end return user beam (hereinafter referred to as a return user beam). Under some conditions, it may be very difficult or impossible to distinguish between the uplink and downlink characteristics. Thus, formed feeder link beams, formed user beam directionality, and individual uplink and downlink carrier-to-interference ratios (C / I) may no longer have their traditional role in system design, although concepts such as uplink and downlink signal-to-noise ratios (Es / No) and end-to-end C / I may still be relevant.

[0074] FIG. 5 is an illustration of an exemplary end-to-end beamforming system 500. The system 500 includes a ground segment 502, an end-to-end relay 503, and multiple user terminals 517. The ground segment 502 comprises M ANs 515 geographically distributed throughout the AN coverage area. The ANs 515 and user terminals 517 may be collectively referred to as terrestrial receivers, terrestrial transmitters, or terrestrial transceivers, depending on the particular function at issue, since they are located on or near the Earth and both transmit and receive signals. In some cases, the user terminals 517 and / or the ANs 515 may be located on aircraft, ships, mounted on ground vehicles, etc. In some cases, the user terminals 517 may be geographically distributed. The ANs 515 may be geographically distributed. The ANs 515 provide signals to CPSs 505 within the ground segment 502 through a distribution network 518. The CPSs 505 are connected to a data source (not shown), such as the Internet, a video headend, or other such entity.

[0075] A user terminal 517 can be grouped with other nearby user terminals 517 (e.g., as illustrated by user terminals 517a and 517b). In some cases, such a group of user terminals 517 is served by the same user beam and is within the same geographic outbound and / or inbound user beam coverage area 519. A user terminal 517 is within a coverage area served by a user beam if that user terminal 517 is within that user beam. Although only one such user beam coverage area 519 is shown in FIG. 5 as having two or more user terminals 517, in some cases a user beam coverage area 519 can have any suitable number of user terminals 517. Furthermore, the depiction of FIG. 5 is not intended to indicate the relative sizes of the different user beam coverage areas 519. That is, all of the user beam coverage areas 519 may be approximately the same size. Alternatively, the user beam coverage areas 519 can vary in size, with some user beam coverage areas 519 being much larger than others. In some cases, the number of ANs 515 is not equal to the number of user beam coverage areas 519.

[0076] The end-to-end relay 503 wirelessly relays signals between a user terminal 517 and several network access nodes, such as the AN 515 shown in FIG. 5. The end-to-end relay 503 has multiple signal paths. For example, each signal path can include at least one receive antenna element, at least one transmit antenna element, and at least one transponder (as discussed in detail below). In some cases, multiple receive antenna elements are arranged to receive signals reflected by a receive reflector, forming a receive antenna array. In some cases, multiple transmit antenna elements are arranged to transmit signals, thus forming a transmit antenna array.

[0077] In some cases, the end-to-end relay 503 is provided on a satellite. In other cases, the end-to-end relay 503 is provided on an aircraft, a balloon, a tower, an underwater structure, or any other suitable structure or vehicle in which the end-to-end relay 503 can reside. In some cases, the system uses different frequency ranges (in the same or different frequency bands) for the uplink and downlink. In some cases, the feeder link and the user link are in different frequency ranges. In some cases, the end-to-end relay 503 acts as a passive or active reflector.

[0078] As described herein, various features of the end-to-end relay 503 enable end-to-end beamforming. One feature is that the end-to-end relay 503 includes multiple transponders that induce multiple paths between the ANs 515 and the user terminals 517 in the context of an end-to-end beamforming system. Another feature is that the antennas (e.g., one or more antenna subsystems) of the end-to-end relay 503 contribute to end-to-end beamforming, such that a forward and / or return user beam is formed when appropriately beam-weighted signals are communicated through the multiple paths induced by the end-to-end relay 503. For example, during forward communication, each of the multiple transponders receives a respective superimposed composite (hereinafter referred to as a composite input forward signal) of (beam-weighted) forward uplink signals 521 from multiple (e.g., all) ANs 515, and the transponder outputs a corresponding composite signal (hereinafter referred to as a forward downlink signal). Each forward downlink signal can be a unique composite portion of the beam-weighted forward uplink signal 521, which, when transmitted by the transmit antenna elements of the end-to-end relay 503, superimposes to form a user beam 519 at a desired location (e.g., in this case, a restoration location within the forward user beam). Return end-to-end beamforming is similarly enabled. Thus, the end-to-end relay 503 can produce multiple superimpositions, thereby enabling end-to-end beamforming across induced multipath channels. Return journey data

[0079] FIG. 6 is an illustration of an exemplary model of a signal path for a signal carrying backhaul data on the end-to-end backhaul link. Backhaul data is data flowing from a user terminal 517 to an AN 515. The signal in FIG. 6 flows from right to left. The signal originates from the user terminal 517. The user terminal 517 transmits a backhaul uplink signal 525 (having a backhaul user data stream) to the end-to-end relay 503. The backhaul uplink signal 525 from the user terminal 517 within K user beam coverage areas 519 is received by an array of L receive / transmit signal paths 1702. In some cases, the uplink coverage area of ​​the end-to-end relay 503 is defined by the set of points at which all of the L receive antenna elements 406 can receive the signal. In other cases, the relay coverage area is defined by the set of points at which a subset (e.g., a desired number greater than or equal to two, but less than all) of the L receive antenna elements 406 can receive the signal. Similarly, in some cases, the downlink coverage area is defined by the set of points from which all L transmit antenna elements 409 can reliably transmit signals. In other cases, the downlink coverage area of ​​the end-to-end relay 503 is defined as the set of points from which a subset of the transmit antenna elements 409 can reliably transmit signals. In some cases, the size of the subset of receive antenna elements 406 or transmit antenna elements 409 is at least four. In other cases, the size of the subset is six, ten, twenty, one hundred, or any other number that provides desired system performance.

[0080] For simplicity, some embodiments are described and / or illustrated as all L receive antenna elements 406 receiving signals from all points in the uplink coverage area and / or all L transmit antenna elements 409 transmitting to all points in the downlink coverage area. Such description is not intended to require that all L elements receive and / or transmit signals at significant signal levels. For example, in some cases, a subset of the L receive antenna elements 406 receives an uplink signal (e.g., a return uplink signal 525 from a user terminal 517 or an outgoing uplink signal 521 from an AN 515), and thus the subset of receive antenna elements 406 receives the uplink signal at a signal level that is close to the peak received signal level of the uplink signal (e.g., not significantly lower than the signal level corresponding to the uplink signal having the highest signal level), while others of the L antenna elements 406 not in the subset receive the uplink signal at a significantly lower level (e.g., much lower than the peak received signal level of the uplink signal). In some cases, the uplink signal received by each receive antenna element of the subset is at a signal level within 10 dB of the maximum signal level received by any of the receive antenna elements 406. In some cases, the subset includes at least 10% of the receive antenna elements 406. In some cases, the subset includes at least 10 receive antenna elements 406.

[0081] For example, on the transmit side, a subset of the L transmit antenna elements 409 may transmit downlink signals to a terrestrial receiver (e.g., return downlink signal 527 to AN 515 or outgoing downlink signal 522 to user terminal 517), such that the subset of transmit antenna elements 409 transmit downlink signals to the receiver at received signal levels that are close to the peak transmission signal level of the downlink signal (e.g., not significantly lower than the signal level corresponding to the downlink signal having the highest received signal level), while others of the L transmit antenna elements 409 that are not in the subset transmit downlink signals to be received at a significantly lower level (e.g., much lower than the peak transmission signal level of the downlink signal). In some cases, the signal level is within 3 dB of the signal level corresponding to the peak gain of the transmit antenna elements 409. In other cases, the signal level is within 6 dB of the signal level corresponding to the peak gain of the transmit antenna elements 409. In still other cases, the signal level is within 10 dB of the signal level corresponding to the peak gain of the transmit antenna elements 409.

[0082] In some cases, the signals received by each receive antenna element 406 originate from the same source (e.g., one of the user terminals 517) due to overlap in the receive antenna patterns of each receive antenna element. However, in some cases, there may be points within the end-to-end relay coverage area where user terminals are located and not all of the receive antenna elements can receive the signal. In some such cases, there may be a significant number of receive antenna elements that do not (or cannot) receive signals from user terminals that are within the end-to-end relay coverage area. However, as described herein, guiding multipath by the end-to-end relay 503 can rely on receiving signals by at least two receive elements.

[0083] As shown in FIG. 6 and discussed in more detail below, in some cases, a receive / transmit signal path 1702 includes a receive antenna element 406, a transponder 410, and a transmit antenna element 409. In such cases, a return uplink signal 525 is received by each of the multiple transponders 410 via a respective receive antenna element 406. The output of each receive / transmit signal path 1702 is a return downlink signal 527 corresponding to a respective composite of the received return uplink signal. The return downlink signal is created by the receive / transmit signal path 1702. The return downlink signal 527 is transmitted to an array of M ANs 515. In some cases, the ANs 515 are located at geographically distributed locations (e.g., receiving or restoration locations) throughout the end-to-end relay coverage area. In some cases, each transponder 410 couples a respective one of the receive antenna elements 406 to a respective one of the transmit antenna elements 409. Thus, there are L different signal paths from a user terminal 517 located within a user beam coverage area 519 to a particular AN 515. This creates L paths between the user terminal 517 and an AN 515. The L paths between one user terminal 517 and one AN 515 are collectively referred to as an end-to-end backhaul multipath channel 1908 (see FIG. 8). Thus, receiving a backhaul uplink signal 525 from a transmitting location within the user beam coverage area 519 through L transponders 410 creates L backhaul downlink signals 527, each transmitted from one of the transponders 410 (i.e., through L collocated communication paths). Each end-to-end backhaul multipath channel 1908 is represented by a vector A of the uplink radiation matrix. r , the payload matrix E, and the downlink radiation matrix vector C t. Note that due to the coverage patterns of the antenna elements, in some instances, some of the L paths will have relatively less energy (e.g., 6 dB, 10 dB, 20 dB, 30 dB, or any other suitable power ratio less than the other paths). A superposition 1706 of return path downlink signals 527 is received at each of the ANs 515 (e.g., M geographically distributed receiving or recovery locations). Each return path downlink signal 527 includes a superposition of multiple transmitted return path downlink signals 527, resulting in a respective composite return path signal. Each composite return path signal is coupled to a return path beamformer 531 (see FIGS. 5 and 29).

[0084] 7 illustrates an exemplary end-to-end return link 523 from one user terminal 517 located within the user beam coverage area 519 to the AN 515. The return uplink signal 525 transmitted from the user terminal 517 is received by an array of L receive antenna elements 406 (e.g., or by a subset of the L receive antenna elements 406) on the end-to-end relay 503.

[0085] Ar is an L×K return uplink radiation matrix. The return uplink radiation matrix values ​​model the signal path from the reference location in the user beam coverage area 519 to the end-to-end relay receive antenna element 406. For example, Ar L,1 is the value of one element of the return uplink radiation matrix (i.e., the amplitude and phase of the path) from the reference location to the Lth receive antenna element in the first user beam coverage area 519. In some cases, all values ​​of the return uplink radiation matrix Ar may be non-zero (e.g., there are significant signal paths from the reference location to each of the receive antenna elements of the receive antenna array).

[0086] E (dimension L×L) is the payload matrix and provides a model (amplitude and phase) of the path from the receive antenna element 406 to the transmit antenna element 409. The “payload” of the end-to-end relay 503, as used herein, generally includes the set of components of the end-to-end relay 503 that affect and / or are affected by signal communications as they are received by, relayed through, and transmitted from the end-to-end relay 503. For example, the end-to-end relay payload may include antenna elements, reflectors, transponders, etc., but the end-to-end relay may also include batteries, solar cells, sensors, and / or other components not considered herein as part of the payload (because they do not affect the signal when operated normally). Consideration of the set of components as the payload may allow the overall effect of the end-to-end relay to be mathematically modeled (as a single payload matrix E). The dominant paths from each receive antenna element 406 to each corresponding transmit antenna element 409 are modeled by values ​​on the diagonal of the payload matrix E. If there is no crosstalk between receive / transmit signal paths, the off-diagonal values ​​of the payload matrix are zero. In some cases, the crosstalk may be non-zero. Separating the signal paths from each other minimizes the crosstalk. In some cases, the crosstalk is negligible, so the payload matrix E can be estimated by a diagonal matrix. In some cases, to reduce mathematical complexity and / or for other reasons, the off-diagonal values ​​of the payload matrix can be treated as zero (or any other suitable values), even if there is some signal contribution corresponding to those values.

[0087] Ct is an M×L downlink radiation matrix. The return downlink radiation matrix values ​​model the signal path from the transmit antenna element 409 to the AN 515. For example, Ct 3,2is the second transmitting antenna element 409 b AN515, the third c The values ​​of the return downlink radiation matrix Ct (e.g., path gains and phases) to the AN515 are the values ​​of the return downlink radiation matrix Ct (e.g., path gains and phases). In some cases, all values ​​of the downlink radiation matrix Ct can be non-zero. In some cases, some of the values ​​of the downlink radiation matrix Ct are essentially zero (e.g., the antenna pattern established by the corresponding transmit antenna element 409 of the transmit antenna array is such that the transmit antenna element 409 does not transmit useful signals to some of the AN515).

[0088] As can be seen in FIG. 7, the end-to-end backhaul multipath channel from a user terminal 517 to a particular AN 515 within a particular user beam coverage area 519 is the sum of L distinct paths. The end-to-end backhaul multipath channel has multipath induced by L unique paths through the end-to-end relay transponder 410. As with many multipath channels, the amplitudes and phases of the paths can add constructively to produce a high end-to-end channel gain or destructively to produce a low end-to-end channel gain. When the number L of distinct paths between a user terminal and an AN is large, the end-to-end channel gain may have a Rayleigh distribution of amplitude. With such a distribution, it is not uncommon to see some end-to-end channel gain from a particular user terminal 517 to a particular AN 515 that is 20 dB or more below the average level of the channel gain from the user terminal 517 to the AN 515. This end-to-end beamforming system intentionally induces a multipath environment for the end-to-end path from any user terminal to any AN.

[0089] 8 is a simplified diagram of an exemplary model of all end-to-end backhaul multipath channels from a user beam coverage area 519 to an AN 515. There are M×K such end-to-end backhaul multipath channels in the end-to-end backhaul link (i.e., M from each of the K user beam coverage areas 519). Channel 1908 connects user terminals in one user beam coverage area 519 to one AN 515 through L different receive / transmit signal paths 1702, each via a different one of the relay's L receive / transmit signal paths (and associated transponders). This effect is referred to herein as "multipath," but this multipath differs from traditional multipath (e.g., in mobile radio or multiple-input multiple-output (MIMO) systems) because the multipath herein is intentionally induced (and affected, as described herein) by the L receive / transmit signal paths. Each of the M×K end-to-end backhaul multipath channels originating from a user terminal 517 within a particular user beam coverage area 519 can be modeled by an end-to-end backhaul multipath channel. Each such end-to-end backhaul multipath channel is from a reference (or restored) location within the user beam coverage area 519 to one of the ANs 515.

[0090] Each of the M×K end-to-end backhaul multipath channels 1908 can be individually modeled to calculate a corresponding element of the M×K backhaul channel matrix Hret. The backhaul channel matrix Hret has K vectors, each with a dimensionality equal to M, such that each vector models an end-to-end backhaul channel gain for multipath communication between a reference location in one of the K user beam coverage areas and M ANs 515. Each end-to-end backhaul multipath channel couples one of the M ANs 515 to a reference location in one of the K backhaul user beams via L transponders 410 (see FIG. 7). In some cases, only a subset of the L transponders 410 on the end-to-end relay 503 are used to create the end-to-end backhaul multipath channel (e.g., by contributing significant energy to the end-to-end backhaul multipath channel, only a subset is considered to be in the signal path). In some cases, the number of user beams K is greater than the number of transponders L in the signal path of the end-to-end backhaul multipath channel. Furthermore, in some cases, the number of ANs M is greater than the number of transponders L in the signal path of the end-to-end backhaul multipath channel 1908. In one embodiment, the elements Hret of the backhaul channel matrix Hret 4,2is associated with a channel from a reference location in the second user beam coverage area 1903 to the fourth AN 1901. The matrix Hret models the end-to-end channel as the product of matrices Ct×E×Ar (see FIG. 6). Each element of Hret models the end-to-end gain of one end-to-end backhaul multipath channel 1908. Due to the multipath nature of the channel, the channel may experience deep fades. Backhaul user beams can be formed by the CPS 505. The CPS 505 calculates backhaul beam weights based on a model of these M×K signal paths and forms backhaul user beams by applying the backhaul beam weights to multiple composite backhaul signals, each weight calculated for each end-to-end backhaul multipath channel that couples a user terminal 517 in one user beam coverage area with one of multiple ANs 515. In some cases, the backhaul beam weights are calculated before receiving the composite backhaul signals. There is one end-to-end backhaul link from each of the K user beam coverage areas 519 to the M ANs 515. The weighting (i.e., complex relative phase / amplitude) of each of the signals received by the M ANs 515 allows the signals to be combined to form backhaul user beams using the beamforming capabilities of the CPS 505 in the ground segment 502. Beam weight matrix calculations, as described in more detail below, are used to determine how to weight each end-to-end backhaul multipath channel 1908 to form multiple backhaul user beams. User beams are not formed by directly adjusting the relative phase and amplitude of signals transmitted by one end-to-end relay antenna element relative to the phase and amplitude of signals transmitted by another end-to-end relay antenna element. Rather, user beams are formed by applying weighting values ​​associated with M×K channel matrices to the M AN signals. Receive path diversity, which provides a single transmitter (user terminal) with multiple receivers (ANs) to enable successful transmission of information from any user terminal in the presence of intentionally induced multipath channels. Outbound data

[0091] 9 is an illustration of an exemplary model of the signal path of a signal carrying forward data on the end-to-end forward link 501. Forward data is data flowing from the AN 515 to the user terminal 517. In this diagram, the signal flows from right to left. The signal originates from M ANs 515 located within the footprint of the end-to-end relay 503. There are K user beam coverage areas 519. The signal from each AN 515 is relayed by L receive / transmit signal paths 2001.

[0092] Receive / transmit signal path 2001 transmits the relayed signal to a user terminal 517 within a user beam coverage area 519. Thus, there may be L different signal paths from a particular AN 515 to a user terminal 517 located within the user beam coverage area 519. This creates L paths between each AN 515 and each user terminal 517. Note that due to the coverage pattern of the antenna elements, some of the L paths may have less energy than other paths.

[0093] FIG. 10 illustrates an exemplary end-to-end inbound link 501 that couples multiple access nodes at geographically distributed locations with user terminals 517 in a user beam (e.g., located at restoration locations within a user beam coverage area 519) via an end-to-end relay 503. In some cases, an inbound data signal is received at a beamformer before generating an inbound uplink signal. Multiple inbound uplink signals are generated at the beamformer and communicated to multiple ANs 515. For example, each AN 515 receives a unique (beam-weighted) inbound uplink signal generated according to a beam weight value corresponding to that AN 515. Each AN 515 has an output for transmitting an inbound uplink signal via one of M uplinks. Each inbound uplink signal includes an inbound data signal associated with an inbound user beam. An inbound data signal is “associated” with an inbound user beam because it is intended to be received by a user terminal 517 served by the user beam. In some cases, the forward data signal comprises two or more user data streams. The user data streams may be multiplexed together by time division or frequency division multiplexing, etc. In some cases, each user data stream is intended for transmission to one or more of multiple user terminals within the same forward user beam.

[0094] As discussed in more detail below, each outgoing uplink signal is transmitted in a time-synchronized manner by its respective transmission of the AN 515. The outgoing uplink signals 521 transmitted from the AN 515 are received by multiple transponders 410 on the end-to-end relay 503 via receive antenna elements 406 on the end-to-end relay 503. A superposition 550 of the outgoing uplink signals 521 received from geographically distributed locations creates a composite incoming outgoing signal 545. Each transponder 410 receives the composite incoming outgoing signal 545 simultaneously. However, each transponder 410 receives the signal at slightly different times due to differences in the location of the receive antenna elements 406 associated with each transponder 401.

[0095] Cr is an L×M forward uplink radiation matrix. The values ​​of the forward uplink radiation matrix model the signal path (amplitude and phase) from the AN515 to the receive antenna elements 406. E is an L×L payload matrix, providing a model of the transponder signal path from the receive antenna elements 406 to the transmit antenna elements 409. The direct path gain from each receive antenna element 406 to each corresponding transmit antenna element 409 through a corresponding one of the multiple transponders is modeled by the diagonal values ​​of the payload matrix. As discussed above with respect to the return link, if there is no crosstalk between the antenna elements, the off-diagonal elements of the payload matrix are zero. In some cases, the crosstalk may not be zero. Isolating the signal paths from each other minimizes crosstalk. In this embodiment, each of the transponders 410 couples a respective one of its receive antenna elements 406 to a respective one of its transmit antenna elements 409. Thus, the forward downlink signal 522 output from each of the transponders 410 is transmitted by each of the multiple transponders 410 (see FIG. 9) via the transmit antenna element 409, and thus the forward downlink signal 522 forms a forward user beam (by constructively and destructively overlapping to form a beam at a desired geographic restoration location). In some cases, multiple user beams are formed, each corresponding to a geographic user beam coverage area 519 that respectively serves a set of user terminals 517 within the user beam coverage area 519. The path from the first transmit antenna element 409a (see FIG. 10) to the reference (or restoration) location within the first user beam coverage area 519 is represented by the At 11As noted with respect to the return link, this end-to-end beamforming system intentionally induces a multipath environment in the end-to-end path from any AN 515 to any user terminal 517. In some cases, a subset of the transmit antenna elements 409 transmits forward downlink signals 522 with significant energy to the user terminal 517. The user terminal 517 (or, more generally, a receiving or recovery location within the user beam coverage area 519 for reception and / or recovery) receives the multiple forward downlink signals 522 and recovers at least a portion of the forward data signal from the received multiple forward downlink signals 522. The transmitted forward downlink signals 522 can be received by the user terminal 517 at a signal level that is within 10 dB of the maximum signal level from any of the other signals transmitted by the transmit antenna elements 409 in the subset. In some cases, the subset of transmit antenna elements includes at least 10% of the multiple transmit antenna elements present in the end-to-end relay 503. In some cases, the subset of transmit antenna elements includes at least 10 transmit antenna elements, regardless of how many transmit antenna elements 409 are present in the end-to-end relay 503. In one case, receiving the plurality of inbound downlink signals includes receiving a superposition 551 of the plurality of inbound downlink signals.

[0096] Figure 11 is a simplified illustration of a model of all end-to-end forward multipath channels 2208 from M ANs 515 to K user beam coverage areas 519. As shown in Figure 11, there is an end-to-end forward multipath channel 2208 coupling each AN 515 to each user beam coverage area 519. Each channel 2208 from one AN 515 to one user beam coverage area 519 has multipath induced as a result of L unique paths from the AN 515 to the user beam coverage area 519 through multiple transponders. Thus, the K x M multipath channels 2208 can be modeled individually, with each model serving as an element of the K x M forward channel matrix Hfwd. The forward channel matrix Hfwd has M vectors, each with a dimensionality equal to K, such that each vector models the end-to-end forward gain of multipath communication between a respective one of the M ANs 515 and a reference (or restoration) location within the K forward user beam coverage areas. Each end-to-end forward multipath channel couples one of the M ANs 515 with a user terminal 517 served by one of the K forward user beams via L transponders 410 (see FIG. 10). In some cases, only a subset of the L transponders 410 on the end-to-end relay 503 are used to create the end-to-end forward multipath channel (i.e., are in the signal path of the end-to-end forward multipath channel). In some cases, the number of user beams, K, is greater than the number of transponders, L, in the signal path of the end-to-end forward multipath channel. Furthermore, in some cases, the number M of ANs is greater than the number L of transponders in the signal path of the end-to-end forward multipath channel.

[0097] Hfwd can represent the end-to-end forward link as the product of the matrix At × E × Cr. Each element of Hfwd is the end-to-end forward gain and may experience deep fades due to the multipath nature of the path. Appropriate beam weights can be calculated by the CPS 505 in the ground segment 502 for each of the multiple end-to-end forward multipath channels 2208 to form a forward user beam from a set of M ANs 515 to each user beam coverage area 519. Multiple ANs 515 provide transmission path diversity to a single receiver (user terminal) by using multiple transmitters (ANs), enabling successful transmission of information to any user terminal 517 in the presence of intentionally induced multipath channels. Combined outbound and inbound data

[0098] FIG. 12 illustrates an exemplary end-to-end relay supporting forward and return communications. In some cases, the same end-to-end relay signal path (e.g., a set of receive antenna elements, transponders, and transmit antenna elements) can be used for the end-to-end forward link 501 and the end-to-end return link 523. Some other cases include forward link transponders and return link transponders that may or may not share receive and transmit antenna elements. In some cases, the system 1200 has multiple ANs and user terminals located within the same general geographic region 1208 (which may be, for example, a particular state, an entire country, a region, an entire visibility area, or any other suitable geographic region 1208). A single end-to-end relay 1202 (located on a satellite or any other suitable end-to-end relay) receives forward uplink signals 521 from the ANs and transmits forward downlink signals 522 to the user terminals. At alternate times or alternate frequencies, the end-to-end relay 1202 also receives return uplink signals 525 from the user terminal and transmits return downlink signals 527 to the AN. In some cases, the end-to-end relay 1202 is shared between forward and return data using techniques such as time domain duplexing, frequency domain duplexing, and the like. In some cases, time domain duplexing between forward and return data uses the same frequency range, with the forward data being transmitted during a time interval that is different (non-overlapping) from the time interval used to transmit the return data. In some cases, frequency domain duplexing allows different frequencies to be used for the forward and return data, thereby enabling simultaneous, non-interfering transmission of the forward and return data.

[0099] Figure 13 is an illustration of an uplink frequency range divided into two parts. The lower frequency (left) part of the range is allocated to the outbound uplink, and the higher frequency (right) part of the range is allocated to the return uplink. The uplink range can be divided into multiple parts for either outbound or return data.

[0100] FIG. 14 is an illustration of time-division multiplexed forward and return data. A data frame period is shown, in which forward data is transported during the first time interval of the frame, while return data is transported during the last time interval of the frame. The end-to-end relay receives from one or more access nodes during a first (forward) receive time interval and receives from one or more user terminals during a second (return) receive time interval that does not overlap with the first receive time interval. The end-to-end relay transmits to one or more user terminals during a first (forward) transmit time interval and transmits to one or more access nodes during a second (return) transmit time interval that does not overlap with the first receive time interval. The data frame can be repeated or dynamically changed. The frame can be divided into multiple (e.g., non-contiguous) portions for the forward and return data. End-to-end beamforming satellite

[0101] In some cases, the end-to-end relay 503 is implemented on a satellite, and thus the satellite is used to relay signals from the AN (which in such cases may be referred to as a satellite access node (SAN)) to the user terminal and vice versa. In some cases, the satellite is in geostationary orbit. An exemplary satellite operating as an end-to-end relay has an array of receive antenna elements, an array of transmit antenna elements, and several transponders connecting the receive antenna elements to the transmit antenna elements. The array has multiple antenna elements with overlapping antenna element coverage areas, similar to a conventional single-link phased array antenna. It is the overlapping antenna element coverage areas of both the transmit and receive antenna elements that create the multipath environment described above. In some cases, the antenna patterns established by corresponding antenna elements and the antenna patterns resulting in the overlapping antenna element coverage areas (e.g., overlapping component beam antenna patterns) are identical. For purposes of this disclosure, the term "identical" means that the antenna patterns follow essentially the same power distribution over a given set of points in space, considering the antenna elements as reference points to indicate those points in space. Perfect identity is very difficult to achieve. Thus, patterns that have relatively little deviation from one pattern to another are within the scope of "identical" patterns. In other cases, the receive component beam antenna patterns may not be identical, and in fact may be significantly different. However, such antenna patterns may still result in overlapping antenna element coverage areas, but the resulting coverage areas will not be identical.

[0102] Antenna types include, but are not limited to, array-fed reflectors, confocal arrays, direct-radiating arrays, and other forms of antenna arrays. Each antenna can be a system that includes additional optical components to assist in signal reception and / or transmission, such as one or more reflectors. In some cases, satellites include components that assist in system timing adjustment and beamforming calibration.

[0103] FIG. 15 is a diagram of an exemplary satellite 1502 that can be used as an end-to-end relay 503. In some cases, the satellite 1502 has an array-fed reflector transmit antenna 401 and an array-fed reflector receive antenna 402. The receive antenna 402 comprises a receive reflector (not shown) and an array of receive antenna elements 406. The receive antenna elements 406 are illuminated by the receive reflector. The transmit antenna 401 comprises a transmit reflector (not shown) and an array of transmit antenna elements 409. The transmit antenna elements 409 are arranged to illuminate the transmit reflector. In some cases, the same reflector is used for both receive and transmit. In some cases, one port of the antenna element is used for receive and another port is used for transmit. Some antennas have the ability to distinguish between signals of different polarizations. For example, an antenna element may include four waveguide ports for right-hand circularly polarized (RHCP) receive, left-hand circularly polarized (LHCP) receive, RHCP transmit, and LHCP transmit, respectively. In some cases, dual polarization may be used to increase system capacity, while in other cases, single polarization may be used to reduce interference (e.g., with other systems using different polarizations).

[0104] The exemplary satellite 1502 also includes multiple transponders 410. The transponders 410 connect the output from one receive antenna element 406 to the input of a transmit antenna element 409. In some cases, the transponders 410 amplify the received signal. Each receive antenna element outputs a unique receive signal. In some cases, a subset of the receive antenna elements 406 receives signals from an Earth transmitter, such as the user terminal 517 in the case of a return link signal or the AN 515 in the case of a forward link signal. In some of these cases, the gain of each receive antenna element in the subset for the receive signal is within a relatively small range. In some cases, the range is 3 dB. In other cases, the range is 6 dB. In still other cases, the range is 10 dB. Thus, the satellite receives a signal at each of the satellite's multiple receive antenna elements 406, where the communication signal originates from the Earth transmitter, and thus a subset of the receive antenna elements 406 receives the communication signal at a signal level that is not significantly less than the signal level corresponding to the peak gain of the receive antenna element 406.

[0105] In some cases, at least 10 transponders 410 are provided within the satellite 1502. In other cases, at least 100 transponders 410 are provided within the satellite 1502. In still other cases, the number of transponders per polarity can range from 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, or any intermediate or greater number. In some cases, the transponder 410 includes a low noise amplifier (LNA) 412, a frequency converter and associated filter 414, and a power amplifier (PA) 420. In some cases where the uplink and downlink frequencies are the same, the transponder does not include a frequency converter. In other cases, multiple receive antenna elements operate at a first frequency. Each receive antenna element 406 is associated with one transponder 410. The receive antenna element 406 is coupled to the input of the LNA 412. Thus, the LNAs independently amplify unique receive signals provided by receive antenna elements associated with the transponder 410. In some cases, the output of the LNA 412 is coupled to a frequency converter 414. The frequency converter 414 converts the amplified signal to a second frequency.

[0106] The output of a transponder is coupled to an associated one of the transmit antenna elements. In these embodiments, there is a one-to-one relationship between a transponder 410, an associated receive antenna element 406, and an associated transmit antenna element 409, such that the output of each receive antenna element 406 is connected to the input of one and only one transponder, and the output of that transponder is connected to the input of one and only one transmit antenna element.

[0107] FIG. 16 is an illustration of an exemplary transponder 410. The transponder 410 may be one embodiment of a transponder of the end-to-end relay 503, as described above (e.g., satellite 1502 of FIG. 15). In this embodiment, the transponder includes a phase shifter 418 in addition to a low-noise amplifier (LNA) 412, a frequency converter and associated filter 414, and a power amplifier (PA) of the transponder 410. As illustrated in FIG. 16, the exemplary transponder 410 may also be coupled to a phase shift controller 427. For example, the phase shift controller 427 may be coupled (directly or indirectly) to each of some or all of the transponders of the end-to-end relay 503, such that the phase shift controller 427 can individually set the phase for each transponder. The phase shifter may be useful, for example, for calibration, as discussed below. antenna

[0108] To create a multipath environment, an antenna element coverage area can overlap with the antenna element coverage area of ​​at least one other antenna element of the same polarity, frequency, and type (respectively, transmit or receive). In some cases, multiple receive component beam antenna patterns can operate at the same receive polarization and receive frequency (e.g., have at least a portion of a common receive frequency) and overlap with one another. For example, in some cases, at least 25% of the receive component beam antenna patterns can operate at the same receive polarization and receive frequency (e.g., have at least a portion of a common receive frequency) and overlap with at least five other receive component beam antenna patterns of the receive antenna element. Similarly, in some cases, at least 25% of the transmit component beam antenna patterns can operate at the same transmit polarization and transmit frequency (e.g., have at least a portion of a common transmit frequency) and overlap with at least five other transmit component beam antenna patterns. The amount of overlap varies depending on the system. In some cases, at least one of the receive antenna elements 406 has a component beam antenna pattern that overlaps with the antenna pattern of another receive antenna element 406 that is operable at the same receive frequency (e.g., having at least a portion of the receive frequency in common) and the same receive polarization. Thus, at least some of the multiple receive antenna elements can receive the same signal from the same source. Similarly, at least one of the transmit antenna elements 409 has a component beam antenna pattern that overlaps with the antenna pattern of another transmit antenna element 409 that is operable at the same transmit frequency (e.g., having at least a portion of the transmit frequency in common) and transmit polarization. Thus, at least some of the multiple transmit antenna elements can transmit signals having the same frequency with the same polarization to the same receiver. In some cases, the overlapping component beam antenna patterns can have gains that differ by less than 3 dB (or any other suitable value) over a common geographic area. Antenna elements, whether receive or transmit, can have wide component beam antenna patterns and thus relatively wide antenna element coverage areas.In some cases, signals transmitted by a terrestrial transmitter, such as a user terminal 517 or an access node 515, are received by all receive antenna elements 406 of an end-to-end relay (e.g., a satellite). In some cases, a subset of the elements 406 receives signals from the terrestrial transmitter. In some cases, the subset includes at least 50% of the receive antenna elements. In other cases, the subset includes at least 75% of the receive antenna elements. In still other cases, the subset includes at least 90% (e.g., up to and including all) of the receive antenna elements. Different subsets of the receive antenna elements 406 can receive signals from different terrestrial transmitters. Similarly, in some cases, subsets of the elements 409 transmit signals that can be received by the user terminal 517. In some cases, the subset includes at least 50% of the transmit antenna elements. In other cases, the subset includes at least 75% of the transmit antenna elements. In still other cases, the subset includes at least 90% (e.g., up to and including all) of the transmit antenna elements. Different subsets of elements 409 can transmit signals that are received by different user terminals. Furthermore, user terminals can be within several formed user beam coverage areas 519. For purposes of this disclosure, an antenna pattern is a distribution pattern of energy transmitted to or received from an antenna. In some cases, energy can radiate directly from and to an antenna element. In other cases, energy from one or more transmitting antenna elements can be reflected by one or more reflectors that shape the antenna element pattern. Similarly, a receiving element can receive energy directly or after the energy reflects off one or more reflectors. In some cases, an antenna can be composed of several elements, each having a component beam antenna pattern that establishes a corresponding antenna element coverage area.Similarly, all or a subset of the receive and transmit antenna elements that transmit and receive signals to and from AN515 may overlap, such that multiple receive antenna elements receive signals from the same AN515 and / or multiple transmit antenna elements transmit signals to the same AN515.

[0109] 17 is an illustration of component beam antenna patterns produced by several antenna elements (either receive antenna elements 406 or transmit antenna elements 409) that intersect at a 3 dB point. Component beam antenna pattern 1301 of a first antenna element has a peak component beam antenna gain along boresight 1303. Component beam antenna pattern 1301 is shown to attenuate by approximately 3 dB before it intersects with component beam antenna pattern 1305. Because each pair of two adjacent component beam antenna patterns overlaps around the 3 dB line 1307 over only a relatively small portion of the component beam antenna pattern, the antenna elements producing these component beam antenna patterns are considered non-overlapping.

[0110] FIG. 18 shows ideal 3 dB antenna contours 3901, 3902, 3903 for several elements 406, 409, with peak gains indicated by the letter "x." Contours 3901, 3902, 3903 are referred to herein as "ideal" because, for simplicity, the contours are shown as circles. However, contours 3901, 3902, 3903 need not be circular. Each contour indicates where the transmitted or received signal is 3 dB below its peak level. Outside the contour, the signal is 3 dB or more below the peak. Inside the contour, the signal is less than 3 dB below the peak (i.e., within 3 dB of the peak). In a system where the coverage area of ​​a receiving component beam antenna pattern is all points for which the receiving component beam antenna gain is within 3 dB of the peak receiving component beam antenna gain, the area inside the contour is referred to as the antenna element coverage area. The 3 dB antenna contours of each element 406, 409 do not overlap, i.e., only a relatively small portion of the area inside the 3 dB antenna contour 3901 overlaps with the area inside the adjacent 3 dB antenna patterns 3902, 3903.

[0111] Figure 19 is an illustration of antenna patterns 1411, 1413, 1415 of several antenna elements (either receive antenna elements 406 or transmit antenna elements 409). In contrast to the component beam antenna patterns of Figure 17, the component beam antenna patterns shown in Figure 19 intersect 1417 above the 3 dB line 1307.

[0112] 20A-20E illustrate the 3 dB antenna contours of several antenna elements 406, 409 with the beam center point (peak gain) indicated by the letter "x." FIG. 20A shows a specific antenna contour 1411 for a first antenna element 406. FIG. 20B shows the 3 dB antenna contours 1411, 1413 for two specific elements 406. FIG. 20C shows the 3 dB antenna contours for three elements 406. FIG. 20D shows the 3 dB antenna contours for four antenna elements 406. FIG. 20E shows the 3 dB antenna contours for an array of 16 antenna elements 406. The 3 dB antenna contours show overlap 1418 (e.g., 16 such 3 dB antenna contours are shown). The antenna elements of a receive or transmit antenna can be arranged in any of several different configurations. For example, if the elements have generally circular feed horns, the elements can be arranged in a honeycomb configuration to pack the elements closely into a small amount of space. In some cases, the antenna elements are aligned in horizontal rows and vertical columns.

[0113] FIG. 21 is an exemplary illustration of the relative positions of receive antenna elements 406 and their associated 3 dB antenna contours. The beam centers of the elements 406 are numbered 1 through 16, with element 4064 identified by the number "4" in the upper left corner of the supporting "x" in the beam center. In some cases, there are significantly more than 16 receive antenna elements 406. However, for simplicity, only 16 are shown in FIG. 21. The corresponding array of transmit antenna elements 409 and their associated 3 dB antenna contours would have a similar appearance to FIG. 21. Therefore, for simplicity, only the array of receive antenna elements 406 is shown. In the central area 2101, all of the antenna element coverage areas overlap.

[0114] In some cases, at least one point within a relay coverage area (e.g., satellite coverage area) falls within the 3 dB antenna contour of component beams of some antenna elements 406. In one such case, at least one point is within the 3 dB antenna contour of at least 100 different antenna elements 406. In another case, at least 10% of the relay coverage area is within the 3 dB antenna contour of at least 30 different antenna elements. In another case, at least 20% of the relay coverage area is within the 3 dB antenna contour of at least 20 different antenna elements. In another case, at least 30% of the relay coverage area is within the 3 dB antenna contour of at least 10 different antenna elements. In another case, at least 40% of the relay coverage area is within the 3 dB antenna contour of at least 8 different antenna elements. In another case, at least 50% of the relay coverage area is within the 3 dB antenna contour of at least 4 different antenna elements. However, in some cases, one or more of these relationships may be true.

[0115] In some cases, the end-to-end relay has a relay coverage area (e.g., satellite coverage area) in which at least 25% of the points in the uplink relay coverage area are within (e.g., within) the overlapping coverage area of ​​at least six receive antenna elements 406. In some cases, 25% of the points in the uplink relay coverage area are within (e.g., within) the overlapping coverage area of ​​at least four receive antenna elements 406. In some cases, the end-to-end relay has a coverage area in which at least 25% of the points in the downlink relay coverage area are within (e.g., within) the overlapping coverage area of ​​at least six transmit antenna elements 409. In some cases, 25% of the points in the downlink relay coverage area are within (e.g., within) the overlapping coverage area of ​​at least four transmit antenna elements 409.

[0116] In some cases, the receive antenna 402 may be oriented toward roughly the same coverage area as the transmit antenna 401, such that some receive antenna element coverage areas can naturally correspond to specific transmit antenna element coverage areas. In these cases, the receive antenna elements 406 may be mapped to their corresponding transmit antenna elements 409 via the transponder 410, resulting in similar transmit and receive antenna element coverage areas for each receive / transmit signal path. However, in some cases, it may be advantageous to map receive antenna elements 406 to transmit antenna elements 409 that do not correspond to the same component beam coverage areas. Thus, the mapping of elements 406 of the receive antenna 402 to elements 409 of the transmit antenna 401 may be randomly (or otherwise) permuted. Such permutations include cases that result in receive antenna elements 406 not being mapped to transmit antenna elements 409 in the same relative location within the array or with the same coverage area. For example, each receive antenna element 406 in the receive antenna element array can be associated with the same transponder 410 as a transmit antenna element 409 located at a mirror location in the transmit antenna element array. Any other permutation can be used to map the receive antenna elements 406 to the transmit antenna elements 409 according to the permutation (e.g., pairing each receive antenna element 406 with the same transponder to which the associated transmit antenna element 409 is coupled according to a particular permutation of the receive antenna element 406 and the transmit antenna element 409).

[0117] 22 is a table 4200 illustrating an example mapping of receive antenna elements 406 to transmit antenna elements 409 through 16 transponders 410. Each transponder 410 has an input that is coupled exclusively to the associated receive antenna element 406 and an output that is coupled exclusively to the associated transmit antenna element 409 (e.g., there is a one-to-one relationship between each receive antenna element 406, one transponder 410, and one transmit antenna element 409). In some cases, other receive antenna elements, transponders, and transmit antenna elements may be present on an end-to-end relay (e.g., a satellite) that is not configured in a one-to-one relationship (and does not operate as part of an end-to-end beamforming system).

[0118] The first column 4202 of table 4200 identifies a transponder 410. The second column 4204 identifies the receive antenna element 406 to which the transponder 410 in the first column is coupled. The third column 4206 of table 4200 identifies the associated transmit antenna element 409 to which the output of the transponder 410 is coupled. Each receive antenna element 406 is coupled to the input of the transponder 410 identified in the same row of table 4200. Similarly, each transmit antenna element 409 is coupled to the output of the transponder 410 identified in the same row of table 4200. The third column of table 4200 shows an example of direct mapping, in which each receive antenna element 406 of the receive antenna array is coupled to the same transponder 410 as the transmit antenna element 409 in the same relative location within the transmit antenna array. Fourth column 4208 of table 4200 shows one example of an interleaved mapping in which a first receive antenna element 406 is coupled to a first transponder 410 and to a tenth transmit antenna element 409. A second receive antenna element 406 is coupled to a second transponder 410 and to a ninth transmit antenna element 409, etc. Some cases have other permutations, including random mappings in which particular pairings of receive antenna elements 406 and transmit elements 409 with transponders 410 are randomly selected.

[0119] Direct mapping, which attempts to keep the transmit and receive antenna element coverage areas as similar as possible for each receive / transmit signal path, generally results in a system with the highest total capacity. Random and interleaved permutations generally produce slightly less capacity, but provide a system that is more robust to the loss of a receive / transmit signal path due to an AN failure, a fiber failure in the terrestrial network, or an electronic failure (e.g., in one or more transponders) on the end-to-end relay. Random and interleaved permutations allow the use of lower-cost non-redundant ANs. Random and interleaved permutations also provide less variation between the capacity of the best-performing beam and the capacity of the worst-performing beam. Random and interleaved permutations are also useful for initially operating a system with only a portion of the ANs, utilizing only a fraction of the total capacity but without any loss in coverage area. One example of this is the gradual rollout of ANs, where the system is initially operated with only 50% of the deployed ANs. This may provide less than full capacity, but still allow operation across the entire coverage area. As demand increases, more ANs can be deployed to increase capacity until full capacity is achieved with all ANs active. In some cases, a change in the configuration of the ANs results in a recalculation of beam weights. A configuration change may include changing the number or characteristics of one or more ANs. This may require a re-estimation of the end-to-end forward and / or return path gains.

[0120] In some cases, the antenna is an array-fed reflector antenna having a parabolic reflector. In other cases, the reflector does not have a parabolic shape. An array of receive antenna elements 406 can be arranged to receive signals reflected by the reflector. Similarly, an array of transmit antenna elements 409 can be arranged to form an array for illuminating the reflector. One way to provide elements with overlapping component beam antenna patterns is to defocus the elements 406, 409 as a result of the reflector's focal plane being behind (or in front of) the array of elements 406, 409 (i.e., positioning the receive antenna array outside the focal plane of the receive reflector).

[0121] 23 is an illustration of a cross section of a central-feed parabolic reflector 1521. The focal point 1523 is at a focal plane 1525 that is perpendicular to the central axis 1527 of the reflector 1521. Received signals that strike the reflector 1521 parallel to the central axis 1527 are focused at the focal point 1523. Similarly, signals transmitted from antenna elements positioned at the focal point and striking the reflector 1521 are reflected from the reflector 1521 parallel to the central axis 1527 in a focused beam. Such an arrangement is often used in single-feed-per-beam systems to maximize the directivity of each beam and minimize overlap with beams formed by adjacent feeds.

[0122] FIG. 24 is an illustration of another parabolic reflector 1621. By positioning the antenna element 1629 (either the receive antenna element or the transmit antenna element 406, 409, 3416, 3419, 3426, 3429) outside the focal plane (e.g., in front of the focal plane 1625 of the reflector 1621), the paths of the transmit signal 1631 impinging on the reflector 1621 are no longer parallel to each other when the transmit signal reflects off the reflector 1621, resulting in a wider beamwidth than in the focused case. In some cases, reflectors having shapes other than parabolic are used. Such reflectors may also result in defocusing of the antenna. An end-to-end beamforming system can use this type of defocused antenna to create overlapping coverage areas of adjacent antenna elements, thus providing multiple useful receive / transmit paths for a given beam location within the relay coverage area.

[0123] In one case, a relay coverage area is established where, when the end-to-end relay is deployed (e.g., the end-to-end satellite relay is in service orbit), 25% of the points within the relay coverage area are within the antenna element coverage areas of at least six component beam antenna patterns. Alternatively, 25% of the points within the relay coverage area are within the antenna element coverage areas of at least four receive antenna elements. Figure 25 is an illustration of an exemplary relay coverage area (for an end-to-end satellite relay, also referred to as a satellite coverage area) 3201 (shown with a single crosshatch) and an area 3203 (shown with double crosshatch) defined by points within the relay coverage area 3201 that are also included within six antenna element coverage areas 3205, 3207, 3209, 3211, 3213, and 3215. The coverage area 3201 and antenna element coverage areas 3205, 3207, 3209, 3211, 3213, and 3215 can be receive antenna element coverage areas or transmit antenna element coverage areas, and can be associated with only the forward link or only the return link. The size of the antenna element coverage areas 3205, 3207, 3209, 3211, 3213, and 3215 is determined by the desired performance provided by the system. A system that is more tolerant of errors can have larger antenna element coverage areas than a system that is less tolerant. In some cases, each antenna element coverage area 3205, 3207, 3209, 3211, 3213, and 3215 is all points where the component beam antenna gain is within 10 dB of the peak component beam antenna gain of the antenna elements that establish the component beam antenna pattern. In another case, each antenna element coverage area 3205, 3207, 3209, 3211, 3213, 3215 is all points where the component beam antenna gain is within 6 dB of the peak component beam antenna gain. In yet another case, each antenna element coverage area 3205, 3207, 3209, 3211, 3213, 3215 is all points where the component beam antenna gain is within 3 dB of the peak component beam antenna gain.Even when an end-to-end relay has not yet been deployed (e.g., an end-to-end satellite relay is not in a serving orbit), the end-to-end relay still has a component beam antenna pattern that conforms to the above definition. That is, the antenna element coverage area corresponding to an on-orbit end-to-end relay can be calculated from the component beam antenna patterns even when the end-to-end relay is not in a serving orbit. The end-to-end relay may include additional antenna elements that do not contribute to beamforming and therefore may not have the characteristics described above.

[0124] 26 is an illustration of an end-to-end relay (e.g., satellite) antenna pattern 3300 in which all points within a relay coverage area 3301 (e.g., satellite coverage area) are also included within at least four antenna element coverage areas 3303, 3305, 3307, 3309. Other antenna elements may be present on the end-to-end relay and may have antenna element coverage areas 3311 that include fewer than all points within the relay coverage area 3301.

[0125] The system may operate in any suitable spectrum. For example, the end-to-end beamforming system may operate in one or more of the C, L, S, X, V, Ka, Ku, or other suitable bands. In some such systems, the receiving means operates in one or more of the C, L, S, X, V, Ka, Ku, or other suitable bands. In some cases, the forward uplink and return uplink may operate in the same frequency range (e.g., near 30 GHz), and the return downlink and forward downlink may operate in non-overlapping frequency ranges (e.g., near 20 GHz). The end-to-end system may use any suitable bandwidth (e.g., 500 MHz, 1 GHz, 2 GHz, 3.5 GHz, etc.). In some cases, the forward link and return link use the same transponder.

[0126] To aid in system timing alignment, the path lengths between the L transponders are set, in some cases, to match signal path time delays, for example, through selection of appropriate cable lengths. The end-to-end relay (e.g., a satellite) in some cases includes a relay beacon generator 426 (e.g., a satellite beacon) within the calibration support module 424 (see FIG. 15). The beacon generator 426 generates a relay beacon signal. The end-to-end relay broadcasts the relay beacon signal to further aid in system timing alignment and support feeder link calibration. In some cases, the relay beacon signal is a pseudorandom (PN) sequence, such as a direct sequence spread spectrum signal operating at a high chip rate (e.g., 100,000,000,000,000 chips per second (Mcps), or any other suitable value). In some cases, linearly polarized relay (e.g., satellite) beacons, which can be received by the RHCP and LHCP antennas, are broadcast by an antenna, such as an antenna horn (not shown), over a wide coverage area for transmission through associated transmit antenna elements 409 or are coupled to one or more transponders 410. In an exemplary system, beams are formed over Ka band in multiple 500 MHz bandwidth channels, and a 400 Mcps PN code is filtered or pulse-shaped to fit within the 500 MHz bandwidth channel. When multiple channels are used, the same PN code can be transmitted on each of the channels. The system can use one beacon for each channel, or one beacon for two or more channels.

[0127] Because there can be multiple receive / transmit signal paths in an end-to-end relay, redundancy of individual receive / transmit signal paths may not be required. When a receive / transmit signal path fails, the system can still function at a performance level very close to its previous state, but may use beamforming coefficient modifications to compensate for the loss. Terrestrial Network

[0128] The terrestrial network of an exemplary end-to-end beamforming system includes several geographically distributed access nodes (ANs) directed to a common end-to-end relay. Looking first at the inbound link, a central processing system (CPS) calculates beam weights for transmitting user data and interfaces to the ANs through a distribution network. The CPS also interfaces to the data source provided to the user terminals. The distribution network can be implemented in various ways, for example, using a fiber optic cable infrastructure. Timing between the CPS and the SAN can be deterministic (e.g., using circuit-switched channels) or non-deterministic (e.g., using a packet-switched network). In some cases, the CPS is implemented at a single site, for example, using a special application-specific integrated circuit (ASIC) to handle signal processing. In some cases, the CPS is implemented in a distributed manner, for example, using cloud computing technologies.

[0129] Returning to the embodiment of FIG. 5 , the CPS 505 may include multiple feeder link modems 507. For the forward link, the feeder link modems 507 each receive a forward user data stream 509 from a data source such as the Internet, a video headend (not shown), or the like. The received forward user data streams 509 are conditioned by the modems 507 into K forward beam signals 511. In some cases, K can range from 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, or an intermediate or greater number. Each of the K forward beam signals carries a forward user data stream that is transmitted to one of the K forward user beams. Thus, if K=400, there are 400 forward beam signals 511, each transmitted to the forward user beam coverage area 519 through an associated one of the 400 forward user beams. The K forward beam signals 511 are coupled to a forward beamformer.

[0130] If M ANs 515 are present in the ground portion 502, the output of the forward beamformer is M access node-specific forward signals 516, each including weighted forward beam signals corresponding to some or all of the K forward beam signals 511. The forward beamformer can generate the M access node-specific forward signals 516 based on a matrix product of the K×M forward beam weighting matrices and the K forward data signals. A distribution network 518 distributes each of the M access node-specific forward signals to a corresponding one of the M ANs 515. Each AN 515 transmits a forward uplink signal 521 comprising its respective access node-specific forward signal 516. Each AN 515 transmits the forward uplink signal 521 of each of its relays to one or more (e.g., less than or equal to all) of its forward user beam coverage areas via one or more (e.g., less than or equal to all) of the end-to-end relay's forward receive / transmit signal paths. The transponders 410, 411 in the end-to-end relay 503 receive a composite incoming forward signal that includes a superposition 550 of forward uplink signals 521 transmitted by multiple (e.g., all or fewer) ANs 515. Each transponder (e.g., each receive / transmit signal path through the relay) relays the composite incoming forward signal as a respective forward downlink signal to the user terminal 517 over the forward downlink.

[0131] FIG. 27 is an illustration of an exemplary distribution of ANs 515. Each numbered smaller circle represents the location of an AN 515. Each larger circle indicates a user beam coverage area 519. In some cases, the ANs 515 are spaced approximately evenly throughout the coverage area of ​​the end-to-end relay 503. In other cases, the ANs 515 can be distributed unevenly throughout the coverage area. In still other cases, the ANs 515 can be distributed evenly or unevenly across one or more subregions of the relay coverage area. Generally, system performance is best when the ANs 515 are distributed evenly throughout the coverage area. However, considerations may dictate compromises in the placement of the ANs. For example, the ANs 515 can be placed based on the amount of interference, rain, or other environmental conditions, the cost of real estate, access to the distribution network, etc. For example, in the case of a satellite-based end-to-end relay system that is sensitive to rain, the majority of the ANs 515 can be placed in areas that are unlikely to experience rain-induced attenuation (e.g., the western United States). As another example, AN515s can be deployed at higher densities in high rainfall areas (e.g., the southeastern United States) to provide some diversity gain and counter the effects of rain attenuation. AN515s can be located along fiber routes to reduce distribution costs associated with AN515s.

[0132] The number M of ANs 515 is a selectable parameter that can be selected based on several criteria. Fewer ANs can result in a simpler, lower-cost ground segment and lower operational costs for the distribution network. More ANs can result in greater system capacity. Figure 28 shows a simulation of normalized forward and return link capacities as a function of the number of ANs deployed in an exemplary system. Normalized capacity is the capacity with M ANs divided by the capacity achieved with the maximum number of ANs in the simulation. Capacity increases as the number of ANs increases, but not without bound. Both forward and return link capacities approach asymptotic limits as the number of ANs increases. This simulation was with L = 517 transmit and receive antenna elements, with ANs uniformly distributed across the coverage area, but the asymptotic behavior of this capacity can be discerned with other values ​​of L and the spatial distribution of other ANs. Curves such as those shown in FIG. 28 can be useful in selecting the number M of ANs to be deployed, as discussed above, and in understanding how system capacity can be phased in as ANs are incrementally deployed.

[0133] Figure 29 is a block diagram of an example ground segment 502 of an end-to-end beamforming system. Figure 29 can, for example, illustrate the ground segment 502 of Figure 5. The ground segment 502 includes a CPS 505, a distribution network 518, and an AN 515. The CPS 505 includes a beam signal interface 524, a forward / return beamformer 513, a distribution interface 536, and a beam weight generator 910.

[0134] For the forward link, the beam signal interface 524 obtains a forward beam signal (FBS) 511 associated with each of the forward user beams. The beam signal interface 524 may include a forward beam data multiplexer 526 and a forward beam data stream modulator 528. The forward beam data multiplexer 526 may receive a forward user data stream 509 comprising forward data for transmission to a user terminal 517. The forward user data stream 509 may comprise, for example, data packets (e.g., TCP packets, UDP packets, etc.) for transmission to the user terminal 517 via the end-to-end beamforming system 500 of FIG. 5. The forward beam data multiplexer 526 groups (e.g., multiplexes) the forward user data streams 509 according to their respective forward user beam coverage areas to obtain a forward beam data stream 532. The forward beam data multiplexer 526 may generate the forward beam data stream 532 using, for example, time domain multiplexing, frequency domain multiplexing, or a combination of multiplexing techniques. The forward beam data stream modulator 528 may modulate the forward beam data stream 532 according to one or more modulation schemes (e.g., by mapping data bits to modulation symbols) to create the forward beam signal 511 that is passed to the forward / return beamformer 513. In some cases, the modulator 528 may frequency multiplex multiple modulated signals to create the multi-carrier beam signal 511. The beam signal interface 524 may, for example, implement the functionality of the feeder link modem 507 discussed with reference to FIG. 5.

[0135] The forward / return beamformer 513 may include a forward beamformer 529 and a return beamformer 531. The beam weight generator 910 generates M×K forward beam weight matrices 918. Techniques for generating the M×K forward beam weight matrices 918 are discussed in further detail below. The forward beamformer 529 may include a matrix multiplier that calculates the M access node-specific forward signals 516. For example, this calculation may be based on a matrix product of the M×K forward beam weight matrices 918 and the vectors of the K forward beam signals 511. In some embodiments, each of the K forward beam signals 511 may be associated with one of the F forward frequency subbands. In this case, the forward beamformer 529 may generate samples of the M access node-specific forward signals 516 in each of the F forward frequency subbands (e.g., effectively implementing a matrix multiplication operation for each of the F subbands of each subset of the K forward beam signals 511). The distribution interface 536 distributes the M access node-specific forward signals 516 to respective ANs 515 (e.g., via the distribution network 518).

[0136] For the return link, the distribution interface 536 obtains the composite return signal 907 from the AN 515 (e.g., via the distribution network 518). Each return data signal from the user terminal 517 can be included in multiple (e.g., less than or equal to all) of the composite return signals 907. The beam weight generator 910 generates K×M return beam weight matrices 937. Techniques for generating the K×M return beam weight matrices 937 are discussed in further detail below. The return beamformer 531 calculates K return beam signals 915 for the K return user beam coverage areas. For example, this calculation can be based on a matrix product of the return beam weight matrices 937 and the vectors of the respective composite return signals 907. The beam signal interface 524 can include a return beam signal demodulator 552 and a return beam data demultiplexer 554. The return beam signal demodulator 552 can demodulate each of the return beam signals to obtain K return beam data streams 534 associated with the K return user beam coverage areas. The return beam data demultiplexer 554 can demultiplex each of the K return beam data streams 534 into a respective return user data stream 535 associated with the return data signal transmitted from the user terminal 517. In some embodiments, each of the return user beams can be associated with one of R return frequency subbands. In this case, the return beamformer 531 can generate a respective subset of return beam signals 915 associated with each of the R return frequency subbands (e.g., effectively implementing a matrix multiplication operation for each of the R return frequency subbands to generate a respective subset of return beam signals 915).

[0137] 30 is a block diagram of an exemplary forward / return beamformer 513. The forward / return beamformer 513 includes a forward beamformer 529, a forward timing module 945, a return beamformer 531, and a timing module 947. The forward timing module 945 associates each of the M access node-specific forward signals 516 with a timestamp indicating when the signal was desired to arrive at the end-to-end relay (e.g., multiplexing the timestamp with the access node-specific forward signal among the multiplexed access node-specific forward signals). In this way, data for the K forward beam signals 511 split in the splitting module 904 within the forward beamformer 529 can be transmitted at the appropriate time by each of the ANs 515. The timing module 947 aligns the received signals based on the timestamps. Samples of the M AN composite return signals (CRS) 907 are associated with timestamps indicating when a particular sample was transmitted from the end-to-end relay. Timing considerations and timestamp generation are discussed in more detail below.

[0138] The forward beamformer 529 has a data input 925, a beam weight value input 920, and an access node output 923. The forward beamformer 529 applies values ​​of the M×K beam weight matrix to each of the K forward data signals 511 to generate M access node-specific forward signals 521, each having K weighted forward beam signals. The forward beamformer 529 may include a splitting module 904 and M forward weighting and summing modules 533. The splitting module 904 splits each of the K forward beam signals 511 into M groups 906 of K forward beam signals, one group 906 for each of the M forward weighting and summing modules 533. Thus, each forward weighting and summing module 533 receives all K forward data signals 511.

[0139] The forward beam weight generator 917 generates M×K forward beam weight matrices 918. In some cases, the forward beam weight matrices 918 are generated based on a channel matrix that is an estimate of the end-to-end forward gain of each of the K×M end-to-end forward multipath channels to form a forward channel matrix, as discussed further below. The estimation of the end-to-end forward gain is performed in the channel estimator module 919. In some cases, the channel estimator includes a channel data store 921 that stores data related to various parameters of the end-to-end multipath channels, as discussed in more detail below. The channel estimator 919 outputs an estimated end-to-end gain signal to enable the forward beam weight generator 917 to generate the forward beam weight matrices 918. Each of the weighting and summing modules 533 is coupled to receive a respective vector of beamforming weights for the forward beam weight matrices 918 (for simplicity, only one such connection is shown in FIG. 30 ). The first weighting and summing module 533 applies a weighting value equal to the value of the 1,1 element of the M×K forward beam weighting matrix 918 to the first of the K forward beam signals 511 (discussed in more detail below). A weighting value equal to the value of the 1,2 element of the M×K forward beam weighting matrix 918 is applied to the second of the K forward beam signals 511. The other weighting values ​​of the matrix are similarly applied up to the Kth forward beam signal 511, which is weighted by a value equal to the 1,K element of the M×K forward beam weighting matrix 918. Each of the K weighted forward beam signals 903 are then summed and output from the first weighting and summing module 533 as the access node-specific forward signal 516. The access node-specific forward signal 516 output by the first weighting and summing module 533 is then coupled to a timing module 945. The timing module 945 outputs an access node specific outbound signal 516 to the first AN 515 through the distribution network 518 (see FIG. 5).Similarly, each of the other weighting and summing modules 533 receives the K outbound beam signals 511 and weights and sums the K outbound beam signals 511. The outputs from each of the M weighting and summing modules 533 are coupled to the associated M ANs 515 through the distribution network 518, such that the output from the mth weighting and summing module is coupled to the mth AN 515. In some cases, jitter and uneven delays through the distribution network, as well as some other timing considerations, are handled by the timing module 945 by associating a timestamp with the data. Details of exemplary timing techniques are provided below with respect to Figures 36 and 37.

[0140] As a result of beam weights applied by the forward beamformer 529 in the ground segment 502, signals transmitted from the ANs 515 through the end-to-end relays 503 form user beams. The size and location of the beams that can be formed can be a function of the number of ANs 515 deployed, the number and pattern of relay antenna elements through which the signals pass, the location of the end-to-end relays 503, and / or the geographic spacing of the ANs 515.

[0141] Referring now to the end-to-end return link 523 shown in Figure 5, a user terminal 517 in one of the user beam coverage areas 519 transmits a signal to the end-to-end relay 503. The signal is then relayed to the ground segment 502. The signal is received by the AN 515.

[0142] 30 , the M return downlink signals 527 are received by the M ANs 515 and combined as a composite return signal 907 from the M ANs 515 through the distribution network 518 and received at an access node input 931 of the return beamformer 531. A timing module 947 aligns the composite return signals from the M ANs 515 with one another and outputs the time-aligned signal to the return beamformer 531. A return beam weight generator 935 generates return beam weights as K×M return beam weight matrices 937 based on information stored in a channel data store 941 within the channel estimator 943. The return beamformer 531 has a beam weight input 939 from which the return beamformer 531 receives the return beam weight matrices 937. Each of the M AN composite return path signals 907 is coupled to an associated one of M splitter and weighting modules 539 in the return path beamformer 531. Each splitter and weighting module 539 splits the time-aligned signal into K copies 909. The splitter and weighting module 539 weights each of the K copies 909 using the k, m elements of a K×M return path beam weighting matrix 937. Further details regarding the K×M return path beam weighting matrix are provided below. Each set of K weighted composite return path signals 911 is then coupled to a combining module 913. In some cases, the combining module 913 combines the kth weighted composite return path signal 911 output from each splitter and weighting module 539. The return beamformer 531 has a return data signal output 933 that outputs K return beam signals 915, each having samples associated with one of the K return user beams 519 (e.g., samples received through each of the M ANs). Each of the K return beam signals 915 can have samples from one or more user terminals 517. The combined, aligned, and beamformed K return beam signals 915 are coupled to the feeder link modem 507 (see FIG. 5). Note that return timing adjustment can be performed after dividing and weighting.Similarly, for the inbound link, the inbound timing adjustment can be performed before beamforming.

[0143] As discussed above, the forward beamformer 529 can perform a matrix multiplication operation on input samples of the K forward beam signals 511 to calculate the M access node-specific forward signals 516 in real time. As the beam bandwidth increases (e.g., to support shorter symbol durations) and as K and M become larger, the matrix multiplication operation becomes computationally intensive and may exceed the capabilities of a single computing node (e.g., a single computer server, etc.). The operation of the return beamformer 531 is similarly computationally intensive. Various methods can be used to divide the computing resources of multiple computing nodes among the forward / return beamformers 513. In one embodiment, the forward beamformer 529 of FIG. 30 can be divided into separate weighting and summing modules 533 for each of the M ANs 515, which may be distributed within different computing nodes. In general, implementation considerations include cost, power consumption, scalability for K, M, and bandwidth, system availability (e.g., due to node failures, etc.), upgradeability, and system latency. The above example is per row (or column). The reverse is also possible. Other ways of grouping matrix operations can be considered (e.g., split into 4 parts by [1, 1~K / 2, M / 2], [...], calculate individually, and add).

[0144] In some cases, the forward / return beamformer 513 can include a time-domain multiplexing architecture for processing the beam weighting calculations by the time-slice beamformer. Figure 31 is a block diagram of an exemplary forward beamformer 529 comprising multiple forward time-slice beamformers with time-domain demultiplexing and multiplexing. The forward beamformer 529 includes one forward beam signal demultiplexer 3002, N forward time-slice beamformers 3006, and one forward access node signal multiplexer 3010.

[0145] The forward beam signal demultiplexer 3002 receives the forward beam signals 511 and demultiplexes the K forward beam signals 511 onto the forward time slice inputs 3004 for input to the N forward time slice beamformers 3006. For example, the forward beam signal demultiplexer 3002 transmits a first time domain subset of samples of the K forward beam signals 511 to the first forward time slice beamformer 3006, which generates samples associated with M access node-specific forward signals corresponding to the first time domain subset of samples. The forward time slice beamformer 3006 outputs the samples associated with the M access node-specific forward signals for the first time domain subset of samples via its forward time slice output 3008 to the forward access node signal multiplexer 3010. The forward time slice beamformer 3006 can output samples associated with each of the M access node-specific forward signals along with synchronization timing information (e.g., corresponding time slice index, etc.) used by the access node to synchronize (e.g., by pre-correcting) each access node-specific forward signal when received by the end-to-end relay. The signal multiplexer 3010 of the forward access node multiplexes time-domain subsets of samples of the M access node-specific forward signals via N forward time slice outputs 3008 to generate M access node-specific forward signals 516. Each of the forward time slice beamformers 3006 can include a data buffer, a beam matrix buffer, and a beam weight processor that implements a matrix multiplication operation. That is, each of the forward time slice beamformers 3006 can implement calculations mathematically equivalent to the splitting module 904 and forward weight and summing module 533 shown for the forward beamformer 529 of FIG. 30 during processing of samples of a one-time slice index. The updating of the beam weight matrix can be done iteratively.For example, the beam weight matrix buffer of the forward time slice beamformer can be updated during idle times in the rotation of the time slice index t through the N forward time slice beamformers 3006. Alternatively, each forward time slice beamformer can have two buffers that can be used in a ping-pong configuration (e.g., one can be updated while the other is in use). In some cases, multiple buffers can be used to store beam weights corresponding to multiple user beam patterns (e.g., multiple user coverage areas). The beam weight buffer and data buffer of the forward time slice beamformer 3006 can be implemented as any type of memory or storage device, including dynamic or static random access memory (RAM). The beam weight processing can be implemented in an application-specific integrated circuit (ASIC) and / or a field-programmable gate array (FPGA) and can include one or more processing cores (e.g., in a cloud computing environment). Additionally or alternatively, the beam weight buffer, data buffer, and beam weight processor can be integrated into a single component.

[0146] FIG. 32 illustrates a simplified exemplary ground segment showing the operation of the forward time slice beamformer 529. In the example of FIG. 32, the forward beamformer 529 receives four forward beam signals (e.g., K=4), generates access node-specific forward signals for five ANs (e.g., M=5), and has three forward time slice beamformers (e.g., N=3). The forward beam signals are denoted by FBk:t, where k is the forward beam signal index and t is the time slice index (e.g., corresponding to a time domain subset of samples). The forward beam signal demultiplexer 3002 receives four time domain subsets of forward beam signal samples associated with the four forward user beams and demultiplexes each forward beam signal so that one forward time slice input 3004 includes a time domain subset of samples from each of the forward beam signals 511 for a particular time slice index t. For example, the time-domain subset can be a single sample, a contiguous block of samples, or non-contiguous (e.g., interleaved) blocks of samples, as described below. The forward time slice beamformer 3006 generates each of M access node-specific forward signals for time slice index t, denoted by AFm:t (e.g., based on the forward beam signals 511 and the forward beam weight matrix 918). For example, the time-domain subsets of samples FB1:0 (FB2):0 (FB3):0), and FB4:0 for time slice index t=0 are input to the first forward time slice beamformer TSBF[1] 3006, which generates corresponding samples of access node-specific forward signals AF1:0 (AF2):0 (AF3):0 (AF4):0), and AF5:0 at the forward time slice output 3008. For subsequent time slice index values ​​t=1, 2, the time domain subset of samples of the forward beam signal 511 is demultiplexed by the forward beam signal demultiplexer 3002 for input to the second and third forward time slice beamformers 3006, generating an access node-specific forward signal associated with the corresponding time slice index t at the forward time slice output 3008.32 also shows that at time slice index value t=3, the first forward time slice beamformer generates an access node-specific forward signal associated with the corresponding time slice index 3. The matrix multiplication operation performed by each forward time slice beamformer 3006 for one time slice index value t is performed on a time domain subset of samples (e.g., sampling rate t. S t)。 However, each forward time slice beamformer 3006 can process only one time domain subset of samples for each of the N time slice indices t. The forward access node signal multiplexer 3010 receives the forward time slice output 3030 from each of the forward time slice beamformers 3006 and multiplexes the time domain subsets of samples to generate M access node specific forward signals 516 for distribution to the respective ANs.

[0147] 33 is a block diagram of an exemplary return beamformer 531 comprising multiple return time-slice beamformers with time-domain demultiplexing and multiplexing. The return beamformer 531 includes one return composite signal demultiplexer 3012, N return time-slice beamformers 3016, and one return beam signal multiplexer 3020. The return composite signal demultiplexer 3012 receives M composite return signals 907 (e.g., from M ANs) and demultiplexes the M composite return signals 907 into return time slice inputs 3014 for input to the N return time-slice beamformers 3016. Each of the return time-slice beamformers 3016 outputs samples associated with K return beam signals 915 of a corresponding time-domain subset of samples to the return beam signal multiplexer 3020 via a respective return time slice output 3018. The return beam signal multiplexer 3020 multiplexes time-domain subsets of the K return beam signal samples received via the N return time slice outputs 3018 to generate K return beam signals 915. Each return time slice beamformer 3016 can include a data buffer, a beam matrix buffer, and a beam weight processor that implements a matrix multiplication operation. That is, each return time slice beamformer 3016 can implement calculations mathematically equivalent to the divider and weight module 539 and combine module 913 shown for the return beamformer 531 in FIG. 30 during processing of samples for one slice index. As discussed above for the forward time slice beamformer, this can be done sequentially using a ping-pong beam weight buffer configuration (e.g., one can be updated while the other is in use). In some cases, multiple buffers can be used to store beam weights corresponding to multiple user beam patterns (e.g., multiple user coverage areas). The beam weight buffers and data buffers of the return path time slice beamformer 3016 may be implemented as any type of memory or storage device, including dynamic or static random access memory (RAM).The beam weight processing may be implemented in an application specific integrated circuit (ASIC) and / or a field programmable gate array (FPGA) and may include one or more processing cores. Additionally or alternatively, the beam weight buffer, data buffer, and beam weight processor may be integrated into one component.

[0148] Figure 34 illustrates a simplified exemplary ground segment showing the operation of the return beamformer 531 using time-domain multiplexing. In the example of Figure 33, the return beamformer 531 receives five composite return signals (e.g., M = 5), generates return beam signals for four return user beams (e.g., K = 5), and has three time-slice beamformers (e.g., N = 3). The composite return signals are denoted by RCm:t, where m is the AN index and t is the time slice index (e.g., corresponding to a time-domain subset of samples). The return composite signal demultiplexer 3012 receives four time-domain subsets of samples of the composite return signal from the five ANs and demultiplexes each composite return signal such that one return time slice input 3014 contains a corresponding time-domain subset of samples from each of the composite return signals 907 for a particular time slice index t. For example, the time-domain subsets can be a single sample, a contiguous block of samples, or non-contiguous (e.g., interleaved) blocks of samples, as described below. The return time slice beamformer 3016 generates each of the K return beam signals for time slice index t, denoted by RBk:t (e.g., based on the composite return signal 907 and the return beam weight matrix 937). For example, the time-domain subsets of samples RC1:0 (RC2:0 (RC3:0 (RC4:0), and RC5:0 for time slice index t=0 are input to the first return time slice beamformer 3016, which generates corresponding samples of return beam signals RB1:0 (RB2):0 (RB3:0) and RB4:0 at the return time slice output 3018. For subsequent time slice index values ​​t=1, 2, the time domain subsets of samples of the composite return signal 907 are demultiplexed by the return composite signal demultiplexer 3012 for input to the second and third return time slice beamformers 3016, respectively, to generate return beam signal samples associated with the corresponding time slice index t at the return time slice output 3018.FIG. 34 also shows that at time slice index value t=3, the first return time slice beamformer generates samples of the return beam signal associated with the corresponding time slice index 3. The matrix multiplication operation performed by each forward time slice beamformer 3016 for one time slice index value t is a time domain subset of the samples (e.g., at a sampling rate t. S The time-domain subset of samples (S multiplied by K) may take longer than the actual time required for the return beam signal 915 to be processed. However, each return time slice beamformer 3016 can process only one time-domain subset of samples for each of the N time slice indices t. The return beam signal multiplexer 3020 receives the return time slice outputs 3018 from each of the return time slice beamformers 3016 and multiplexes the time-domain subsets of samples to generate K return beam signals 915.

[0149] 31-34 illustrate the same number N of forward time slice beamformers 3006 as return time slice beamformers 3016, some implementations may have more or fewer forward time slice beamformers 3006 than return time slice beamformers 3016. In some embodiments, forward beamformer 529 and / or return beamformer 531 may have spare capacity for robustness against node failures. For example, each forward time slice beamformer 3006 may be configured to operate over a real time time slice period t D For a time slice index t with FTS In this case, t FTS = N t Dwhere N+E forward time slice beamformers 3006 can be included in the forward beamformer 529. In some embodiments, N+E forward time slice beamformers 3006 are each used for operation, with each forward time slice beamformer 3006 having an effective spare capacity of E / N. If one forward time slice beamformer 3006 fails, operation can be transferred to another forward time slice beamformer 3006 (e.g., by adjusting how time-domain samples (or groups of samples) are routed through time-domain demultiplexing and multiplexing). Thus, the forward beamformer 529 can tolerate up to E failed forward time slice beamformers 3006 before system performance is affected. Additionally, the extra capacity allows for system maintenance and time slice beamformer upgrades while the system is in operation. For example, the system can tolerate different performance between time slice beamformers, allowing time slice beamformer upgrades to be performed sequentially. The data samples associated with a time slice index t may be interleaved. For example, the first time slice index t0 may include samples 0, P, 2P, ..., (S-1) * P, while the time slice index t1 corresponds to samples 1, P+1, 2P+1, ..., (S-1) *P+1, etc., where S is the number of samples in each set of samples and P is the interleaving period. Interleaving can also make the system more robust to time slice beamformer failures because each time slice beamformed block of samples is separated in time so that errors due to lost blocks are distributed in time, similar to the benefits of interleaving in forward path error correction. In practice, distributed errors caused by time slice beamformer failures may produce an effect similar to noise and not result in any errors to user data, especially when forward path error coding is used. Although an embodiment in which N=3 is illustrated, other values ​​of N can be used, and N need not have any particular relationship to K or M.

[0150] As discussed above, the forward beamformer 529 and return beamformer 531 illustrated in Figures 31 and 33 can perform time-domain demultiplexing and multiplexing to perform time-sliced ​​beamforming for one channel or frequency subband. Multiple subbands can be processed independently using an additional subband multiplexing / demultiplexing switching layer. Figure 35 is a block diagram of an exemplary multi-band forward / return beamformer 513 using subband demultiplexing and multiplexing. The multi-band forward / return beamformer 513 can support F forward subbands and R return subbands.

[0151] The multi-band forward / return beamformer 513 includes F forward subband beamformers 3026, R return subband beamformers 3036, and one subband multiplexer / demultiplexer 3030. For example, the forward beam signal 511 may be divided into F forward subbands. Each of the F forward subbands may be associated with a subset of K forward user beam coverage areas. That is, the K forward user beam coverage areas may include multiple subsets of forward user beam coverage areas associated with different (e.g., different frequency and / or polarization, etc.) frequency subbands, where the forward user beam coverage areas within each of the subsets may not overlap (e.g., at a 3 dB signal contour, etc.). Thus, each of the forward subband beamformer inputs 3024 may include a subset K1 of the forward beam signal 511. Each of the F forward beamformers 3026 may include the functionality of a forward beamformer 529 and generate a forward subband beamformer output 3028 including M access node-specific forward signals associated with a subset of the forward beam signals 511 (e.g., a matrix product of the K1 forward beam signals with M×K1 forward beam weighting matrices). Thus, each of the ANs 515 may receive multiple access node-specific forward signals associated with different frequency subbands (e.g., for the F forward subbands). The ANs may combine (e.g., add) signals in different subbands into the forward uplink signal, as discussed in further detail below. Similarly, the ANs 515 may generate multiple composite backlink signals 907 for R different backlink subbands. Each of the R backlink subbands may be associated with a subset of the K backlink user beam coverage areas. That is, the K return user beam coverage areas may include multiple subsets of return user beam coverage areas associated with different frequency subbands, where the return user beam coverage areas within each of the subsets may not overlap (e.g., at the 3 dB signal contour, etc.).The subband multiplexer / demultiplexer 3030 can split the composite return signal 907 into R return subband beamformer inputs 3034. Each of the return subband beamformers 3036 can then generate a return subband beamformer output 3038, which can include a return beam signal 915 of a subset of the return user beams (e.g., to the feeder link modem 507 or a return beam signal demodulator, etc.). In some embodiments, the multi-band forward / return beamformer 513 can support multiple polarizations (e.g., right-hand circular polarization (RHCP), left-hand circular polarization (LHCP), etc.), which can effectively double the number of subbands in some cases.

[0152] In some cases, the time slice multiplexing and demultiplexing of the forward beamformer 529 and the return beamformer 531 (e.g., beam signal demultiplexer 3002, forward access node signal multiplexer 3010, return composite signal demultiplexer 3012, return beam signal multiplexer 3020), and the sub-band multiplexing / demultiplexing (sub-band multiplexer / demultiplexer 3030) can be performed by packet switching (e.g., Ethernet switching, etc.). In some cases, the time slice and sub-band switching can occur in the same switching node or in a different order. For example, a fabric switching architecture can be used where each switch fabric node can be coupled to a subset of the ANs 515, the forward time slice beamformer 3006, the return time slice beamformer 3016, or the feeder link modems 507. The fabric switching architecture may, for example, allow any AN to be connected (e.g., via a switch and / or switch fabric interconnect) to any forward or return time-sliced ​​beamformer in a low-latency, hierarchically flat architecture. In one embodiment, a system supporting K≦600, M≦600, and 500 MHz bandwidth (e.g., per sub-band) with 14 sub-bands in the forward or return links may be realized with a commercially available interconnect switch platform with 2048 10 GigE ports. Delay Equalization

[0153] In some cases, the difference in propagation delay along each path between the end-to-end relay 503 and the CPS 505 is small. For example, on the return link, when the same signal (e.g., data to or from a particular user) is received by multiple ANs 515, each instance of the signal can arrive at a CPS that is essentially aligned with each other instance of the signal. Similarly, when the same signal is transmitted to a user terminal 517 through several ANs 515, each instance of the signal can arrive at the user terminal 517 that is essentially aligned with each other instance of the signal. In other words, the signals can be phase and time aligned with sufficient precision to coherently combine the signals, and thus the impact of path delay and beamforming is small relative to the transmission symbol rate. As an illustrative example, if the difference in path delay is 10 microseconds, the beamforming bandwidth can be on the order of tens of kHz, allowing the use of narrow-bandwidth signals, e.g., ≈10 ksps, with little potential performance degradation. A signaling rate of 10 ksps has a symbol duration of 100 microseconds, and a delay spread of 10 microseconds is only 1 / 10 of a symbol duration. In these cases, as explained above, for purposes of system analysis, it can be assumed that signals received by an end-to-end relay at one instance are relayed and transmitted essentially simultaneously.

[0154] In other cases, there may be significant differences in propagation delay for a signal interval (transmission symbol interval) of a signal transmitted from the transmit antenna element 409 to the AN 515. The path that the signal takes from each AN 515 through the distribution network 518 may include significant delay variation. In these cases, delay equalization may be used to match the path delay.

[0155] For end-to-end return link signals received by the CPS 505 through the distribution network 518, the signals can be time-aligned by using a relay beacon transmitted from the end-to-end relay, such as the PN beacon described above. Each AN 515 can time-stamp the composite return link signal using the relay beacon signal as a reference. Thus, different ANs 515 can receive the same signal at different times, but the received signal at each AN 515 can be time-stamped to allow the CPS 505 to time-align the signal. The CPS 505 can buffer the signal so that beamforming can be performed by combining signals with the same timestamp.

[0156] Returning to Figures 33 and 34, delay equalization for the return link can be performed by demultiplexing the composite return signal to the return time slice beamformer 3016. For example, each AN can divide the composite return signal into sets of samples associated with a time slice index t, which may include interleaved samples of the composite return signal. The time slice index t can be determined based on a relay beacon signal. The AN can transmit a subset of the multiplexed samples with the corresponding time slice index t to the return beamformer 531 (e.g., as a multiplexed composite return signal), which can serve as synchronization timing information for the return link. The subset of samples from each AN can be demultiplexed (e.g., via switching), and one return time slice beamformer 3016 can receive the subset of samples from each AN for time slice index t (in some cases, for one of multiple sub-bands). By performing a matrix product of the return beam weight matrix with a subset of samples from each of the M composite return signals associated with the time slice index t, the return time slice beamformer 3016 can simultaneously align the signals relayed by the end-to-end relay for applying the return beam weight matrix.

[0157] For the outbound link, the beamformer 513 in the CPS 505 can generate a timestamp indicating when each access node-specific outbound signal transmitted by the AN 515 was desired to arrive at the end-to-end relay 503. Each AN 515 can transmit an access node beacon signal 2530, e.g., a loopback PN signal. Each such signal can be looped back and transmitted by the end-to-end relay 503 to the AN 515 again. The AN 515 can receive both relay beacon signals and relayed (looped back) access node beacon signals from any or all of the ANs. The timing of the reception of the access node beacon signal relative to the timing of the reception of the relay beacon signal indicates when the access node beacon signal arrived at the end-to-end relay. After relaying by the end-to-end relay, the timing of the access node beacon signal is adjusted to arrive at the same time as the relay beacon signal arrives at the AN, thereby allowing the access node beacon signal to arrive at the end-to-end relay synchronized with the relay beacon. Having all ANs perform this function allows all access node beacon signals to reach the end-to-end relay synchronized with the relay beacon. The final step in this process is to have each AN transmit its access node-specific outbound signal synchronized with its access node beacon signal. This can be done using timestamps, as described later. Alternatively, the CPS can manage delay equalization by sending each access node-specific outbound signal to the ANs offset by their respective time-domain offsets (e.g., if timing through the distribution network is deterministic).

[0158] Figure 36 is an illustration of PN sequences used to align the system timing. The horizontal axis of the diagram represents time. AN1 PN sequence 2301 at chip 2303 is transmitted in the access node beacon signal from the first AN. The relative time of arrival of this sequence at the end-to-end relay is represented by PN sequence 2305. Due to propagation delay from the AN to the end-to-end relay, there is a time shift of PN sequence 2305 relative to AN1 PN sequence 2301. Relay PN beacon sequence 2307 is generated within and transmitted from the end-to-end relay in the relay beacon signal. PN chip 2315 of relay PN beacon sequence 2307 at time T0 is aligned with PN chip 2316 of AN1 PN received signal 2305 at time T0. When the AN1 transmission timing is adjusted by the appropriate amount, PN chip 2316 of AN1 PN received signal 2305 is aligned with PN chip 2315 of relay PN beacon 2307. PN sequence 2305 is looped back from the end-to-end relay, and PN sequence 2317 is received at AN1. PN sequence 2319, transmitted from the end-to-end relay in the relay PN beacon, is received at AN1. Note that PN sequences 2317, 2319 are aligned at AN1, indicating that they are aligned at the end-to-end relay.

[0159] Figure 37 shows an example of AN2 not properly adjusting the timing of the PN sequence generated at AN2. Note that the PN sequence 2311 generated by AN2 is received at the end-to-end relay, shown as sequence 2309, with an offset of an amount dt from the relay PN beacon PN sequence 2307. This offset is due to an error in the timing used to generate AN2's sequence. Also note that the arrival of the AN2 PN sequence 2321 at AN2 is offset by the same amount dt from the arrival of the relay PN beacon PN sequence 2323 at AN2. The signal processing at AN2 can observe this error and make a correction to the transmission timing by adjusting the timing by the amount dt to align the PN sequences 2321, 2323.

[0160] In Figures 36 and 37, the same PN chip rate is used for the relay PN beacon and all AN (loopback) PN signals to simplify the illustration of the concept. The same timing concept can be applied with different PN chip rates. Returning to Figures 31 and 32, the time slice index t can be used to synchronize the access node-specific outbound signals received from each of the ANs at the end-to-end relay. For example, the time slice index t can be multiplexed with the access node-specific outbound signal 516. Each AN can transmit samples of its access node-specific outbound signal with a particular time slice index t that is aligned with the corresponding timing information of the PN sequence of chips transmitted in the respective access node beacon signal. Because each access node beacon signal is adjusted to compensate for the respective path delays and phase shifts between the AN and the end-to-end relay, the samples associated with time slice index t arrive at the end-to-end relay properly time-synchronized and phase-aligned with respect to each other.

[0161] In cases where ANs receive their own access node beacon signals, the access node beacon signals can be looped back using the same end-to-end relay communication hardware that is also carrying the outbound communication data. In these cases, the relative gain and / or phase of the transponders in the end-to-end relay can be adjusted as described below.

[0162] 38 is a block diagram of an exemplary AN 515. The AN 515 includes a receiver 4002, a receive timing and phase adjuster 4024, a relay beacon signal demodulator 2511, a multiplexer 4004, a network interface 4006, a controller 2523, a demultiplexer 4060, a transmit timing and phase compensator 4020, and a transmitter 4012. The network interface 4006 can be connected to the CPS 505, for example, via a network port 4008.

[0163] On the return link, the receiver 4002 receives the return downlink signal 527. The return downlink signal 527 may include, for example, a composite of the return uplink signal and the relay beacon signal relayed by the end-to-end relay (e.g., via multiple receive / transmit signal paths, etc.). The receiver 4002 may perform, for example, downconversion and sampling. The relay beacon signal demodulator 2511 may demodulate the relay beacon signal of the digitized composite return signal 907 to obtain the relay timing information 2520. For example, the relay beacon signal demodulator 2511 may perform demodulation to recover chip timing associated with the relay PN code and generate a timestamp corresponding to the transmission time from the end-to-end relay for the sample of the digitized composite return signal 527. The multiplexer 4004 may multiplex the relay timing information 2520 with samples of the digitized composite backhaul signal that is transmitted to the CPS 505 (e.g., via the network interface 4006) (e.g., to form a multiplexed composite backhaul signal). Multiplexing the relay timing information 2520 may include generating a subset of samples corresponding to the time slice index t for transmission to the CPS 505. For example, the multiplexer 4004 may output the subset of samples associated with each time slice index t for input to the backhaul time slice beamforming architecture described above with reference to Figures 33, 34, and 35. The multiplexer 4004 may, in some cases, include an interleaver 4044 for interleaving the samples for each subset of samples.

[0164] On the forward link, the network interface 4006 may obtain an AN input signal 4014 (e.g., via a network port 4008). The demultiplexer 4060 may demultiplex the AN input signal 4014 to obtain an access node-specific forward signal 516 and forward signal transmission timing information 4016 indicating the transmission timing of the access node-specific forward signal 516. For example, the access node-specific forward signal 516 may include the forward signal transmission timing information (e.g., multiplexed with data samples, etc.). In one embodiment, the access node-specific forward signal 516 comprises multiple sets of samples (e.g., in a data packet), where each set of samples is associated with a time slice index t. For example, each set of samples may be samples of the access node-specific forward signal 516 generated in accordance with the forward time slice beamforming architecture discussed above with reference to Figures 31, 32, and 35. The demultiplexer 4060 may include a deinterleaver 4050 for deinterleaving samples associated with the time slice index t.

[0165] The transmit timing and phase compensator 4020 can receive and buffer the access node-specific outbound signal 516 and output outbound uplink signal samples 4022 for transmission by the transmitter 4012 at the appropriate time as the outbound uplink signal 521. The transmitter 4012 can perform digital-to-analog conversion and upconversion to output the outbound uplink signal 521. The outbound uplink signal samples 4022 can include the access node-specific outbound signal 516 and an access node beacon signal 2530 (e.g., a loopback PN signal), which can include transmit timing information (e.g., PN code chip timing information, frame timing information, etc.). The transmit timing and phase compensator 4020 can multiplex the access node-specific outbound signal 516 with the access node beacon signal 2530 such that the outbound signal transmit timing and phase information 4016 is synchronized to the corresponding transmit timing and phase information of the access node beacon signal 2530.

[0166] In some embodiments, generation of the access node beacon signal 2530 occurs locally in the AN 515 (e.g., in the access node beacon signal generator 2529). Alternatively, generation of the access node beacon signal 2530 can occur in a separate component (e.g., the CPS 505) and be transmitted to the AN 515 (e.g., via the network interface 4006). As discussed above, the access node beacon signal 2530 can be used to compensate the outbound uplink signal 521 for path differences and phase shifts between the AN and the end-to-end relay. For example, the access node beacon signal 2530 can be transmitted in the outbound uplink signal 521 and relayed by the end-to-end relay to be received at the receiver 4002. The controller 2523 can compare relayed transmit timing and phase information 4026 obtained (e.g., by demodulation, etc.) from the relayed access node beacon signal with received timing and phase information 4028 obtained (e.g., by demodulation, etc.) from the relayed beacon signal. The controller 2523 generates timing and phase adjustments 2524 for input to the transmit timing and phase compensator 4020 to adjust the access node beacon signal 2530 to compensate for path delays and phase shifts. For example, the access node beacon signal 2530 may include a PN code and frame timing information (e.g., one or more bits of a frame number, etc.). The transmit timing and phase compensator 4020 may, for example, adjust the frame timing information to coarsely compensate for path delays (e.g., output the frame timing information of the access node beacon signal so that the relayed access node beacon signal has relayed transmit frame timing information that is coarsely aligned with the corresponding frame timing information of the relay beacon signal, change which chip of the PN code is considered the LSB, etc.).Additionally or alternatively, the transmit timing and phase compensator 4020 may perform timing and phase adjustments on the forward uplink signal samples 4022 to compensate for timing or phase differences between the relayed transmit timing and phase information 4026 and the received timing and phase information 4028. For example, if the access node beacon signal 2530 is generated based on a local oscillator, the timing or phase difference between the local oscillator and the received relay beacon signal may be corrected by timing and phase adjustments on the forward uplink signal samples 4022. In some embodiments, demodulation of the access node beacon signal is performed locally in the AN 515 (e.g., in the access node beacon signal demodulator 2519). Alternatively, demodulation of the access node beacon signal may be performed in a separate component (e.g., the CPS 505), and the relayed transmit timing and phase information 4026 may be obtained from other signal transmissions (e.g., via the network interface 4006). For example, deep fading may make it difficult for an AN to receive and demodulate its own relayed access node beacon signal without transmitting at a higher power than other signal transmissions, which may reduce the power budget of the communication signal. Thus, combined reception of relayed access node beacon signals from multiple ANs 515 can increase the effective received power and demodulation accuracy of the relayed access node beacon signal. Thus, demodulation of an access node beacon signal from a single AN 515 can be performed using downlink signals received at multiple ANs 515. Demodulation of the access node beacon signal can be performed in the CPS 505 based on a composite return path signal 907, which may also include signal information of access node beacon signals from most or all of the ANs 515. If desired, end-to-end beamforming of the access node beacon signal can be performed using the access node beacon uplink (e.g., CPS 505). r ), relay loopback (e.g., E), and / or access node beacon downlink (e.g., C t ) can be taken into consideration. Feeder link fault removal

[0167] In addition to delay equalization of the signal paths from all ANs to the end-to-end relay, phase shifts induced by the feeder links can be removed before beamforming. The phase shifts of each link between the end-to-end relay and the M ANs are different. Causes of different phase shifts for each link include, but are not limited to, propagation path length, atmospheric conditions such as scintillation, Doppler frequency shift, and errors in different AN oscillators. These phase shifts are typically different for each AN and time-varying (due to differences in scintillation, Doppler shift, and AN oscillator errors). By removing dynamic feeder link impairments, the speed at which the beam weights adapt can be slower than alternatives where the beam weights adapt fast enough to track the dynamics of the feeder links.

[0168] In the return direction, feeder downlink impairments to the AN are common to both the relay PN beacon and the user data signal (e.g., the return downlink signal). In some cases, coherent demodulation of the relay PN beacon provides channel information used to remove most or all of these impairments from the return data signal. In some cases, the relay PN beacon signal is a known PN sequence that is continuously transmitted and positioned in-band with the communication data. The equivalent (or effective) isotropic radiated power (EIRP) of the PN signal in this band is set so that interference to the communication data is no greater than a maximum acceptable level. In some cases, the return link feeder link impairment removal process includes coherent demodulation and tracking of the receive timing and phase of the relay PN beacon signal. For example, the relay beacon signal demodulator 2511 can determine receive timing and phase adjustments 2512 to compensate for the feeder link impairments based on a comparison of the relay PN beacon signal to a local reference signal (e.g., a local oscillator or PLL). The recovered timing and phase difference is then removed from the return downlink signal (e.g., by receive timing and phase adjuster 4024), thus removing the feeder link impairment from the communication signal (e.g., return downlink signal 527). After feeder link impairment removal, the return link signal from the beam has a common frequency error at all ANs and is therefore suitable for beamforming. The common frequency error may include, but is not limited to, contributions from user terminal frequency error, user terminal uplink Doppler, end-to-end relay frequency translation frequency error, and relay PN beacon frequency error.

[0169] On the outbound leg, access node beacon signals from each AN can be used to assist in removing feeder uplink impairments. Feeder uplink impairments are imposed on outbound link communication data (e.g., access node-specific signals) as well as access node beacon signals. Coherent demodulation of the access node beacon signals can be used to recover the timing and phase difference of the access node beacon signals (e.g., relative to the relay beacon signals). The recovered timing and phase difference are then removed from the transmitted access node beacon signals so that the access node beacon signals arrive in phase with the relay beacon signals.

[0170] In some cases, the forward feeder link removal process is a phase-locked loop (PLL) with a path delay from the AN to the end-to-end relay and back into the loop structure. In some cases, the round-trip delay from the AN to the end-to-end relay and back to the AN can be significant. For example, a geosynchronous satellite acting as an end-to-end relay generates a round-trip delay of approximately 250 milliseconds (ms). To keep this loop stable in the presence of large delays, a very low loop bandwidth can be used. For a 250 ms delay, the PLL closed-loop bandwidth can typically be less than 1 Hz. In such cases, high-stability oscillators can be used in both the satellite and the AN to maintain reliable phase lock, as shown by block 2437 (see below) in FIG. 39.

[0171] In some instances, the access node beacon signal is a burst signal transmitted only during the calibration interval. During the calibration interval, no communication data is transmitted to eliminate this interference to the access node beacon signal. Because no communication data is transmitted during the calibration interval, the transmission power of the access node beacon signal can be increased compared to the transmission power required if it were broadcast during the communication data. This is because there is no concern of causing interference with the communication data (no communication data is present at this time). This technique enables a high signal-to-noise ratio (SNR) of the access node beacon signal when it is transmitted during the calibration interval. The frequency of occurrence of the calibration interval is the inverse of the elapsed time between the calibration intervals. Since each calibration interval provides a phase sample to the PLL, this calibration frequency is the sampling rate of the discrete-time PLL. In some instances, the sampling rate is high enough to support the closed-loop bandwidth of the PLL with a negligible amount of aliasing. The product of the calibration frequency (loop sampling rate) and the calibration interval represents the fraction of time during which the end-to-end relay cannot be used to communicate data without additional interference from the channel emitting the probe signal. In some cases, values ​​less than 0.1 are used, and in some cases, values ​​less than 0.01 are used.

[0172] FIG. 39 is a block diagram of an exemplary AN transceiver 2409. An input 2408 to the AN transceiver 2409 receives an end-to-end backlink signal received by the AN 515 (e.g., for one of a plurality of frequency subbands). The input 2408 is coupled to an input 2501 of a downconverter (D / C) 2503. The output of the D / C 2503 is coupled to an analog-to-digital converter (A / D) 2509. The output of the A / D 2509 is coupled to an Rx time adjuster 2515 and / or an Rx phase adjuster 2517. The Rx time adjuster 2515 and the Rx phase adjuster 2517 may exemplify aspects of the receive timing and phase adjuster 4024 of FIG. 38. The D / C 2503 is a quadrature downconverter. Thus, the D / C 2503 outputs in-phase and quadrature outputs to the A / D 2509. The received signals may include communication signals (e.g., a composite of return uplink signals transmitted by the user terminal), access node beacon signals (e.g., transmitted from the same AN ​​and / or other ANs), and relay beacon signals. The digital samples are coupled to a relay beacon signal demodulator 2511. The relay beacon signal demodulator 2511 demodulates the relay beacon signal. Additionally, the relay beacon signal demodulator 2511 generates time control signals 2513 and phase control signals 2514 to remove feeder link impairments based on the received relay beacon signal. Such impairments include Doppler, AN frequency error, scintillation effects, path length variations, and the like. Coherent demodulation of the relay beacon signal can correct most or all of these errors using a phase-locked loop (PLL). By correcting errors in the relay beacon signal, corresponding errors in the communication signals on the feeder link and the access node beacon signal are similarly corrected (e.g., because such errors are common to the relay beacon signal, the access node beacon signal, and the communication signal). After removing the feeder link impairment, the end-to-end return link communication signal from the user terminal 517 nominally has the same frequency error in each of the M ANs 515.The common errors include user terminal frequency error, user link Doppler, end-to-end relay frequency translation error, and relay beacon signal frequency error.

[0173] The feeder link impairment-removed digital samples are coupled to a multiplexer 2518, which may be one embodiment of the multiplexer 4004 of FIG. 38. The multiplexer 2518 associates (e.g., timestamps) the samples with relay timing information 2520 from the relay beacon signal demodulator 2511. The output of the multiplexer 2518 is coupled to an output port 2410 of the AN transceiver 2409. The output port 2410 is coupled to a multiplexer 2413 and also to the CPS 505 through an interface 2415 (see FIG. 40). The CPS 505 can then align the digital samples received from each of the ANs 515 using the timestamps associated with the received digital samples. Additionally, or alternatively, the removal of the feeder link impairments can occur in the CPS 505. For example, digital samples of the end-to-end backhaul link signals with embedded relay beacon signals can be transmitted from the AN 515 to the CPS 505, and the CPS 505 can use the synchronization timing information of each of the composite backhaul signals (e.g., the embedded relay beacon signals) to determine the adjustment of each of the respective composite backhaul signals to compensate for downlink channel impairments.

[0174] The access node beacon signal 2530 may be generated locally by an access node beacon signal generator 2529. The access node beacon signal demodulator 2519 demodulates the access node beacon signal received by the AN 515 (e.g., after being relayed by an end-to-end relay and received at input 2408). The relay beacon signal demodulator 2511 provides a received relay timing and phase information signal 2521 to a controller 2523. The controller 2523 also receives a relayed transmit timing and phase information signal 2525 from the access node beacon signal demodulator 2519. The controller 2523 compares the received relay timing and phase information with the relayed transmit timing and phase information and generates a coarse time adjustment signal 2527. The coarse time adjustment signal 2527 is coupled to the access node beacon signal generator 2529. The access node beacon signal generator 2529 generates an access node beacon signal 2530 with embedded transmit timing information that is transmitted from the AN 515 to the end-to-end relay 503. As mentioned in the discussion above, the difference between the relay timing and phase information (embedded in the relay beacon signal) and the transmit time and phase information (embedded in the access node beacon signal) is used to adjust the transmit timing and phase information to synchronize the relayed transmit timing and phase information with the received relay timing and phase information. The coarse time is adjusted by a signal 2527 to the access node beacon signal generator 2529, and the fine time is adjusted by a signal 2540 to the Tx time adjuster 2539. With relayed transmit timing and phase information 2525 from the access node beacon signal demodulator 2519 synchronized with received relay timing and phase information 2521, the access node beacon signal generator 2529 generates a timestamp 2531 that aids in synchronizing the transmitted access node beacon signal 2530 from the CPS 505 and the access node specific outbound signal. That is, data samples from the CPS 505 are received at input port 2423 along with a timestamp 2535 indicating when the associated data sample was desired to arrive at the end-to-end relay 503.The buffer, time align, and sum module 2537 buffers the combined data samples from the CPS 505 and sums them with samples from the access node beacon signal generator 2529 based on timestamps 2535, 2531. PN samples and communication data samples having the same time are summed together as indicated by the timestamps. In this embodiment, multiple beam signals (x, k (n)×b k ) are added together in the CPS 505, and an access node-specific outbound signal comprising a composite of the multiple beam signals is transmitted by the CPS 505 to the AN.

[0175] When properly aligned by the AN, the data samples arrive at the end-to-end relay 503 at the desired time (e.g., simultaneously with the arrival of the same data samples from other ANs). The transmit time adjuster 2539 performs fine time adjustments based on the fine time controller output signal 2540 from the time controller module 2523. The transmit phase adjuster 2541 performs signal phase adjustments in response to the phase control signal 2542 generated by the access node beacon signal demodulator 2519. The transmit time adjuster 2539 and the transmit phase adjuster 2541 may, for example, illustrate aspects of the transmit timing and phase compensator 4020 of FIG. 38.

[0176] The output of the transmit phase adjuster 2541 is coupled to the input of a digital-to-analog converter (D / A) 2543. The quadrature analog output from the D / A 2543 is coupled to an up-converter (U / C) 2545 and transmitted by the HPA 2433 (see FIG. 40) to the end-to-end relay 503. An amplitude control signal 2547 provided by the access node beacon signal demodulator 2519 provides amplitude feedback to the U / C 2545 to compensate for items such as uplink rain fade.

[0177] In some cases, the PN code used by each AN for the access node beacon signal 2530 is different from that used by all other ANs. In some cases, the PN codes of the access node beacon signals are each different from the relay PN codes used in the relay beacon signals. Thus, each AN 515 may be able to distinguish between its own access node beacon signal and the access node beacon signals of other ANs 515. The AN 515 can distinguish between its own access node beacon signal and the relay beacon signal.

[0178] As explained previously, the end-to-end gain from any point within a coverage area to any other point within that area is a multipath channel with L distinct paths, which can result in very deep fades for some point-to-point channels. Transmit diversity (forward link) and receive diversity (return link) are very effective in mitigating deep fades and allow the communication system to function. However, in the case of access node beacon signals, transmit and receive diversity are not present. As a result, the point-to-point link of a loopback signal, which is a transmission of a signal from an AN back to the same AN, may experience an end-to-end gain that is much lower than average. Values ​​of 20 dB below average can occur due to the large number of receive / transmit signal paths (L). These slightly lower end-to-end gains result in lower SNRs for those ANs and can make link closure difficult. Therefore, in some cases, higher gain antennas are used at the ANs. Alternatively, referring to the example transponder of FIG. 16, a phase adjuster 418 can be included in each of the receive / transmit signal paths. The phase adjusters 418 can be individually adjusted by a phase shift controller 427 (e.g., under control of a telemetry, tracking, and command (TT&C) link from a terrestrial control center). Adjusting the relative phase can be effective in increasing the end-to-end gain of a low-gain loopback path. For example, one objective may be to select a phase shift setting to increase the worst-case loopback gain (the gain from the AN back to itself). Note that the phase selection generally does not change the distribution of gain when evaluated for all points in the coverage area to all other points in the coverage area, but may increase the gain of the low-gain loopback path.

[0179] For precision, consider a set of gains from each of the M AN515s to every other AN515. M 2There are M gains, of which only M are loopback paths. Considering two gain distributions, the first gain distribution is M 2 The total number of paths (M 2 The total distribution of M loopback gains is the total distribution of M loopback paths (number of loopback paths). For ANs evenly distributed throughout the coverage area, this distribution can represent the distribution of end-to-end gains from any point in the coverage area to any other point. The second distribution is the loopback gain distribution (loopback distribution), which can be estimated by compiling histograms of only M loopback paths. In many cases, the particular choice of phase settings (and optionally, gain settings) of the receive / transmit signal paths does not provide significant changes to the total distribution. This is especially true when involving random or interleaved mapping to receive elements. However, in most cases, the loopback distribution can be improved by the particular choice of phase (and optionally, gain) settings (as opposed to random values). This is because a set of loopback gains (M 2 This is because the loopback gain consists of M paths (as opposed to M total paths) and the number of degrees of freedom for phase and gain adjustment is L. Often, the time L is approximately the same as M, which allows for significant improvement of low loopback gains with special phase selection. Another way to look at this is that special phase selection does not necessarily eliminate low end-to-end gains, but rather reduces them from a set of loopback gains (M elements in the set) to a set of loopback gains (M 2 -M elements). For non-trivial values ​​of M, the larger set is often much larger than the former.

[0180] The AN 515 can process one or more frequency sub-bands. Figure 40 is a block diagram of an exemplary AN 515 in which multiple frequency sub-bands are processed separately. Over the end-to-end return link 523 (see Figure 5), the AN 515 receives a return downlink signal 527 from the end-to-end relay 503 through a low-noise amplifier (LNA) 2401. The amplified signal is coupled from the LNA 2401 to a power divider 2403. The power divider 2403 splits the signal into multiple output signals. Each signal is output at one of the output ports 2405, 2407 of the power divider 2403. One of the output ports 2407 can be provided as a test port. The other port 2405 is coupled to an input 2408 of a corresponding one of multiple AN transceivers 2409 (only one shown). The AN transceiver 2409 processes the signal received in the corresponding sub-band. The AN transceiver 2409 performs several functions discussed in detail above. The output 2410 of the AN transceiver 2409 is coupled to an input port 2411 of a sub-band multiplexer 2413. The output is combined at an output to the sub-band multiplexer 2413 and a distribution network interface 2415. The interface 2415 provides an interface for data exchange between the AN 515 and the CPS 505 over the distribution network (see FIG. 5). Processing frequency sub-bands can be advantageous in reducing the performance requirements for the RF components used to implement the end-to-end relay and AN. For example, by dividing a 3.5 GHz bandwidth (e.g., as may be used in a Ka-band system) into seven sub-bands, each sub-band is only 500 MHz wide. That is, each access node-specific outbound signal can include multiple sub-signals associated with different sub-bands (e.g., associated with different subsets of the outbound user beam coverage area), and the AN transceiver 2409 can up-convert the sub-signals to different carrier frequencies. This bandwidth division allows for the use of lower tolerance components, since amplitude and phase variations between different sub-bands can be compensated for by separate beamforming weights, calibration, etc.Of course, other systems may use a different number of sub-bands and / or test ports. Some cases may use a single sub-band and may not include all of the components shown herein (e.g., omitting power divider 2403 and mux 2413).

[0181] On the end-to-end forward link 501, data is received from the CPS 505 by interface 2415. The received data is coupled to an input 2417 of a sub-band demultiplexer 2419. The sub-band demultiplexer 2419 splits the data into multiple data signals. The data signals are coupled from an output port 2421 of the sub-band demultiplexer 2419 to an input port 2423 of the AN transceiver 2409. An output port 2425 of the AN transceiver 2409 is coupled to an input port 2427 of a summer module 2429. The summer module 2429 sums the signals output from the seven AN transceivers 2409. An output port 2431 of the summer module 2429 couples the output of the summer module 2429 to an input port 2433 of a high power amplifier (HPA) 2435. The output of the HPA 2435 is coupled to an antenna (not shown) that transmits the signal output to the end-to-end relay 503. In some instances, an ultra-stable oscillator 2437 is coupled to the AN transceiver 2409 to provide a stable reference frequency source. Beam Weight Calculation

[0182] Returning to FIG. 8, which is an exemplary illustration of the signaling on the return link, a mathematical model of the end-to-end return link can be used to describe the link as follows: TIFF0007824989000001.tif18128In formula, x is a K-by-1 column vector of the transmitted signal. In some cases, the element-wise magnitude squared of x is defined to be 1 (equal transmit power). In some cases, this is not always the case. y is a K×1 column vector of received signals after beamforming. Ar is the L×K return path uplink radiation matrix. lk contains the gain and phase of the path from a reference location located on beam K to the lth (letter "el") receive antenna element 406 in the Rx array. In some cases, the values ​​of the return path uplink radiation matrix are stored in a channel data store 941 (see FIG. 30). E is an L×L payload matrix. Element e ij defines the gain and phase of the signal from the jth antenna element 406 of the receive array to the ith antenna element 409 of the transmit array. In some cases, the E matrix is ​​a diagonal matrix, excluding incidental crosstalk between paths (caused by finite isolation of electronic components). The matrix E can be normalized so that the sum of the squared magnitudes of all elements of the matrix is ​​L. In some cases, the values ​​of the payload matrix are stored in a channel data store 941 (see FIG. 29). Ct is the M × L downlink radiation matrix. ml contains the gain and phase of the path from the lth (letter "el") antenna element in the Tx array to the mth AN 515 among the M ANs 515. In some cases, the return path downlink radiation matrix values ​​are stored in a channel data store 941 (see FIG. 29). Hret is an M×K return channel matrix, which is equal to the product of Ct×E×Ar. n ul is an L × 1 noise vector of complex Gaussian noise. The covariance of the uplink noise is TIFF0007824989000002.tif10128. is an L×L identity matrix. σ 2 is the noise variance. TIFF0007824989000003.tif8128 is experienced on the uplink, while TIFF0007824989000004.tif8128 is experienced on the downlink. n dl is an M × 1 noise vector of complex Gaussian noise. The covariance of the downlink noise is TIFF0007824989000005.tif10128 is an M x M identity matrix. Bret is a K×M matrix of end-to-end return link beam weights.

[0183] Embodiments have generally been described above (e.g., with reference to FIGS. 6-11 ) in a manner that assumes some degree of similarity between forward and return end-to-end multipath channels. For example, forward and return channel matrices have generally been described above with reference to M, K, E, and other models. However, such descriptions are intended merely for simplicity of explanation and for the purpose of further clarity, and are not intended to be limited to cases with identical configurations in the forward and return directions. For example, in some cases, the same transponder is used for both forward and return traffic, and accordingly, the payload matrix E can be the same for both forward and return end-to-end beamforming (and corresponding beam weight calculations). In other cases, different transponders are used for forward and return traffic, and different forward payload matrices (Efwd) and return payload matrices (Eret) can be used to model the corresponding end-to-end multipath channels and calculate the corresponding beam weights. Similarly, in some cases, the same M ANs 515 and K user terminals 517 are considered part of both the forward and return end-to-end multipath channels. In other cases, M and K can refer to different subsets of ANs 515 and / or user terminals 517 and / or different numbers of ANs 515 and / or user terminals 517 in the forward and return directions.

[0184] The beam weights can be calculated in a number of ways to meet system requirements. In some cases, the beam weights are calculated after deployment of the end-to-end relay. In some cases, the payload matrix E is measured before deployment. In some cases, the beam weights are calculated with the goal of increasing the signal-to-interference-plus-noise (SINR) of each beam, and can be calculated as follows: TIFF0007824989000006.tif20128In the formula, R is the covariance of the received signal, ( * ) H is the conjugate transpose (Hermetian) operator.

[0185] The k, m elements of the K × M return beam weight matrix Bret provide weights for forming the kth user beam from the user terminal to the mth AN 515. Thus, in some cases, each of the return beam weights used to form the return user beam is calculated by estimating the end-to-end return gain (i.e., an element of the channel matrix Hret) for each end-to-end multipath channel (e.g., each end-to-end return multipath channel).

[0186] Equation 2 applies when R is the covariance of the received signals as provided in Equation 3. Therefore, when all the matrices in Equations 1 and 2 are known, the beam weights used to form the end-to-end beams can be directly determined.

[0187] This set of beam weights reduces the mean square error between x and y and also increases the end-to-end signal-to-noise-plus-interference ratio (SINR) of each of the K end-to-end backlink signals 525 (arising from each of the K beams).

[0188] The first term of Equation 3 TIFF0007824989000007.tif8128 is the covariance of the (uncorrelated) downlink noise. The second term in Eq. TIFF0007824989000008.tif8128 is the covariance of the uplink noise (correlated at the AN). The third term in Equation 3, HH H is the signal covariance. We set the uplink noise variance to zero and the last term (HH H ) results in a set of weights that increase the signal-to-downlink noise ratio by phase-aligning the received signal at each of the M AN515s. Setting the downlink noise variance to zero and ignoring the third term results in a set of weights that increase the uplink SINR. Setting the uplink noise variance and downlink noise variance to zero results in a decorrelated receiver that increases the carrier-to-interference (C / I) ratio.

[0189] In some cases, the beam weights are normalized so that the sum of the squared amplitudes of any row of Bret adds up to one.

[0190] In some cases, the solution to Equation 2 is given by the matrices Ar, Ct, and E, and the noise vector n ul and n dl The matrix is ​​determined by a priori knowledge of the variance of Ar, Ct, and E. Knowledge of the matrix element values ​​can be obtained from measurements made during manufacturing and testing of the relevant components of the end-to-end relay. This can work well for systems where the matrix values ​​are not expected to change significantly during operation of the system. However, for some systems, particularly those operating in higher frequency bands, no such expectation may exist. In such cases, the matrices Ar, Ct, and E can be estimated after deployment of the craft (e.g., satellite) on which the end-to-end relay is deployed.

[0191] In some cases where no a priori information is used to set the weights, the solution to Equation 2 can be determined by estimating the values ​​of R and H. In some cases, a designated user terminal 517 in the center of each user beam coverage area 519 transmits a known signal x during a calibration period. The vector received at the AN 515 is: u=Hx+Ct E n ul +n dl formula 4

[0192] In one embodiment, CPS 505 estimates the values ​​of R and H based on the following relationships: TIFF0007824989000009.tif27128

[0193] TIFF0007824989000010.tif6128 is the estimate of the covariance matrix R, TIFF0007824989000011.tif6128 is the estimate of the channel matrix H, TIFF0007824989000012.tif6128 is the estimated correlation vector, TIFF0007824989000013.tif6128 is the conjugate of the kth component of the transmission vector with the frequency error introduced by the uplink transmission. In some cases, backhaul communication data is not transmitted during the calibration period. That is, To enable the value of TIFF0007824989000014.tif6128 to be determined from the received vector u using the above equation, only a calibration signal known to the AN is transmitted on the end-to-end return link during the calibration period. This allows us to determine the value of TIFF0007824989000015.tif6128. Covariance matrix estimate TIFF0007824989000016.tif6128 and channel matrix estimates Both TIFF0007824989000017.tif6128 are determined based on the signal received during the calibration period.

[0194] In some cases, the CPS 505 may calculate the covariance matrix x while the communication data is present (e.g., even when x is not known). TIFF0007824989000018.tif6128 can be estimated. This is This can be seen from the fact that TIFF0007824989000019.tif6128 is determined based only on the received signal u. The value of TIFF0007824989000020.tif6128 is estimated based on the signal received during a calibration period when only the calibration signal is transmitted on the return link.

[0195] In some cases, the channel matrix TIFF0007824989000021.tif6128 and covariance matrix Both estimates of TIFF0007824989000022.tif6128 are performed while the communication data is transmitted on the return link. In this case, the covariance matrix TIFF0007824989000023.tif6128 is estimated as described above. However, the value of x is determined by demodulating the received signal. Once the value of x is known, the channel matrix can be estimated as described above in Equations 6 and 7.

[0196] The signal and interference components of the signal after beamforming are contained in the vector Bret H x. The signal and interference power of each beam is contained in a K x K matrix Bret H. The power of the kth diagonal element of Bret H is the desired signal power from beam k. The sum of the magnitude squared of all elements in row k other than the diagonal elements is the interference power of beam k. Therefore, the C / I of beam k is: TIFF0007824989000024.tif27128, s kj is an element of Bret H. The uplink noise is the vector Bret Ct Enul and the vector is TIFF0007824989000025.tif7128. The k-th diagonal element of the covariance matrix contains the uplink noise power in beam k. The uplink signal-to-noise ratio of beam k is then calculated as follows: TIFF0007824989000026.tif18128

[0197] In the formula, t kk is the k-th diagonal element of the uplink covariance matrix. The downlink noise is the vector Bret n dl and the vector is expressed by the normalized beam weights TIFF0007824989000027.tif7128. The downlink signal-to-noise ratio is therefore: TIFF0007824989000028.tif18128

[0198] The end-to-end SINR is a combination of Equations 8 to 10. TIFF0007824989000029.tif25128

[0199] The above equation describes how to calculate the end-to-end SINR given a payload matrix E. The payload matrix can be constructed by intelligently selecting the gain and phase of each of the elements of E. The gain and phase of the diagonal elements of E that optimize some utility metric (generally a function of the K beam SINRs calculated above) can be selected and achieved by configuring the phase shifters 418 on each of the L transponders 411. Candidate utility functions include: SINR k Addition of (total SINR), Log(1+SINR k) (proportional to the total throughput), or the total power H in the channel matrix. In some cases, the improvement in the utility function by customizing the gain and phase is very small and insignificant. This may be the case when random or interleaved mapping of antenna elements is used. In some cases, the utility function can be improved by a non-trivial amount by special selection of receive / transmit signal gain and phase.

[0200] Returning to FIG. 9, a mathematical model of the end-to-end outgoing link 501 can be used to describe the link 501 as follows: TIFF0007824989000030.tif22128In formula, x is a K-by-1 column vector of transmit signals. The element-wise magnitude squared of x is defined to be 1 (equal signal power). In some cases, unequal transmit power can be achieved through the selection of forward beam weights. y is a K×1 column vector of the received signal. Cr is an L × M forward uplink radiation matrix. lm contains the gain and phase of the path 2002 from the mth AN 515 to the lth (letter "el") receive antenna element 406 of the Rx array on the antenna end-to-end relay 503. In some cases, the values ​​of the forward uplink radiation matrix are stored in the channel data store 921 (see FIG. 29). E is an L×L payload matrix. Element e ijdefines the gain and phase of the signal from the jth receive array antenna element to the ith antenna element of the transmit array. Except for incidental crosstalk between paths (caused by finite isolation of electronic components), the E matrix is ​​a diagonal matrix. In some cases, the matrix E is normalized so that the sum of the squared magnitudes of all elements of the matrix is ​​L. In some cases, the values ​​of the payload matrix are stored in a channel data store 921 (see FIG. 29). At is the radiation matrix for K × L outbound downlinks. kl contains the gain and phase of the path from antenna element L (letter "el") of the Tx array of the end-to-end relay 503 to the reference location of user beam k. In some cases, the values ​​of the forward downlink radiation matrix are stored in the channel data store 921 (see FIG. 29). Hfwd is a K × M forward channel matrix, which is the product A t EC r is equal to. n ul is an L×1 noise vector of complex Gaussian noise. The covariance of the uplink noise is: TIFF0007824989000031.tif14128In formula, I L are L×L identity matrices. n dl is a K×1 noise vector of complex Gaussian noise. The covariance of the downlink noise is: TIFF0007824989000032.tif14128In formula, I K is a K×K identity matrix. Bfwd is an M×K beam weight matrix of end-to-end forward link beam weights.

[0201] The beam weight of user beam k is the element of column k of Bfwd. Unlike the backlink, the C / I of beam k is not determined by the beam weight of beam k. The beam weight of beam k determines the uplink signal-to-noise ratio (SNR) and downlink SNR, as well as the carrier (C) power at C / I. However, the interference power of beam k is determined by the beam weights of all other beams except beam k. In some cases, the beam weight of beam k is selected to increase the SNR. Such a beam weight also increases the C / I of beam k, following an increase in C. However, interference may occur in other beams. Therefore, unlike the backlink case, the optimal beam weight is not calculated on a per-beam basis (independently of other beams).

[0202] In some cases, the beam weights (including the radiation and payload matrices used to calculate the beam weights) are determined after deployment of the end-to-end relay. In some cases, the payload matrix E is measured before deployment. In some cases, a set of beam weights can be calculated by using the interference created by beam k on other beams and treating it as the interference of beam k. While this method may not calculate the optimal beam weights, it can be used to simplify the weight calculation. This allows a set of weights to be determined for each beam independently of all other beams. The resulting outbound beam weights are then calculated in the same way as the return beam weights. TIFF0007824989000033.tif23128 Term 1 of Equation 14 TIFF0007824989000034.tif9128 is the covariance of the (uncorrelated) downlink noise. TIFF0007824989000035.tif9128 is the covariance of the uplink noise (correlated at AN). The third term, HH H is the signal covariance. We set the uplink noise variance to zero and the last term (HH H) results in a set of weights that increase the signal-to-downlink noise ratio by phase-aligning the received signals at the M AN515s. Setting the downlink noise variance to zero and ignoring the third term results in a set of weights that increase the uplink SNR. Setting the uplink noise variance and downlink noise variance to zero results in a decorrelated receiver that increases the C / I ratio. For the outbound link, downlink noise and interference are generally dominant. Therefore, these terms are generally useful in calculating the beam weights. In some cases, the second term in Equation 14 (uplink noise) is insignificant compared to the first term (downlink noise). In such cases, the second term can be ignored in calculating the covariance, further simplifying the calculation but still resulting in a set of beam weights that increase the end-to-end SINR.

[0203] As with the return link, the beam weights can be normalized. For transmitter beam weights with equal power allocated to all K outgoing link signals, each column of Bfwd can be scaled so that the sum of the squared magnitudes of the elements in any column add up to 1. Equal power sharing means that each of the signals contributes a fraction of the total AN power (signal x k The beam weights for unequal power sharing are given equal shares of the total power from all ANs assigned to the beam. In some cases, unequal power sharing among the outbound link signals is achieved for the outbound link. Thus, in some cases, some beam signals will get more than an equal share of the total AN power. This can be used to equalize the SINR in all beams, or to give more important beams a higher SINR than less important beams. To create the beam weights for unequal power sharing, the M×K equal power beam weight matrix Bfwd is right-multiplied by the K×K diagonal matrix P, so that now Bfwd = Bfwd P. Then, TIFF0007824989000036.tif12128The squared value of the k-th diagonal element is the user signal x kThe power sharing matrix P is normalized so that the sum or square of the diagonal elements is equal to K (off-diagonal elements are zero).

[0204] In some cases, the solution to Equation 13 is given by the matrices At, Cr, and E, and the noise vector n ul and n dl In some cases, knowledge of the matrix can be obtained from measurements made during manufacturing and testing of the relevant components of the end-to-end relay. This can work well for systems where the values ​​of the matrix are not expected to change significantly from the values ​​measured during operation of the system. However, for some systems, especially those operating in higher frequency bands, this may not be the case.

[0205] In some cases where no a priori information is used to set the weights, the values ​​of R and H for the inbound link can be estimated to determine the solution to Equation 13. In some cases, the AN transmits a channel sounding probe during the calibration period. The channel sounding probe can be a number of different types of signals. In one case, a different, orthogonal, and known PN sequence is transmitted by each AN. The channel sounding probe can be pre-corrected in time, frequency, and / or phase to remove feeder link impairments (as discussed further below). All communication data can be turned off during the calibration interval to reduce interference to the channel sounding probe. In some cases, the channel sounding probe can be the same signal used to remove feeder link impairments.

[0206] During the calibration interval, the central terminal of each beam can be designated to receive and process the channel sounding probes. The K × l vector u of received signals during the calibration period is given by u = Hx + At E n ul +n dlwhere x is an M×l vector of transmission channel sounding probes. In some cases, each designated terminal first removes accidental frequency errors (caused by Doppler shift and terminal oscillator errors) and then correlates the resulting signal with M known orthogonal PN sequences. The results of these correlations are M complex numbers (amplitude and phase) for each terminal, which are transmitted back to the CPS via the return link. The M complex numbers computed by the central terminal of the kth beam are an estimate of the channel matrix can be used to form the kth row of TIFF0007824989000037.tif6128. Using measurements from all K designated terminals, an estimate of the entire channel matrix is ​​obtained. In many cases, combining measurements from multiple calibration intervals is useful to improve the estimate of the channel matrix. Once the estimate of the channel matrix is ​​determined, the covariance matrix is ​​obtained from Equation 14 using a value of 0 for the second term: TIFF0007824989000038.tif6128 can be determined. This can be a very accurate estimate of the covariance matrix when the uplink noise (the second term in Equation 14) is negligible relative to the downlink noise (the first term in Equation 14). The forward link beam weights can then be calculated using the channel matrix and covariance matrix estimates of Equation 13. Thus, in some cases, calculating the beam weights involves estimating the end-to-end forward gains (i.e., the values ​​of the elements of the channel matrix Hfwd) for each end-to-end forward multipath channel between the AN515 and a reference location within the user beam coverage area. In other cases, calculating the beam weights involves estimating the end-to-end forward gains for K×M end-to-end forward multipath channels from M AN515s to reference locations located within the K user beam coverage areas.

[0207] The signal and interference components of the signal after beamforming are contained in the vector H Bfwd x (the product of H, Bfwd, and x). The signal and interference powers of each beam are contained in a K x K matrix H Bfwd. The power of the k-th diagonal element of H Bfwd is the desired signal power intended for beam k. The sum of the magnitude squared of all elements in row k other than the diagonal elements is the interference power of beam k. Therefore, the C / I of beam k is: TIFF0007824989000039.tif27128 formula, s kj is an element of HB fwd. The uplink noise is expressed as a vector A t En ul and the vector is TIFF0007824989000040.tif9128. The k-th diagonal element of the covariance matrix contains the uplink noise power in beam k. The uplink signal-to-noise ratio of beam k is then calculated as follows: TIFF0007824989000041.tif23128 formula, t kk is the k-th diagonal element of the uplink covariance matrix. The downlink noise is the vector n dl and the vector is TIFF0007824989000042.tif9128. The downlink signal-to-noise ratio is therefore: TIFF0007824989000043.tif23128

[0208] The end-to-end SINR is a combination of Equations 15 to 17. TIFF0007824989000044.tif23128

[0209] The above equation describes how to calculate the end-to-end SINR given a payload matrix E. The payload matrix can be constructed by intelligently selecting the gain and phase of each of the elements of E. The gain and phase of the diagonal elements of E that optimize some utility metric (generally a function of the K beam SINRs calculated above) can be selected and achieved by configuring the phase shifters 418 of each of the L transponders 411. Candidate utility functions include SINR k Addition of (total SINR), Log(1+SINR k ) (proportional to the total throughput), or the total power H in the channel matrix. In some cases, the improvement in the utility function by customizing the gain and phase is very small and insignificant. This may be the case when random or interleaved mapping of antenna elements is used. In some cases, the utility function can be improved by a non-trivial amount by special selection of receive / transmit signal gain and phase. Different Coverage Areas

[0210] Some embodiments described above assume that the end-to-end relay 503 is designed to serve a single coverage area shared by both the user terminal 517 and the AN 515. For example, some examples describe a satellite having an antenna system that irradiates the satellite coverage area, with both the ANs and user terminals geographically distributed throughout the entire satellite coverage area (e.g., as in FIG. 27). The number of beams that can be formed within the satellite coverage area and the size of those beams (beam coverage area) can be affected by aspects of the antenna system design, such as the number and arrangement of antenna elements, reflector size, etc. For example, achieving very large capacity may involve deploying a large number (e.g., hundreds) of ANs with sufficient spacing between them to enable end-to-end beamforming. As discussed above with reference to FIG. 28, for example, increasing the number of ANs can increase system capacity, but with the accompanying decrease in backhaul. When one antenna system supports user terminals and ANs, achieving such a deployment with sufficient spacing between ANs may force a very wide geographic distribution of ANs (e.g., throughout the entire satellite coverage area, as in FIG. 27). In reality, achieving such distribution may involve deploying ANs in undesirable locations, such as in areas with poor access to high-speed networks (e.g., insufficient fiber infrastructure back to CPS 505, one or more oceans, etc.), in multiple jurisdictions, in expensive and / or highly populated areas, etc. Thus, deploying ANs often involves various trade-offs.

[0211] Some embodiments of the end-to-end relay 503 are designed with multiple antenna systems, thereby enabling a single end-to-end relay 503 to provide separate service to two or more different coverage areas. As described below, the end-to-end relay 503 may include at least a first antenna system serving an AN coverage area and at least a second antenna system serving a user coverage area. Because the user terminals and the AN coverage areas are served by different antenna systems, each antenna system may be designed to meet different design parameters, and each coverage area may differ at least in part (e.g., geographically, in beam size and / or density, in frequency band, etc.). For example, using such a multi-antenna system approach may enable user terminals distributed over a relatively large geographic area (e.g., the entire United States) to be served by multiple ANs distributed over a relatively small geographic area (e.g., parts of the eastern United States). For example, the AN coverage area may be only a small fraction (e.g., less than half, less than a quarter, less than a fifth, or less than a tenth) of the user coverage area in a physical area.

[0212] FIG. 41 is an illustration of an exemplary end-to-end beamforming system 3400. The system 3400 is an end-to-end beamforming system and includes multiple geographically distributed access nodes (ANs) 515, an end-to-end relay 3403, and multiple user terminals 517. The end-to-end relay 3403 may be one example of the end-to-end relay 503 described herein. The ANs 515 are geographically distributed within an AN coverage area 3450, and the user terminals 517 are geographically distributed within a user coverage area 3460. Both the AN coverage area 3450 and the user coverage area 3460 are within the coverage area of ​​the end-to-end relay 3403, but the AN coverage area 3450 is different from the user coverage area 3460. In other words, the AN area is not the same as the user coverage area, but rather has a significant (non-trivial) area (e.g., more than one-quarter, more than one-half, etc. of the AN coverage area) that does not overlap with the user coverage area. For example, in some cases, at least half of the user coverage area does not overlap with the AN coverage area. As described above (e.g., in FIG. 5), the AN 515 can provide signals through a distribution network 518 to a CPS 505 in the terrestrial segment 502, which can connect to a data source.

[0213] The end-to-end relay 3403 includes a separate feeder link antenna subsystem 3410 and a user link antenna subsystem 3420. The feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 can each support end-to-end beamforming. For example, as described below, each antenna subsystem can have its own array(s) of cooperating antenna elements, its own reflector(s), etc. The feeder link antenna subsystem 3410 can include an array of cooperating feeder link configuration receive elements 3416 and an array of cooperating feeder link configuration transmit elements 3419. The user link antenna subsystem 3420 can include an array of cooperating user link configuration receive elements 3426 and an array of cooperating user link configuration transmit elements 3429. The components "cooperate" in the sense that the array of such components makes its respective antenna subsystem suitable for use in a beamforming system. For example, a given user link configuration receiving element 3426 can receive a superimposed composite of backlink uplink signals from multiple (e.g., all) user beam coverage areas 519 in a manner that contributes to forming a backlink user beam. A given user link configuration transmitting element 3429 can transmit an outgoing downlink signal in a manner that, in combination with corresponding transmissions from other user link configuration transmitting elements 3429, forms some or all of the outgoing user beams. A given feeder link configuration receiving element 3416 can receive a superimposed composite of backlink uplink signals from multiple (e.g., all) ANs 515 in a manner that contributes to forming a backlink user beam (e.g., by including multiple paths in the end-to-end relay 3403). A given feeder link configuration transmission element 3419 can transmit a return downlink signal in a manner that, in combination with corresponding transmissions from other feeder link configuration transmission elements 3419, contributes to forming some or all return user beams (e.g., by allowing the AN515 to receive a composite return signal that can be beam-weighted to form a return user beam).

[0214] The exemplary end-to-end relay 3403 includes multiple forward link transponders 3430 and multiple return link transponders 3440. The transponders may be any suitable type of bent-pipe signal path between the antenna subsystems. Each forward link transponder 3430 couples a respective one of the feeder link configuration receive elements 3416 to a respective one of the user link configuration transmit elements 3429. Each return link transponder 3440 couples a respective one of the user link configuration receive elements 3426 to a respective one of the feeder link configuration transmit elements 3419. For example, some embodiments are described as having a one-to-one correspondence between each user link configuration receive element 3426 and a respective feeder link configuration transmit element 3419 (or vice versa), or as each user link configuration receive element 3426 is coupled to “only” one feeder link configuration transmit element 3419 (or vice versa), or the like. In some such cases, one side of each transponder is coupled to a single receiving element, and the other side of the transponder is coupled to a single transmitting element. In other such cases, one or both sides of the transponder may be selectively coupled to one of multiple elements (e.g., by a switch or other means, as described below). For example, the end-to-end relay 3403 may include one feeder link antenna subsystem 3410 and two user link antenna subsystems 3420, and each transponder may have one side coupled to a single feeder link element and the other side selectively coupled to a single user link element of the first user link antenna subsystem 3420 or a single feeder link element of the second user link antenna subsystem 3420. In such selectively coupled cases, each side of each transponder may still be considered to be coupled to “only” one element or the like at any given time (e.g., for particular signal-related processing).

[0215] For forward communications, transmissions from the AN 515 may be received by the feeder link configuration receiving element 3416 (via feeder uplink 521), relayed by the forward link transponder 3430 to the user link configuration transmitting element 3429, and transmitted by the user link configuration transmitting element 3429 to the user terminal 517 in the user coverage area 3460. For return communications, transmissions from the user terminal 517 may be received by the user link configuration receiving element, relayed by the return link transponder 3440 to the feeder link configuration transmitting element 3419, and transmitted by the feeder link configuration transmitting element 3419 (via feeder downlink signal 527) to the AN 515 in the AN coverage area 3450. The entire signal path from the AN 515 to the user terminal 517 via the end-to-end relay 3403 is referred to as the end-to-end forward link 501, and the entire signal path from the user terminal 517 to the AN 515 via the end-to-end relay 3403 is referred to as the end-to-end return link 523. As described herein, the end-to-end forward link 501 and the end-to-end return link 523 can each include multiple multipath channels for forward and return communications.

[0216] In some cases, each of multiple geographically distributed access nodes (e.g., ANs 515) has an end-to-end beam-weighted forward uplink signal output. The end-to-end relay (e.g., end-to-end relay 3403) comprises an array of cooperative feeder link configuration receive elements 3416 that wirelessly communicate with the distributed access nodes, an array of cooperative user link configuration transmit elements 3419 that wirelessly communicate with multiple user terminals 517, and multiple forward link transponders 3430. The forward link transponders 3430 are "bent-pipe" (or unprocessed) transponders, and thus each transponder outputs a signal corresponding to a signal that receives little or no processing. For example, each forward link transponder 3430 may amplify and / or frequency shift its received signal, but not perform more complex processing (e.g., no demodulation and / or modulation, no on-board beamforming, etc.). In some cases, each forward link transponder 3430 receives input in a first frequency band (e.g., 30 GHz LHCP) and outputs in a second frequency band (e.g., 20 GHz RHCP), and each return link transponder 3440 receives input in a first frequency band (e.g., 30 GHz RHCP) and outputs in a second frequency band (e.g., 20 GHz LHCP). Any suitable combination of frequencies and / or polarizations can be used, and the user link and feeder link can use the same or different frequency ranges. Each forward link transponder 3430 is coupled (e.g., in a one-to-one correspondence) between a respective one of the feeder link configuration receiving elements 3416 and a respective one of the user link configuration transmitting elements 3419. The forward link transponder 3430 converts the superposition of the multiple beam-weighted forward uplink signals into a forward downlink signal (e.g., a composite input forward signal) via the feeder link configuration receiving element 3416. The transmission of the forward downlink signal by the user link configuration transmitting element 3429 contributes to forming a forward user beam that serves at least some of the multiple user terminals 517.As described herein, the forwarding uplink signals may be end-to-end beam weighted and synchronized (e.g., phase synchronized and, if desired, time synchronized) before transmission from the AN515, which may enable the desired superposition of those signals at the feeder link constituent receiving element 3416.

[0217] This transmission contributes to forming an outgoing user beam, in the sense that beamforming is end-to-end, as described herein, and the beamforming is effected through multiple steps, including calculating and applying appropriate weights to the outgoing uplink signal before transmission from the AN 515 to the relay, guiding multipaths through multiple outgoing link transponders 3430 of the end-to-end relay 3403, and transmitting the outgoing downlink signal through the user link array antenna. Nevertheless, for simplicity, some descriptions may refer to the outgoing beam as being formed by a superposition of the transmitted outgoing downlink signals. In some instances, each of the multiple user terminals 517 wirelessly communicates with an array of cooperating user link constituent transmission elements 3429 to receive a composite (e.g., superposed) of the transmitted outgoing downlink signals.

[0218] In some cases, the end-to-end relay 3403 further includes a user link configuration receiving element 3426 that communicates with the user terminal 517, an array of cooperative feeder link configuration transmission elements 3419 that communicate with the distributed ANs 515, and an array of multiple return link transponders 3440. The return link transponders 3440 may be similar to or identical to the forward link transponders 3430 (e.g., bent pipe transponders), except that each is coupled between a respective one of the user link configuration receiving elements 3426 and a respective one of the feeder link configuration transmission elements 3419. Reception of the return uplink signal via the array of cooperative user link configuration receiving elements 3426 forms a return downlink signal in the return link transponder 3440. In some cases, each return downlink signal is a superposition of respective return uplink signals received by the user link constituent receiving elements 3426 from multiple user terminals 517 (e.g., from multiple user beam coverage areas 519). In some such cases, each of the multiple user terminals communicates with an array of cooperating user link constituent receiving elements 3426 and transmits a respective return uplink signal to the multiple user link constituent receiving elements 3426.

[0219] In some cases, the return downlink signals are transmitted by feeder link configuration transmission elements 3419 to geographically distributed ANs 515. As described herein, each AN 515 can receive a superimposed composite of the return downlink signals transmitted from the feeder link configuration transmission elements 3419 (i.e., corresponding to the return downlink signal). The received return downlink signals (referred to as composite received signals) can be coupled to a return beamformer, which can combine, synchronize, beamweight, and perform any other appropriate processing. For example, the return beamformer can weight the received superimposed 1706 of the return downlink signals (i.e., apply return beamweights to the composite return signal) before combining the signals. The return beamformer can also synchronize the composite return signal before combining the signals to compensate for at least the respective path delay differences between the end-to-end relay 3403 and the ANs 515. In some cases, the synchronization may be according to a received beacon signal (received by one or more, or all, of the ANs 515).

[0220] Because of the end-to-end nature of beamforming, even if the return beamformer can be coupled to the feeder link side of the end-to-end multipath channel, appropriate application of return beam weights by the return beamformer enables the formation of a return user beam, and the user beam can be formed on the user link side of the end-to-end multipath channel. Thus, the return beamformer can be referred to as contributing to the formation of a return user beam (some other aspects of the system 3400 also contribute to end-to-end return beamforming, such as the steering of multipath by the return link transponder 3440 of the end-to-end relay 3403). Nevertheless, for simplicity, the return beamformer can be referred to as forming a return user beam.

[0221] In some cases, the end-to-end relay 3403 further includes a feeder link antenna subsystem 3410 to irradiate an access node coverage area (AN coverage area 3450) in which multiple distributed access nodes are located. The feeder link antenna subsystem 3410 comprises an array of cooperative feeder link configuration receive elements 3416. In some cases, the end-to-end relay 3403 also includes a user link antenna subsystem 3420 to irradiate a geographically distributed user coverage area 3460 in which multiple user terminals 517 (e.g., among multiple user beam coverage areas 519) are located. The user link antenna subsystem 3420 comprises an array of cooperative user link configuration transmit elements 3429. In some cases, the user link antenna subsystem 3420 includes a user link receive array and a user link transmit array (e.g., an array of separate, half-duplex cooperative user link components). The user link receive array and the user link transmit array may be spatially interleaved (e.g., pointing toward the same reflector), spatially separated (e.g., pointing toward receive and transmit reflectors, respectively), or arranged in any other suitable manner. In other cases, the user link antenna subsystem 3420 includes full-duplex elements (e.g., each user link constituent transmit element 3429 shares a radiating structure with its respective user link constituent receive element 3426). Similarly, in some cases, the feeder link antenna subsystem 3410 includes a feeder link receive array and a feeder link transmit array, which may be spatially related in any suitable manner and may radiate directly toward a single reflector, toward separate transmit and receive reflectors, or otherwise. In other cases, the feeder link antenna subsystem 3410 includes full-duplex elements. The feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 may have the same or different aperture sizes. In some cases, the feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 operate in the same frequency band (eg, Ka band, etc.).In some cases, the feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 operate in different frequency bands (e.g., the feeder link uses the V band and the user link uses the Ka band, etc.).

[0222] In an embodiment such as that illustrated by FIG. 41 , the AN coverage area 3450 is different from the user coverage area 3460. The AN coverage area 3450 can be a single contiguous coverage area or multiple separate coverage areas. Similarly (and regardless of whether the AN coverage area is single or multiple), the user coverage area 3460 can be a single contiguous coverage area or multiple separate coverage areas. In some cases, the AN coverage area 3450 is a subset of the user coverage area 3460. In some cases, at least half of the user coverage area 3460 does not overlap with the AN coverage area 3450. As described below, in some cases, the feeder link antenna subsystem 3410 further comprises one or more feeder link reflectors, and the user link antenna subsystem 3420 further comprises one or more user link reflectors. In some cases, the feeder link reflector is significantly larger (e.g., at least 2 times, at least 5 times, 10 times, 50 times, 80 times, etc.) than the user link reflector. In some cases, the feeder link reflector is approximately the same physical area (eg, within 5%, 10%, 25%) as the user link reflector.

[0223] In some cases, the system 3400 operates in conjunction with terrestrial network functions, as described with reference to FIG. 5. For example, the end-to-end relay 3403 communicates with the AN 515, which in turn communicates with the CPS 505 via the distribution network 518. In some cases, the CPS 505 includes a forward beamformer 529 and / or a return beamformer 531, as described with reference to FIG. 29, for example. As described above, the forward beamformer 529 can participate in forming a forward end-to-end beam by applying calculated forward beam weights (e.g., provided by the forward beam weight generator 918) to the forward link signals, and the return beamformer 531 can participate in forming a return end-to-end beam by applying calculated return beam weights (e.g., provided by the return beam weight generator 935) to the return link signals. As described above, the end-to-end forward beam weights and / or a set of end-to-end return beam weights can be calculated according to the estimated end-to-end gains of the end-to-end multipath channels, each of which communicatively couples a respective one of the distributed ANs 515 to a respective location (e.g., a user terminal 517 or any suitable reference location) within the user coverage area via a respective plurality of forward link bent-pipe transponders 3430 and / or a respective plurality of return link bent-pipe transponders 3440. In some cases, although not shown, the end-to-end relay 3403 includes a beacon signal transmitter. The beacon signal transmitter can be implemented as described above with reference to the beacon signal generator and calibration support module 424 of FIG. 15. In some cases, the generated beacon signal can be used for the multiple distributed ANs 515 to communicate in time-synchronized wireless communication with the end-to-end relay 3403 (e.g., with multiple feeder link constituent receiving elements 3416 in accordance with the beacon signal).

[0224] In some cases, the system 3400 includes a system for forming multiple outgoing user beams using end-to-end beamforming. Such cases include means for transmitting multiple outgoing uplink signals from multiple geographically distributed locations, where the multiple outgoing uplink signals are formed from a weighted combination of multiple user beam signals, each user beam signal corresponding to a unique user beam. For example, the multiple geographically distributed locations can include multiple ANs 515, and the means for transmitting the multiple outgoing uplink signals can include some or all of the outgoing beamformer 529, the distribution network 518, and the geographically distributed ANs 515 (in communication with the end-to-end relay 3403). Such cases can also include means for relaying the multiple outgoing uplink signals to form multiple outgoing downlink signals, where each outgoing downlink signal is created by amplifying a unique superposition of multiple outgoing uplink signals, where the multiple outgoing downlink signals superpose to form multiple user beams, each user beam signal being dominant within a corresponding user beam. For example, the means for relaying multiple forward uplink signals to form multiple forward downlink signals may include an end-to-end relay 3403 (communicating with one or more user terminals in the user beam coverage area 519) with the multiple signal paths juxtaposed, which may include a forward link transponder 3430 and a return link transponder 3440.

[0225] Some such cases include a first means for receiving a first superimposed one of the plurality of inbound downlink signals and recovering a first one of the plurality of user beam signals. Such first means may include a user terminal 517 (e.g., including a user terminal antenna and modem, or other components, for recovering the user beam signal from the inbound downlink signals). Some such cases also include a second means for receiving a second superimposed one of the plurality of inbound downlink signals and recovering a second one of the plurality of user beam signals (e.g., including a second user terminal 517). For example, the first means for receiving is located in the first user beam, and the second means for receiving is located in the second user beam.

[0226] 42 is an illustration of an exemplary model of signal paths for signals carrying backhaul data on end-to-end backhaul links 523. This exemplary model may operate similarly to the models described with reference to FIGS. 6-8, except that end-to-end relay 3403 includes backhaul link signal paths 3502 dedicated to backhaul link communications. Each backhaul link signal path 3502 may include a backhaul link transponder 3440 coupled between a user link configuration receiving element 3426 and a feeder link configuration transmitting element 3419. Signals originating from user terminals 517 within the K user beam coverage areas 519 are transmitted (as return uplink signals 525) to the end-to-end relay 3403, received by an array of L return link signal paths 3502, communicated through L return link transponders 3440 to L corresponding feeder link configuration transmission elements 3419, and transmitted by the L feeder link configuration transmission elements 3419 to some or all of the M ANs 515 (similar to that shown in FIG. 7). In this manner, multiple return link signal paths 3502 (e.g., return link transponders 3440) guide multiple paths of return link communications. For example, the output of each return link signal path 3502 is a return downlink signal 527 corresponding to a respective one of the received return uplink signals 525 (e.g., corresponding to a received composite of return uplink signals 525 transmitted from multiple user beam coverage areas 519), which is transmitted via the return downlink signal 527 to M ANs 515 (e.g., geographically distributed across the AN coverage area 3450). As explained above, there are L (or up to L) different signal paths from a user terminal 517 located within a user beam coverage area 519 to a particular AN 515. The end-to-end relay 3403 thereby creates L paths between the user terminal 517 and the AN 515, collectively referred to as an end-to-end return multipath channel 1908 (e.g., similar to FIG. 8).

[0227] The end-to-end backhaul multipath channel can be modeled in the same manner as described above. For example, Ar is an L×K backhaul uplink radiation matrix, Ct is an M×L backhaul downlink radiation matrix, and Eret is an L×L backhaul payload matrix for the path from the user link configuration receiving element 3426 to the feeder link configuration transmitting element 3419. As described above, the end-to-end backhaul multipath channel from a user terminal 517 in a particular user beam coverage area 519 to a particular AN 515 is the net effect of L different signal paths induced by L unique backhaul link signal paths 3502 through the end-to-end relay 3403. With K user beam coverage areas 519 and M ANs 515, M×K induced end-to-end backhaul multipath channels can exist in the end-to-end backhaul link 523 (via the end-to-end relay 3403), each individually modeled as a corresponding element (C) of the M×K backhaul channel matrix Hret. t × Eret × Ar) can be calculated. As discussed above (e.g., with reference to FIGS. 6-8), not all ANs 515, user beam coverage areas 519, and / or return link transponders 3440 must participate in the end-to-end return multipath channel. In some cases, the number of user beams K is greater than the number of transponders L in the signal paths of the end-to-end return multipath channel, and / or the number of ANs M is greater than the number of transponders L in the signal paths of the end-to-end return multipath channel. As described with reference to FIG. 5, the CPS 505 can enable the formation of return user beams by applying return beam weights to the received downlink return signals 527 (as described further below, the received signals are referred to as composite return signals 907 after reception by the ANs). The return beam weights can be calculated based on a model of M×K signal paths for each end-to-end return multipath channel that connects a user terminal 517 in one user beam coverage area 519 with one of multiple ANs 515.

[0228] FIG. 43 is an illustration of an exemplary model of a signal path for a signal carrying forward data on the end-to-end forward link 501. This exemplary model may operate similarly to the models described with reference to FIGS. 9-11, except that the end-to-end relay 3403 includes a forward link signal path 3602 dedicated to forward link communications. Each forward link signal path 3602 may include a forward link transponder 3430 coupled between a feeder link configuration receiving element 3416 and a user link configuration transmitting element 3429. As described above, each forward uplink signal 521 is beam weighted (e.g., in a forward beamformer 515 of a CPS 505 of a ground segment 502) prior to transmission from the AN 515. Each AN 515 receives a unique forward uplink signal 521 and transmits the unique forward uplink signal 521 over one of M uplinks (e.g., in a time-synchronous manner). The forward uplink signal 521 is received from geographically distributed locations (e.g., from the AN 515) by some or all of the forward link transponders 3430 in a superimposed fashion creating a composite input forward signal 545. Each forward link transponder 3430 receives the composite input forward signal 545 simultaneously, but with slightly different timing due to differences in the location of each receiving feeder link constituent receive element 3416 associated with each forward link transponder 3430. For example, even if each feeder link constituent receive element 3416 is capable of receiving a composite of the same multiple forward uplink signals 521, the received composite input forward signal 545 may be slightly different. The composite input forward signal 545 is received by L forward link transponders 3430 via respective feeder link configuration receiving elements 3416, communicated through the L forward link transponders 3430 to L corresponding feeder link configuration transmission elements 3429, and transmitted by the L user link configuration transmission elements 3429 to one or more of the K user beam coverage areas 519 (e.g., as forward downlink signals 522, each corresponding to the received composite input forward signal 521).In this manner, the multiple forward link signal paths 3602 (e.g., forward link transponders 3430) guide the multipath of forward link communications. As explained above, there are L different signal paths from the AN 515 to a particular user terminal 517 in the user beam coverage area 519. The end-to-end relay 3403 thereby guides multiple (e.g., up to L) signal paths between one AN 515 and one user terminal 517 (or one user beam coverage area 519), which can be collectively referred to as an end-to-end forward multipath channel 2208 (e.g., similar to FIG. 10).

[0229] The end-to-end forward multipath channel 2208 can be modeled in the same manner as described above. For example, Cr is an L×M forward uplink radiation matrix, At is a K×L forward downlink radiation matrix, and Efwd is an L×L forward payload matrix for the path from the feeder link constituent receiving element 3416 to the user link constituent transmitting element 3429. In some cases, the forward payload matrix Efwd and the return payload matrix Eret may differ to reflect differences between the forward link signal path 3602 and the return link signal path 3502. As described above, the end-to-end forward multipath channel from a particular AN 515 to a user terminal 517 in a particular user beam coverage area 519 is the net effect of L different signal paths induced by L unique forward link signal paths 3602 through the end-to-end relay 3403. With K user beam coverage areas 519 and M ANs 515, M×K induced end-to-end forward multipath channels can exist in the end-to-end forward link 501, each of which can be individually modeled to calculate the corresponding element (At×Efwd×Cr) of the M×K forward channel matrix Hfwd. As described with reference to the return direction, not all ANs 515, user beam coverage areas 519, and / or forward link transponders 3430 must participate in the end-to-end forward multipath channel. In some cases, the number of user beams, K, is greater than the number of transponders, L, of the signal paths of the end-to-end forward multipath channel, and / or the number of ANs, M, is greater than the number of transponders, L, of the signal paths of the end-to-end forward multipath channel. As described with reference to FIG. 5, appropriate beam weights can be calculated for each of the multiple end-to-end forward multipath channels by the CPS 505 to form a forward user beam. The use of multiple transmitters (ANs 515) to a single receiver (user terminal 517) can provide transmission path diversity, allowing successful transmission of information to any user terminal 517 in the presence of intentionally induced multipath channels.

[0230] 41-43 illustrate an end-to-end relay 3403 implemented with separate forward link transponders 3430 and return link transponders 3440. FIGS. 44A and 44B respectively show an illustration of an exemplary forward signal path 3700 (such as forward signal path 3602 of FIG. 43) and return signal path 3750 (such as return signal path 3502 of FIG. 42). As described above, forward signal path 3700 includes forward link transponder 3430 coupled between feeder link configuration receiving element 3416 and user link configuration transmitting element 3429. Return signal path 3750 includes return link transponder 3440 coupled between user link configuration receiving element 3426 and feeder link configuration transmitting element 3419. In some cases, each forward link transponder 3430 and each return link transponder 3440 is a cross-polarity transponder. For example, forward link transponder 3430 may receive forward uplink signals at an uplink frequency with left-handed circular polarization (LHCP) and output forward downlink signals at a downlink frequency with right-handed circular polarization (RHCP), and each return link transponder 3440 may receive return uplink signals at an uplink frequency with right-handed circular polarization (RHCP) and output return downlink signals at a downlink frequency with left-handed circular polarization (LHCP). One such case (according to the polarization described in the previous example) is illustrated by following only the solid lines in Figures 44A and 44B, and another such case (according to the polarization opposite to that described in the previous example) is illustrated by following only the dashed lines in Figures 44A and 44B. In other cases, some or all transponders may provide pairs of dipolar signal paths. For example, following both the solid and dashed lines in Figures 44A and 44B, the forward link transponder 3430 and the return link transponder 3440 can receive forward uplink signals at the same or different uplink frequencies with both polarizations (LHCP and RHCP) and can output downlink signals at the same or different downlink frequencies with both polarizations (RHCP and LHCP).For example, such an example may allow multiple systems to operate in parallel using any suitable type of interference mitigation technique (e.g., using time division, frequency division, etc.). In some examples, the end-to-end relay 3403 includes a large number of transponders, such as 512 forward link transponders 3430 and 512 return link transponders 3440 (e.g., a total of 1,024 transponders). Other implementations may include a smaller number of transponders, such as 10 or any other suitable number. In some examples, the antenna elements are implemented as full-duplex structures, such that each receive antenna element shares a structure with a respective transmit antenna element. For example, each illustrated antenna element may be implemented as two of four waveguide ports of a radiating structure adapted for both transmission and reception of signals. In some examples, only the feeder link elements or only the user link elements are full-duplex. Other implementations may use different types of polarization. For example, in some implementations, the transponder may be coupled between receive and transmit antenna elements of the same polarity.

[0231] Both the exemplary forward link transponder 3430 and return link transponder 3440 may include a low noise amplifier (LNA) 3705, a frequency converter and associated filter 3710, a channel amplifier 3715, a phase shifter 3720, a power amplifier 3725 (e.g., a traveling wave tube amplifier (TWTA), solid state power amplifier (SSPA), etc.), and a harmonic filter 3730. In a dual-pole implementation, as shown, each pole has its own signal path with its own set of transponder components. Some implementations may have more or fewer components. For example, the frequency converter and associated filter 3710 may be useful when the uplink and downlink frequencies are different. As one example, each forward link transponder 3430 can receive input in a first frequency band and output in a second frequency band, and each return link transponder 3440 can receive input in the first frequency band and output in the second frequency band.

[0232] In some cases, multiple sub-bands are used (e.g., seven 500 MHz sub-bands, as described above). For example, in some cases, transponders are provided that operate over the same sub-bands used in a multiple sub-band implementation of the terrestrial network to effectively enable multiple independent parallel end-to-end beamforming systems (each end-to-end beamforming system operating over a different sub-band) through a single end-to-end relay. In other cases, a wideband end-to-end beamforming system may use multiple sub-bands in the terrestrial network, but pass one or more (or all) sub-bands through a wideband transponder (e.g., a 3.5 GHz bandwidth transponder through seven sub-bands, each 500 MHz wide). In such cases, each transponder may include multiple frequency converters and associated filters 3710 and / or other components dedicated to handling one or more of the sub-bands. The use of multiple frequency sub-bands allows for relaxed requirements on the transponder's amplitude and phase response, since the terrestrial network can separately determine the beam weights used in each sub-band, effectively calibrating out-of-band amplitude and phase variations. For example, with separate forward and return transponders and seven sub-bands, a total of 14 different beam weights can be used for each beam, i.e., seven sub-bands x two directions (forward and return). In some cases, each transponder path includes only the LNA 3705, channel amplifier 3715, and power amplifier 3725. Some implementations of the end-to-end relay 3403 include phase shift controllers and / or other controllers that can individually set the phase and / or other characteristics of each transponder, as described above.

[0233] The antenna elements may transmit and / or receive signals in any suitable manner. In some cases, the end-to-end relay 3403 has one or more array feed reflectors. For example, the feeder link antenna subsystem 3410 may have a feeder link reflector for both transmission and reception, or separate feeder link transmit and receive reflectors. Similarly, the user link antenna subsystem 3420 may have a user link reflector for both transmission and reception, or separate user link transmit and receive reflectors. In one exemplary case, the feeder link antenna subsystem 3410 comprises an array of radiating structures, each radiating structure including a feeder link constituent receive element 3416 and a feeder link constituent transmit element 3419. In one such case, the feeder link antenna subsystem 3410 may also include a feeder link reflector that illuminates the feeder link constituent receive element 3416 and is illuminated by the feeder link constituent transmit element 3419. In some cases, the reflector is implemented as multiple reflectors and can be of different shapes, sizes, orientations, etc. In other cases, the feeder link antenna subsystem 3410 and / or the user link antenna subsystem 3420 are implemented without a reflector, for example, as a direct radiating array.

[0234] As noted above, separating the feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 can make it possible to serve one or more AN coverage areas 3450 that are different from one or more user coverage areas 3460. For example, the feeder link antenna subsystem 3410 can be implemented with a reflector that has a significantly larger physical area than the reflector of the user coverage area 3460. The larger reflector allows for a large number of ANs 515 to be geographically distributed within a significantly smaller AN coverage area 3450, such as within a small subset of the user coverage area 3460. Some examples are shown in Figures 45 and 46.

[0235] FIG. 45 shows one example of a visible Earth coverage area 3800 of an end-to-end relay 3403 (e.g., a satellite). In the exemplary end-to-end relay 3403, the feeder link antenna subsystem 3410 includes an 18-meter feeder link reflector, and the user link antenna subsystem 3420 includes a 2-meter user link reflector (e.g., the area of ​​the feeder link reflector is approximately 80 times larger than the area of ​​the user link reflector). Each antenna subsystem also includes an array of 512 cooperating receive / transmit elements. For example, the exemplary end-to-end relay 3403 may include 512 forward link transponders 3430 (e.g., forming 512 forward signal paths 3700, as shown in FIG. 44A) and 512 return link transponders 3440 (e.g., forming 512 return signal paths 3750, as shown in FIG. 44B). The user coverage area 3460 includes 625 user beam coverage areas 519. The small shaded region in the eastern United States is an AN coverage area 3450 with 597 ANs 515 distributed within it. The AN coverage area 3450 is a small subset of the larger user coverage area 3460, but still provides a large capacity with a large number of ANs 515. Such a relatively dense AN coverage area 3450 is referred to herein as an "AN farm."

[0236] Figure 46 shows one embodiment of a continental United States (CONUS) coverage area 3900 for an end-to-end relay 3403 (e.g., satellite). The exemplary end-to-end relay 3403 is similar to the embodiment shown in Figure 45, except that the user link antenna subsystem 3420 includes a 5-meter user link reflector (e.g., the feeder link reflector is approximately four times larger than the user link reflector). The user coverage area 3460 includes 523 user beam coverage areas 519. The AN coverage area 3450 (AN farm), which is the same as that of Figure 45 and is a region of the eastern United States with 597 ANs 515 distributed within it, is a small subset of the user coverage area 3460. Multiple Coverage Areas

[0237] In the example end-to-end relay 3403 described above, the user link antenna subsystem 3420 is described as a single antenna subsystem (e.g., having a single user link reflector) and the feeder link antenna subsystem 3410 is described as a single antenna subsystem (e.g., having a single feeder link reflector). In some cases, the user link antenna subsystem 3420 can include one or more antenna subsystems (e.g., two or more subarrays of constituent antenna elements) associated with one or more user link reflectors, and the feeder link antenna subsystem 3410 can include one or more antenna subsystems associated with one or more feeder link reflectors. For example, some end-to-end relays 3403 may have a user link antenna subsystem 3420 that includes a first set of user link configuration receive / transmit elements associated with a first user link reflector (e.g., each element is arranged to illuminate and / or be illuminated by the first user link reflector) and a second set of user link configuration receive / transmit elements associated with a second user link reflector. In some cases, the two user link reflectors are approximately the same physical area (e.g., within 5%, 10%, 25%, 50%) of each other. In some cases, one user link reflector is much larger than the other (e.g., at least twice the physical area). Each set of user link configuration receive / transmit elements and its associated user link reflector can illuminate a corresponding, different user coverage area. For example, the multiple user coverage areas can be non-overlapping, partially overlapping, fully overlapping (e.g., a smaller user coverage area can be contained within a larger user coverage area), etc. In some cases, multiple user coverage areas can be activated (illuminated) simultaneously. Other cases, as described below, can allow selective activation of different portions of the user link configuration receive / transmit elements, thereby activating different user coverage areas at different times.Switching between multiple coverage areas can be coordinated by the CPS. For example, beamforming calibration, beam weight calculation, and beam weight application can occur in two parallel beamformers, one for each of two different coverage areas. The use of appropriate weights in the beamformers can be adjusted to accommodate end-to-end relay operation. Beam weights may, in some cases, change during a time slice if a time-slicing beamformer is used.

[0238] 47A and 47B illustrate exemplary forward signal paths 4000 and return signal paths 4050, respectively, each having selective activation of multiple user link antenna subsystems 3420. Each signal path has a transponder coupled between constituent antenna elements. Referring initially to FIG. 47A, the forward link transponder 3430 is similar to that described with reference to FIG. 44A, except that the output side of the forward link transponder 3430 is selectively coupled to one of two user link constituent transmission elements 3429, each part of a separate user link antenna subsystem 3420 (e.g., each part of a separate array of cooperating user link constituent transmission elements 3429). As described above, the forward link transponder 3430 can include some or all of the LNA 3705, frequency converter and associated filter 3710, channel amplifier 3715, phase shifter 3720, power amplifier 3725, and harmonic filter 3730.

[0239] The forward link transponder 3430 of FIG. 47A further includes a switch 4010 (forward link switch) that selectively couples the transponder to a first user link configuration transmission element 3429a (of the first user link antenna subsystem 3420) via a first set of power amplifiers 3725 and harmonic filters 3730, or to a second user link configuration transmission element 3429b (of the second user link antenna subsystem 3420) via a second set of power amplifiers 3725 and harmonic filters 3730. For example, in a first switch mode, the inbound link transponder 3430 effectively forms a signal path between the feeder link configuration receiving element 3416 and the first user link configuration transmitting element 3429, and in a second switch mode, the inbound link transponder 3430 effectively forms a signal path between the same feeder link configuration receiving element 3416 and the second user link configuration transmitting element 3429. The switch 4010 can be implemented using any suitable switching means, such as an electromechanical switch, a relay, a transistor, or the like. Although shown as a switch 4010, other implementations can use any other suitable means for selectively coupling the input of the inbound link transponder 3430 to multiple outputs. For example, the power amplifier 3725 can be used as a switch (e.g., providing high gain when “on” and zero gain (or loss) when “off”).

[0240] Referring to Figure 47B, the return link transponder 3440 functionally mirrors the forward link transponder 3430 of Figure 47A. Rather than being selectively coupled to an output side of a transponder as in the case of the forward link of Figure 47A, the input side of the return link transponder 3440 of Figure 47B is selectively coupled to one of two user link configuration receiving elements 3426. Again, each user link configuration receiving element 3426 can be part of a separate user link antenna subsystem 3420 (e.g., each is part of a separate array of cooperating user link configuration receiving elements 3426). As described above (e.g., in Figure 44B), the return link transponder 3440 can include some or all of the LNA 3705, frequency converter and associated filter 3710, channel amplifier 3715, phase shifter 3720, power amplifier 3725, and harmonic filter 3730.

[0241] 47B further includes a switch 4010 (a return link switch) that selectively couples the transponder to either a first user link configuration receive element 3426 (of the first user link antenna subsystem 3420) via a first set of LNAs 3705 or a second user link configuration receive element 3426 (of the second user link antenna subsystem 3420) via a second set of LNAs 3705. For example, in a first switch mode, the return link transponder 3440 effectively forms a signal path between the first user link configuration receive element 3426 and the feeder link configuration transmit element 3419, and in a second switch mode, the return link transponder 3440 effectively forms a signal path between the second user link configuration receive element 3426 and the same feeder link configuration transmit element 3419. The switch 4010 may be implemented using any suitable switching means, such as an electromechanical switch, a relay, a transistor, etc. Although shown as a switch 4010, other implementations may use any other suitable means for selectively coupling the input of the inbound link transponder 3430 to multiple outputs. For example, the amplifier 3705 may be used as a switch (e.g., providing high gain when "on" and zero gain (or loss) when "off").

[0242] An example of the end-to-end relay 3403 can include a switch controller 4070 (or other suitable selective coupling means) for selectively switching some or all of the switches 4010 according to a switching schedule. For example, the switching schedule can be stored in a storage device onboard the end-to-end relay 3403. In some cases, the switching schedule effectively selects which user link antenna subsystems 3420 are activated (e.g., which set of user beams are illuminated) in each of a plurality of time intervals (e.g., time slots). In some cases, the switching allocates equal time to multiple user link antenna subsystems 3420 (e.g., two subsystems are each activated for approximately half the time). In other cases, the switching can be used to realize a goal of capacity sharing. For example, one user link antenna subsystem 3420 can be associated with a higher demand user and can be allocated a longer portion of the schedule, while another user link antenna subsystem 3420 can be associated with a lower demand user and can be allocated a shorter portion of the schedule.

[0243] Figures 48A and 48B show example coverage areas 4100 and 4150 of an end-to-end relay 3403, including multiple selectively activated user coverage areas 3460a, 3460b. The example end-to-end relay 503 is similar to that of Figures 38 and 39, except for the different antenna subsystems. In this example, the user link antenna subsystem 3420 includes two 9-meter user link reflectors, and the transponder is configured to selectively activate only half of the user beams at any given time (e.g., the transponder is implemented as in Figures 47A and 47B). For example, during a first time interval, as shown in Figure 48A, the user coverage area 3460a includes 590 active user beam coverage areas 519. The active user beam coverage areas 519 effectively cover the western half of the United States. The AN coverage area 3450 (AN farm) is the same as that in Figures 38 and 39, with the eastern U.S. region having 597 ANs 515 distributed therein. During a first time interval, the AN coverage area 3450 does not overlap with the active user coverage area 3460. During a second time interval, as shown in Figure 48B, the user coverage area 3460b includes another 590 active user beam coverage areas 519. During the second time interval, the active user beam coverage areas 519 effectively cover the eastern half of the United States. The AN coverage area 3450 does not change. However, during the second time interval, the AN coverage area 3450 is entirely overlapped by (a subset of) the active user coverage area 3460. Capacity can be flexibly allocated to various regions (e.g., between eastern and western user coverage areas) by dynamically adjusting the proportions of time allocated to corresponding user link antenna subsystems.

[0244] While the previous examples illustrate two similarly sized user coverage areas, other numbers (e.g., three or more) of user coverage areas can be provided and can vary in size (e.g., the entire globe, only the continental United States, only the United States, only regionally, etc.). In cases with multiple user coverage areas 3460, the user coverage areas 3460 can have any suitable geographic relationship. In some cases, the first and second user coverage areas 3460 partially overlap (e.g., as shown in Figures 48A and 48B). In other cases, the second user coverage area 3460 can be a subset of the first user coverage area 3460 (e.g., as shown in Figures 45 and 46). In other cases, the first and second user coverage areas do not overlap (e.g., are independent).

[0245] 47A-47B illustrate signal path selection on the user link side. However, some cases alternatively or additionally include signal path switching on the feeder link side. FIG. 49 shows an exemplary forward signal path 4200 with selective activation of multiple user link antenna subsystems 3420 and multiple feeder link antenna subsystems 3410. The signal path has a forward link transponder 3430 coupled between the constituent antenna elements. As described above, the forward link transponder 3430 can include some or all of the LNA 3705, frequency converter and associated filter 3710, channel amplifier 3715, phase shifter 3720, power amplifier 3725, and harmonic filter 3730. The input side of the forward link transponder 3430 is selectively coupled (e.g., using switches 4010a and 4010b, or any other suitable path selection means) to one of two feeder link constituent receiving elements 3416. Each feeder link configuration receive element 3416 may be part of a separate feeder link antenna subsystem 3410 (e.g., each is part of a separate array of cooperating feeder link configuration receive elements 3416). The output of the inbound link transponder 3430 is selectively coupled (e.g., using switches 4010c and 4010d, or any other suitable routing means) to one of two feeder link configuration transmit elements 3429. Each user link configuration transmit element 3429 may be part of a separate user link antenna subsystem 3420 (e.g., each is part of a separate array of cooperating user link configuration transmit elements 3429). One or more switching controllers (not shown) may be included in the end-to-end relay 3403 to select between some or all of the four possible signal paths enabled by the inbound link transponder 3430. The transponders of Figures 47A, 47B, and 49 illustrate only a few of many possible cases. Additionally, some cases may involve routing between more than two user link antenna subsystems 3420 and / or more than two feeder link antenna subsystems 3410.Similarly, additional routing may be included in cases where the user link antenna subsystem 3420 and / or the feeder link constituent receiving element 3416 have separate transmit and receive reflectors, or the like.

[0246] Multiple AN coverage areas can also be provided in a similar manner. As one example, it may be desirable for traffic in specific geographic regions to terminate in their respective regions. For example, an end-to-end relay 3403 can serve a first AN coverage area 3450 and a first user coverage area 3460, both in the northern United States, with or without a pair of transponders as illustrated in FIG. 49, and can also serve a second AN coverage area 3450 and a second user coverage area 3460, both in the southern United States. Using routing (e.g., switching) in the transponders, a single end-to-end relay 3403 (e.g., a single satellite) can use an AN 515 in the northern US AN coverage area 3450 to service traffic associated with the northern US user coverage area 3460, and can also use an AN 515 in the southern US AN coverage area 3450 to service traffic associated with the southern US user coverage area 3460. Capacity can be flexibly allocated to different regions (eg, between user coverage areas in the northern and southern United States) by dynamically adjusting the proportion of time allocated to corresponding antenna subsystems.

[0247] In general, the features of the end-to-end relay 3403 described in FIG. 41 enable serving at least one user beam coverage area 519 that is different from at least one AN coverage area 3450. In some cases, serving different coverage areas can enable the use of an AN farm to provide high capacity to a large user coverage area 3460. FIGS. 45, 46, 48A, and 48B show various examples of implementations of such an AN farm. Deploying a large number of ANs 515 within a relatively small geographic area can provide several features. For example, it may be easier to ensure that more (or even all) of the ANs 515 are deployed near high-speed networks (e.g., in areas with good fiber connectivity back to the CPS 505), within the boundaries of a single country or region, over land, etc., without straying too far from the ideal distribution of the ANs 515. Implementing serving different coverage areas through routing (e.g., as in FIGS. 47A-47B) can provide additional features. For example, as described above, a single AN farm (and a single end-to-end relay 3403) can be used to selectively serve multiple user coverage areas 3460. Similarly, a single end-to-end relay 3403 can be used to differentiate and serve traffic by region.

[0248] In some instances, serving different coverage areas through route selection can enable various interference management and / or capacity management functions. For example, referring again to Figures 48A and 48B, four categories of communication links can be considered: outbound link communication from the AN farm to the western active user coverage area 3460 of Figure 48A ("Link A"); outbound link communication from the AN farm to the eastern active user coverage area 3460 of Figure 48B ("Link B"); return link communication from the western active user coverage area 3460 of Figure 48A to the AN farm ("Link C"); and return link communication from the eastern active user coverage area 3460 of Figure 48B to the AN farm ("Link D"). In a first time interval, the eastern user coverage area 3460 of Figure 48B is active, and thus communications span Link B and Link D. Because there is complete overlap between the AN coverage area 3450 and the eastern user coverage area 3460, links B and D potentially interfere. Thus, during a first time interval, link B may be assigned a first portion of the bandwidth (e.g., 2 GHz), and link D may be assigned a second portion of the bandwidth (e.g., 1.5 GHz). During the first second interval, the western user coverage area 3460 in FIG. 48A is active, and thus communication spans link A and link C. Because there is no overlap between the AN coverage area 3450 and the western user coverage area 3460, link A and link C may use the entire bandwidth (e.g., 3.5 GHz) of the end-to-end relay 3403 during the second time interval. For example, during a first time interval, an outgoing uplink signal may be received using a first frequency range, and a return uplink signal may be received using a second frequency range that is different from the first frequency range, and during a second time interval, the outgoing and return uplink signals may be received using the same frequency range (e.g., the first, second, or other frequency range). In some cases, frequencies may be reused during both the first and second time intervals due to different interference mitigation techniques used during the first time interval.In some cases, route selection timing can be selected to compensate for such differences in bandwidth allocation during different time intervals. For example, a first time interval can be longer than a second time interval, such that links B and D are allocated less bandwidth for a longer period of time to at least partially compensate for the allocation of more bandwidth to links A and C for a shorter period of time.

[0249] In some cases, a first backhaul uplink signal is received by the multiple cooperating user link configuration receiving elements 3426a from a first portion of the multiple user terminals 517 geographically distributed over part or all of a first user coverage area (e.g., an eastern user coverage area 3460) during a first time interval, and a second backhaul uplink signal is received by the multiple cooperating user link configuration receiving elements 3426b from a second portion of the multiple user terminals 517 geographically distributed over part or all of a second user coverage area (e.g., a western user coverage area 3460) during a second time interval. When the AN coverage area 3450 (AN firm) is a subset of the first user coverage area (e.g., as illustrated in Figures 48A and 48B), the AN timing can be calibrated by the end-to-end relay 3403 during the first time frame (e.g., when there is overlap between the user coverage area 3460 and the AN coverage area 3450).

[0250] As described above, some cases may include determining a respective relative timing adjustment for each of the multiple ANs 515, so that associated transmissions from the multiple ANs 515 arrive at the end-to-end relay 3403 in phase (e.g., with timing fully aligned with respect to the symbol interval, such as a fraction of the symbol interval, such as 10%, 5%, 2%, or other suitable value). In such cases, outbound uplink signals are transmitted by the multiple ANs 515 according to their respective relative timing adjustments. In some such cases, a synchronization beacon signal (e.g., a PN signal generated by a beacon signal generator, as described above) is received by at least some of the multiple ANs 515 from the end-to-end relay 3403, and the respective relative timing adjustments are determined according to the synchronization beacon signal. In other such cases, some or all of the ANs 515 may receive a loopback transmission from the end-to-end relay 3403, and the respective relative timing adjustments are determined according to the loopback transmission. Various techniques for calibrating the AN 515 can depend on the ability of the AN 515 to communicate with the end-to-end relay 3403. Thus, some instances may calibrate the AN 515 only during time intervals when the appropriate coverage area is illuminated. For example, loopback transmission may be used only during time intervals when there is some overlap between the AN coverage area 3450 and the user coverage area 3460 (e.g., the AN 515 communicates through a loopback beam that can use both the feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 of the end-to-end relay 3403). In some instances, proper calibration may further depend on some overlap between the feeder downlink frequency range and the user downlink frequency range. conclusion

[0251] While the disclosed methods and apparatus are described above with reference to various embodiments, examples, and implementations, it will be understood that particular features, aspects, and functions described in one or more of the individual embodiments may be applied to other embodiments. Accordingly, the breadth and scope of the claimed invention should not be limited by any of the embodiments provided above, but rather is defined by the claims.

[0252] Terms and phrases used in this document, and variations thereof, unless expressly stated otherwise, should be construed as open-ended, as opposed to limiting. As examples of the foregoing, the term "including" is used to mean "including without limitation" or the like, the term "example" is used to provide representative instances of the items under discussion, and is not intended to provide an exhaustive or exclusive list thereof, and the terms "a" or "an" mean "at least one," "one or more," or the like.

[0253] Throughout this specification, the terms "couple" or "coupled" are used broadly to refer to either a physical or electrical (including wireless) connection between components. In some cases, a first component may be coupled to a second component through an intermediate third component disposed between the first and second components. For example, components may be coupled through a direct connection, an impedance matching network, an amplifier, an attenuator, a filter, a DC block, an AC block, etc.

[0254] A group of items joined by the conjunction "and" does not imply that every item of the items is required to be present in the group, but rather is meant to include all, or any subset of all, unless expressly stated otherwise. Similarly, a group of items joined by the conjunction "or" does not require the items in the group to be mutually exclusive, but rather is meant to include all, or any subset of all, unless expressly stated otherwise. Furthermore, although items, elements, or components of the disclosed methods and apparatus may be described or claimed in the singular, the plural is contemplated as being within its scope unless the singular is expressly stated.

[0255] The presence in some instances of a broadening word or phrase, such as "one or more," "at least," or similar words, does not imply that a narrower instance would be intended or required in the absence of such broadening word or phrase.

[0256] Although the claims may contain reference signs, such reference signs are provided for the sole function of making the claims easier to understand, and the inclusion (or omission) of a reference sign should not be deemed to limit the scope of the matter protected by the claims.

Claims

1. A method for communicating through an end-to-end relay (503, 1202, 1502, 3403), comprising: receiving a communication signal (521, 525) via two or more receive antenna elements in a plurality of receive antenna elements of the end-to-end relay, each of the two or more receive antenna elements having a receive antenna element coverage area that overlaps with the location of an earth transmitter (515, 517) that emits the communication signal, one of the two or more receive antenna elements receiving the communication signal at a peak received signal level and another of the two or more receive antenna elements receiving the communication signal at a received signal level that is within a predetermined dB range of the peak received signal level; outputting a corresponding received signal due to reception of the communication signal at each of two or more of the receive antenna elements; independently amplifying each received signal to form a corresponding amplified received signal; transmitting the amplified received signals from each of two or more transmit antenna elements of a plurality of transmit antenna elements of the end-to-end relay as respective downlink signals, each of the two or more transmit antenna elements having a transmit antenna element coverage area that overlaps the location of one terrestrial receiver (515, 517), one of the downlink signals being irradiated to the terrestrial receiver (515, 517) at a peak transmit signal level and another of the downlink signals being irradiated to the terrestrial receiver (515, 517) at a transmit signal level that is within a predetermined dB range of the peak transmit signal level; A method comprising:

2. 2. The method of claim 1, wherein the terrestrial transmitter is a user terminal (517).

3. 2. The method of claim 1, wherein the terrestrial transmitter is an access node (515).

4. The method of claim 1 or 2, wherein the terrestrial receiver is an access node (515).

5. The method of claim 1 or 3, wherein the terrestrial receiver is a user terminal (517).

6. The method of any one of claims 1 to 5, wherein the two or more receive antenna elements include at least six receive antenna elements of the plurality of receive antenna elements.

7. The method of any one of claims 1 to 5, wherein the two or more receive antenna elements include at least four receive antenna elements of the plurality of receive antenna elements.

8. 8. The method of claim 1, wherein each receive antenna element has an antenna pattern that defines how the antenna gain of the receive antenna element varies as a function of angle, and wherein the receive antenna element coverage area of ​​each receive antenna element is the area in which the antenna gain of the receive antenna element is within 10 dB of the peak antenna gain of the receive antenna element.

9. 8. The method of claim 1, wherein each receive antenna element has an antenna pattern that defines how the antenna gain of the receive antenna element varies as a function of angle, and wherein the receive antenna element coverage area of ​​each receive antenna element is the area in which the antenna gain of the receive antenna element is within 6 dB of the peak antenna gain of the receive antenna element.

10. 8. The method of claim 1, wherein each receive antenna element has an antenna pattern that defines how the antenna gain of the receive antenna element varies as a function of angle, and the receive antenna element coverage area of ​​each receive antenna element is the area in which the antenna gain of the receive antenna element is within 3 dB of the peak antenna gain of the receive antenna element.

11. The method according to any one of claims 1 to 10, wherein the two or more transmitting antenna elements comprise at least six transmitting antenna elements.

12. The method according to any one of claims 1 to 10, wherein the two or more transmitting antenna elements comprise at least four transmitting antenna elements.

13. 13. The method of claim 11 or 12, wherein each transmitting antenna element has an antenna pattern that defines how the antenna gain of the transmitting antenna element varies as a function of angle, and the transmitting antenna element coverage area of ​​each transmitting antenna element is the area in which the antenna gain of the transmitting antenna element is within 10 dB of the peak antenna gain of the transmitting antenna element.

14. 13. The method of claim 11 or 12, wherein each transmitting antenna element has an antenna pattern that defines how the antenna gain of the transmitting antenna element varies as a function of angle, and the transmitting antenna element coverage area of ​​each transmitting antenna element is the area in which the antenna gain of the transmitting antenna element is within 6 dB of the peak antenna gain of the transmitting antenna element.

15. 13. The method of claim 11 or 12, wherein each transmitting antenna element has an antenna pattern that defines how the antenna gain of the transmitting antenna element varies as a function of angle, and the transmitting antenna element coverage area of ​​each transmitting antenna element is the area in which the antenna gain of the transmitting antenna element is within 3 dB of the peak antenna gain of the transmitting antenna element.

16. 16. The method of claim 1, wherein receiving the communication signal comprises receiving the communication signal via a first reflector of the end-to-end relay, and wherein the plurality of receive antenna elements are positioned away from a focal plane of the first reflector.

17. 17. The method of claim 1, wherein transmitting the amplified received signals as respective downlink signals comprises reflecting the respective downlink signals from a second reflector of the end-to-end relay, and wherein the plurality of transmitting antenna elements are positioned away from a focal plane of the second reflector.

18. the communication signal is received on an uplink frequency; The method of any one of claims 1 to 17, further comprising the step of the end-to-end relay converting the uplink frequency to a downlink frequency using the respective downlink signal.

19. 19. The method of any one of claims 1 to 18, wherein the communication signals are in a frequency band selected from the group consisting of C, L, S, X, V, Ka, and Ku.

20. The method of any one of claims 1 to 19, further comprising transmitting a relay beacon signal.

21. The method of claim 20 , wherein the relay beacon signal comprises a pseudorandom (PN) sequence.

22. The terrestrial transmitter (515, 517) is one of a plurality of terrestrial transmitters (515, 517) geographically distributed, The method further includes receiving communication signals from the plurality of terrestrial transmitters (515, 517) via the plurality of receive antenna elements; The method according to any one of claims 1 to 21, wherein the receiving antenna element coverage areas of at least a corresponding portion of the plurality of receiving antenna elements overlap with the location of each terrestrial transmitter (515, 517).

23. The terrestrial receiver (515, 517) is one of a plurality of terrestrial receivers located geographically dispersedly; The method further includes transmitting downlink signals intended for the plurality of terrestrial transmitters (515, 517) via the plurality of transmit antenna elements; 23. The method of claim 22, wherein the transmitting antenna element coverage areas of at least a corresponding portion of the plurality of transmitting antenna elements overlap with the location of each terrestrial receiver (515, 517).

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