End-to-end beamforming system, satellite and communication method thereof

Abstract

The present invention discloses an end-to-end beamforming system (500), which includes an end-to-end repeater (503, 1202, 3403) and a terrestrial network (502) to provide communication to a user terminal (517) located in a user beam coverage area (519). The terrestrial segment may include geographically distributed access nodes (515) and a central processing system (505). A return uplink signal (525) transmitted from the user terminal has multipaths induced by a plurality of receive / transmit signal paths (1702) in the end-to-end repeater and is relayed to the terrestrial network. The terrestrial network uses beamformers (513, 531) to recover the user data stream transmitted by the user terminal from a return downlink signal (527). The terrestrial network uses beamformers (513, 529) to generate a forward uplink signal (521) according to an appropriate weighted combination of the user data streams, and after being relayed by the end-to-end repeater, the user data streams generate a forward downlink signal (522), which is combined to form a user beam.

Description

Technical Field

[0001] The systems, methods, and devices disclosed herein relate to end-to-end beamforming using end-to-end repeaters in a system. Background Art

[0002] Wireless communication systems, such as satellite communication systems, provide a means by which data, including audio, video, and various other types of data, can be transmitted from one location to another. Information originates at a first site, such as a first ground-based site, and is transmitted to a wireless repeater, such as a communication satellite. The information received by the wireless repeater is retransmitted to a second site, such as a second ground-based site. In some wireless relay communication systems, the first site or the second site (or both) is mounted on a vehicle, such as an air vehicle, a water vehicle, or a land vehicle. Information may be transmitted in only one direction (e.g., only from the first ground-based site to the second ground-based site), or it may be transmitted in both directions (e.g., also from the second ground-based site to the first ground-based site).

[0003] In a wireless relay communication system in which the wireless repeater is a satellite, the satellite may be a geostationary satellite. In this case, the orbit of the satellite is synchronized with the rotation of the Earth, so that the coverage area of the satellite remains substantially stationary relative to the Earth. In other cases, the satellite is in an orbit around the Earth, which causes the coverage area of the satellite to move across the Earth's surface as the satellite traverses its orbital path.

[0004] Signals introduced to or exported from the first site may be steered by using an antenna shaped to focus the signal into a narrow beam. Such antennas typically have a reflector of parabolic shape to focus the beam.

[0005] In some cases, a beam may be formed electronically by adjusting the gain and phase (or time delay) of signals transmitted, received, or both, from a number of elements of a phased array antenna. The beam may be steered by appropriately selecting the relative phase and gain of the signals transmitted and / or received by each element of the phased array antenna. In most cases, all of the energy transmitted from a ground-based site is intended to be received by the wireless repeater. Similarly, the information received by the second site is typically received from one wireless repeater at a time. Thus, the transmit beam formed to transmit information to the wireless repeater (whether by using electronic beamforming or by using an antenna with a shaped reflector) is typically relatively narrow to allow as much of the transmitted energy as possible to be steered to the wireless repeater. Similarly, the receive beam formed to receive information from the wireless repeater is typically narrow to collect energy from the direction of the wireless repeater with minimal interference from other sources.

[0006] In many interesting cases, the signals transmitted from a wireless repeater to a first site and a second site are not directed to a single site. Instead, the wireless repeater is capable of transmitting signals over a relatively large geographical area. For example, in a satellite communication system, a satellite can serve the entire continental United States. In this case, the satellite is said to have a satellite coverage area that includes the entire continental United States. However, to increase the amount of data that can be transmitted via the satellite, the energy transmitted by the satellite is focused into beams. The beams can be directed to geographical areas on the Earth. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The drawings are provided solely for purposes of illustration and depict only examples. The drawings are provided to facilitate the reader's understanding of the methods and apparatuses disclosed herein. They do not limit the breadth, scope, or applicability of the invention as claimed. For clarity and ease of illustration, the drawings are not necessarily drawn to scale.

[0008] Figure 1 is a diagrammatic illustration of an example of a satellite communication system.

[0009] Figure 2 is a schematic diagram showing an exemplary beam pattern covering the continental United States.

[0010] Figure 3 is a diagrammatic illustration of an example of a forward link of a satellite communication system, where the satellite has phased array per-beam multi-feed satellite carrier beamforming capabilities.

[0011] Figure 4 is a diagrammatic illustration of an example of a forward link of a satellite communication system with ground-based beamforming.

[0012] Figure 5 is a diagrammatic illustration of an exemplary end-to-end beamforming system.

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

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

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

[0016] Fig. 9 is a diagrammatic illustration of an exemplary signal path in the forward direction.

[0017] Fig.10 is a diagrammatic illustration of an exemplary signal path in the forward direction for a user terminal located within a user beam coverage area.

[0018] Fig.11 is a simplified illustration of an exemplary end - to - end return channel matrix model.

[0019] Fig.12 is an illustration of an exemplary end - to - end repeater satellite that supports forward data and return data.

[0020] Fig.13 is an illustration of an example in which the uplink frequency range is divided into two parts.

[0021] Fig.14 is an illustration of an exemplary end - to - end repeater time - division multiplexing between forward data and return data.

[0022] Fig.15 is a block diagram of components of an exemplary end - to - end repeater implemented as a satellite.

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

[0024] Fig.17 is a graph of an exemplary signal strength pattern of a number of antenna elements.

[0025] Fig.18 is an illustration of an exemplary 3dB signal strength profile of a number of antenna elements.

[0026] Fig.19 is an illustration of an exemplary overlapping signal strength pattern of a number of antenna elements.

[0027] FIG. 20A to FIG. 20E is an illustration of an exemplary overlapping 3dB signal strength profile of a number of antenna elements.

[0028] Fig.21 is an illustration of an exemplary enumeration of 16 antenna elements and their overlapping 3dB signal strength profiles.

[0029] Fig. 22 is a table showing an exemplary mapping of receive antenna elements through 16 transponders to transmit antennas.

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

[0031] Fig.24 is an illustration of a cross - section of a parabolic antenna reflector and an array of elements placed away from the focus of the parabola.

[0032] Fig.25 is an illustration of an exemplary repeater coverage area (shown with single cross - hatching) and an area defined by points within the repeater coverage area that are also within the coverage area of six antenna elements (shown with double cross - hatching).

[0033] Fig.26 It is a diagram of an exemplary repeater antenna pattern where all points within the repeater coverage area are also included in the coverage areas of at least four antenna elements.

[0034] Fig. 27 It is a diagram of an exemplary distribution of an access node (AN) and user beam coverage areas.

[0035] Fig.28 It is an exemplary graph showing the variation of normalized forward link and return link capacities with the number of deployed ANs.

[0036] Fig.29 It is a block diagram of an exemplary ground segment 502 of an end - to - end beamforming system.

[0037] Fig.30 It is a block diagram of an exemplary forward / return beamformer.

[0038] Fig.31 It is a block diagram of an exemplary forward beamformer including multiple return time - slice beamformers with time - domain demultiplexing and multiplexing.

[0039] Fig.32 It is a diagram of a simplified exemplary ground segment showing the operation of a forward time - slice beamformer.

[0040] Fig.33 It is a block diagram of an exemplary return beamformer including multiple return time - slice beamformers with time - domain demultiplexing and multiplexing.

[0041] Fig.34 It is a diagram of a simplified exemplary ground segment showing the operation of a return beamformer using time - domain multiplexing.

[0042] Fig.35 It is a block diagram of an exemplary multi - band forward / return beamformer employing sub - band demultiplexing and multiplexing.

[0043] Fig.36 and Fig.37 It is a diagram of an exemplary timing alignment of the forward link.

[0044] Fig.38 It is a block diagram of an exemplary AN.

[0045] Fig.39 It is a block diagram of a part of an example of an AN.

[0046] Fig.40 It is a block diagram of an exemplary AN 515 where multiple frequency sub - bands are processed separately.

[0047] Fig.41 It is a diagram of an exemplary end - to - end beamforming system for achieving different user link and feeder link coverage areas.

[0048] Fig.42 It is a diagram of an exemplary model of a signal path of a signal carrying return data on an end - to - end return link.

[0049] Fig.43 It is a diagram of an exemplary model of a signal path of a signal carrying forward data on an end - to - end forward link.

[0050] Fig.44A and Fig.44B are diagrams of an exemplary forward signal path and a return signal path respectively.

[0051] Fig.45 It is a diagram of an example of the end - to - end repeater visible earth coverage area.

[0052] Fig.46 It is a diagram of an example of the end - to - end repeater North America coverage area.

[0053] Fig.47A and Fig.47B are block diagrams of an exemplary forward signal path and a return signal path respectively, each having selective activation of multiple user link antenna subsystems.

[0054] Fig.48A and Fig.48B It is a diagram of an example of an end - to - end repeater coverage area including multiple selectively activated user coverage areas.

[0055] Fig.49 It 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] In this document, reference numerals (e.g., 100) are used to refer to aspects of the drawings. Similar or identical aspects are usually shown using the same numbers. A group of similar or identical elements may be uniformly referred to by a single reference numeral (e.g., 200), while individual elements of the group may be referred to by reference numerals with additional letters (e.g., 200a, 200b).

[0057] The drawings are not intended to be exhaustive or to limit the claimed invention to the exact forms disclosed. The methods and devices disclosed herein may be practiced with modifications and variations, and the invention is limited only by the claims and their equivalents. Detailed Description

[0058] The specific implementation is organized as follows. First, an introduction to a wireless relay communication system using satellite communication and beamforming is described. Second, end-to-end beamforming is described generally and at a system level using satellite end-to-end beamforming as an example, but the application of end-to-end beamforming is not limited to satellite communication. Third, the operations of forward data and return data are described in the case of end-to-end beamforming. Fourth, the end-to-end repeater and its antenna are described using a communication satellite as an example. Next, the terrestrial network for forming end-to-end beams is described, including related aspects such as delay equalization, feeder link impairment cancellation, and beam weight calculation. Finally, end-to-end beamforming with different user link coverage areas and feeder link coverage areas, as well as systems with multiple coverage areas, is described.

[0059] Satellite Communications

[0060] Figure 1FIG. is an illustration of an example of a hub and spoke satellite communication system 100. The satellite serves as an example of a wireless repeater. Although many examples are described throughout the disclosure in terms of a satellite or a satellite communication system, such examples are not intended to be limited to satellites; any other suitable wireless repeater may be used and operate in a similar manner. System 100 includes a ground-based earth station 101, a communication satellite 103, and an earth-based source such as a user terminal 105. The satellite coverage area may be broadly defined as the area from which and / or to which an earth-based source or earth-based receiver such as a ground-based earth station or a user terminal can communicate via the satellite. In some systems, the coverage area of each link (e.g., the forward uplink coverage area, the forward downlink coverage area, the return uplink coverage area, and the return downlink coverage area) may be different. The forward uplink coverage area and the return uplink coverage area are collectively referred to as the uplink satellite coverage area. Similarly, the forward downlink coverage area and the return downlink coverage area are collectively referred to as the downlink satellite coverage area. Although the satellite coverage area is only valid for a satellite in service (e.g., in a service orbit), the satellite may be considered to have (e.g., may be designed to have) a satellite antenna pattern that is independent of the relative position of the satellite with respect to the earth; that is, the satellite antenna pattern is a distribution pattern of the energy transmitted (or transmitted from or received by the satellite antenna). When the satellite is in the service orbit, the satellite antenna pattern illuminates (transmits to or receives from) a specific satellite coverage area. The satellite coverage area is defined by the satellite antenna pattern, the orbital position and orbital attitude for which the satellite is designed, and a given antenna gain threshold. Generally speaking, the intersection of the antenna pattern with a specific physical area of interest (e.g., an area above or near the earth's surface) at a specific effective antenna gain with respect to the peak gain (e.g., 3 dB, 4 dB, 6 dB, 10 dB) defines the coverage area of the antenna. The antenna may be designed to provide a specific antenna pattern (and / or coverage area) and such antenna pattern may be determined computationally (e.g., by analysis or simulation) and / or measured experimentally (e.g., within an antenna test range or in actual use).

[0061] Although only one user terminal 105 is shown in the figure for simplicity, there are typically many user terminals 105 in the system. The satellite communication system 100 operates as a point-to-multipoint system. That is, the earth station 101 within the satellite coverage area can send information to and receive information from any user terminal 105 within the satellite coverage area. However, the user terminal 105 communicates only with the earth station 101. The earth station 101 receives forward data from the communication network 107, modulates the data using the feeder link modem 109, and transmits the data to the satellite 103 on the forward feeder uplink 111. The satellite 103 relays the forward data to the user terminal 105 on the forward user downlink (sometimes referred to as the forward service downlink) 113. In some cases, the forward direction communication from the earth station 101 is intended for several user terminals 105 (e.g., the information is multicast to the user terminals 105). In some cases, the forward communication from the earth station 101 is intended for only one user terminal 105 (e.g., unicast to a specific user terminal 105). The user terminal 105 transmits return data to the satellite 103 on the return user uplink (sometimes referred to as the return service uplink) 115. The satellite 103 relays the return data to the earth station 101 on the return feeder downlink 117. The feeder link modem 109 demodulates the return data that is relayed to the communication network 107. This return link function is typically shared by multiple user terminals 105.

[0062] Figure 2FIG. is an example of a configuration showing the beam coverage areas of satellites serving the continental United States. Seventy beams are shown in the exemplary configuration. The first beam 201 covers approximately two-thirds of the state of Washington. The second beam 203 adjacent to the first beam 201 covers the area immediately east of the first beam 201. The third beam 205 generally covers the state of Oregon south of the first beam 201. The fourth beam 207 covers the area generally southeast of the first beam 201. Generally, there is a certain degree of overlap between adjacent beams. In some cases, a multi-color multiplexing pattern (e.g., two-color, three-color, or four-color multiplexing pattern) is used. In an example of a four-color pattern, the beams 201, 203, 205, 207 are each assigned a unique combination of frequency (e.g., one or more frequency ranges or one or more channels) and / or antenna polarization (e.g., in some cases, the antenna can be configured to transmit signals using right-hand circular polarization (RHCP) or left-hand circular polarization (LHCP); other polarization techniques are also available). Thus, there may be relatively little interference between signals transmitted on different beams 201, 203, 205, 207. Subsequently, these combinations of frequency and antenna polarization can be reused in a repeating non-overlapping "four-color" multiplexing pattern. In some situations, the desired communication capacity can be achieved by using a single color. In some cases, time division between beams and / or other interference mitigation techniques can be used.

[0063] Within certain limits, focusing the beams into smaller areas and thus increasing the number of beams increases the data capacity of the satellite by allowing more frequency reuse opportunities. However, increasing the number of beams may increase the complexity of the system and, in many cases, the complexity of the satellite.

[0064] The complexity of satellite design generally results in larger size, greater weight, and greater power consumption. Launching a satellite into orbit is expensive. The cost of launching a satellite depends in part on the weight and size of the satellite. In addition, there are absolute limits on the weight and size of the satellite if currently available rocket technology is to be used to launch it. This results in a trade-off between the features that can be designed for the satellite. In addition, the amount of power that can be provided to the satellite components is limited. Thus, weight, size, and power consumption are parameters to be considered in satellite design.

[0065] Throughout the disclosure, the term receiving antenna element refers to a physical transducer that converts an electromagnetic signal into an electrical signal, and the term transmitting antenna element refers to a physical transducer that emits an electromagnetic signal when excited by an electrical signal. The antenna element can include a horn antenna, a septum-polarized horn antenna (e.g., which can be used as two combined elements with different polarizations), a multi-port multi-band horn antenna (e.g., dual-band 20 GHz / 30 GHz with dual polarization LHCP / RHCP), a cavity-backed slot antenna, an inverted-F antenna, a slotted waveguide antenna, a Vivaldi antenna, a helical antenna, a loop antenna, a patch antenna, or any other configuration of a combination of antenna elements or interconnecting sub-elements. The antenna element has a corresponding antenna pattern that describes the way in which the antenna gain varies with direction (or angle). The antenna element also has a coverage area corresponding to a region (e.g., a portion of the Earth's surface) or volume (e.g., a portion of the Earth's surface plus the space above the surface) where the antenna element provides a desired gain level (e.g., within 3 dB, 6 dB, 10 dB, or other value relative to the peak gain of the antenna element). The coverage area of the antenna element can be modified by various structures such as reflectors, frequency selective surfaces, lenses, radomes, etc. Some satellites, including the satellites described herein, can have a number of transponders, each of which is capable of independently receiving and transmitting signals. Each transponder is coupled to an antenna element (e.g., a receiving element and a transmitting element) to form a receive / transmit signal path that has a different radiation pattern (antenna pattern) from other receive / transmit signal paths, thereby generating a unique beam that can be assigned to different beam coverage areas. An input and / or output multiplexer is typically used to share a single receive / transmit signal path across multiple beams. In both cases, the number of synchronous beams that can be formed is typically limited by the number of receive / transmit signal paths deployed on the satellite.

[0066] Beamforming

[0067] Beamforming of a communication link can be performed by adjusting the signal phase (or time delay) and sometimes the signal amplitude of signals transmitted and / or received by multiple elements of one or more antenna arrays having overlapping coverage regions. In some cases, some or all of the antenna elements are arranged to receive and / or transmit an array of constituent elements that cooperate to achieve end-to-end beamforming, as described below. For transmission (from the transmit elements of one or more antenna arrays), the relative phase and sometimes the amplitude of the transmitted signal are adjusted such that the energy transmitted by the transmit antenna elements will add constructively at the desired location. This phase / amplitude adjustment is commonly referred to as "applying beam weights" to the transmitted signal. For reception (by the receive elements of one or more antenna arrays), the relative phase and sometimes the amplitude of the received signal are adjusted (i.e., the same or different beam weights are applied) such that the energy received by the receive antenna elements from the desired location will add constructively at those receive antenna elements. In some cases, a beamformer calculates the desired antenna element beam weights. In some cases, the term beamforming may refer to the application of beam weights. An adaptive beamformer includes the function of dynamically calculating beam weights. Calculating beam weights may require directly or indirectly discovering communication channel characteristics. The processes of beam weight calculation and beam weight application can be performed in the same or different system elements.

[0068] Antenna beams can be steered, selectively formed, and / or otherwise reconfigured by applying different beam weights. For example, the number of effective beams, the coverage area of the beams, the size of the beams, the relative gain of the beams, and other parameters can vary over time. In certain situations, such versatility is desirable. Beamforming antennas can typically form relatively narrow beams. Narrow beams can allow signals transmitted on one beam to be distinguished from signals transmitted on other beams (e.g., to avoid interference). Thus, narrow beams can allow for greater frequency and polarization reuse when forming larger beams. For example, a narrowly formed beam can serve two non-contiguous coverage regions that do not overlap. Each beam can use both right-hand and left-hand polarizations. More reuse can increase the amount of data transmitted and / or received.

[0069] 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 the satellite 302 has the on-board multi-feed per beam (MFPB) beamforming capability. In this example, the beam weights are calculated at a ground-based computing center and then transmitted to the satellite or pre-stored in the satellite for application (not shown). In Figure 3The forward link is shown, although this architecture can be used for the forward link, the return link, or both the forward and return links. Beamforming can be used on the user link, the feeder link, or both. The forward link shown is the signal path from one of a plurality of gateways (GWs) 304 to one or more of a plurality of user terminals within one or more point beam coverage areas 306. The satellite 302 has 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 both the feeder link 308 and the user link 310. Each of the L elements of the receive array 307 receives K signals from the K GWs 304. For each of the K feeder link beams to be generated (e.g., one beam for each GW 304), different beam weights are applied (e.g., phase / amplitude adjusted) 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 the K beams to be formed using the receive antenna array 307 having L receive antenna elements, K different beam weight vectors of length L are applied to the L signals received by the L receive antenna array elements. The receive beamformer 313 within the satellite 302 adjusts the phase / amplitude of the signals received by the L receive antenna array elements to produce 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 the signal received from each transmit GW 304.

[0070] The D / C and gain module 311 downconverts each of the K receive beam signals and appropriately adjusts the gain. The K signals are output from the D / C and gain module 311 and coupled to the transmit beamformer 315. The transmit beamformer 315 applies a vector of L weights to each of the K signals for a total of L×K transmit beam weights to form K beams on the user downlink 310.

[0071] 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 beams. Such processing power increases the complexity of the satellite. In some cases, the satellite can operate using ground-based beamforming (GBBF) to reduce the complexity of the satellite while still providing the advantages of electronically forming narrow beams.

[0072] Figure 4FIG. 0 is an illustration of an example of a satellite communication system 400 with a forward GBBF. The GBBF is performed on the forward user link 317 via an L-element array similar to the above. The phase / amplitude of the signal transmitted on the user link 317 is weighted such that a beam is formed. The feeder link 319 uses a single-feed-per-beam (SFPB) scheme, where each receive and transmit antenna element of the antenna 324 is dedicated to one feeder link beam.

[0073] Before transmission from one or more GWs 304, for each of the K forward feeder link beams, the transmit beamformer 321 applies the corresponding one of the K beam weight vectors, each of length L, to each of the K signals to be transmitted. The K vectors of L weights are determined and applied to the signals such that K forward beams can be formed on the ground for the forward user downlink 317. On the feeder uplink 319, each of the L different signals is multiplexed by a multiplexer 323 (etc.) into a frequency-division multiplexed (FDM) signal. Each FDM signal is transmitted by the GW 304 on the feeder link 319 to one of the receive antenna elements in the antenna 324. The FDM receiver 325 on the satellite 327 receives the signal from the antenna 324. The analog-to-digital converter (A / D) 326 converts the received analog signal into a digital signal. The digital channel processor 328 demultiplexes the FDM signal, and each of the FDM signals is appropriately weighted by the beamformer 321 for transmission through one of the L elements of the transmit antenna element array of the transmit antenna 329. The digital channel processor 328 outputs these signals to the digital-to-analog converter (D / A) 331 to be converted back to analog form. The analog output of the D / A 331 is up-converted and amplified by the up-converter (U / C) and gain stage 330 and transmitted by the associated element of the transmit antenna 329. For the return beam, the opposite complementary process occurs. Note that in this type of system, the FDM feeder link requires up to L times more bandwidth than the user beam, which makes systems with a wide data bandwidth or a large number of elements L impractical.

[0074] End-to-end beamforming system

[0075] The end-to-end beamforming system described herein forms an end-to-end beam through an end-to-end repeater. The end-to-end beamforming system can connect a user terminal to a data source / data sink. Contrary to the above-described beamforming system, in the end-to-end beamforming system, the beam weights are calculated at a central processing system (CPS) and the end-to-end beam weights are applied within the terrestrial network (rather than at the satellite). The signals within the end-to-end beam are transmitted and received at an array of access nodes (ANs) that can be satellite access nodes (SANs). As described above, any suitable type of end-to-end repeater can be used in the end-to-end beamforming system, and different types of ANs can be used to communicate with different types of end-to-end repeaters. The term "central" means that the CPS is accessible to the ANs involved in signal transmission and / or reception and does not refer to a specific geographical location where the CPS resides. The beamformer within the CPS calculates a set of end-to-end beam weights that take into account: (1) the wireless signal uplink path all the way to the end-to-end repeater; (2) the receive / transmit signal path through the end-to-end repeater; and (3) the wireless signal downlink path from the end-to-end repeater downward. The beam weights can be represented mathematically as a matrix. As described above, the OBBF and GBBF satellite systems have a beam weight vector dimension set by the number of antenna elements on the satellite. In contrast, the end-to-end beam weight vector has a dimension set by the number of ANs rather than the number of elements on the end-to-end repeater. Generally speaking, the number of ANs is different from the number of antenna elements on the end-to-end repeater. In addition, the formed end-to-end beam does not terminate at the transmit or receive antenna elements of the end-to-end repeater. Instead, the formed end-to-end beam is effectively relayed because the end-to-end beam has an uplink signal path, a relay signal path (via a satellite or other suitable end-to-end repeater), and a downlink signal path.

[0076] Since end-to-end beamforming takes into account both the user link and the feed link (as well as the end-to-end repeater), only a single set of beam weights is needed to form the desired end-to-end user beam (e.g., a forward user beam or a return user beam) in a specific direction. Thus, an end-to-end forward beam weight set (hereinafter simply referred to as forward beam weights) causes the combination of signals transmitted from the AN, through the forward uplink, through the end-to-end repeater, and through the forward downlink to form an end-to-end forward user beam (hereinafter referred to as the forward user beam). Conversely, the signals transmitted from the return user, through the return uplink, through the end-to-end repeater, and through the return downlink have end-to-end return beam weights (hereinafter referred to as return beam weights), and these end-to-end return beam weights are applied to form an end-to-end return user beam (hereinafter referred to as the return user beam). Under some conditions, it may be very difficult or impossible to distinguish the characteristics of the uplink and the downlink. Thus, the formed feed link beam, the formed user beam directivity, and the individual uplink and downlink carrier-to-interference ratios (C / I) may no longer have their traditional roles in system design, while the concepts of uplink and downlink signal-to-noise ratios (Es / No) and end-to-end C / I may still be relevant.

[0077] Figure 5 is an illustration of an exemplary end-to-end beamforming system 500. System 500 includes: a ground segment 502; an end-to-end repeater 503; and a plurality of user terminals 517. The ground segment 502 includes M ANs 515 that are geographically distributed within the AN coverage area. The ANs 515 and the user terminals 517 may be collectively referred to as earth receivers, earth transmitters, or earth transceivers depending on the particular function being discussed, since they are located above 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 in air vehicles, water vehicles, or mounted on land 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 the CPS 505 within the ground segment 502 via a distribution network 518. The CPS 505 is connected to a data source (not shown), such as the Internet, a video headend, or other such entities.

[0078] The user terminals 517 may be grouped with other nearby user terminals 517 (e.g., as shown by user terminals 517a and 517b). In some cases, such groups of user terminals 517 are served by the same user beam and thus reside within the same geographical forward and / or return user beam coverage area 519. If a user terminal 517 is within the coverage area served by a user beam, the user terminal 517 is within that user beam. Although only one such user beam coverage area 519 is shown in Figure 5is shown as having more than one user terminal 517, but in some cases, the user beam coverage area 519 can have any suitable number of user terminals 517. Additionally, Figure 5 the depiction in does not purport to indicate the relative sizes of the different user beam coverage areas 519. That is, the user beam coverage areas 519 can all have approximately the same size. Alternatively, the user beam coverage areas 519 can have different sizes, where some user beam coverage areas 519 are much larger than others. In some cases, the number of ANs 515 is not equal to the number of user beam coverage areas 519.

[0079] The end-to-end repeater 503 wirelessly relays signals between the user terminals 517 and multiple network access nodes (such as, Figure 5 the AN 515 shown in ). The end-to-end repeater 503 has multiple signal paths. For example, each signal path can include at least one receiving antenna element, at least one transmitting antenna element, and at least one transponder (as discussed in detail below). In some cases, the multiple receiving antenna elements are arranged to receive signals reflected by a receiving reflector to form a receiving antenna array. In some cases, the multiple transmitting antenna elements are arranged to transmit signals and thus form a transmitting antenna array.

[0080] In some cases, the end-to-end repeater 503 is disposed on a satellite. In other cases, the end-to-end repeater 503 is disposed in an air vehicle, a blimp, a tower, an underwater structure, or any other suitable structure or vehicle in which the end-to-end repeater 503 can reside. In some cases, the system uses different frequency ranges (within the same or different frequency bands) for the uplink and the downlink. In some cases, the feeder link and the user link are in different frequency ranges. In some cases, the end-to-end repeater 503 acts as a passive or active reflector.

[0081] As described herein, various features of the end-to-end repeater 503 enable end-to-end beamforming. One feature is that the end-to-end repeater 503 includes a plurality of transponders that, in the case of an end-to-end beamforming system, cause multipaths between the AN 515 and the user terminal 517. Another feature is that the antennas (e.g., one or more antenna subsystems) of the end-to-end repeater 503 contribute to end-to-end beamforming such that when appropriately beam-weighted signals are transmitted over the multipaths caused by the end-to-end repeater 503, forward and / or return user beams are formed. For example, during forward communication, each of the plurality of transponders receives a corresponding superposition synthesis (referred to herein as a synthesized input forward signal) of the (beam-weighted) forward uplink signals 521 from a plurality (e.g., all) of the ANs 515, and the transponder outputs a corresponding synthesized signal (referred to herein as a forward downlink signal). Each of the forward downlink signals can be a unique synthesis of the beam-weighted forward uplink signals 521 that, when transmitted by the transmit antenna elements of the end-to-end repeater 503, are superimposed to form a user beam 519 at a desired location (e.g., in this case, a recovery location within the forward user beam). Return end-to-end beamforming is implemented similarly. Thus, the end-to-end repeater 503 can cause multiple superpositions to occur, thereby enabling end-to-end beamforming over the induced multipath channel.

[0082] Return data

[0083] Figure 6 It is a diagram of an exemplary model of the signal path of a signal that carries return data on the end-to-end return link. The return data is data that flows from the user terminal 517 to the AN 515. Figure 6The signals in [the figure] flow from right to left. These signals originate from the user terminal 517. The user terminal 517 transmits a return uplink signal 525 (which has a return user data stream) to the end-to-end repeater 503. The return uplink signals 525 from the user terminals 517 in the K user beam coverage areas 519 are received by an array of L receive / transmit signal paths 1702. In some cases, the uplink coverage area of the end-to-end repeater 503 is defined by the set of points from which all L receive antenna elements 406 can receive signals. In other cases, the repeater coverage area is defined by the set of points from which a subset of the L receive antenna elements 406 (e.g., a desired number greater than one but less than all) can receive signals. Similarly, in some cases, the downlink coverage area is defined by the set of points to which all L transmit antenna elements 409 can reliably transmit signals. In other cases, the downlink coverage area of the end-to-end repeater 503 is defined by the set of points to which a subset of the transmit antenna elements 409 can reliably transmit signals. In some cases, the size of the subset of the receive antenna elements 406 or the transmit antenna elements 409 is at least four. In other cases, the size of the subset is 6, 10, 20, 100, or any other number that provides the desired system performance.

[0084] For simplicity, some examples are described and / or illustrated as all L receive antenna elements 406 receiving signals from all points in the uplink coverage area and / or all L transmit antenna elements 409 transmitting signals to all points in the downlink coverage area. Such descriptions are 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., receives the return uplink signal 525 from the user terminal 517 or the forward uplink signal 521 from the AN 515) such that the subset of the receive antenna elements 406 receives the uplink signal at a signal level close to the peak received signal level of the uplink signal (e.g., not significantly less than the signal level corresponding to the uplink signal with the highest signal level); the other receive antenna elements among the L receive antenna elements 406 that are not in the subset receive the uplink signal at a significantly lower level (e.g., far below the peak received signal level of the uplink signal). In some cases, the uplink signals received by each receive antenna element in the subset are at a signal level within 10 dB of the maximum signal level received by any receive antenna element 406. In some cases, the subset includes at least 10% of the receive antenna elements 406. In some cases, the subset includes at least 10 receive antenna elements 406.

[0085] Similarly, on the transmission side, a subset of the L transmit antenna elements 409 transmits a downlink signal to an Earth receiver (e.g., a return downlink signal 527 to the AN 515 or a forward downlink signal 522 to the user terminal 517), such that the subset of transmit antenna elements 409 transmits the downlink signal to the receiver at a received signal level that is close to the peak transmission signal level of the downlink signal (e.g., not significantly less than the signal level corresponding to the downlink signal having the highest received signal level); the other transmit antenna elements of the L transmit antenna elements 409 that are not in the subset transmit the downlink signal such that the downlink signal is received at a significantly lower level (e.g., far 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 element 409. In other cases, the signal level is within 6 dB of the signal level corresponding to the peak gain of the transmit antenna element 409. In other cases, the signal level is within 10 dB of the signal level corresponding to the peak gain of the transmit antenna element 409.

[0086] 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 pattern of each receive antenna element. However, in some cases, there may be multiple points within the end-to-end repeater coverage area where user terminals are located and not all receive antenna elements can receive signals from them. In some such cases, there may be a significant amount of receive antenna elements that do not (or cannot) receive signals from user terminals located within the end-to-end repeater coverage area. However, as described herein, multipath induced by the end-to-end repeater 503 can rely on at least two receive elements to receive signals.

[0087] As Figure 6As shown and discussed in more detail below, in some cases, the receive / transmit antenna path 1702 includes a receive antenna element 406, a transponder 410, and a transmit antenna element 409. In such cases, the return uplink signal 525 is received by each of the plurality of transponders 410 via a respective receive antenna element 406. The output of each receive / transmit signal path 1702 is a respective combined return downlink signal 527 corresponding to the received return uplink signal. The return downlink signal is generated by the receive / transmit signal path 1702. The return downlink signal 527 is transmitted to an array of M ANs 515. In some cases, the ANs 515 are placed at geographically distributed locations (e.g., receive or recovery locations) throughout the end-to-end repeater 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 ways for a signal to travel from a user terminal 517 located within the user beam coverage area 519 to a particular AN 515. This results in L paths between the user terminal 517 and the AN 515. The L paths between a single user terminal 517 and a single AN 515 are collectively referred to as the end-to-end return multipath channel 1908 (see Figure 8 ). Thus, receiving the return uplink signal 525 through L transponders 410 from a transmission location within the user beam coverage area 519 results in L return downlink signals 527, each transmitted from one of the transponders 410 (i.e., through L juxtaposed communication paths). Each end-to-end return multipath channel 1908 is associated with a vector in the uplink radiation matrix A r , a vector in the payload matrix E, and a vector in the downlink radiation matrix C t . Note that due to the antenna element coverage pattern, in some cases, some of the L paths may have relatively less energy (e.g., 6 dB, 10 dB, 20 dB, 30 dB, or any other suitable power ratio less than the other paths). The superposition 1706 of the return downlink 527 signals is received at each AN 515 (e.g., at M geographically distributed receive or recovery locations). Each return downlink signal 527 includes a superposition of a plurality of transmitted return downlink signals 527, resulting in a respective combined return signal. The respective combined return signal is coupled to a return beamformer 531 (see Figure 5 and Fig.29 ).

[0088] Figure 7An exemplary end - to - end return link 523 from a user terminal 517 located within a user beam coverage area 519 to an AN 515 is shown. The return uplink signal 525 transmitted from the user terminal 517 is received by an array of L receive antenna elements 406 on the end - to - end repeater 503 (e.g., or by a subset of the L receive antenna elements 406).

[0089] Ar is an L×K return uplink radiation matrix. The values of the return uplink radiation matrix model the signal paths from a reference position in the user beam coverage area 519 to the receive antenna elements 406 of the end - to - end repeater. For example, Ar L,1 is the value of an element of the return uplink radiation matrix (i.e., the amplitude and phase of the path) for the path from the reference position in the first user beam coverage area 519 to the Lth receive antenna element. In some cases, all values in the return uplink radiation matrix Ar may be non - zero (e.g., there are significant signal paths from the reference position to each receive antenna element of the receive antenna array).

[0090] E (dimension L×L) is the payload matrix and provides a model (amplitude and phase) of the paths from the receive antenna elements 406 to the transmit antenna elements 409. As used herein, the “payload” of the end - to - end repeater 503 generally includes a set of components of the end - to - end repeater 503 that affect and / or are affected by signal communication when receiving signal communication by the end - to - end repeater 503, relaying signal communication through the end - to - end repeater 503, and transmitting signal communication from the end - to - end repeater 503. For example, the end - to - end repeater payload can include antenna elements, reflectors, transponders, etc.; but the end - to - end repeater can also include batteries, solar cells, sensors, and / or other components not considered part of the payload herein (because they do not affect the signal during normal operation). Treating the set of components as the payload enables the overall effect of the end - to - end repeater to be mathematically modeled as a single payload matrix E). The main paths from each receive antenna element 406 to each corresponding transmit antenna element 409 are modeled by the values located on the diagonal of the payload matrix E. Assuming no crosstalk between the receive / transmit signal paths, the off - diagonal values of the payload matrix are zero. In some cases, the crosstalk may not be zero. Isolating the signal paths from each other will minimize crosstalk. In some cases, since the crosstalk can be neglected, the payload matrix E can be estimated by a diagonal matrix. In some cases, the off - diagonal values (or any other appropriate values) of the payload matrix can be considered zero, even if there are some signal effects corresponding to those values, to reduce mathematical complexity and / or for other reasons.

[0091] Ct returns the downlink radiation matrix for M×L. The value of the returned downlink radiation matrix models the signal path from the transmit antenna element 409 to the AN 515. For example, Ct 3,2 is the value of the returned downlink radiation matrix (e.g., the gain and phase of the path), and the path is from the second transmit antenna element 409 b to the third AN 515 c . In some cases, all values of the downlink radiation matrix Ct can be non-zero. In some cases, some values of the downlink radiation matrix Ct are substantially zero (e.g., the antenna pattern established by the corresponding transmit antenna element 409 of the transmit antenna array causes the transmit antenna element 409 not to transmit useful signals to some ANs 515).

[0092] From Figure 7 it can be seen that the end-to-end return multipath channel from the user terminal 517 in the specific user beam coverage area 519 to the specific AN 515 is the sum of L different paths. The end-to-end return multipath channel has multipaths caused by L unique paths passing through the transponder 410 in the end-to-end repeater. Like many multipath channels, the amplitudes and phases of the paths can be advantageously (constructively) summed to produce a large end-to-end channel gain, or disadvantageously (destructively) summed to produce a low end-to-end channel gain. When the number L of different paths between the user terminal and the AN is large, the end-to-end channel gain can have a Rayleigh amplitude distribution. With this distribution, it is usually seen that some end-to-end channel gains from a specific user terminal 517 to a specific AN 515 are 20 dB or more lower than the average channel gain level from the user terminal 517 to the AN 515. This end-to-end beamforming system intentionally creates a multipath environment for the end-to-end path from any user terminal to any AN.

[0093] Figure 8is a simplified illustration of an exemplary model of all end-to-end return multipath channels from a user beam coverage area 519 to an AN 515. There are M×K such end-to-end return multipath channels in the end-to-end return link (i.e., M end-to-end return multipath channels from each of the K user beam coverage areas 519). Channel 1908 connects a user terminal in a user beam coverage area 519 to an AN 515 via L different receive / transmit signal paths 1702, each path passing through a different one of the L receive / transmit signal paths (and associated transponders) of the repeater. Although this effect is referred to herein as "multipath", this multipath is different from conventional multipath (e.g., multipath in mobile radio or multiple-input multiple-output (MIMO) systems) because the multipath herein is intentionally induced by the L receive / transmit signal paths (and is affected by these signal paths as described herein). Each of the M×K end-to-end return multipath channels originating from a user terminal 517 within a particular user beam coverage area 519 can be modeled by an end-to-end return multipath channel. Each such end-to-end return multipath channel is from a reference (or recovery) position within the user beam coverage area 519 to one of the ANs 515.

[0094] Each of the M×K end-to-end return multipath channels 1908 can be individually modeled to compute the corresponding elements of the M×K return channel matrix Hret. The return channel matrix Hret has K vectors, each having a dimension equal to M, such that each vector models the end-to-end return channel gain for multipath communication between a reference position in one of the corresponding K user beam coverage areas and the M ANs 515. Each end-to-end return multipath channel couples one of the M ANs 515 to a reference position within one of the K return user beams via L transponders 410 (see Figure 7 ). In some cases, only a subset of the L transponders 410 on the end-to-end repeater 503 is used to generate the end-to-end return multipath channels (e.g., only a subset is considered to be in the signal path by contributing significant energy to the end-to-end return multipath channels). In some cases, the number K of user beams is greater than the number L of transponders in the signal path of the end-to-end return multipath channels. Additionally, 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 return multipath channels 1908. In one example, the element Hret of the return channel matrix Hret 4,2 is associated with the channel from a reference position in the second user beam coverage area 1903 to the fourth AN 1901. The matrix Hret models the end-to-end channel as the matrix product Ct×E×Ar (see Figure 6)。Each element in Hret models the end - to - end gain of an end - to - end return multi - path channel 1908. Due to the multi - path nature of the channel, the channel may experience deep fades. The return user beam can be formed by CPS505. CPS505 calculates the return beam weights based on the models of these M×K signal paths of the channel and forms the return user beam by applying the return beam weights to multiple synthesized return signals, where each weight is calculated for each end - to - end return multi - path channel that couples a user terminal 517 in a user beam coverage area to one of the multiple ANs 515. In some cases, the return beam weights are calculated before the synthesized return signals are received. There is an end - to - end return link from each of the K user beam coverage areas 519 to the M ANs 515. The weighting (i.e., complex relative phase / amplitude) of each signal received by the M ANs 515 allows the beamforming capabilities of CPS 505 within the ground segment 502 to combine these signals to form the return user beam. The calculation of the beam weight matrix is used to determine how to weight each end - to - end return multi - path channel 1908 to form multiple return user beams, as described in more detail below. The user beam is not formed by directly adjusting the relative phase and amplitude of the signal transmitted by one end - to - end relay antenna element relative to the phase and amplitude of the signals transmitted by other end - to - end relay antenna elements. Instead, the user beam is formed by applying weights associated with the M×K channel matrix to the M AN signals. It is the multiple ANs that provide receive path diversity (single reflector (user terminal) to multiple receivers (ANs)) to enable successful transmission of information from any user terminal in the presence of an intentionally induced multi - path channel.

[0095] Forward Data

[0096] Fig. 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. The forward data is data flowing from the ANs 515 to the user terminals 517. The signals in this figure flow from right to left. The signals originate from the M ANs 515 located within the coverage area of the end - to - end repeater 503. There are K user beam coverage areas 519. The signals from each AN 515 are relayed by L receive / transmit signal paths 2001.

[0097] The receive / transmit signal paths 2001 transmit the relayed signals to the user terminals 517 in the user beam coverage areas 519. Thus, there may be L different ways for a signal to reach a user terminal 517 located in a user beam coverage area 519 from a particular AN 515. This creates L paths between each AN 515 and each user terminal 517. Note that due to the antenna element coverage pattern, some of the L paths may have less energy than others.

[0098] Fig.10 An exemplary end-to-end forward link 501 is shown that couples multiple access nodes at geographically distributed locations to a user terminal 517 in a user beam (e.g., at a recovery location within a user beam coverage area 519) via an end-to-end repeater 503. In some cases, the forward data signal is received at the beamformer before the forward uplink signal is generated. Multiple forward uplink signals are generated at the beamformer and transmitted to multiple ANs 515. For example, each AN 515 receives a unique (beam-weighted) forward uplink signal generated according to the beam weights corresponding to that AN 515. Each AN 515 has an output for transmitting the forward uplink signal via one of M uplinks. Each forward uplink signal includes a forward data signal associated with the forward user beam. The forward data signal is "associated" with the forward user beam because it is intended to be received by the user terminal 517 served by the user beam. In some cases, the forward data signal includes two or more user data streams. The user data streams can be multiplexed together, such as by time division or frequency division multiplexing. In some cases, each user data stream is for transmission to one or more of multiple user terminals within the same forward user beam.

[0099] As discussed in more detail below, each forward uplink signal is transmitted by its corresponding transmitting AN 515 in a time-synchronized manner. The forward uplink signals 521 transmitted from the AN 515 are received by multiple transponders 410 on the end-to-end repeater 503 via the receiving antenna elements 406 on the end-to-end repeater 503. The superposition 550 of the forward uplink signals 521 received from geographically distributed locations produces a composite input forward signal 545. Each transponder 410 receives the composite input forward signal 545 simultaneously. However, due to differences in the positions of the receiving antenna elements 406 associated with each transponder 401, each transponder 410 will receive signals with slightly different timings.

[0100] Cr is the L×M forward uplink radiation matrix. The values ​​of the forward uplink radiation matrix model the signal path (amplitude and phase) from AN 515 to the receiving antenna element 406. E is an L×L payload matrix and provides a model of the transponder signal path from the receiving antenna element 406 to the transmitting antenna element 409. The direct path gain from each receiving antenna element 406 through a corresponding one of the multiple transponders to each corresponding transmitting antenna element 409 is modeled by the diagonal values ​​of the payload matrix. As described above with respect to the return link, assuming no crosstalk between antenna elements, the non-diagonal elements of the payload matrix are zero. In some cases, the crosstalk may not be zero. Isolating the signal paths from each other will minimize the crosstalk. In this example, each transponder 410 couples a corresponding one of the receiving antenna elements 406 to a corresponding one of the transmitting antenna elements 409. Therefore, the forward downlink signal 522 output from each transponder 410 is transmitted by each of the multiple transponders 410 via the transmitting antenna element 409 (see Fig. 9 ), so that the forward downlink signal 522 forms a forward user beam (by constructively and destructively adding to form a beam in the desired geographic recovery location). In some cases, multiple user beams are formed, each corresponding to a geographic user beam coverage area 519 serving a respective set of user terminals 517 within the user beam coverage area 519. At the forward downlink radiation matrix 11 The values ​​are given in Table 1 for the transmission from the first transmitting antenna element 409a (see Fig.10 ) to a reference (or recovery) position in the first user beam coverage area 519. As noted with respect to the return link, the end-to-end beamforming system intentionally induces a multipath environment for the end-to-end path from any AN 515 to any user terminal 517. In some cases, a subset of the transmit antenna elements 409 transmits a forward downlink signal 522 having significant energy to the user terminal 517. The user terminal 517 (or more generally, a reference or recovery position in the user beam coverage area 519 for reception and / or recovery) receives the plurality of forward downlink signals 522 and recovers at least a portion of the forward data signal from the received plurality of forward downlink signals 522. The transmitted forward downlink signal 522 can be received by the user terminal 517 at a signal level within 10 dB of the maximum signal level of any other signal transmitted by the transmit antenna elements 409 in the subset. In some cases, the subset of transmit antenna elements includes at least 10% of the plurality of transmit antenna elements present in the end-to-end repeater 503. In some cases, the subset of transmit antenna elements includes at least 10 transmit antenna elements, regardless of how many transmit antenna elements 409 are present in the end-to-end repeater 503. In one case, receiving the multiple forward downlink signals includes receiving a superposition 551 of the multiple forward downlink signals.

[0101] Fig.11 is a simplified illustration of a model of all end - to - end forward multipath channels 2208 from M ANs 515 to the K user beam coverage areas 519. As Fig.11 shown, there are end - to - end forward multipath channels 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 multipaths caused by L unique paths from the AN 515 through multiple transponders to the user beam coverage area 519. Thus, the K×M multipath channels 2208 can be individually modeled, and the model of each multipath channel is used as an element of the K×M forward channel matrix Hfwd. The forward channel matrix Hfwd has M vectors, each vector having a dimension equal to K, such that each vector models the end - to - end forward gain of the multipath communication between the corresponding one of the M ANs 515 and the reference (or recovery) position in the K forward user beam coverage areas. Each end - to - end forward multipath channel couples one of the M ANs 515 to a user terminal 517 served by one of the K forward user beams via L transponders 410 (see Fig.10 ). In some cases, only a subset of the L transponders 410 on the end - to - end repeater 503 is used to generate the end - to - end forward multipath channels (i.e., in the signal path of the end - to - end forward multipath channels). In some cases, the number K of user beams is greater than the number L of transponders in the signal path of the end - to - end forward multipath channels. Additionally, 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 channels.

[0102] Hfwd can represent the end - to - end forward link as the matrix product At×E×Cr. Each element in Hfwd is the end - to - end forward gain due to the multipath nature of the paths and may be subject to deep fading. Appropriate beam weights can be calculated by the CPS 505 within the ground segment 502 for each of the multiple end - to - end forward multipath channels 2208 to form forward user beams from the set of M ANs 515 to each user beam coverage area 519. The multiple ANs 515 provide transmission path diversity to a single receiver (user terminal) by using multiple transmitters (ANs) so that information can be successfully transmitted to any user terminal 517 in the presence of intentionally induced multipath channels.

[0103] Combined forward and return data

[0104] Fig.12An exemplary end-to-end repeater that supports both forward communication and return communication is shown. In some cases, both the end-to-end forward link 501 and the end-to-end return link 523 can use the same end-to-end relay signal path (e.g., a set of receive antenna elements, transponders, and transmit antenna elements). Some other cases include a forward link transponder and a return link transponder, which may or may not share receive antenna elements and transmit antenna elements. In some cases, the system 1200 has multiple ANs and user terminals that are located in the same general geographic area 1208 (the general geographic area can be, for example, a specific state, an entire country, a region, an entire visible area, or any other suitable geographic area 1208). A single end-to-end repeater 1202 (set on a satellite or any other suitable end-to-end repeater) receives a forward uplink signal 521 from the AN and transmits a forward downlink signal 522 to the user terminal. At alternate times or alternate frequencies, the end-to-end repeater 1202 also receives a return uplink signal 525 from the user terminal and transmits a return downlink signal 527 to the AN. In some cases, techniques such as time-domain multiplexing, frequency-domain multiplexing, etc. are used to share the end-to-end repeater 1202 between forward data and return data. In some cases, time-domain multiplexing between forward data and return data uses the same frequency range: forward data is transmitted during a time interval that is different (non-overlapping) from the time interval used for transmitting return data. In some cases, in the case of frequency-domain multiplexing, different frequencies are used for forward data and return data, allowing for concurrent, non-interfering transmission of forward data and return data.

[0105] Fig.13 is an illustration where the uplink frequency range is divided into two parts. The lower frequency (left) part of the range is assigned to the forward uplink, and the upper frequency (right) part of the range is assigned to the return uplink. The uplink range can be divided into multiple parts for forward data or return data.

[0106] Fig.14It is an illustration where forward data and return data are time-division multiplexed. A data frame period is shown, where forward data is transmitted during the first time interval of the frame, while return data is transmitted during the last time interval of the frame. The end-to-end repeater receives from one or more access nodes during a first (forward) reception time interval and receives from one or more user terminals during a second (return) reception time interval that does not overlap with the first reception time interval. The end-to-end repeater transmits to one or more user terminals during a first (forward) transmission time interval and transmits to one or more access nodes during a second (return) transmission time interval that does not overlap with the first reception time interval. The data frame can be repeated or can vary dynamically. The frame can be divided into multiple (e.g., non-consecutive) portions for forward data and return data.

[0107] End-to-end beamforming satellite

[0108] In some cases, the end-to-end repeater 503 is implemented on a satellite such that the satellite is used to relay signals from an AN (which can be referred to as a satellite access node (SAN) in such cases) to user terminals and vice versa. In some cases, the satellite is in a geostationary orbit. An exemplary satellite operating as an end-to-end repeater has an array of receiving antenna elements, an array of transmitting antenna elements, and a plurality of transponders that connect the receiving antenna elements to the transmitting antenna elements. These arrays have a large number of 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 on both the transmitting antenna elements and the receiving antenna elements that create the multipath environment described previously. In some cases, the antenna patterns established by the corresponding antenna elements are the same as the antenna patterns (e.g., overlapping component beam antenna patterns) that create the overlapping antenna element coverage areas. For the purposes of this disclosure, the term "same" means that they substantially follow the same power distribution over a given set of points in space, such that the antenna elements serve as reference points for locating points in space. However, it is difficult to be exactly the same. Therefore, patterns with relatively small deviations from one pattern to another are within the scope of "same" patterns. In other cases, the receiving component beam antenna patterns may not be the same and may actually be significantly different. Such antenna patterns may also result in an overlap of the antenna element coverage areas; however, the resulting coverage areas will not be the same.

[0109] Antenna types include, but are not limited to, array-fed reflectors, confocal arrays, direct radiation arrays, and other forms of antenna arrays. Each antenna can be a system that includes additional optical components such as one or more reflectors that assist in receiving and / or transmitting signals. In some cases, the satellite includes components that assist in system timing alignment and beamforming calibration.

[0110] Fig.15FIG. is a diagram of an exemplary satellite 1502 that can be used as an end-to-end repeater 503. In some cases, satellite 1502 has an array-fed reflector transmit antenna 401 and an array-fed reflector receive antenna 402. Receive antenna 402 includes a receive reflector (not shown) and an array of receive antenna elements 406. Receive antenna elements 406 are illuminated by the receive reflector. Transmit antenna 401 includes a transmit reflector (not shown) and an array of transmit antenna elements 409. Transmit antenna elements 409 are arranged to illuminate the transmit reflector. In some cases, the same reflector is used for reception and transmission. In some cases, one port of the antenna element is used for reception and the other port is used for transmission. Some antennas are capable of distinguishing signals with different polarizations. For example, the antenna elements can each include four waveguide ports for right-hand circular polarization (RHCP) reception, left-hand circular polarization (LHCP) reception, RHCP transmission, and LHCP transmission, respectively. In some cases, dual polarization can be used to increase the capacity of the system; in other cases, single polarization can be used to reduce interference (e.g., by using other systems with different polarizations).

[0111] Exemplary satellite 1502 also includes a plurality of transponders 410. Transponders 410 connect the output from one receive antenna element 406 to the input of transmit antenna element 409. In some cases, transponders 410 amplify the received signal. Each receive antenna element outputs a unique receive signal. In some cases, a subset of receive antenna elements 406 receives signals from an earth transmitter, which is a user terminal 517 in the case of a return link signal or an AN 515 in the case of a forward link signal. In some of these cases, for the received signal, the gain of each receive antenna element in the subset is within a relatively small range. In some cases, the range is 3 dB. In other cases, the range is 6 dB. In other cases, the range is 10 dB. Thus, the satellite will receive signals at each of the plurality of receive antenna elements 406 of the satellite, the communication signals originating from an earth transmitter, such that the subset of receive antenna elements 406 receives the communication signals at a signal level that is substantially not less than the signal level corresponding to the peak gain of the receive antenna elements 406.

[0112] In some cases, at least 10 transponders 410 are disposed within the satellite 1502. In another case, at least 100 transponders 410 are disposed within the satellite 1502. In another case, the number of transponders per polarity can be in the range of 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024 or can be a number between or greater than them. In some cases, the transponder 410 includes a low-noise amplifier (LNA) 412, a frequency converter and associated filters 414, and a power amplifier (PA) 420. In some cases where the uplink frequency and the downlink frequency are the same, the transponder does not include a frequency converter. In other cases, multiple receive antenna elements operate at a first frequency. Each receive antenna element 406 is associated with one transponder 410. The receive antenna element 406 is coupled to the input of the LNA 412. Thus, the LNA independently amplifies the unique received signal provided by the receive antenna element associated with the transponder 410. In some cases, the output of the LNA 412 is coupled to the frequency converter 414. The frequency converter 414 converts the amplified signal to a second frequency.

[0113] The output of the transponder is coupled to an associated one of the transmit antenna elements. In these examples, there is a one-to-one relationship between the transponder 410, the associated receive antenna element 406, and the associated transmit antenna element 409 such that the output of each receive antenna element 406 is connected to the input of one and only one transponder, and the output of that transponder is connected to the input of one and only one transmit antenna element.

[0114] Fig.16 is an illustration of an exemplary transponder 410. The transponder 410 can be an example of the transponder of the end-to-end repeater 503 as described above (e.g., Fig.15 of the satellite 1502). In this example, in addition to the low-noise amplifier (LNA) 412, the frequency converter and associated filters 414, and the power amplifier (PA) of the transponder 410, the transponder further includes a phase shifter 418. As Fig.16 shown, the exemplary transponder 410 can also be coupled to a phase shift controller 427. For example, the phase shift controller 427 can be coupled to each of some or all of the transponders of the end-to-end repeater 503 (directly or indirectly) such that the phase shift controller 427 can individually set the phase of each transponder. The phase shifter can, for example, assist in calibration as described below.

[0115] antenna

[0116] To create a multipath environment, the antenna element coverage area can overlap with the antenna element coverage area of at least one other antenna element having the same polarization, frequency, and type (either transmit or receive). In some cases, multiple receive component beam antenna patterns operating at the same receive polarization and receive frequency (e.g., at least a portion of the receive frequencies are common) overlap with each other. For example, in some cases, at least 25% of the receive component beam antenna patterns operating at the same receive polarization and receive frequency (e.g., at least a portion of the receive frequencies are common) 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 operating at the same transmit polarization and transmit frequency (e.g., at least a portion of the transmit frequencies are common) overlap with at least five other transmit component beam antenna patterns. The amount of overlap will vary from system to system. In some cases, at least one of the receive antenna elements 406 has a component beam antenna pattern that overlaps with the antenna patterns of other receive antenna elements 406 that can operate at the same receive frequency (e.g., at least a portion of the receive frequencies are common) and the same receive polarization. Thus, at least some of the multiple receive antenna elements are able to 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 patterns of other transmit antenna elements 409 that can operate at the same transmit frequency (e.g., at least a portion of the receive frequencies are common) and transmit polarization. Thus, at least some of the multiple transmit antenna elements are able to transmit signals of the same frequency with the same polarization to the same receiver. In some cases, the overlapping component beam antenna patterns can have a gain that differs by less than 3 dB (or any other suitable value) within a common geographic area. The antenna elements (whether for receive or transmit) can have wide component beam antenna patterns and thus have a relatively wide antenna element coverage area. In some cases, signals transmitted by a terrestrial transmitter such as user terminal 517 or access node 515 are received by all of the receive antenna elements 406 of an end-to-end repeater (e.g., a satellite). In some cases, a subset of the elements 406 receives the signal from the terrestrial transmitter. In some cases, the subset includes at least 50% of the transmit antenna elements. In other cases, the subset includes at least 75% of the transmit antenna elements. In other cases, the subset includes at least 90% (e.g., up to and including all) of the receive antenna elements. Different subsets of the receive antenna elements 406 can receive signals from different terrestrial transmitters. Similarly, in some cases, a subset of the elements 409 transmits signals that can be received by user terminal 517. In some cases, the subset includes at least 50% of the transmit antenna elements. In other cases, the subset includes at least 75% of the transmit antenna elements. In other cases, the subset includes at least 90% (e.g., up to and including all) of the transmit antenna elements.Different subsets of element 409 may transmit signals received by different user terminals. Additionally, the user terminals may be within a number of user beam coverage areas 519 formed. For purposes of this disclosure, an antenna pattern is a distribution pattern of energy transmitted to or received from an antenna. In some cases, energy may be radiated directly from / to an antenna element. In other cases, energy from one or more transmit antenna elements may be reflected by one or more reflectors that shape the antenna element pattern. Similarly, a receiving element may receive energy directly or after the energy is reflected off one or more reflectors. In some cases, an antenna may be composed of a number of elements, each having a component beam antenna pattern that establishes a corresponding antenna element coverage area. Similarly, all or subsets of the receive and transmit antenna elements that receive and transmit signals to / from AN 515 may overlap such that multiple receive antenna elements receive signals from the same AN 515 and / or multiple transmit antenna elements transmit signals to the same AN 515.

[0117] Fig.17 is an illustration of component beam antenna patterns that intersect at the 3dB points and are generated by a number of antenna elements (receive antenna element 406 or transmit antenna element 409). The component beam antenna pattern 1301 of the first antenna element has a peak component beam antenna gain along the line of sight 1303. The component beam antenna pattern 1301 is shown to attenuate by approximately 3dB before intersecting with the component beam antenna pattern 1305. Since each pair of two adjacent component beam antenna patterns only overlap around the 3dB line 1307 in a relatively small portion of the component beam antenna pattern, the antenna elements that generate these component beam antenna patterns are considered non-overlapping.

[0118] Fig.18 Illustrates idealized 3dB antenna profiles 3901, 3902, 3903 of a number of elements 406, 409 with peak gains marked with the letter 'x'. The profiles 3901, 3902, 3903 are referred to as "idealized" herein because, for simplicity, the profiles are shown as circular. However, the profiles 3901, 3902, 3903 are not necessarily circular. Each profile indicates the locations where the transmitted or received signal is 3dB lower than the peak level. Outside the profile, the signal is more than 3dB lower than the peak. Inside the profile, the signal is less than 3dB lower than the peak (i.e., within 3dB of the peak). In a system where the coverage area of the receive component beam antenna pattern is all points where the receive component beam antenna gain is within 3dB of the peak receive component beam antenna gain, the area inside the profile is referred to as the antenna element coverage area. The 3dB antenna profiles of each element 406, 409 do not overlap. That is, only a relatively small portion of the area within the 3dB antenna profile 3901 overlaps with the areas within the adjacent 3dB antenna patterns 3902, 3903.

[0119] Fig.19 Illustrations of the antenna patterns 1411, 1413, 1415 of a number of antenna elements (receiving antenna element 406 or transmitting antenna element 409). Compared with Fig.17 the component beam antenna patterns, Fig.19 the component beam antenna pattern shown intersects with 1417 above the 3 dB line 1307.

[0120] FIG. 20A to FIG. 20E Shows the 3 dB antenna profiles of a number of antenna elements 406, 409 with the beam center points (peak gains) marked with the letter 'x'. Fig. 20A Shows the specific antenna profile 1411 of the first antenna element 406. Fig. 20B Shows the 3 dB antenna profiles 1411, 1413 of two specific elements 406. Fig. 20C Shows the 3 dB antenna profiles of three elements 406. Fig.20D Shows the 3 dB antenna profiles of four antenna elements 406. Fig.20E Shows the 3 dB antenna profiles of an array of 16 antenna elements 406. The 3 dB antenna profiles are shown as overlapping with 1418 (e.g., 16 such 3 dB antenna profiles are shown). The antenna elements in the receiving antenna or transmitting antenna can be arranged in any of a number of different configurations. For example, if the elements have a generally circular feed horn, the elements can be arranged in a cellular configuration to closely pack the elements in a small amount of space. In some cases, the antenna elements are aligned in horizontal rows and vertical columns.

[0121] Fig.21 Is an exemplary illustration of the relative positions of the 3 dB antenna profiles of the receiving antenna associated with the receiving antenna element 406. The beam centers of the elements 406 are numbered from 1 to 16, where the element 4064 is identified by the number '4' in the upper left corner of the beam center indicator 'x'. In some cases, there may be more than 16 receiving antenna elements 406. However, for simplicity, only 16 are shown in Fig.21 The corresponding array of the transmitting antenna element 409 and its associated 3 dB antenna profiles looks similar to Fig.21 . Therefore, for simplicity, only the array of the receiving antenna elements 406 is shown. The area 2101 in the center is the location where the coverage areas of all the antenna elements overlap.

[0122] In some cases, at least one point within a repeater coverage area (e.g., a satellite coverage area) falls within the 3 dB antenna contour of the component beams of a number of 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 repeater coverage area is within the 3 dB antenna contour of at least 30 different antenna elements. In another case, at least 20% of the repeater coverage area is within the 3 dB antenna contour of at least 20 different antenna elements. In another case, at least 30% of the repeater coverage area is within the 3 dB antenna contour of at least 10 different antenna elements. In another case, at least 40% of the repeater coverage area is within the 3 dB antenna contour of at least eight different antenna elements. In another case, at least 50% of the repeater coverage area is within the 3 dB antenna contour of at least four different antenna elements. However, in some cases, more than one of these relationships can be true.

[0123] In some cases, an end-to-end repeater has a repeater coverage area (e.g., a satellite coverage area) where at least 25% of the points in the uplink repeater coverage area are within the overlapping coverage area of at least six receive antenna elements 406 (e.g., across these overlapping coverage areas). In some cases, 25% of the points within the uplink repeater coverage area are within the overlapping coverage area of at least four receive antenna elements 406 (e.g., across these overlapping coverage areas). In some cases, the end-to-end repeater has a coverage area where at least 25% of the points in the downlink repeater coverage area are within the overlapping coverage area of at least six transmit antenna elements 409 (e.g., across these overlapping coverage areas). In some cases, 25% of the points within the downlink repeater coverage area are within the overlapping coverage area of at least four transmit antenna elements 409 (e.g., across these overlapping coverage areas).

[0124] In some cases, the receive antenna 402 can be pointed generally in 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 can be mapped to their corresponding transmit antenna elements 409 via the transponders 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 the receive antenna elements 406 to transmit antenna elements 409 that do not correspond to the same component beam coverage area. Thus, the mapping of the elements 406 of the receive antenna 402 to the elements 409 of the transmit antenna 401 can be arranged randomly (or otherwise). Such arrangements include cases where the receive antenna elements 406 are not mapped to transmit antenna elements 409 that are in the same relative position within the array or have the same coverage area. For example, each receive antenna element 406 within the receive antenna element array can be associated with the same transponder 410 as the transmit antenna element 409 located in the mirror image position within the transmit antenna element array. Any other arrangement can be used to map the receive antenna elements 406 to the transmit antenna elements 409 according to the arrangement (e.g., pair each receive antenna element 406 with the same transponder coupled to the associated transmit antenna element 409 according to a particular arrangement of the receive antenna elements 406 and the transmit antenna elements 409).

[0125] Fig. 22 Table 4200 shows an exemplary mapping of the receive antenna elements 406 to the transmit antenna elements 409 via 16 transponders 410. Each transponder 410 has an input uniquely coupled to an associated receive antenna element 406 and an output uniquely coupled to an associated transmit antenna element 409 (e.g., there is a one-to-one relationship between each receive antenna element 406, one transponder 410, and one transmit antenna element 409). In some cases, other receive antenna elements, transponders, and transmit antenna elements can exist on an end-to-end repeater (e.g., a satellite) that is not configured for a one-to-one relationship (and does not operate as part of an end-to-end beamforming system).

[0126] The first column 4202 of Table 4200 identifies transponder 410. The second column 4204 identifies the receive antenna element 406 coupled to transponder 410 of the first column. The third column 4206 of Table 4200 identifies the associated transmit antenna element 409 coupled to the output of transponder 410. Each receive antenna element 406 is coupled to the input of transponder 410 identified in the same row of Table 4200. Similarly, each transmit antenna element 409 is coupled to the output of transponder 410 identified in the same row of Table 4200. The third column of Table 4200 shows an example of direct mapping, where each receive antenna element 406 of the receive antenna array is coupled to the same transponder 410 as the transmit antenna element 409 in the same relative position within the transmit antenna array. The fourth column 4208 of Table 4200 shows examples of interleaved mapping, where the first receive antenna element 406 is coupled to the first transponder 410 and the tenth transmit antenna element 409. The second receive antenna element 406 is coupled to the second transponder 410 and the ninth transmit antenna element 409, and so on. Some cases have other arrangements, including random mapping, where the specific pairing of receive antenna elements 406 and transmit elements 409 with transponder 410 is randomly selected.

[0127] Direct mapping, which attempts to make the transmit antenna element coverage area and the receive antenna element coverage area as similar as possible for each receive / transmit signal path, generally results in the highest total capacity of the system. Random and interleaved arrangements generally result in slightly less capacity, but provide a more robust system in the face of AN failures, fiber optic failures in the terrestrial network, or loss of the receive / transmit signal path due to electronic failures on end-to-end repeaters (e.g., in one or more transponders). Random and interleaved arrangements allow the use of less costly non-redundant ANs. Random and interleaved arrangements also result in less variation between the capacity in the best performing beam and the capacity in the worst performing beam. Random and interleaved arrangements may also be more useful for initially operating the system using only a small fraction of the ANs, resulting in only a small fraction of the total capacity being available, but with no loss of coverage area. An example of this is the progressive turn-up of ANs, where the system initially operates with only 50% of the ANs deployed. This provides less than full capacity, while still allowing operation over 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 composition of the ANs results in the recalculation of the beam weights. Changes in composition can include changing the number or characteristics of one or more ANs. This may require re-estimation of the end-to-end forward and / or return gain.

[0128] In some cases, the antenna is an array-fed reflector antenna with 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 an overlapping component beam antenna pattern is to defocus (unfocus) the elements 406, 409 (i.e., the receive antenna array is positioned outside the focal plane of the receive reflector) because the focal plane of the reflector lies behind (or in front of) the array of elements 406, 409.

[0129] Fig.23 FIG. is a cross-sectional view of a centrally-fed parabolic reflector 1521. The focus 1523 lies on a focal plane 1525 perpendicular to the central axis 1527 of the reflector 1521. Signals received by the reflector 1521 parallel to the central axis 1527 are focused onto the focus 1523. Similarly, signals transmitted from an antenna element positioned at the focus and impinging on the reflector 1521 will be reflected from the reflector 1521 in a focused beam parallel to the central axis 1527. Such an arrangement is typically used in single-feed systems for each beam to maximize the directivity of each beam and to minimize the overlap with the beams formed by adjacent feeds.

[0130] Fig.24 FIG. is a diagram of another parabolic reflector 1621. By positioning the antenna element 1629 (receive antenna element or transmit antenna elements 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 signals 1631 transmitted and impinging on the reflector 1621 are not parallel to each other when they are reflected away from the reflector 1621, thereby forming a beamwidth wider than in the focused case. In some cases, reflectors with shapes other than parabolic are used. Such reflectors may also cause the antenna to defocus. An end-to-end beamforming system can use this type of defocused antenna in the coverage areas of adjacent antenna elements to create an overlap and thus provide a large number of useful receive / transmit paths for a given beam position in the repeater coverage area.

[0131] In one case, a repeater coverage area is established where, when an end-to-end repeater (e.g., an end-to-end satellite repeater in a service orbit) is deployed, 25% of the points within the repeater coverage area are within the antenna element coverage areas of at least six component beam antenna patterns. Alternatively, 25% of the points within the repeater coverage area are within the antenna element coverage areas of at least four receive antenna elements. Fig.25Is an illustration of an exemplary repeater coverage area (also referred to as a satellite coverage area for an end-to-end satellite repeater) 3201 (shown with a single cross-hatch) and an area 3203 (shown with a double cross-hatch) defined by points within the repeater coverage area 3201 that are also included within six antenna element coverage areas 3205, 3207, 3209, 3211, 3213, 3215. The coverage area 3201 and the antenna element coverage areas 3205, 3207, 3209, 3211, 3213, 3215 can be receive antenna coverage areas or transmit antenna element coverage areas and can be associated with only the forward link or only the return link. The size of the antenna element coverage areas 3205, 3207, 3209, 3211, 3213, 3215 is determined by the desired performance to be provided by the system. A system with a greater error tolerance can have larger antenna element coverage areas than a system with a smaller error tolerance. In some cases, each antenna element coverage area 3205, 3207, 3209, 3211, 3213, 3215 is all points where the component beam antenna gain is within 10 dB of the peak component beam antenna gain of the antenna element for which the component beam antenna pattern has been established. In other cases, each antenna element coverage area 3205, 3207, 3209, 3211, 3213, 3215 is all points where the component beam antenna gain is within 6 dB of the peak component beam antenna gain. In other cases, each antenna element coverage area 3205, 3207, 3209, 3211, 3213, 3215 is all points where the component beam antenna gain is within 3 dB of the peak component beam antenna gain. Even when the end-to-end repeater has not been deployed (e.g., an end-to-end satellite repeater is not in a service orbit), the end-to-end repeater still has a component beam antenna pattern that conforms to the above definition. That is, even when the end-to-end repeater is not in a service orbit, the antenna element coverage areas corresponding to the end-to-end repeater in orbit can be calculated based on the component beam antenna pattern. The end-to-end repeater can include additional antenna elements that do not contribute to beamforming and may not have the above characteristics.

[0132] Fig.26 Is an illustration of an end-to-end repeater (e.g., satellite) antenna pattern 3300 where all points within the repeater 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 can be present on the end-to-end repeater and can have antenna element coverage areas 3311 that include fewer than all points within the repeater coverage area 3301.

[0133] The system can operate in any suitable spectrum. For example, an end-to-end beamforming system can operate in the C, L, S, X, V, Ka, Ku, or one or more other suitable bands. In some such systems, the receiving device operates in the C, L, S, X, V, Ka, Ku, or one or more other suitable bands. In some cases, the forward uplink and the return uplink can operate in the same frequency range (e.g., approximately 30 GHz); and the return downlink and the forward downlink can operate in non-overlapping frequency ranges (e.g., approximately 20 GHz). The end-to-end system can use any suitable bandwidth (e.g., 500 MHz, 1 GHz, 2 GHz, 3.5 GHz, etc.). In some cases, the forward link and the return link use the same transponder.

[0134] To assist in system timing alignment, in some cases, for example, by appropriate cable length selection, the path length between L transponders is set to match the signal path time delay. In some cases, the end-to-end repeater (e.g., a satellite) has a delay beacon generator 426 (satellite beacon) within the calibration support module 424 (see Fig.15 ). The beacon generator 426 generates a delay beacon signal. The end-to-end repeater broadcasts a repeater beacon signal to further assist in system timing alignment and support feeder link calibration. In some cases, the repeater beacon signal is a pseudo-random (referred to as PN) sequence, such as a PN direct sequence spread spectrum signal operating at a high chip rate (e.g., 100 million, 200 million, 400 million, or 800 million chips per second (Mcp) or any other suitable value). In some cases, a linearly polarized repeater (e.g., a satellite) beacon that can be received by both RHCP and LHCP antennas is broadcast in a wide coverage area by an antenna such as an antenna horn (not shown) or coupled to one or more transponders 410 for transmission through the associated transmit antenna element 409. In an exemplary system, beams are formed in multiple 500 MHz bandwidth channels in the Ka band, and a 400 Mcp PN code is filtered or pulse-shaped to fit the 500 MHz bandwidth channel. When multiple channels are used, the same PN code can be transmitted in each channel. The system can employ one beacon per channel or one beacon for two or more channels.

[0135] Due to the large number of receive / transmit signal paths that may exist in the end-to-end repeater, redundancy of individual receive / transmit signal paths may not be required. Once a receive / transmit signal path fails, the system can still operate very close to its previous performance level, but modifications to the beamforming coefficients can be used to account for the loss.

[0136] Ground Network

[0137] The terrestrial network of an exemplary end-to-end beamforming system includes a plurality of geographically distributed access node (AN) earth stations that point to a common end-to-end repeater. Looking first at the forward link, a central processing system (CPS) calculates beam weights for transmitting user data and interfaces to the ANs over the distribution network. The CPS also interacts with data sources that are provided to user terminals. The distribution network can be implemented in various ways, such as using a fiber optic cable infrastructure. The timing between the CPS and the SAN can be deterministic (e.g., using a circuit-switched channel) or non-deterministic (e.g., using a packet-switched network). In some cases, the CPS is implemented at a single site, such as using a custom application-specific integrated circuit (ASIC), to perform signal processing. In some cases, the CPS is implemented in a distributed manner, such as using cloud computing technology.

[0138] Returning to Figure 5 the example of, the CPS 505 can include a plurality of feeder link modems 507. For the forward link, each of the feeder link modems 507 receives a forward user data stream 509 from various data sources (such as the Internet, a video front end (not shown), etc.). The received forward user data stream 509 is modulated by the modems 507 into K forward beam signals 511. In some cases, K can be in the range of 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024 or can be a number between or greater than them. Each of the K forward beam signals carries a forward user data stream that will be transmitted on one of the K forward user beams. Thus, if K = 400, then there are 400 forward beam signals 511, each of which will be transmitted to the forward user beam coverage area 519 on an associated one of the 400 forward user beams. The K forward beam signals 511 are coupled to a forward beamformer.

[0139] If M ANs 515 are present in the terrestrial segment 502, then the output of the forward beamformer is M access-node-specific forward signals 516, each of which includes weighted forward beam signals corresponding to some or all of the K forward beam signals 511. The forward beamformer may generate the M access-node-specific forward signals 516 based on the matrix product of a K×M forward beam weight matrix and the matrix of K forward data signals. The distribution network 518 distributes each of the M access-node-specific forward signals to a corresponding one of the M ANs 515. Each AN 515 transmits a forward uplink signal 521 that includes the corresponding access-node-specific forward signal 516. Each AN 515 transmits its corresponding forward uplink signal 521 to be relayed to one or more (e.g., up to and including all) of the forward user beam coverage areas via one or more (e.g., up to and including all) of the forward receive / transmit signal paths of the end-to-end repeater. The transponders 410, 411 within the end-to-end repeater 503 receive a combined input forward signal that includes a superposition 550 of the forward uplink signals 521 transmitted by the plurality (e.g., up to and including all) of ANs 515. Each transponder (e.g., through each receive / transmit signal path of the repeater) relays the combined input forward signal as a corresponding forward downlink signal to the user terminal 517 via the forward downlink.

[0140] Fig. 27 FIG. is an illustration of an exemplary distribution of ANs 515. Each smaller numbered circle represents the location of an AN 515. Each larger circle represents a user beam coverage area 519. In some cases, the ANs 515 are spaced apart generally evenly within the coverage area of the end-to-end repeater 503. In other cases, the ANs 515 may be distributed unevenly throughout the coverage area. In other cases, the ANs 515 may be distributed evenly or unevenly within one or more sub-regions of the repeater coverage area. Generally, system performance is best when the ANs 515 are distributed evenly throughout the coverage area. Then, considerations may dictate a compromise in the AN placement. For example, the ANs 515 may be placed based on the amount of interference, rain or other environmental conditions, real estate costs, access to the distribution network, etc. For example, for a satellite-based end-to-end relay system that is sensitive to rain, more ANs 515 may be placed in areas where rain-induced attenuation is less likely to occur (e.g., the western United States). As another example, the ANs 515 may be placed more densely in high-rainfall areas (e.g., the southeastern United States) to provide some diversity gain to counter the effects of rain fade. The ANs 515 may be located along fiber optic routes to reduce the distribution costs associated with the ANs 515.

[0141] The number M of AN 515 is an optional parameter that can be selected based on several criteria. Fewer ANs can result in a simpler, less costly ground segment and lower operating costs for the distribution network. More ANs can result in a larger system capacity. Fig.28 is a simulation of the variation of the normalized forward and return link capacities with the number of ANs deployed in an exemplary system. The normalized capacity is the capacity obtained with M ANs divided by the capacity obtained with the maximum number of ANs in the simulation. The capacity increases with the number of ANs, but does not increase indefinitely. Both the forward link capacity and the return link capacity approach an asymptotic limit as the number of ANs increases. This simulation was performed using L = 517 transmit and receive antenna elements and ANs evenly distributed within the coverage area, but the asymptotic behavior of the capacity can be achieved with other values of L and other AN spatial distributions. The same curves as Fig.28 shown can assist in selecting the number M of ANs to be deployed and in understanding how the phased system capacity can be achieved when ANs are deployed incrementally, as described above.

[0142] Fig.29 is a block diagram of an exemplary ground segment 502 of an end-to-end beamforming system. Fig.29 may show, for example, Figure 5 the ground segment 502. The ground segment 502 includes a CPS 505, a distribution network 518, and 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.

[0143] For the forward link, the beam signal interface 524 obtains forward beam signals (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 that includes forward data for transmission to the user terminal 517. The forward user data stream 509 may include, for example, data for transmission via Figure 5The data packets (e.g., TCP packets, UDP packets, etc.) transmitted by the end-to-end beamforming system 500 to the user terminal 517. 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 the forward beam data streams 532. The forward beam data multiplexer 526 can use, for example, time-domain multiplexing, frequency-domain multiplexing, or a combination of multiplexing techniques to generate the forward beam data streams 532. The forward beam data stream modulator 528 can modulate the forward beam data streams 532 according to one or more modulation schemes (e.g., mapping data bits to modulation symbols) to generate the forward beam signals 511, which are passed to the forward / return beamformer 513. In some cases, the modulator 528 can frequency-division multiplex multiple modulation signals to generate the multi-carrier beam signals 511. The beam signal interface 524 can, for example, implement the functions of the feeder link modem 507 discussed in reference Figure 5 as discussed.

[0144] The forward / return beamformer 513 can include a forward beamformer 529 and a return beamformer 531. The beam weight generator 910 generates an M×K forward beam weight matrix 918. Techniques for generating the M×K forward beam weight matrix 918 are discussed in more detail below. The forward beamformer 529 can include a matrix multiplier that calculates M access node-specific forward signals 516. For example, this calculation can be based on the matrix product of the M×K forward beam weight matrix 918 and a vector of K forward beam signals 511. In some examples, each of the K forward beam signals 511 can be associated with one of F forward frequency subbands. In this case, the forward beamformer 529 can generate samples of the M access node-specific forward signals 516 for each of the F forward frequency subbands (e.g., effectively implementing the matrix product operation for each of the F subbands for a corresponding subset of the K forward beam signals 511). The distribution interface 536 distributes (e.g., via the distribution network 518) the M access node-specific forward signals 516 to the respective ANs 515.

[0145] For the return link, the allocation interface 536 obtains the combined return signal 907 from the AN 515 (e.g., via the allocation network 518). Each return data signal from the user terminal 517 can be included in multiple combined return signals (e.g., up to and including all) in the combined return signal 907. The beam weight generator 910 generates the K×M return beam weight matrix 937. Techniques for generating the K×M return beam weight matrix 937 are discussed in more detail below. The return beamformer 531 calculates K return beam signals 915 for the K return user beam coverage areas. For example, this calculation can be based on the matrix product of the return beam weight matrix 937 and the vector of the corresponding combined return signal 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 the corresponding return user data streams 535 associated with the return data signals transmitted from the user terminal 517. In some examples, 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 corresponding subset of the return beam signals 915 associated with each of the R return frequency subbands (e.g., effectively performing the matrix product operation for each of the R return frequency subbands to generate the corresponding subset of the return beam signals 915).

[0146] Fig.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 a timestamp with each of the M access node-specific forward signals 516 (e.g., multiplexing the timestamp with the access node-specific forward signal in the multiplexed access node-specific forward signals), which indicates the desired time for the signal to reach the end-to-end repeater. In this way, the data split in the split module 904 within the forward beamformer 529 of the K forward beam signals 511 can be transmitted by each of the ANs 515 at the appropriate time. The timing module 947 aligns the received signals based on the timestamp. Samples of the M AN combined return signals (CRS) 907 are associated with a timestamp indicating when the particular sample is transmitted from the end-to-end repeater. Timing considerations and generation of the timestamp are discussed in more detail below.

[0147] The forward beamformer 529 has a data input 925, a beam weight input 920, and an access node output 923. The forward beamformer 529 applies the values of an 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 (e.g., duplicates) each of the K forward beam signals 511 into M groups 906 of the K forward beam signals, with 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.

[0148] The forward beam weight generator 917 generates an M×K forward beam weight matrix 918. In some cases, the forward beam weight matrix 918 is generated based on a channel matrix in which the elements are estimates of the end-to-end forward gains for each of the K×M end-to-end forward multipath channels that form the 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 has a channel data repository 921 that stores data related to the various parameters of the end-to-end multipath channels, as discussed further in detail below. The channel estimator 919 outputs the estimated end-to-end gain signal to allow the forward beam weight generator 917 to generate the forward beam weight matrix 918. Each of the weighting and summing modules 533 is coupled to receive a respective vector of the beamforming weights of the forward beam weight matrix 918 (only one such connection is shown for simplicity in Fig.30 ). The first weighting and summing module 533 applies a weight equal to the value of the 1,1 element of the M×K forward beam weight matrix 918 to the first of the K forward beam signals 511 (as discussed in more detail below). A weight equal to the value of the 1,2 element of the M×K forward beam weight matrix 918 is applied to the second of the K forward beam signals 511. The other weights of the matrix are applied in a similar manner, all the way to the Kth forward beam signal 511, which is weighted using a value equal to the 1,K element of the M×K forward beam weight matrix 918. Each of the K weighted forward beam signals 903 is then summed and output from the first weighting and summing module 533 as an access node-specific forward signal 516. The access node-specific forward signal 516 output from the first weighting and summing module 533 is then coupled to the timing module 945. The timing module 945 passes the access node-specific forward signal 516 through the distribution network 518 (see Figure 5)Output to the first AN 515. Similarly, each of the other weighting and summing modules 533 receives the K forward beam signals 511, weights and sums the K forward beam signals 511. The output from each of the M weighting and summing modules 533 is coupled to the associated M ANs 515 via a distribution network 518 such that the output from the m-th weighting and summing module is coupled to the m-th AN 515. In some cases, the timing module 945 processes jitter and uneven delays through the distribution network and some other timing considerations by associating timestamps with the data. Details of exemplary timing techniques are provided with respect to Fig.36 and Fig.37 below.

[0149] Due to the beam weights applied by the forward beamformer 529 at the ground segment 502, the signals transmitted from the AN 515 through the end-to-end repeater 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 antenna patterns of the repeater antenna elements through which the signals pass, the location of the end-to-end repeater 503, and / or the geographical spacing of the ANs 515.

[0150] Now referring to Figure 5 the end-to-end return link 523 shown, a user terminal 517 within one of the user beam coverage areas 519 transmits a signal up to the end-to-end repeater 503. These signals are then relayed down to the ground segment 502. These signals are received by the AN 515.

[0151] Referring again to Fig.30, M downlink return signals 527 are received by M ANs 515, coupled as a combined return signal 907 from the M ANs 515 through a distribution network 518, and received at the access node input 931 of a return beamformer 531. A timing module 947 aligns the combined return signals from the M ANs 515 with each other and outputs the time-aligned signals to the return beamformer 531. A return beam weight generator 935 generates return beam weights as a K×M return beam weight matrix 937 based on information stored in a channel data repository 941 within a channel estimator 943. The return beamformer 531 has a beam weight input 939 through which the return beamformer 531 receives the return beam weight matrix 937. Each of the M AN combined return signals 907 is coupled to an associated one of M splitters and weighting modules 539 within the return 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 element of the K×M return beam weight matrix 937. Additional details regarding the K×M return beam weight matrix are provided below. Each set of K weighted combined return signals 911 is then coupled to a combining module 913. In some cases, the combining module 913 combines the k-th weighted combined return signals 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 by each of the M ANs). Each of the K return beam signals 915 may have samples from one or more user terminals 517. The K combined and aligned beamformed return beam signals 915 are coupled to a feeder link modem 507 (see Figure 5 ). Note that return timing adjustment can be performed after splitting and weighting. Similarly, for the forward link, forward timing adjustment can be performed before beamforming.

[0152] As described above, the forward beamformer 529 can perform a matrix multiplication operation on the input samples of the K forward beam signals 511 to compute in real time M access node-specific forward signals 516. As the beam bandwidth increases (e.g., to support shorter symbol durations) and / or K and M grow larger, the matrix multiplication operation becomes computationally intensive and may exceed the capabilities of a single computing node (e.g., a single computing server, etc.). The operation of the return beamformer 531 is similarly computationally intensive. Various methods can be used to partition the computing resources of multiple computing nodes within the forward / return beamformer 513. In one example, Fig.30The forward beamformer 529 can be partitioned into individual weighting and summing modules 533 for each of the M ANs 515, and these ANs 515 can be assigned to different computing nodes. Generally speaking, implementation considerations include cost, power consumption, scalability with respect to K, M, and bandwidth, system availability (e.g., due to node failures, etc.), upgradability, and system latency. The above example is by row (or column). Vice versa. Other ways of grouping matrix operations can also be considered (e.g., partitioning into four, where [1,1 to K / 2,M / 2], […], computing and summing them individually).

[0153] In some cases, the forward / return beamformer 513 can include a time-domain multiplexing architecture for processing beam weighting operations by a time-slot beamformer. Fig.31 is a block diagram of an exemplary forward beamformer 529 that includes multiple forward time-slot beamformers with time-domain demultiplexing and multiplexing. The forward beamformer 529 includes a forward beam signal demultiplexer 3002, N forward time-slot beamformers 3006, and a forward access node signal multiplexer 3010.

[0154] The forward beam signal demultiplexer 3002 receives the forward beam signal 511 and demultiplexes the K forward beam signals 511 into the forward time slice input terminals 3004 for input into the N forward time slice beamformers 3006. For example, the forward beam signal demultiplexer 3002 sends a first time-domain subset of samples of the K forward beam signals 511 to the first forward time 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 samples associated with the M access node-specific forward signals of the first time-domain subset of samples to the forward access node signal multiplexer 3010 via its forward time slice output terminal 3008. The forward time slice beamformer 3006 can utilize the synchronization timing information (e.g., corresponding time slice index, etc.) used by the access node to output samples associated with each of the M access node-specific forward signals, so as to cause (e.g., through precorrection) the corresponding access node-specific forward signals to be synchronized when received by the end-to-end repeater. The forward access node signal multiplexer 3010 multiplexes the time-domain subsets of samples of the M access node-specific forward signals received via the N forward time slice output terminals 3008 to generate the 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 implement matrix multiplication operations. That is, each of the forward time slice beamformers 3006 can perform calculations that are mathematically equivalent to the splitting module 904 and the forward weighting and summing module 533 shown for the forward beamformer 529 for Fig.30 during the sample processing of one time segment index. The update of the beam weight matrix can be performed incrementally. For example, the beam weight matrix buffer for the forward time slice beamformer can be updated in the rotation of the time slice index t by the N forward time slice beamformers 3006 during idle time. Alternatively, each forward time slice beamformer can have two buffers that can be used in a reciprocating configuration (e.g., one can be used while the other is being updated). In some cases, multiple buffers can be used to store beam weights corresponding to multiple user beam patterns (e.g., multiple user coverage areas). The beam weight buffer and data buffer for the 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). In addition or alternatively, the beam weight buffer, data buffer, and beam weight processor can be integrated within one component.

[0155] Fig.32 shows a simplified exemplary ground segment, which shows the operation of the forward time - slice beamformer 529. In Fig.32 the example, the forward beamformer 529 receives four forward beam signals (e.g., K = 4), generates access - node - specific forward signals for five ANs (e.g., M = 5), and has three forward time - slice beamformers (e.g., N = 3). The forward beam signals are denoted as FBk:t, where k is the forward beam signal index and t is the time - slice index (e.g., corresponding to a time - domain subset of samples). The forward beam signal demultiplexer 3002 receives four time - domain subsets of samples of the forward beam signals associated with four forward user beams and demultiplexes each forward beam signal such that one forward time - slice input 3004 for a particular time - slice index t includes a time - domain subset of samples from each of the forward beam signals 511. For example, the time - domain subset can be a single sample, a block of consecutive samples, or a non - consecutive (e.g., interleaved) block of samples, as described below. The forward time - slice beamformer 3006 generates each of the M access - node - specific forward signals, denoted as AFm:t, for the time - slice index t (e.g., based on the forward beam signals 511 and the forward beam weight matrix 918). For example, for the time - slice index t = 0, the time - domain subsets of the samples FB1:0, FB2:0, FB3:0, and FB4:0 are input to the first forward time - slice beamformer TSBF[1]3006, which generates the corresponding samples of the access - node - specific forward signals AF1:0, AF2:0, AF3:0, AF4:0, and AF5:0 at the forward time - slice output 3008. For subsequent time - slice index values t = 1, 2, the time - domain subsets of the samples of the forward beam signals 511 are demultiplexed by the forward beam signal demultiplexer 3002 for input to the second and third forward time - slice beamformers 3006, which generate the access - node - specific forward signals associated with the corresponding time - slice index t at the forward time - slice output 3008. Fig.32 It is also shown that at the time - slice index value t = 3, the first forward time - slice beamformer generates the access - node - specific forward signal associated with the corresponding time - slice index 3. The matrix - product operation performed by each forward time - slice beamformer 3006 for one time - slice index value t may take longer than the actual time of the time - domain subset of samples (e.g., the number of samples S multiplied by the sampling rate t S)。However, each forward time - slice beamformer 3006 can process only one time - domain subset of the samples every N time - slice indices t. The forward access - node signal multiplexer 3010 receives the forward time - slice outputs 3030 from each of the forward time - slice beamformers 3006 and multiplexes the time - domain subsets of the samples to generate M access - node - specific forward signals 516 for distribution to the corresponding ANs.

[0156] Fig.33 is a block diagram of an exemplary return beamformer 531 that includes a plurality of return time - slice beamformers with time - domain demultiplexing and multiplexing. The return beamformer 531 includes a return combined - signal demultiplexer 3012, N return time - slice beamformers 3016, and a return beam - signal multiplexer 3020. The return combined - signal demultiplexer 3012 receives M combined return signals 907 (e.g., from M ANs) and demultiplexes the M combined return signals 907 into return time - slice inputs 3014 for input to the N return time - slice beamformers 3016. Each of the return time - slice beamformers 3016 outputs samples associated with K return beam signals 915 for a corresponding time - domain subset of the samples via a respective return time - slice output 3018 to the return beam - signal multiplexer 3020. The return beam - signal multiplexer 3020 multiplexes the time - domain subsets of the samples of the K return beam signals received via the N return time - slice outputs 3018 to generate K return beam signals 915. Each of the return time - slice beamformers 3016 can include a data buffer, a beam - matrix buffer, and a beam - weight processor that implement a matrix - product operation. That is, each of the return time - slice beamformers 3016 can, during the processing of samples for one time - segment index, implement calculations that are mathematically equivalent to the splitter and weighting module 539 and the combining module 913 shown for the Fig.30 return beamformer 531. As discussed above for the forward time - slice beamformers, a reciprocating beam - weight buffer configuration can be used to incrementally perform updates of the beam - weight matrix (e.g., one can be used while the other is being updated). In some cases, multiple buffers can be used to store beam weights corresponding to multiple user beam patterns (e.g., multiple user coverage regions). The beam - weight buffer and data buffer for the return time - slice beamformers 3016 can be implemented as any type of memory or storage device that includes dynamic or static random - access memory (RAM). The beam - weight processing can be implemented in an application - specific integrated circuit (ASIC) and / or a field - programmable gate array (FPGA) and can include one or more processing cores. In addition or alternatively, the beam - weight buffer, data buffer, and beam - weight processor can be integrated within one component.

[0157] Fig.34 illustrates a simplified exemplary ground segment that illustrates the operation of a return beamformer 531 employing time division multiplexing. In the Fig.33 example, the return beamformer 531 receives five combined 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 combined return signals are denoted as RCm:t, where m is the AN index and t is the time slice index (e.g., corresponding to a time domain subset of samples). The return combined signal demultiplexer 3012 receives four time domain subsets of samples of the combined return signals from five ANs and demultiplexes each combined return signal such that one return time slice input 3014 for a particular time slice index t includes the corresponding time domain subset of samples from each of the combined return signals 907. For example, the time domain subset may be a single sample, a block of consecutive samples, or a non - consecutive (e.g., interleaved) block of samples, as described below. The return time slice beamformer 3016 generates (e.g., based on the combined return signal 907 and the return beam weight matrix 937) each of the K return beam signals, denoted as RBk:t, for the time slice index t. For example, for the time slice index t = 0, the time domain subset of samples RC1:0, RC2:0, RC3:0, RC4:0, and RC5:0 are input to the first return time slice beamformer 3016, which generates the corresponding samples of the 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 combined return signal 907 are demultiplexed by the return combined signal demultiplexer 3012 for input to the second and third return time slice beamformers 3016, respectively, which generate the samples of the return beam signals associated with the corresponding time slice index t at the return time slice output 3018. Fig.34 It is also shown that at the time slice index value t = 3, the first return time slice beamformer generates the samples of the return beam signal associated with the corresponding time slice index 3. The matrix multiplication operation performed by each return time slice beamformer 3016 for one time slice index value t may take longer than the actual time of the time domain subset of samples (e.g., the number of samples S multiplied by the sampling rate t S ). However, each return time slice beamformer 3016 can process only one time domain subset of samples every 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 the K return beam signals 915.

[0158] Although Figures 31 to 34Shows the same number N of forward time - slice beamformers 3006 as the return time - slice beamformer 3016, but some embodiments may have more or fewer forward time - slice beamformers 3006 than the return time - slice beamformer 3016. In some examples, the forward beamformer 529 and / or the return beamformer 531 may have spare capacity to achieve robustness against node failures. For example, if each forward time - slice beamformer 3006 takes t FTS to process a set of samples for time - slice index t, which has a real - time time - slice duration t D , where t FTS =N·t D , then the forward beamformer 529 may have N + E forward time - slice beamformers 3006. In some examples, each of the N + E forward time - slice beamformers 3006 is used in operation, where each forward time - slice beamformer 3006 has an effective extra capacity of E / N. If one forward time - slice beamformer 3006 fails, the operations can be transferred to another forward time - slice beamformer 3006 (e.g., by adjusting how time - domain samples (or groups of samples) are routed through time - domain demultiplexing and multiplexing). Thus, the forward beamformer 529 can tolerate up to E forward time - slice beamformers 3006 failing before system performance is affected. Additionally, the extra capacity allows for system maintenance and upgrade of the time - slice beamformers while the system is running. For example, the upgrade of the time - slice beamformers can be performed incrementally because the system can tolerate different performances between the time - slice beamformers. The data samples associated with the time - slice index t can be interleaved. For example, the first time - slice index t0 may be associated with samples 0, P, 2P, …(S - 1)*P, while the second time - slice index t1 may be associated with samples 1, P + 1, 2P + 1…(S - 1)*P + 1, and so on, where S is the number of samples in each sample set, and P is the interleaving duration. Interleaving can also make the system more robust to time - slice beamformer failures because each time - slice beamformer block of samples is separated in time, such that the errors due to lost blocks will be distributed in time, which is similar to the advantage resulting from interleaving in forward error correction. In fact, the distributed errors caused by time - slice beamformer failures may result in an effect similar to noise and will not cause any errors in user data, especially in the case where forward error - correction coding is employed. Although an example where N = 3 has been shown, other values of N can also be used, and N does not need to have any specific relationship with K or M.

[0159] As described above, respectively, in Fig.31 and Fig.33The forward beamformer 529 and the return beamformer 531 shown may perform time-sliced beamforming time-domain demultiplexing and multiplexing for one channel or frequency subband. Multiple subbands may be processed independently using additional subband multiplexing / demultiplexing switching layers. Fig.35 is a block diagram of an exemplary multi-band forward / return beamformer 513 that employs subband demultiplexing and multiplexing. The multi-band forward / return beamformer 513 may support F forward subbands and R return subbands.

[0160] The multi-band forward / return beamformer 513 includes F forward sub-band beamformers 3026, R return sub-band beamformers 3036, and a sub-band multiplexer / demultiplexer 3030. For example, the forward beam signal 511 can be divided into F forward sub-bands. Each of the F forward sub-bands can be associated with a subset of the K forward user beam coverage regions. That is, the K forward user beam coverage regions can include multiple subsets of forward user beam coverage regions associated with different (e.g., different frequencies and / or polarizations, etc.) frequency sub-bands, where the forward user beam coverage regions within each of these subsets can be non-overlapping (e.g., at the 3dB signal contour, etc.). Thus, each of the forward sub-band beamformer inputs 3024 can include a subset K1 of the forward beam signal 511. Each of the F forward beamformers 3026 can include the functionality of the forward beamformer 529 to generate a forward sub-band beamformer output 3028 that includes M access node-specific forward signals associated with the subset of the forward beam signal 511 (e.g., the matrix product of K1 forward beam signals and an M×K1 forward beam weight matrix). Thus, each of the ANs 515 can receive multiple access node-specific forward signals associated with different frequency sub-bands (e.g., each of the F forward sub-bands). The AN can combine (e.g., add) the signals in different sub-bands in the forward uplink signal, as discussed in more detail below. Similarly, the AN 515 can generate multiple composite return signals 907 for R different return sub-bands. Each of the R return sub-bands can be associated with a subset of the K return user beam coverage regions. That is, the K return user beam coverage regions can include multiple subsets of return user beam coverage regions associated with different frequency sub-bands, where the return user beam coverage regions within each of these subsets can be non-overlapping (e.g., at the 3dB signal contour, etc.). The sub-band multiplexer / demultiplexer 3030 can split the composite return signal 907 into R return sub-band beamformer inputs 3034. Each of the return sub-band beamformers 3036 can then generate a return sub-band beamformer output 3038 that can include a return beam signal 915 for a subset of the return user beams (e.g., to the feeder link modem 507 or the return beam signal demodulator, etc.). In some examples, the multi-band forward / return beamformer 513 can support multiple polarizations (e.g., right-hand circular polarization (RHCP), left-hand circular polarization (LHCP), etc.), which in some cases can effectively double the number of sub-bands.

[0161] In some cases, time-slot multiplexing and demultiplexing (e.g., beam signal demultiplexer 3002, forward access node signal multiplexer 3010, return composite signal demultiplexer 3012, return beam signal multiplexer 3020) and sub-band multiplexing / demultiplexing (sub-band multiplexer / demultiplexer 3030) for the forward beamformer 529 and the return beamformer 531 can be performed by group switching (e.g., Ethernet switching, etc.). In some cases, time-slot and sub-band switching can be performed in the same switching node or in a different order. For example, a structured switching architecture can be used, where each switching structure node can be coupled to a subset of the AN 515, the forward time-slot beamformer 3006, the return time-slot beamformer 3016, or the feeder link modem 507. The structured switching architecture can allow any AN, for example, to be connected (e.g., via switches and / or switch fabric interconnects) to any forward time-slot beamformer or return time-slot beamformer in a low-latency hierarchical plane architecture. In one example, a commercially available interconnect switch platform with 2048 10 GigE ports can be used to implement a system with support for fourteen sub-bands for the forward or return link with K≤600, M≤600, and a 500 MHz bandwidth (e.g., for each sub-band).

[0162] Delay Equalization

[0163] In some cases, the difference in propagation delay on each path between the end-to-end repeater 503 and the CPS 505 is not significant. For example, on the return link, when the same signal (e.g., data going to and from a particular user) is received by multiple ANs 515, each instance of the signal can reach the CPS substantially aligned with every other instance of the signal. Similarly, when the same signal is transmitted through several ANs 515 to the user terminal 517, each instance of the signal can reach the user terminal 517 substantially aligned with every other instance of the signal. In other words, the signals can be phase and time-aligned with sufficient accuracy such that the signals combine coherently, such that the path delay and beamforming effects are 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 a few tens of kHz, and a narrow bandwidth signal, say, ≈10 ksps, can be used with little performance degradation. The symbol duration for a 10 ksps signaling rate is 100 microseconds, and a 10 microsecond delay spread is only one-tenth of the symbol duration. In these cases, for the purpose of system analysis, it can be assumed that the signal received by the end-to-end repeater at one instant will be relayed and transmitted at substantially the same time, as described above.

[0164] In other cases, there may be significant differences in propagation delays relative to the signaling interval (transmission symbol duration) of the signals transmitted from the transmit antenna element 409 to the AN 515. The paths taken by the signals from each AN 515 through the distribution network 518 can include significant delay variations. In these cases, delay equalization can be employed to match the path delays.

[0165] For the end-to-end return link signals received by the CPS 505 through the distribution network 518, the signals can be time-aligned by using the repeater beacon signals transmitted from the end-to-end repeater (e.g., the PN beacon as described previously). Each AN 515 can use the repeater beacon signal as a reference to timestamp the combined return signal. Thus, different AN 515s can receive the same signal at different times, but the signals received in each AN 515 can be timestamped to allow the CPS 505 to time-align them. The CPS 505 can buffer the signals such that beamforming is accomplished by combining the signals with the same timestamp.

[0166] Returning to Fig.33 and Fig.34 , delay equalization of the return link can be performed by demultiplexing the combined return signal into the return time-slot beamformer 3016. For example, each AN can split the combined return signal into sets of samples associated with the time-slot index t, which can include interleaved samples of the combined return signal. The time-slot index t can be determined based on the repeater beacon signal. The AN can send a subset of the samples multiplexed with the corresponding time-slot index t (e.g., as the multiplexed combined return signal) to the return beamformer 531, and these corresponding time-slot indices can be used as synchronization timing information on the return link. The subsets of samples from each AN can be demultiplexed (e.g., via switching), and one return time-slot beamformer 3016 can receive the subsets of samples from each AN for the time-slot index t (in some cases, for one of the multiple subbands). By performing the matrix product of the return beam weight matrix with the subsets of samples from each of the M combined return signals associated with the time-slot index t, the return time-slot beamformer 3016 can align the signals relayed simultaneously by the end-to-end repeater for the application of the return beam weight matrix.

[0167] For the forward link, the beamformer 513 within the CPS 505 can generate timestamps indicating the desired time for each access-node-specific forward signal transmitted by the AN 515 to reach the end-to-end repeater 503. Each AN 515 may transmit an access-node beacon signal 2530, such as a loopback PN signal. Each such signal may be looped back and transmitted by the end-to-end repeater 503 back to the AN 515. The AN 515 can receive the repeater beacon signal and the relayed (looped-back) access-node beacon signal from any one or all of the ANs. The timing of the received access-node beacon signal relative to the reception timing of the repeater beacon signal indicates the time the access-node beacon signal reaches the end-to-end repeater. The timing of the access-node beacon signal is adjusted such that, after being relayed by the end-to-end repeater, the access-node beacon signal arrives at the AN simultaneously with the repeater beacon signal, forcing the access-node beacon signal to reach the end-to-end repeater in synchronization with the repeater beacon. Having all ANs perform this function enables all access-node beacon signals to reach the end-to-end repeater in synchronization with the repeater beacon. The last step in this process is for each AN to transmit its access-node-specific forward signal in synchronization with its access-node beacon signal. This can be done using the timestamps described subsequently. Alternatively, the CPS can manage delay equalization by sending the respective access-node-specific forward signals offset by respective time-domain offsets to the ANs (e.g., where the timing via the distribution network is deterministic).

[0168] Fig.36 is an illustration of a PN sequence for aligning system timing. The horizontal axis of the figure represents time. The AN1 PN sequence 2301 of chip 2303 is transmitted in the access-node beacon signal from the first AN. The PN sequence 2305 depicts the relative time the sequence reaches the end-to-end repeater. Due to the propagation delay from the AN to the end-to-end repeater, there is a time shift of the PN sequence 2305 relative to the AN1 PN sequence 2301. The repeater PN beacon sequence 2307 is generated within the end-to-end repeater and transmitted from the end-to-end repeater in the repeater beacon signal. The PN chip 2315 of the repeater PN beacon sequence 2307 at time T0 aligns with the PN chip 2316 of the AN1 PN received signal 2305 at time T0. The PN chip 2316 of the AN1 PN received signal 2305 aligns with the PN chip 2315 of the repeater PN beacon 2307 when the AN1 transmission timing is adjusted by an appropriate amount. The PN sequence 2305 is looped back from the end-to-end repeater, and the PN sequence 2317 is received at AN1. The PN sequence 2319 transmitted from the end-to-end repeater in the repeater PN beacon is received at AN1. Note that the PN sequences 2317, 2319 align at AN1, indicating that they are aligned at the end-to-end repeater.

[0169] Fig.37An example of AN2 is shown, which has not yet properly adjusted the timing of the PN sequence generated in AN2. Note that the PN sequence 2311 generated by AN2 is received at the end-to-end repeater, shown as sequence 2309 with an offset dt relative to the repeater PN beacon PN sequence 2307. This offset is caused by the timing error used to generate the sequence in AN2. Additionally, note that the AN2 PN sequence 2321 arrives at AN2 offset by the same amount dt relative to the arrival of the repeater PN beacon PN sequence at AN2 2323. The signal processing in AN2 will observe this error and can correct the transmission timing by adjusting the timing by an amount dt to align the PN sequences 2321, 2323.

[0170] In Fig.36 and Fig.37 the same PN chip rate has been used for the repeater PN beacon and all AN (loopback) PN signals to facilitate illustration of the concept. The same timing concept can be applied with different PN chip rates. Returning to Fig.31 and Fig.32 the time slice index t can be used to synchronize the access node-specific forward signals received from each AN at the end-to-end repeater. For example, the time slice index t can be multiplexed with the access node-specific forward signal 516. Each AN can transmit samples of the access node-specific forward signal using a specific time slice index t aligned with the corresponding timing information in the PN sequence of the chips transmitted in the corresponding access node beacon signal. Since the corresponding access node beacon signals have been adjusted to compensate for the corresponding path delays and phase shifts between the AN and the end-to-end repeater, the samples associated with the time slice index t will arrive at the end-to-end repeater correctly timed and phase-aligned with each other.

[0171] In the case where an AN receives its own access node beacon signal, the same end-to-end repeater communication hardware that also carries the forward communication data can be used to loop back the access node beacon signal. In these cases, the relative gain and / or phase of the transponder in the end-to-end repeater can be adjusted as described subsequently.

[0172] Fig.38 is a block diagram of an exemplary AN 515. AN 515 includes a receiver 4002, a receive timing and phase regulator 4024, a repeater beacon signal demodulator 2511, a multiplexer 4004, a network interface 4006, a controller 2523, a demultiplexer 4060, a transmit timing and phase compensator 4020, and a transmitter 4012. The network interface 4006 can be connected via a network port 4008 to, for example, CPS 505.

[0173] On the return link, receiver 4002 receives return downlink signal 527. The return downlink signal 527 can include, for example, a combination of a return uplink signal relayed by an end-to-end repeater (e.g., via multiple receive / transmit signal paths, etc.) and a repeater beacon signal. Receiver 4002 can perform, for example, down-conversion and sampling. Repeater beacon signal demodulator 2511 can demodulate the repeater beacon signal in the digitized combined return signal 907 to obtain repeater timing information 2520. For example, repeater beacon signal demodulator 2511 can perform demodulation to recover chip timing associated with the repeater PN code and generate a timestamp corresponding to the transmission time from the end-to-end repeater for samples of the digitized combined return signal 527. Multiplexer 4004 can multiplex the repeater timing information 2520 with samples of the digitized combined return signal to be sent to CPS 505 (e.g., via network interface 4006) (e.g., to form a multiplexed combined return signal). Multiplexing the repeater timing information 2520 can include generating a subset of samples corresponding to time slice index t for transmission to CPS 505. For example, multiplexer 4004 can output a subset of samples associated with each time slice index t for input to the return time slice beamforming architecture referred to above Fig.33 , Fig.34 and Fig.35 . Multiplexer 4004 can include interleaver 4044, which is used to interleave samples of each subset of samples in some cases.

[0174] On the forward link, network interface 4006 can obtain AN input signal 4014 (e.g., via network port 4008). Demultiplexer 4060 can demultiplex 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 can include forward signal transmission timing information (e.g., multiplexed with data samples, etc.). In one example, the access node-specific forward signal 516 includes a set of samples (e.g., in a data packet), where each set of samples is associated with a time slice index t. For example, each set of samples can be a sample of the access node-specific forward signal 516 generated according to the forward time slice beamforming architecture referred to above Fig.31 , Fig.32 and Fig.35 . Demultiplexer 4060 can include deinterleaver 4050, which is used to deinterleave samples associated with time slice index t.

[0175] The transmission timing and phase compensator 4020 can receive and buffer the access-node-specific forward signal 516, and output forward uplink signal samples 4022 for transmission by the transmitter 4012 as the forward uplink signal 521 at an appropriate time. The transmitter 4012 can perform digital-to-analog conversion and up-conversion to output the forward uplink signal 521. The forward uplink signal samples 4022 can include the access-node-specific forward signal 516 and the access-node beacon signal 2530 (e.g., a loopback PN signal), which can include transmission timing information (e.g., PN chip timing information, frame timing information, etc.). The transmission timing and phase compensator 4020 can multiplex the access-node-specific forward signal 516 with the access-node beacon signal 2530 such that the forward signal transmission timing and phase information 4016 is synchronized with the corresponding transmission timing and phase information in the access-node beacon signal 2530.

[0176] In some examples, the generation of the access node beacon signal 2530 is performed locally at the AN 515 (e.g., in the access node beacon signal generator 2529). Alternatively, the generation of the access node beacon signal 2530 can be performed in a separate component (e.g., the CPS 505) and sent (e.g., via the network interface 4006) to the AN 515. As described above, the access node beacon signal 2530 can be used to compensate for the path difference and phase shift between the AN and the end-to-end repeater for the forward uplink signal 521. For example, the access node beacon signal 2530 can be transmitted in the forward uplink signal 521 and relayed by the end-to-end repeater so as to be received back at the receiver 4002. The controller 2523 can compare the relayed transmission timing and phase information 4026 obtained from the relayed access node beacon signal (e.g., by demodulation, etc.) with the received timing and phase information 4028 obtained from the repeater beacon signal (e.g., by demodulation, etc.). The controller 2523 can generate the timing and phase adjustment 2524 for input to the transmission timing and phase compensator 4020 to adjust the access node beacon signal 2530 so as to compensate for the path delay and phase shift. For example, the access node beacon signal 2530 can include a PN code and frame timing information (e.g., one or more bits of the frame number, etc.). The transmission timing and phase compensator 4020 can, for example, adjust the frame timing information for the coarse compensation of the path delay (e.g., the output frame timing information in the access node beacon signal such that the relayed access node beacon signal will roughly align the relayed transmission frame timing information with the corresponding frame timing information in the repeater beacon signal, thereby changing which chip of the PN code is considered the LSB, etc.). In addition or alternatively, the transmission timing and phase compensator 4020 can perform timing and phase adjustment on the forward uplink signal samples 4022 to compensate for the timing or phase difference between the relayed transmission timing and phase information 4026 and the received timing and phase information 4028. For example, in the case where the access node beacon signal 2530 is generated based on a local oscillator, the timing or phase difference between the local oscillator and the received repeater beacon signal can be corrected by the timing and phase adjustment of the forward uplink signal samples 4022. In some examples, the demodulation of the access node beacon signal is performed locally at the AN 515 (e.g., in the access node beacon signal demodulator 2519). Alternatively, the demodulation of the access node beacon signal can be performed in a separate component (e.g., the CPS 505), and the relayed transmission timing and phase information 4026 can be obtained in other signaling (e.g., via the network interface 4006). For example, deep fading can make it difficult for the AN to receive and demodulate its own relayed access node beacon signal without transmitting at a higher power than other signaling, which may reduce the power budget of the communication signal.Therefore, the reception of relay access node beacon signals combined from multiple AN 515s can improve the effective received power and demodulation accuracy of the relay access node beacon signals. Therefore, the downlink signals received at multiple AN 515s can be used to perform the demodulation of the access node beacon signals from a single AN 515. The demodulation of the access node beacon signals can be performed at the CPS 505 based on the synthesized return signal 907, which may also include the signal information of the access node beacon signals from most or all of the AN 515s. If needed, the end-to-end beamforming of the access node beacon signals can be performed taking into account the access node beacon uplink (e.g., C. r ), repeater loopback (e.g., E), and / or access node beacon downlink (e.g., C t ).

[0177] Feeder Link Damage Elimination

[0178] In addition to the delay equalization of the signal paths from all ANs to the end-to-end repeater, the phase shift caused by the feeder link can be eliminated before beamforming. The phase shift of each link between the end-to-end repeater and the M ANs will be different. The reasons for the different phase shifts of each link include but are not limited to the propagation path length, atmospheric conditions such as scintillation, Doppler shift, and different AN oscillator errors. These phase shifts are usually different for each AN and are time-varying (due to differences in scintillation, Doppler shift, and AN oscillator errors). By eliminating the dynamic feeder link impairments, the rate of beam weight adaptation may be slower than an alternative where the beam weights adapt fast enough to track the dynamic characteristics of the feeder link.

[0179] In the return direction, the feeder downlink impairments of AN are common to both the repeater PN beacon and the user data signal (e.g., the return downlink signal). In some cases, coherent demodulation of the repeater PN beacon provides channel information for eliminating most or all of these impairments from the return data signal. In some cases, the repeater PN beacon signal is a known PN sequence that is continuously transmitted and positioned within the communication data band. The equivalent (or effective) isotropic radiated power (EIRP) of this in-band PN signal is set such that the interference to the communication data is not greater than the maximum acceptable level. In some cases, the feeder link impairment cancellation process for the return link involves coherent demodulation and tracking of the received timing and phase of the repeater PN beacon signal. For example, the repeater beacon signal demodulator 2511 can determine the receive timing and phase adjustment 2512 based on comparing the repeater PN beacon signal with a local reference signal (e.g., a local oscillator or PLL) to compensate for the feeder link impairments. The recovered timing and phase differences are then removed from the return downlink signal (e.g., via the receive timing and phase adjuster 4024), and thus the feeder link impairments are removed from the communication signal (e.g., the return downlink signal 527). After feeder link impairment cancellation, the return link signals from the beams will have a common frequency error at all ANs and are thus suitable for beamforming. The common frequency error can include, but is not limited to, contributions from user terminal frequency error, user terminal uplink Doppler error, end-to-end repeater frequency conversion frequency error, and repeater PN beacon frequency error.

[0180] In the forward direction, the access node beacon signals from each AN can be used to help cancel the feeder uplink impairments. The feeder uplink impairments will be imposed on the forward link communication data (e.g., signals specific to the access node) as well as the access node beacon signals. Coherent demodulation of the access node beacon signals can be used to recover the timing and phase differences of the access node beacon signals (e.g., relative to the repeater beacon signal). The recovered timing and phase differences are then removed from the transmitted access node beacon signals such that the access node beacon signals arrive in phase with the repeater beacon signals.

[0181] In some cases, the forward feeder link cancellation process is a phase-locked loop (PLL) with a path delay from the AN to the end-to-end repeater and back within a loop structure. In some cases, the round-trip delay from the AN to the end-to-end repeater and back to the AN can be large. For example, a geostationary satellite acting as an end-to-end repeater will generate a round-trip delay of approximately 250 milliseconds (ms). To maintain the stability of the loop in the presence of a large delay, a very low loop bandwidth can be used. For a 250-ms delay, the PLL closed-loop bandwidth will typically be less than 1 Hz. In this case, both the satellite and the AN can use high-stability oscillators to maintain reliable phase locking, as Fig.39 as shown by block 2437 in (see below).

[0182] In some cases, the access node beacon signal is a burst signal transmitted only during a calibration interval. During the calibration interval, communication data is not transmitted to eliminate this interference to the access node beacon signal. Since no communication data is transmitted during the calibration interval, the transmission power of the access node beacon signal may be high compared to what is required when it is broadcast during communication data. This is because interference to communication data (which does not exist at this time) is not considered. When the access node beacon signal is transmitted during the calibration interval, this technique gives the access node beacon signal a strong signal-to-noise ratio (SNR). The occurrence frequency of the calibration interval is the reciprocal of the elapsed time between calibration intervals. Since each calibration interval provides a phase sample to the PLL, this calibration frequency is the sampling rate of this discrete-time PLL. In some cases, the sampling rate is high enough to support the closed-loop bandwidth of the PLL with a small amount of aliasing. The product of the calibration frequency (loop sampling rate) and the calibration interval represents the fraction of time that the end-to-end repeater cannot be used for communication data without additional interference from the channel sounding probe signal. In some cases, a value less than 0.1 is used, and in some cases, a value less than 0.01 is used.

[0183] Fig.39 is a block diagram of an exemplary AN transceiver 2409. The input terminal 2408 of the AN transceiver 2409 receives the end-to-end return link signal received by the AN 515 (e.g., for one of a plurality of frequency sub-bands). The input terminal 2408 is coupled to the input terminal 2501 of a down-converter (D / C) 2503. The output terminal of the D / C 2503 is coupled to an analog-to-digital converter (A / D) 2509. The output terminal of the A / D 2509 is coupled to a receive time regulator 2515 and / or a receive phase regulator 2517. The receive time regulator 2515 and the receive phase regulator 2517 may be shown Fig.38Aspects of the receive timing and phase adjuster 4024. The D / C 2503 is an orthogonal downconverter. Thus, the D / C 2503 outputs in-phase and quadrature outputs to the A / D 2509. The received signals can include communication signals (e.g., the composite of the return uplink signals transmitted by user terminals), access node beacon signals (e.g., transmitted from the same AN and / or other ANs), and repeater beacon signals. The digital samples are coupled to the repeater beacon signal demodulator 2511. The repeater beacon signal demodulator 2511 demodulates the repeater beacon signals. In addition, the repeater beacon signal demodulator 2511 generates a time control signal 2513 and a phase control signal 2514 to eliminate feeder link impairments based on the received repeater beacon signals. Such impairments include Doppler errors, AN frequency errors, scintillation effects, path length variations, etc. By performing coherent demodulation of the repeater beacon signals, a phase-locked loop (PLL) can be used to correct most or all of these errors. By correcting the errors in the repeater beacon signals, the corresponding errors in the communication signals and access node beacon signals on the feeder link are also corrected (e.g., since such errors are common to the repeater beacon signals, access node beacon signals, and communication signals). After feeder link impairment cancellation, the end-to-end return link communication signals from the user terminal 517 nominally have the same frequency error at each of the M ANs 515. This common error includes user terminal frequency error, user link Doppler error, end-to-end repeater frequency conversion error, and repeater beacon signal frequency error.

[0184] The digital samples with feeder link impairments eliminated are coupled to a multiplexer 2518, which can be an Fig.38 example of the multiplexer 4004. The multiplexer 2518 associates (e.g., time stamps) these samples with the repeater timing information 2520 from the repeater beacon signal demodulator 2511. The output of the multiplexer 2518 is coupled to the output port 2410 of the AN transceiver 2409. The output port 2410 is coupled to the multiplexer 2413 and is coupled to the CPS 505 through an interface 2415 (see Fig.40 ). The CPS 505 can then use the time stamps associated with the received digital samples to align the digital samples received from each AN 515. In addition or alternatively, feeder link impairment cancellation can be performed at the CPS 505. For example, digital samples of the end-to-end return link signals with embedded repeater beacon signals can be sent from the ANs 515 to the CPS 505, and the CPS 505 can use the synchronization timing information (e.g., the embedded repeater beacon signals) in each of the composite return signals to determine the corresponding adjustments to the respective composite return signals to compensate for downlink channel impairments.

[0185] The access node beacon signal 2530 can be locally generated by the access node beacon signal generator 2529. The access node beacon signal demodulator 2519 demodulates the access node beacon signal received by the AN 515 (e.g., after the access node beacon signal is relayed by the end-to-end repeater and received at the input terminal 2408). The repeater beacon signal demodulator 2511 provides the received repeater timing and phase information signal 2521 to the controller 2523. The controller 2523 also receives the relayed transmission timing and phase information signal 2525 from the access node beacon signal demodulator 2519. The controller 2523 compares the received repeater timing and phase information with the relayed transmission 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 transmission timing information for transmission from the AN 515 to the end-to-end repeater 503. As pointed out in the above discussion, the difference between the repeater timing and phase information (embedded in the repeater beacon signal) and the transmission time and phase information (embedded in the access node beacon signal) is used to adjust the transmission timing and phase information to synchronize the relayed transmission timing and phase information with the received repeater timing and phase information. The access node beacon signal generator 2529 is coarsely time-adjusted by the signal 2527, and the receive time regulator 2539 is finely time-adjusted by the signal 2540. When the relayed transmission timing and phase information 2525 from the access node beacon signal demodulator 2519 is synchronized with the received repeater timing and phase information 2521, the access node beacon signal generator 2529 generates a timestamp 2531 that helps synchronize the access node beacon signal 2530 with the access node-specific forward signal from the transmitted CPS 505. That is, data samples from the CPS 505 are received at the input port 2423 together with the timestamp 2535, which indicates the expected time for the associated data samples to reach the end-to-end repeater 503. The buffer, time alignment, and addition module 2537 buffers the data samples coupled from the CPS 505 and adds them to the samples from the access node beacon signal generator 2529 based on the timestamps 2535, 2531. PN samples and communication data samples with the same time (as indicated by the timestamp) are added together. In this example, multiple beam signals (x k (n)*b k ) are added together in the CPS 505, and the access node-specific forward signal synthesized including the multiple beam signals is sent from the CPS 505 to the AN.

[0186] When properly aligned by the AN, data samples arrive at the end-to-end repeater 503 at the desired time (e.g., simultaneously with the arrival of the same data samples from other ANs). The transmission time regulator 2539 performs fine time adjustment based on the fine time controller output signal 2540 from the time controller module 2523. The transmission phase regulator 2541 adjusts the phase of the signal in response to the phase control signal 2542 generated by the access node beacon signal demodulator 2519. The transmission time regulator 2539 and the transmission phase regulator 2541 can illustrate aspects of, for example Fig.38 the transmission timing and phase compensator 4020.

[0187] The output of the transmission phase regulator 2541 is coupled to the input of a digital-to-analog converter (D / A) 2543. The quadrature analog output of the D / A 2543 is coupled to an upconverter (U / C) 2545 for transmission to the end-to-end repeater 503 by the HPA 2433 (see Fig.40 ). The amplitude control signal 2547 provided by the access node beacon signal demodulator 2519 provides amplitude feedback to the U / C 2545 to compensate for terms such as uplink rain fade.

[0188] In some cases, the PN code used by each AN for the access node beacon signal 2530 is different from the PN code used by each other AN. In some cases, the PN codes in the access node beacon signals are each different from the repeater PN code used in the repeater beacon signal. Thus, each AN 515 can be able to distinguish its own access node beacon signal from the access node beacon signals of other ANs 515. The AN 515 can distinguish its own access node beacon signal from the repeater beacon signal.

[0189] As previously described, the end-to-end gain from any point in the coverage area to any other point in that area is a multipath channel with L different paths, which can result in very deep fades in some point-to-point channels. Transmit diversity (forward link) and receive diversity (return link) are very effective in mitigating deep fades and enabling the communication system to operate. However, for the access node beacon signal, there is no transmit and receive diversity. Thus, the point-to-point link of the loopback signal (i.e., the signal transmission from the AN back to the same AN) can experience an end-to-end gain that is much lower than the average. In the case of a large number of receive / transmit signal paths (L), values 20 dB lower than the average can occur. These few low end-to-end gains result in a reduced SNR for these ANs and can make link closure challenging. Thus, in some cases, higher gain antennas are used at the AN. Alternatively, refer to Fig.16Exemplary transponders can include a phase regulator 418 in each of the receive / transmit signal paths. The phase regulator 418 can be individually adjusted by a phase shift controller 427 (e.g., under the control of a telemetry, tracking, and command (TT&C) link from a ground-based control center). Adjusting the relative phase can help increase the end-to-end gain of the low-gain loopback path. For example, the goal can be to select a phase shift setting to increase the value of the worst-case loopback gain (the gain from AN back to itself). Note that the choice of phase generally does not change the distribution of gains when evaluating all points in the coverage area to the distribution of gains when evaluating all other points in the coverage area, but can increase the gain of the low-gain loopback path.

[0190] For a detailed illustration, consider the set of gains from each of the M ANs 515 to all other ANs 515. There are M 2 gains, and only M of them are the gains of the loopback paths. Consider two gain distributions. The first distribution is the total distribution of all paths (M 2 ) that can be estimated by compiling a histogram of all M 2 paths. For ANs uniformly 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 a histogram of only the M loopback paths. In many cases, a custom selection of the receive / transmit signal path phase settings (and optionally, gain settings) does not bring about a significant change to the total distribution. This is especially true for the case of a random or interleaved mapping of transmit elements to receive elements. However, in most cases, the loopback distribution can be improved by a custom selection of phase (and optionally, gain) settings (as opposed to random values). This is because the set of loopback gains consists of M paths (as opposed to M 2 total paths), and the number of degrees of freedom in phase and gain adjustment is L. Typically, L is of the same order as M, which enables significant improvement of the low loopback gain through a custom phase selection. From another perspective, a custom phase selection may not necessarily eliminate low end-to-end gains, but rather move them from the loopback gain set (the M members in the set) to the non-loopback gain set (M 2 - M members). For non-trivial values of M, the larger set is usually much larger than the former.

[0191] The AN 515 can handle one or more frequency subbands. Fig.40 is a block diagram of an exemplary AN 515 in which multiple frequency subbands are processed separately. On the end-to-end return link 523 (see Figure 5),The AN515 receives the return downlink signal 527 from the end-to-end repeater 503 via the low-noise amplifier (LNA) 2401. The amplified signal is coupled from the LNA 2401 to the power splitter 2403. The power splitter 2403 divides the signal into multiple output signals. Each signal is output on one of the output ports 2405, 2407 of the power splitter 2403. One of the output ports 2407 can be set as a test port. The other ports 2405 are coupled to the input 2408 of a corresponding one of the multiple AN transceivers 2409 (only one is shown). The AN transceiver 2409 processes the signals received on the corresponding subbands. The AN transceiver 2409 performs several functions discussed in detail above. The output 2410 of the AN transceiver 2409 is coupled to the input port 2411 of the subband multiplexer 2413. These outputs are combined in the subband multiplexer 2413 and output to the distribution network interface 2415. The interface 2415 provides an interface for data from the AN 515 to the CPS 505 or from the CPS 505 to the AN 515 via the distribution network (see Figure 5 ) Processing frequency subbands can help reduce the performance requirements for the RF components used to implement the end-to-end repeater and the AN. For example, by dividing a 3.5 GHz bandwidth (such as can be used in a Ka-band system) into seven subbands, each subband is only 500 MHz wide. That is, each of the forward signals specific to the access node can include multiple sub-signals associated with different subbands (e.g., associated with different subsets of the forward user beam coverage area), and the AN transceiver 2409 can up-convert the sub-signals to different carrier frequencies. This bandwidth division can allow the use of lower tolerance components because the amplitude and phase variations between different subbands can be compensated for by separate beamforming weights, calibration, etc. for the different subbands. Of course, other systems can use different numbers of subbands and / or test ports. In some cases, a single subband can be used and may not include all the components shown here (e.g., omitting the power splitter 2403 and the multiplexer 2413).

[0192] On the end-to-end repeater link 501, data is received from the CPS 505 by the interface 2415. The received data is coupled to the input 2417 of the subband demultiplexer 2419. The subband demultiplexer 2419 divides the data into a plurality of data signals. These data signals are coupled from the output port 2421 of the subband demultiplexer 2419 to the input port 2423 of the AN transceiver 2409. The output port 2425 of the AN transceiver 2409 is coupled to the input port 2427 of the adder module 2429. The adder module 2429 adds the signals output from the seven AN transceivers 2409. The output port 2431 of the adder module 2429 couples the output of the adder module 2429 to the input port 2433 of the high power amplifier (HPA) 2435. The output of the HPA 2435 is coupled to an antenna (not shown) that transmits the output signal to the end-to-end repeater 503. In some cases, an ultra-stable oscillator 2437 is coupled to the AN transceiver 2409 to provide a stable reference frequency source.

[0193] Beam weight calculation

[0194] Return to Figure 8 , Figure 8 is an exemplary description of the signal on the return link. A mathematical model of the end-to-end return link can be used to describe the link as:

[0195]

[0196] where,

[0197] x is a K×1 column vector of the transmitted signal. In some cases, the magnitude squared of each element in x is defined as one (equal transmitted power). In some cases, this is not always the case.

[0198] y is a K×1 column vector of the received signal after beamforming.

[0199] Ar is the L×K return uplink radiation matrix. The element a lk contains the gain and phase of the path from the reference position in beam K to the lth (letter "el") receiving antenna element 406 in the receiving array. In some cases, the values of the return uplink radiation matrix are stored in the channel data repository 941 (refer to Fig.30 ).

[0200] E is the L×L payload matrix. The element e ijDefine the signal gain and phase from the j-th antenna element 406 in the receive array to the i-th antenna element 409 in the transmit array. In some cases, the E matrix is a diagonal matrix, except for accidental crosstalk between paths (caused by limited isolation of the electronics). The matrix E can be normalized such that the sum of the squares of the magnitudes of all elements in the matrix is L. In some cases, the values of the payload matrix are stored in the channel data repository 941 (see Fig.29 ).

[0201] Ct returns the downlink radiation matrix for M×L. Element c ml contains the gain and phase of the path from the l-th (letter "el") antenna element in the transmit array to the m-th AN 515 among the M ANs 515. In some cases, the value of the downlink radiation matrix returned is stored in the channel data repository 941 (see Fig.29 ).

[0202] Hret returns the channel matrix for M×K, which is equal to the product Ct×E×Ar.

[0203] n ul is an L×1 noise vector of complex Gaussian noise. The covariance of the uplink noise is the L×L identity matrix.

[0204] σ 2 is the noise variance. is experienced on the uplink, while is experienced on the downlink.

[0205] n dl is an M×1 noise vector of complex Gaussian noise. The covariance of the downlink noise is the M×M identity matrix.

[0206] Bret is the K×M matrix of end-to-end return link beam weights.

[0207] Generally speaking, the above describes multiple examples in a way that assumes certain similarities between the forward end-to-end multipath channel and the return end-to-end multipath channel (e.g., see Figures 6 to 11)。For example, generally speaking, the forward and return channel matrices were described above with reference to the M, K, E, and other models. However, these descriptions were only used to simplify the description for increased clarity and do not limit the examples to cases where the forward and return directions have the same configuration. For example, in some cases, the same transponder is used for both forward traffic and return traffic, and thus the payload matrix E can be the same for both forward and return end-to-end beamforming (and the corresponding beam weight calculations). In other cases, different transponders are used for forward traffic and return traffic, and different forward payload matrices (Efwd) and return payload matrices (Eret) can be used to model the corresponding end-to-end multipath channels and calculate the corresponding beam weights. Similarly, in some cases, the same M ANs 515 and K user terminals 517 are considered to be 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.

[0208] The beam weights can be calculated in many ways to meet system requirements. In some cases, they are calculated after the end-to-end repeater deployment. In some cases, the payload matrix E is measured before deployment. In some cases, the beam weights are calculated with the aim of increasing the signal-to-noise-plus-interference ratio (SINR) of each beam and can be calculated as follows:

[0209]

[0210] where R is the covariance of the received signal, and (*) H is the conjugate transpose (Hermetian) operator.

[0211] The k,m element of the K×M return beam weight matrix Bret provides the weight to form a beam from the user terminal in the kth user beam 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., the elements of the channel matrix Hret) of each of the end-to-end multipath channels (e.g., each of the end-to-end return multipath channels).

[0212] Equation 2 is true, where R is the covariance of the received signal provided in Equation 3. Thus, when all the matrices of Equations 1, 2, and 3 are known, the beam weights for forming the end-to-end beam can be directly determined.

[0213] This weight set reduces the mean square error between x and y. It also increases the end - to - end signal - to - interference - plus - noise ratio (SINR) of each of the K end - to - end return - link signals 525 (from each of the K beams).

[0214] The first term in Equation 3 is the covariance of the downlink noise (which is uncorrelated). The second term in Equation 3 is the covariance of the uplink noise (which is correlated at the AN). The third term HH in Equation 3 H is the covariance of the signal. Setting the variance of the uplink to zero and ignoring the last term (HH H ) results in a weight set that increases the downlink signal - to - noise ratio by phase - aligning the received signals on each of the M ANs 515. Setting the downlink noise variance to zero and ignoring the 3rd term results in a weight set that increases the uplink SINR. Setting both the uplink and downlink noise variances to zero results in a decorrelating receiver that increases the carrier - to - interference (C / I) ratio.

[0215] In some cases, the beam weights are normalized such that the sum of the squares of the magnitudes of any row of Bret is one.

[0216] In some cases, the solution of Equation 2 is determined by prior knowledge of: the matrices Ar, Ct, and E, and the noise vectors n ul and n dl and their variances. Knowledge of the matrix element values can be obtained during measurement procedures that can be carried out during the manufacture and testing of the relevant components of the end - to - end repeater. This may work well for systems where it is not expected that the values in the matrix will change significantly during system operation. However, for some systems, especially those operating at higher frequency bands, such an expectation may not exist. In such cases, the matrices Ar, Ct, and E can be estimated after deploying the vehicle (such as a satellite) on which the end - to - end repeater is installed.

[0217] In some cases where no prior information is used to set the weights, the solution of Equation 2 can be determined by estimating the values of R and H. In some cases, a designated user terminal 517 located at the center of each user beam coverage area 519 transmits a known signal x during a calibration period. The vector received at the AN 515 is:

[0218] u = H x + Ct E n ul + n dl Equation 4

[0219] In one example, the CPS 505 estimates the values of R and H based on the following relationship:

[0220]

[0221]

[0222]

[0223] is the estimate of the covariance matrix R, is the estimate of the channel matrix H, and is the estimate of the correlation vector, is the conjugate of the k-th component of the transmitted vector with a frequency error induced by the uplink transmission. In some cases, no return communication data is transmitted during the calibration period. That is, during the calibration period, only the calibration signal known to the AN is transmitted on the end-to-end return link to allow The value of is determined using the above equation based on the received vector u. This in turn allows the determination of The value of. The covariance matrix estimate and the channel matrix estimate Both are determined based on the signals received during the calibration period.

[0224] In some cases, the CPS 505 can estimate the covariance matrix This can be seen from the fact that is determined based only on the received signal u. Nevertheless, The value of is estimated based on the signals received during the calibration period, during which only the calibration signal is transmitted on the return link.

[0225] In some cases, when communication data is transmitted on the return link, estimates are made of both the channel matrix and the covariance matrix In this case, the covariance matrix is estimated as pointed out 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 pointed out above in Equations 6 and 7.

[0226] The signal after beamforming and the interference components of the signal are included in the vector Bret H x. The signal and interference power of each of these beams are included in the K×K matrix Bret H. The power of the k-th diagonal element of Bret H is the desired signal power from beam k. The sum of the squared magnitudes of all elements other than the diagonal element in row k is the interference power in beam k. Therefore, the C / I of beam k is:

[0227]

[0228] where s kj is an element of Bret H. The uplink noise is included in the vector Bret Ct En ul which has a K×K covariance matrix The k-th diagonal element of the covariance matrix contains the uplink noise in beam k. The uplink signal-to-noise ratio for beam k is then calculated as:

[0229]

[0230] where t kk is the k-th diagonal element of the uplink covariance matrix. The downlink noise is included in the vector Bretn dl which has a covariance by means of the normalized beam weights Therefore, the downlink signal-to-noise ratio is:

[0231]

[0232] The end-to-end SINR is the combination of equations 8 to 10:

[0233]

[0234] The above equations describe how to calculate the end-to-end SINR taking into account the payload matrix E. The payload matrix can be constructed by the intelligent selection of the gain and phase of each element of E. The gain and phase of the diagonal elements of E that optimize certain utility metrics (which are typically functions of the K-beam SINR calculated as above) can be selected and implemented by setting the phase shifters 418 in each of the L transponders 411. Candidate utility functions include but are not limited to the sum of SINR k (total SINR), the sum of Log(1 + SINR k ) (proportional to the total throughput), or the total power in the channel matrix H. In some cases, the improvement of the utility function by customizing the gain and phase is very small and negligible. This is sometimes the case when using a random or interleaved mapping of the antenna elements. In some cases, the utility function can be improved by a non-trivial amount by customizing the selection of the gain and phase of the received / transmitted signals.

[0235] Returning to Fig. 9 , the mathematical model of the end-to-end forward link 501 can be used to describe the link 501 as:

[0236]

[0237] where,

[0238] x is a K×1 column vector of the transmitted signal. The squared magnitude of each element in x is defined to be one (equal signal power). In some cases, unequal transmission power can be achieved by selecting the forward beam weights.

[0239] y is a K×1 column vector of the received signal.

[0240] Cr is an L×M forward uplink radiation matrix. The element c lm includes the gain and phase of the path 2002 from the m-th AN 515 to the l-th (letter "el") receiving antenna element 406 of the receiving antenna array on the end-to-end repeater 503. In some cases, the values of the forward uplink radiation matrix are stored in the channel data repository 921 (see Fig.29 ).

[0241] E is an L×L payload matrix. The element e ij defines the gain and phase of the signal from the j-th receiving array antenna element to the i-th antenna element in the transmitting array. Except for the accidental crosstalk between paths (caused by the limited isolation of the electronics), the E matrix is a diagonal matrix. In some cases, the matrix E is normalized such that the sum of the squared magnitudes of all elements in the matrix is L. In some cases, the values of the payload matrix are stored in the channel data repository 921 (see Fig.29 ).

[0242] At is a K×L forward downlink radiation matrix. The element a kl includes the gain and phase of the path from the antenna element L (letter "el") in the transmitting array of the end-to-end repeater 503 to the reference position in the user beam k. In some cases, the values of the forward downlink radiation matrix are stored in the channel data repository 921 (see Fig.29 ).

[0243] Hfwd is a K×M forward channel matrix, which is equal to the product A t EC r .

[0244] n ul is an L×1 noise vector of complex Gaussian noise. The covariance of the uplink noise is:

[0245]

[0246] where I L is an L×L identity matrix.

[0247] n dl is a K×1 noise vector of complex Gaussian noise. The covariance of the downlink noise is:

[0248]

[0249] where I K is the K×K identity matrix.

[0250] Bfwd is the M×K beamweight matrix of the end-to-end forward link beam weights.

[0251] The beam weight of user beam k is the elements in column k of Bfwd. Different from the return link, the C / I of beam k is not determined by the beam weight of beam k. The beam weight of beam k determines the uplink signal-to-noise ratio (SNR) and the downlink SNR, as well as the carrier (C) power in the C / I. However, the interference power in beam k is determined by the beam weights of all other beams except beam k. In some cases, the beam weight of beam k is selected to increase the SNR. Since C increases, such beam weights also increase the C / I of beam k. However, it may cause interference to other beams. Therefore, different from the case of the return link, the optimal beam weights are not calculated beam by beam (independent of other beams).

[0252] In some cases, the beam weights (including the radiation matrix and the payload matrix used to calculate them) are determined after the end-to-end repeater is deployed. In some cases, the payload matrix E is measured before deployment. In some cases, the beam weight set can be calculated by using the interference generated by beam k in other beams and counting it as the interference in beam k. Although this method may not calculate the optimal beam weights, it can be used to simplify the weight calculation. This allows the weight set to be determined for each beam independently of all other beams. Subsequently, the resulting forward beam weights are calculated similarly to the return beam weights:

[0253] Bfwd = H H R -1 , where, Equation 13

[0254]

[0255] The first term in Equation 14 is the covariance of the downlink noise (uncorrelated). The second term is the covariance of the uplink noise (which is correlated at AN). The third term HH H is the covariance of the signal. Set the variance of the uplink noise to zero and ignore the last term (HH H) Results in a weight set that increases the downlink signal-to-noise ratio by phase-aligning the signals received at the M ANs 515. Setting the downlink noise variance to zero and ignoring the third term results in a weight set that increases the uplink SNR. Setting both the uplink and downlink noise variances to zero results in a decorrelating receiver that increases the C / I ratio. For the forward link, downlink noise and interference generally dominate. Therefore, these terms are usually useful in beam weight calculations. In some cases, the second term (uplink noise) in Equation 14 is negligible compared to the first term (downlink noise). In such cases, the second term can be ignored in the covariance calculation, further simplifying the calculation while still producing a beam weight set that increases the end-to-end SINR.

[0256] As with the return link, the beam weights can be normalized. For transmitter beam weights where equal power is allocated to all K forward link signals, each column of Bfwd can be scaled such that the sum of the squared magnitudes of the elements in any column adds up to one. Equal power sharing will provide each signal with the same fraction of the total AN power (the total power obtained from all ANs allocated to signal x k ). In some cases, for the forward link, unequal power sharing among the forward link signals is achieved. Therefore, in some cases, some beam signals receive more than one equal share of the total AN power. This can be used to equalize the SINR across all beams, or to provide a larger SINR for more important beams compared to less important beams. To generate beam weights for unequal power sharing, the M×K equal power beam weight matrix Bfwd is right-multiplied by the K×K diagonal matrix P, so the new Bfwd = Bfwd P. Assume

[0257]

[0258] Then the squared value of the kth diagonal element represents the power allocated to the user signal x k . The power sharing matrix P is normalized such that the sum or squares of the diagonal elements equals K (the off-diagonal elements are zero).

[0259] In some cases, the solution to Equation 13 is determined by prior knowledge of the matrices At, Cr, and E, and the noise vectors n ul and n dl and their variances. In some cases, knowledge of the matrices can be obtained during the measurement process that can be carried out during the manufacture and testing of the relevant components of the end-to-end repeater. This may work well for systems where it is not expected that the values in the matrices will change significantly relative to previously measured values during system operation. However, for some systems, especially those operating at higher frequency bands, this may not be the case.

[0260] In some cases where prior information is not used to set the weights, the values of R and H for the forward link can be estimated to determine the solution of Equation 13. In some cases, the AN transmits channel sounding probes during a calibration period. The channel sounding probes can be many different types of signals. In one case, different, orthogonal, and known PN sequences are transmitted by each AN. The channel sounding probes can be pre-corrected in time, frequency, and / or phase to eliminate feeder link impairments (discussed further below). All communication data can be turned off during the calibration interval to reduce interference to the channel sounding probes. In some cases, the channel sounding probes can be the same signals as those used for feeder link impairment cancellation.

[0261] During the calibration interval, terminals located at the center of each beam can be designated to receive and process the channel sounding probes. The K×1 vector u received during the calibration period is u = Hx + AtEn ul + n dl , where x is the M×1 vector of the transmitted channel sounding probes. In some cases, each designated terminal first eliminates spurious frequency errors (caused by Doppler shift and terminal oscillator errors), and then correlates the resulting signal with each of the M known orthogonal PN sequences. These correlation results are M complex numbers (amplitude and phase) for each terminal, and these results are transmitted back to the CPS via the return link. The M complex numbers calculated by the terminal located at the center of the kth beam can be used to form the estimated kth row of the channel matrix . By using the measurements obtained from all K designated terminals, an estimate of the entire channel matrix is obtained. In many cases, it is useful to combine the measurements from multiple calibration intervals to improve the estimate of the channel matrix. Once the estimate of the channel matrix is determined, the covariance matrix can be estimated by using a value of 0 for the second term according to Equation 14. If the uplink noise (the second term in Equation 14) is negligible relative to the downlink noise (the first term in Equation 14), this can be a very accurate estimate of the covariance matrix. Subsequently, the forward link beam weights can be calculated by using the estimates of the channel matrix and the covariance matrix in Equation 13. Thus, in some cases, the calculation of the beam weights includes estimating the end-to-end forward gain of each in the end-to-end forward multipath channel between the AN 515 and a reference position in the user beam coverage area (i.e., the value of the element of the channel matrix Hfwd). In other cases, the calculation of the beam weights includes estimating the end-to-end forward gain of the K×M end-to-end forward multipath channels from the M ANs 515 to a reference position located within the K user beam coverage areas.

[0262] The signal after beamforming and the interference components of the signal are included in the vector H Bfwd x (the product of H, Bfwd, and x). The signal and interference power of each of these beams are included in the K×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 squared magnitudes of all elements in row k except the diagonal element is the interference power in beam k. Therefore, the C / I for beam k is:

[0263]

[0264] where s kj is an element of H B fwd. The uplink noise is included in the vector A t E n ul , which has a K×K covariance matrix The k-th diagonal element of the covariance matrix contains the uplink noise in beam k. The uplink signal-to-noise ratio for beam k is then calculated as:

[0265]

[0266] where t kk is the k-th diagonal element of the uplink covariance matrix. The downlink noise is included in the vector n dl , which has a covariance Therefore, the downlink signal-to-noise ratio is:

[0267]

[0268] The end-to-end SINR is the combination of equations 15 to 17:

[0269]

[0270] The above equations describe how to calculate the end-to-end SINR considering the payload matrix E. The payload matrix can be constructed by the intelligent selection of the gain and phase of each element of E. The gain and phase of the diagonal elements of E that optimize certain utility metrics (which are typically functions of the K-beam SINR calculated as above) can be selected and implemented by setting the phase shifters 418 in each of the L transponders 411. Candidate utility functions include but are not limited to the sum of SINR k (total SINR), the sum of Log(1 + SINR k ) (proportional to the total throughput), or the total power in the channel matrix H. In some cases, the improvement of the utility function by customizing the gain and phase is very small and negligible. This is sometimes the case when using random or interleaved mapping of antenna elements. In some cases, the utility function can be improved by a non-trivial amount by customizing the selection of the gain and phase of the received / transmitted signals.

[0271] Different coverage areas

[0272] Some of the examples described above assume that the end-to-end repeater 503 is designed to serve a single coverage area shared by both the user terminal 517 and the AN 515. For example, some scenarios describe a satellite with an antenna system that illuminates a satellite coverage area, and both the AN and the user terminal are geographically distributed throughout the satellite coverage area (e.g., as Fig. 27 shown). The number of beams that can be formed within the satellite coverage area and the size of these beams (beam coverage area) can be affected by various aspects of the antenna system design such as the number and arrangement of antenna elements, reflector size, and so on. For example, achieving very high capacity can involve deploying a large number of ANs (e.g., hundreds) with sufficient spacing between the ANs to enable end-to-end beamforming. For example, as pointed out above with reference to Fig.28 , increasing the number of ANs can increase system capacity, although there are diminishing returns as the number increases. When an antenna system supports both the user terminal and the AN, achieving such a deployment with sufficient spacing between the ANs can force the ANs to have a very wide geographical distribution (e.g., across the entire satellite coverage area, as Fig. 27 shown). In practice, achieving such a distribution can involve placing the ANs in undesirable locations, such as in areas with poor fiber infrastructure that are difficult to access high-speed networks (e.g., retreating to the poorer fiber infrastructure of the CPS 505, one or more oceans, etc.), in multiple legal jurisdictions, in expensive and / or densely populated areas. Thus, AN placement typically involves various trade-offs.

[0273] Some examples of the end-to-end repeater 503 are designed to have multiple antenna systems, thereby enabling a single end-to-end repeater 503 to separately serve two or more different coverage areas. As described below, the end-to-end repeater 503 can include at least a first antenna system that serves the AN coverage area and at least a second antenna system that serves the user coverage area. Since the user terminal and the AN coverage areas are served by different antenna systems, each antenna system can be designed to meet different design parameters, and each coverage area can be at least partially different (e.g., geographically, in beam size and / or density, in frequency band, etc.). For example, using such a multi-antenna system approach can enable user terminals distributed over a relatively large geographical area (e.g., the entire United States) to be served by a large number of ANs distributed over a relatively small geographical area (e.g., a part of the eastern United States). For example, the physical area of the AN coverage area can be a small fraction of the user coverage area (e.g., less than half, less than a quarter, less than a fifth, less than a tenth).

[0274] Fig.41FIG. 3400 is an illustration of an exemplary end-to-end beamforming system 3400. The system 3400 is an end-to-end beamforming system that includes: a plurality of geographically distributed access nodes (ANs) 515; an end-to-end repeater 3403; and a plurality of user terminals 517. The end-to-end repeater 3403 can be an example of the end-to-end repeater 503 described herein. The ANs 515 are geographically distributed in an AN coverage area 3450, and the user terminals 517 are geographically distributed in 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 repeater 3403, but the AN coverage area 3450 is different from the user coverage area 3460. In other words, the AN area is different from the user coverage area and has a substantial (non-trivial) area that does not overlap with the user coverage area (e.g., more than a quarter, half, etc. of the AN 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 Figure 5 ), the AN 515 can provide signals to the CPS 505 within the ground segment 502 via a distribution network 518, and the CPS 505 can be connected to a data source.

[0275] The end-to-end repeater 3403 includes a separate feeder link antenna subsystem 3410 and a user link antenna subsystem 3420. Each of the feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 is capable of supporting end-to-end beamforming. For example, as described below, each antenna subsystem may have its own one or more cooperating antenna element arrays, its own one or more reflectors, etc. The feeder link antenna subsystem 3410 may include a cooperating feeder link receive element 3416 array and a cooperating feeder link transmit element 3419 array. The user link antenna subsystem 3420 may include a cooperating user link receive element 3426 array and a cooperating user link transmit element 3429 array. The constituent elements are "cooperating" in the sense that the arrays of such constituent elements have characteristics that make their respective antenna subsystems suitable for a beamforming system. For example, a given user link receive element 3426 may receive a superposition synthesis of return uplink signals from multiple (e.g., all) user beam coverage areas 519 in a manner that contributes to forming a return user beam. A given user link transmit element 3429 may transmit a forward downlink signal in a manner that is superimposed with corresponding transmissions from other user link transmit elements 3429 to form some or all of the forward user beams. A given feeder link receive element 3416 may receive a superposition synthesis of forward uplink signals from multiple (e.g., all) ANs 515 in a manner that contributes to forming a forward user beam (e.g., by inducing multipath at the end-to-end repeater 3403). A given feeder link transmit element 3419 may transmit a return downlink signal in a manner that is superimposed with corresponding transmissions from other feeder link transmit elements 3419 to contribute to forming some or all of the return user beams (e.g., by enabling the AN 515 to receive a composite return signal that can be beam weighted to form a return user beam).

[0276] Exemplary end - to - end repeater 3403 includes a plurality of forward - link transponders 3430 and a plurality of return - link transponders 3440. These transponders can be any suitable type of bent - pipe signal path between antenna subsystems. Each forward - link transponder 3430 couples a corresponding one of the receiving elements 3416 in the feeder link to a corresponding one of the transmitting elements 3429 in the user link. Each return - link transponder 3440 couples a corresponding one of the receiving elements 3426 in the user link to a corresponding one of the transmitting elements 3419 in the feeder link. For example, some examples are described as having a one - to - one correspondence (or vice versa) between each receiving element 3426 in the user link and a corresponding transmitting element 3419 in the feeder link, or each receiving element 3426 in the user link is coupled to "one and only one" transmitting element 3419 in the feeder link (or vice versa), and so on. 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 can be selectively coupled to one of a plurality of elements (e.g., via a switch or other means as described below). For example, the end - to - end repeater 3403 can include one feeder - link antenna subsystem 3410 and two user - link antenna subsystems 3420; and each transponder can be coupled on one side to a single feeder - circuit element and on the other side selectively coupled to a single user - link element of the first user - link antenna subsystem 3420 or to a single user - link element of the second user - link antenna subsystem 3420. In such cases of selective coupling, each side of each transponder can still be considered to be coupled to "one and only one" element at any given time (e.g., for a particular signal - related transaction), and so on.

[0277] For forward communication, transmissions from the AN 515 can be received by the feeder link component receiving element 3416 (via the feeder uplink 521), relayed by the forward link transponder 3430 to the user link component transmitting element 3429, and transmitted by the user link component transmitting element 3429 to the user terminal 517 in the user coverage area 3460. For return communication, transmissions from the user terminal 517 can be received by the user link component receiving element, relayed by the return link transponder 3440 to the feeder link component transmitting element 3419, and transmitted by the feeder link component transmitting element 3419 to the AN 515 in the AN coverage area 3450 (via the feeder downlink signal 527). The full signal path from the AN 515 via the end-to-end repeater 3403 to the user terminal 517 is referred to as the end-to-end forward link 501; and the full signal path from the user terminal 517 via the end-to-end repeater 3403 to the AN 515 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 communication.

[0278] In some cases, each of a plurality of geographically distributed access nodes (e.g., AN 515) has an end-to-end beamweighted forward uplink signal output. The end-to-end repeater (e.g., end-to-end repeater 3403) includes an array of cooperating feed link components receiving elements 3416 for wireless communication with the distributed access nodes, an array of cooperating user link components transmitting elements 3419 for wireless communication with a plurality of user terminals 517, and a plurality of forward link transponders 3430. The forward link transponders 3430 are "bent pipe" (or non-processing) transponders such that each transponder outputs a signal corresponding to the signal it receives with less processing or no processing. For example, each forward link transponder 3430 may amplify and / or frequency convert its received signal but does not perform more complex processing (e.g., no demodulation and / or modulation, no satellite carrier beamforming, etc.). In some cases, each forward link transponder 3430 receives an 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 an 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 may be used, and the user link and the feed link may use the same or different frequency ranges. Each forward link transponder 3430 is coupled between a corresponding one of the feed link components receiving elements 3416 and a corresponding one of the user link components transmitting elements 3419 (e.g., in a one-to-one correspondence). The forward link transponders 3430 convert the superposition of the plurality of beamweighted forward uplink signals into a forward downlink signal (e.g., a synthesized input forward signal) via the feed link components receiving elements 3416. Transmission of the forward downlink signal by the user link components transmitting elements 3429 helps to form a forward user beam serving at least some of the plurality of user terminals 517. As described herein, the forward uplink signals may be end-to-end beamweighted and synchronized (e.g., phase synchronization, and if needed, time synchronization) before being transmitted from the AN 515, which can achieve the desired superposition of those signals at the feed link components receiving elements 3416.

[0279] As described herein, transmission contributes to the formation of forward user beams, in the sense that beamforming is end-to-end; beamforming is the result of multiple steps, which include: calculating and applying appropriate weights to the forward uplink signal before transmission from the AN 515 to the repeater; causing multipath by multiple forward link transponders 3430 of the end-to-end repeater 3403; and transmitting the forward downlink signal using the user link array antenna. However, for simplicity, some descriptions may refer to the forward beam as being formed by the superposition of the transmitted forward downlink signals. In some cases, each of the multiple user terminals 517 wirelessly communicates with an array of cooperating user link constituent transmit elements 3429 to receive the combination (e.g., superposition) of the transmitted forward downlink signals.

[0280] In some cases, the end-to-end repeater 3403 further includes an array of user link constituent receive elements 3426 that wirelessly communicate with the user terminals 517, an array of cooperating feeder link constituent transmit elements 3419 that wirelessly communicate with the distributed AN 515, and multiple return link transponders 3440. The return link transponders 3440 may be similar or identical to the forward link transponders 3430 (e.g., bend pipe transponders), except that they are each coupled between a respective one of the user link constituent receive elements 3426 and a respective one of the feeder link constituent transmit elements 3419. The received return uplink signal forms a return downlink signal in the return link transponders 3440 via the array of cooperating user link constituent receive elements 3426. In some cases, each return downlink signal is a respective superposition of the return uplink signals received by the user link constituent receive 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 wirelessly communicates with the array of cooperating user link constituent receive elements 3426 to transmit a respective return uplink signal to the multiple user link constituent receive elements 3426.

[0281] In some cases, the return downlink signal is transmitted by the feeder link component transmitting element 3419 to the geographically distributed ANs 515. As described herein, each AN 515 may receive a superposition synthesis of the return downlink signals transmitted from the feeder link component transmitting element 3419 (i.e., which corresponds to the return downlink signal). The received return downlink signals (referred to as the combined received signals) may be coupled to a return beamformer, which may combine, synchronize, beam weight, and perform any other suitable processing. For example, the return beamformer may weight the received superposition 1706 of these signals (e.g., apply a return beam weight to the combined return signal) before combining the return downlink signals. The return beamformer may also synchronize these combined return signals before combining the combined return signals to at least account for the corresponding path delay differences between the end-to-end repeater 3403 and the AN 515. In some cases, the synchronization may be based on the received beacon signals (received by one or more or all of the ANs 515).

[0282] Due to the end-to-end nature of beamforming, the proper application of the return beam weights by the return beamformer enables the formation of the return user beam, even though the return beamformer may be coupled to the feeder link side of the end-to-end multipath channel and the user beam may be formed at the user link side of the end-to-end multipath channel. Thus, the return beamformer may be referred to as contributing to the formation of the return user beam (many other aspects of the system 3400 also contribute to the end-to-end return beamforming, such as the multipath induced by the return link transponder 3440 of the end-to-end repeater 3403). However, for simplicity, the return beamformer may be referred to as forming the return user beam.

[0283] In some cases, the end-to-end repeater 3403 further includes a feeder link antenna subsystem 3410 for irradiating an access node coverage area (AN coverage area 3450) where a plurality of distributed access nodes are located. The feeder link antenna subsystem 3410 includes an array of receiving elements 3416 that cooperate with the feeder link. In some cases, the end-to-end repeater 3403 further includes a user link antenna subsystem 3420 for irradiating a user coverage area 3460 in which a plurality of user terminals 517 are geographically distributed (e.g., within a plurality of user beam coverage areas 519). The user link antenna subsystem 3420 includes an array of transmitting elements 3429 that cooperate with the user link. In some cases, the user link antenna subsystem 3420 includes a user link receiving array and a user link transmitting array (e.g., separate half-duplex arrays that cooperate with the user link to form elements). The user link receiving array and the user link transmitting array can be spatially interleaved (e.g., pointing to the same reflector), spatially separated (e.g., pointing to a receiving reflector and a transmitting reflector 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 forming transmitting element 3429 shares a radiation structure with the corresponding user link forming receiving element 3426). Similarly, in some cases, the feeder link antenna subsystem 3410 includes a feeder link receiving array and a feeder link transmitting array, and the feeder link receiving array and the feeder link transmitting array can be spatially related in any suitable manner and can directly radiate and point to a single reflector, separate transmitting and receiving reflectors, etc. In other cases, the feeder link antenna subsystem 3410 includes full-duplex elements. The feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 can have the same or different aperture sizes. In some cases, the feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 can operate in the same frequency band (e.g., 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.).

[0284] In such as Fig.41In the example shown, the AN coverage area 3450 is different from the user coverage area 3460. The AN coverage area 3450 can be a single continuous coverage area or multiple non - overlapping coverage areas. Similarly (and regardless of whether the AN coverage area is single or multiple), the user coverage area 3460 can be a single continuous coverage area or multiple non - overlapping 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 includes one or more feeder link reflectors, and the user link antenna subsystem 3420 further includes one or more user link reflectors. In some cases, the feeder link reflector is significantly larger than the user link reflector (e.g., the physical area of the feeder link reflector is at least twice, at least five times, ten times, fifty times, eighty times, etc. that of the user link reflector). In some cases, the physical area of the feeder link reflector is approximately the same as that of the user link reflector (the physical area of the feeder link reflector is within 5%, 10%, 25% of the physical area of the user link reflector).

[0285] In some cases, the system 3400 operates in the context of a terrestrial network function, as referenced Figure 5 as described. For example, the end - to - end repeater 3403 communicates with the AN 515, which 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, e.g., as referenced Fig.29 as described. As described above, the forward beamformer 529 can participate in forming the forward end - to - end beam by applying the calculated forward beam weights (e.g., supplied by the forward beam weight generator 918) to the forward link signal; and the return beamformer 531 can participate in forming the return end - to - end beam by applying the calculated return beam weights (e.g., supplied by the return beam weight generator 935) to the return link signal. As described above, the set of end - to - end forward beam weights and / or end - to - end return beam weights can be calculated based on the estimated end - to - end gain of the end - to - end multipath channel, each end - to - end multipath channel communicatively coupling a corresponding one in the distributed AN 515 to a corresponding location in the user coverage area (e.g., the user terminal 517 or any suitable reference location) via a corresponding plurality of forward link bent - pipe transponders 3430 and / or via a corresponding plurality of return link bent - pipe transponders 3440. In some cases, although not shown, the end - to - end repeater 3403 includes a beacon signal transmitter. The beacon signal transmitter can be as referenced above Fig.15implemented by the beacon signal generator and calibration support module 424 described above. In some cases, the generated beacon signal can be used to enable wireless communication for time synchronization of multiple distributed ANs 515 with the end-to-end repeater 3403 (e.g., using multiple feeder links to form the receiving element 3416 according to the beacon signal).

[0286] In some cases, the system 3400 includes a system for forming multiple forward user beams using end-to-end beamforming. Such cases include means for transmitting multiple forward uplink signals from multiple geographically distributed locations, where the multiple forward uplink signals are formed by a weighted combination of multiple user beam signals, and where each user beam signal corresponds to one and only one user beam. For example, the multiple geographically distributed locations may include multiple ANs 515, and the means for transmitting multiple forward uplink signals may include a forward beamformer 529, a distribution network 518, and some or all of the geographically distributed ANs 515 (communicating with the end-to-end repeater 3403). Such cases may also include means for relaying multiple forward uplink signals to form multiple forward downlink signals. Each forward downlink signal is formed by amplifying a unique superposition of multiple forward uplink signals, and the multiple forward downlink signals are superimposed to form multiple user beams, where each user beam signal is dominant within the corresponding user beam. For example, the means for relaying multiple forward uplink signals to form multiple forward downlink signals may include the end-to-end repeater 3403 (communicating with one or more user terminals within the user beam coverage area 519), which is juxtaposed with multiple signal paths, and the multiple signal paths may include a forward link transponder 3430 and a return link transponder 3440.

[0287] Some such cases include a first means for receiving a first superposition of multiple forward downlink signals and recovering a first user beam signal among the multiple user beam signals. Such a first means may include a user terminal 517 (e.g., including a user terminal antenna and a modem or other components for recovering the user beam signal from the forward downlink signal). Some such cases also include a second means for receiving a second superposition of multiple forward downlink signals and recovering a second user beam signal among the multiple user beam signals (e.g., including a second user terminal 517). For example, the first means for receiving is located within a first user beam, and the second means for receiving is located within a second user beam.

[0288] Fig.42 is a diagram of an exemplary model of a signal path for a signal carrying return data on the end-to-end return link 523. The exemplary model may be similar to the reference Figures 6 to 8operated by the model described above, except that the end-to-end repeater 3403 includes a return link signal path 3502 dedicated to return link communication. Each return link signal path 3502 may include a return link transponder 3440 coupled between a user link component receiving element 3426 and a feeder link component transmitting element 3419. Signals from user terminals 517 in the K user beam coverage areas 519 are transmitted upward (as return uplink signals 525) to the end-to-end repeater 3403, received by an array of L return link signal paths 3502, transmitted through the L return link transponders 3440 to the L corresponding feeder link component transmitting elements 3419, and transmitted by each of the L feeder link component transmitting elements 3419 to some or all of the M ANs 515 (similar to Figure 7 as shown). The multiple return link signal paths 3502 (e.g., return link transponders 3440) induce multipath in the return link communication in this way. 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 the received synthesis of return uplink signals 525 transmitted from multiple user beam coverage areas 519), and is transmitted to the M ANs 515 (e.g., geographically distributed within the AN coverage area 3450) via the return downlink signal 527. As described above, there are L (or at most L) different ways for a signal to enter a particular AN 515 from a user terminal 517 located in a user beam coverage area 519. The end-to-end repeater 3403 thus creates L paths between the user terminal 517 and the AN 515, which are collectively referred to as the end-to-end return multipath channel 1908 (e.g., similar to Figure 8 ).

[0289] The end-to-end return multipath channel can be modeled in the same way as described above. For example, Ar is an L×K return uplink radiation matrix, Ct is an M×L return downlink radiation matrix, and Eret is an L×L return payload matrix for the paths from the user link component receiving element 3426 to the feeder link component transmitting element 3419. As described above, the end-to-end return multipath channel from a user terminal 517 in a particular user beam coverage area 519 to a particular AN 515 is the net effect of L different signal paths induced by the L unique return link signal paths 3502 passing through the end-to-end repeater 3403. In the case of K user beam coverage areas 519 and M ANs 515, there can be M×K induced end-to-end return multipath channels in the end-to-end return link 523 (via the end-to-end repeater 3403), and each can be individually modeled to calculate the M×K return channel matrix Hret (C tThe corresponding element of ×Eret×Ar). As described above (e.g., refer to Figures 6 to 8 ), not all of the AN 515s, user beam coverage regions 519, and / or return link transponders 3440 need to participate in the end-to-end return multipath channel. In some cases, the number K of user beams is greater than the number L of transponders in the signal path of the end-to-end return multipath channel; and / or the number M of ANs is greater than the number L of transponders in the signal path of the end-to-end return multipath channel. As referred to in Figure 5 , the CPS 505 can enable the formation of a return user beam by applying a return beam weight to the received downlink return signal 527 (the received signal is referred to as the combined return signal 907 after being received by the AN, as further explained below). The return beam weight can be calculated based on a model of the M×K signal paths of each end-to-end return multipath channel used to couple a user terminal 517 in a user beam coverage region 519 to one of the multiple AN 515s.

[0290] Fig.43 is a diagram of an exemplary model of the signal path of a signal carrying forward data on the end-to-end forward link 501. The exemplary model can be similar to the reference Figures 9 to 11operate using the model described above, except that the end-to-end repeater 3403 includes a forward link signal path 3602 dedicated to forward link communication. Each forward link signal path 3602 may include a forward link transponder 3430 coupled between a receiving element 3416 of the feeder link assembly and a transmitting element 3429 of the user link assembly. As described above, each forward uplink signal 521 is beam weighted (e.g., at the forward beamformer 515 in the CPS 505 of the ground segment 502) before being transmitted from the AN 515. Each AN 515 receives a unique forward uplink signal 521 and transmits the unique forward uplink signal 521 via one of the M uplinks (e.g., in a time-synchronized manner). The forward uplink signals 521 are received by some or all of the forward link transponders 3430 in a superimposed manner to produce a composite input forward signal 545 from geographically distributed locations (e.g., from the AN 515). Each forward link transponder 3430 receives the composite input forward signal 545 simultaneously, although there is a slight difference in timing due to the difference in the location of each receiving element 3416 of the receiving feeder link assembly associated with each forward link transponder 3430. For example, even though each receiving element 3416 of the feeder link assembly may receive the composite of the same number of 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 the respective receiving elements 3416 of the feeder link assembly, transmitted by the L forward link transponders 3430 to L corresponding transmitting elements 3429 of the user link assembly, and transmitted by the L transmitting elements 3429 of the user link assembly to one or more of the K user beam coverage areas 519 (e.g., as forward downlink signals 522, each corresponding to a respective one of the received composite input forward signals 521). Multiple forward link signal paths 3602 (e.g., forward link transponders 3430) cause multipath in forward link communication in this way. As described above, there are L different ways for a signal to reach a particular user terminal 517 in the user beam coverage area 519 from the AN 515. The end-to-end repeater 3403 thus causes 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 may be collectively referred to as the end-to-end forward multipath channel 2208 (e.g., similar to Fig.10 ).

[0291] 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 of the path from the receiving element 3416 of the feeder link to the transmitting element 3429 of the user link. In some cases, the forward payload matrix Efwd and the return payload matrix Eret may be different to reflect the difference between the forward link signal path 3602 and the return link signal path 3502. As described above, the end-to-end forward multipath channel from a particular AN 515 to a user terminal 517 in a particular user beam coverage area 519 is the net effect of L different signal paths initiated by L unique forward link signal paths 3602 passing through the end-to-end repeater 3403. In the case of K user beam coverage areas 519 and M ANs 515, there can be M×K initiated end-to-end forward multipath channels in the end-to-end forward link 501, and each can be modeled separately to calculate the corresponding elements of the M×K forward channel matrix Hfwd (At×Efwd×Cr). As noted with reference to the return direction, not all ANs 515, user beam coverage areas 519, and / or forward link transponders 3430 need to participate in the end-to-end forward multipath channel. In some cases, the number K of user beams is greater than the number L of transponders in the signal path of the end-to-end forward multipath channel; and / or 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. As referenced Figure 5 It can be seen that the CPS 505 can calculate appropriate beam weights for each of the multiple end-to-end forward multipath channels to form forward user beams. Using multiple transmitters (ANs 515) for a single receiver (user terminal 517) can provide transmission path diversity, so as to enable successful transmission of information to any user terminal 517 in the presence of an intentionally induced multipath channel.

[0292] Figure 41 to Figure 43 An end-to-end repeater 3403 implemented using a separate forward link transponder 3430 and a return link transponder 3440 is described. Fig.44A and Fig.44B respectively show an exemplary forward signal path 3700 (similar to Fig.43 the forward signal path 3602) and a return signal path 3750 (similar to Fig.42Illustration of the return signal path 3502). As described above, the forward signal path 3700 includes a forward link transponder 3430 coupled between the feed link component receiving element 3416 and the user link component transmitting element 3429. The return signal path 3750 includes a return link transponder 3440 coupled between the user link component receiving element 3426 and the feed link component transmitting element 3419. In some cases, each forward link transponder 3430 and each return link transponder 3440 are cross-polar transponders. For example, the forward link transponder 3430 receives the forward uplink signal via left-hand circular polarization (LHCP) at the uplink frequency and outputs the forward downlink signal via right-hand circular polarization (RHCP) at the downlink frequency; and each return link transponder 3440 receives the return uplink signal via right-hand circular polarization (RHCP) at the uplink frequency and outputs the return downlink signal via left-hand circular polarization (LHCP) at the downlink frequency. One such case (i.e., after the polarization described in the previous example) is shown only by following Fig.44A and Fig.44B 's solid lines, and another such case (i.e., after the polarization opposite to that described in the previous example) is shown only by following Fig.44A and Fig.44B 's dashed lines. In other cases, some or all of the transponders may provide bipolar signal path pairs. For example, by following both the solid and dashed lines of Fig.44A and Fig.44B , the forward link transponder 3430 and the return link transponder 3440 can receive the forward uplink signal via both polarizations (LHCP and RHCP) at the same or different uplink frequencies, and can both output the forward downlink signal via both polarizations (LHCP and RHCP) at the same or different downlinks. For example, such cases can enable multiple systems to operate in parallel using any suitable type of interference mitigation technique (e.g., using time division, frequency division, etc.). In some cases, the end-to-end repeater 3403 includes a large number of transponders, such as 512 forward link transponders 3430 and 512 return link transponders 3440 (e.g., a total of 1,024 transponders). Other specific implementations may include a smaller number of transponders, such as 10 or any other suitable number of transponders. In some cases, the antenna elements are implemented as full-duplex structures such that each receiving antenna element shares the structure with the corresponding transmitting antenna element. For example, each of the illustrated antenna elements can be implemented as two of the four waveguide ports of a radiation structure adapted to transmit and receive signals. In some cases, only the feed link elements or only the user link elements are full-duplex. Other specific implementations may use different types of polarizations. For example, in some specific implementations, the transponders may be coupled between receiving and transmitting antenna elements with the same polarity.

[0293] Both the exemplary forward link transponder 3430 and the return link transponder 3440 may include a low-noise amplifier (LNA) 3705, a frequency converter and associated filters 3710, a channel amplifier 3715, a phase shifter 3720, a power amplifier 3725 (e.g., a traveling wave tube amplifier (TWTA), a solid-state power amplifier (SSPA), etc.), and a harmonic filter 3730. In the bipolar embodiment shown, each pole has its own signal path with its own set of transponder components. Some embodiments may have more or fewer components. For example, the frequency converter and associated filters 3710 may be useful where the uplink frequency and the downlink frequency are different. As an example, each forward link transponder 3430 may receive an input in a first frequency band and may output in a second frequency band; and each return link transponder 3440 may receive an input in a first frequency band and may output in a second frequency band.

[0294] In some cases, multiple sub-bands are used (e.g., seven 500 MHz sub-bands as described above). For example, in some cases, transponders operating on the same sub-bands as used in the multiple sub-band embodiments of the terrestrial network may be provided, effectively implementing multiple independent and parallel end-to-end beamforming systems (each end-to-end beamforming system operating in a different sub-band) through a single end-to-end repeater. In 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) of the sub-bands through a wideband transponder (e.g., passing seven sub-bands each 500 MHz wide through a 3.5 GHz bandwidth transponder). In such cases, each transponder may include multiple frequency converters and associated filters 3710 and / or other components dedicated to processing one or more sub-bands.). The use of multiple frequency sub-bands can relax the requirements on the amplitude and phase response of the transponder, as the terrestrial network can separately determine the beam weights used in each sub-band, effectively calibrating out the passband amplitude and phase variations of the transponder. For example, in the case of separate forward and return transponders, and by using seven sub-bands, a total of 14 different beam weights can be used for each beam, i.e., 7 sub-bands × 2 directions (forward and return). In some cases, each transponder path includes only the LNA 3705, the channel amplifier 3715, and the power amplifier 3725. Some embodiments of the end-to-end repeater 3403 include a phase shift controller and / or other controllers that can separately set the phase and / or other characteristics of each transponder as described above.

[0295] An antenna element can transmit and / or receive signals in any suitable manner. In some cases, the end-to-end repeater 3403 has one or more array-fed reflectors. For example, the feeder link antenna subsystem 3410 can have a feeder link reflector for transmission and reception, or separate feeder link transmit and receive reflectors. Similarly, the user link antenna subsystem 3420 can have a user link reflector for transmission and reception, or separate user link transmit and receive reflectors. In an exemplary case, the feeder link antenna subsystem 3410 includes an array of radiating structures, and each radiating structure includes a feeder link component receiving element 3416 and a feeder link component transmitting element 3419. In this case, the feeder link antenna subsystem 3410 can also include a feeder link reflector that illuminates the feeder link component receiving element 3416 and is illuminated by the feeder link component transmitting element 3419. In some cases, the reflector is implemented as multiple reflectors, which can have different shapes, sizes, orientations, etc. In other cases, the feeder link antenna subsystem 3410 and / or the user link antenna subsystem 3420 are implemented as, for example, direct-radiation arrays without reflectors.

[0296] As described above, separating the feeder link antenna subsystem 3410 and the user link antenna subsystem 3420 can enable serving 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 having a much larger physical area than the reflector of the user coverage area 3460. The larger reflector can allow a large number of ANs 515 to be geographically distributed in a significantly smaller AN coverage area 3450, such as distributed in a small subset of the user coverage area 3460. Examples are shown in Fig.45 and Fig.46 Some examples are shown in

[0297] Fig.45 An example of the visible earth coverage area 3800 of the end-to-end repeater 3403 (e.g., a satellite) is shown. In the exemplary end-to-end repeater 3403, the feeder link antenna subsystem 3410 includes an 18-meter feeder link reflector, and the user link antenna subsystem 3420 includes a 2-meter user link reflector (e.g., the area of the feeder link reflector is eight times larger than the area of the user link reflector). Each antenna subsystem also includes an array of 512 combined receive / transmit elements. For example, the exemplary end-to-end repeater 3403 can 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., as shown in Fig.44BAs shown, 512 return signal paths 3750 are formed. The user coverage area 3460 includes 625 user beam coverage areas 519. The small shaded area in the eastern United States is the AN coverage area 3450, in which 597 ANs 515 are distributed. The AN coverage area 3450 is a small subset of the large user coverage area 3460, but still provides a large capacity with a large number of ANs 515. This relatively dense AN coverage area 3450 is referred to herein as the "AN field".

[0298] Fig.46 An example of the end-to-end repeater 3403 (e.g., a satellite) continental United States (CONUS) coverage area 3900 is shown. The exemplary end-to-end repeater 3403 is similar to Fig.45 the example shown, except that the user link antenna subsystem 3420 includes a 5-meter user link reflector (e.g., the feed link reflector is approximately four times that of the user link reflector). The user coverage area 3460 includes 523 user beam coverage areas 519. The AN coverage area 3450 (AN field) is the same as Fig.45 that: the area in the eastern United States that is a small subset of the user coverage area 3460 and in which 597 ANs 515 are distributed.

[0299] Multiple coverage areas

[0300] In the above-described exemplary end-to-end repeater 3403, the user link antenna subsystem 3420 is described as a single antenna subsystem (e.g., having a single user link reflector), and the feed link antenna subsystem 3410 is described as a single antenna subsystem (e.g., having a single feed link reflector). In some cases, the user link antenna subsystem 3420 may include one or more antenna subsystems associated with one or more user link reflectors (e.g., two or more subarrays that make up the antenna elements), and the feed link antenna subsystem 3410 may include one or more antenna subsystems associated with one or more feed link reflectors. For example, some end-to-end repeaters 3403 may have a user link antenna subsystem 3420 that includes a first set of user link constituent 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 constituent receive / transmit elements associated with a second user link reflector. In some cases, the physical areas of the two user link reflectors are approximately the same (within 5%, 10%, 25%, 50% of each other). In some cases, one user link reflector is significantly larger than the other (e.g., the physical area of one user link reflector is at least twice that of the other). Each set of user link constituent receive / transmit elements and its associated user link reflector may illuminate a corresponding different user coverage area. For example, multiple user coverage areas may be non-overlapping, partially overlapping, fully overlapping (e.g., a smaller user coverage area may be contained within a larger user coverage area), etc. In some cases, multiple user coverage areas may be active (illuminated) simultaneously. Other cases described below may enable selective activation of different portions of the user link constituent receive / transmit elements, thereby activating different user coverage areas at different times. Switching between multiple coverage areas may utilize CPS to coordinate. For example, beamforming calibration, beam weight calibration, and beam weight application may occur in two parallel beamformers, one for each of the two different coverage areas. The use of appropriate weights in the beamformers may be timed to correspond to the operation of the end-to-end repeater. In some cases, where a time-sliced beamformer is used, the beam weights may change during a time slice.

[0301] Fig.47A and Fig.47B respectively illustrate an exemplary forward signal path 4000 and a return signal path 4050, each having selective activation of multiple user link antenna subsystems 3420. Each signal path has a transponder coupled between the constituent antenna elements. Turning first to Fig.47A , the forward link transponder 3430 is referenced to Fig.44ASimilar to the above, except that the output side of the forward link transponder 3430 is selectively coupled to one of two user link constituent transmitting elements 3429 and to each part of a separate user link antenna subsystem 3420 (e.g., each part of a separate array that mates with the user link constituent transmitting element 3429). As described above, the forward link transponder 3430 may include some or all of the following: an LNA 3705, a frequency converter and associated filters 3710, a channel amplifier 3715, a phase shifter 3720, a power amplifier 3725, and a harmonic filter 3730.

[0302] Fig.47A The forward link transponder 3430 further includes a switch 4010 (forward link switch) that selectively couples the transponder via a first set of the power amplifier 3725 and the harmonic filter 3730 to a first user link constituent transmitting element 3429a (of the first user link antenna subsystem 3420) or via a second set of the power amplifier 3725 and the harmonic filter 3730 to a second user link constituent transmitting element 3429b (of the second user link antenna subsystem 3420). For example, in a first switch mode, the forward link transponder 3430 effectively forms a signal path between the feed link constituent receiving element 3416 and the first user link constituent transmitting element 3429; and in a second switch mode, the forward link transponder 3430 effectively forms a signal path between the same feed link constituent receiving element 3416 and the second user link constituent transmitting element 3429. The switch 4010 can be implemented using any suitable switching device such as an electromechanical switch, a relay, a transistor, etc. Although shown as the switch 4010, other embodiments can also use any other suitable device to selectively couple the input of the forward 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").

[0303] Turning to Fig.47B , the return link transponder 3440 functionally reflects Fig.47A the forward link transponder 3430. Unlike selectively coupling the output side of the transponder as in the Fig.47A forward link case, Fig.47B the input side of the return link transponder 3440 of Fig.44BIn the return link transponder 3440, some or all of the following may be included: LNA 3705, a frequency converter and associated filters 3710, a channel amplifier 3715, a phase shifter 3720, a power amplifier 3725, and a harmonic filter 3730.

[0304] Fig.47B The return link transponder 3440 also includes a switch 4010 (return link switch) that selectively couples the transponder via a first set of LNAs 3705 to a first user link component receiving element 3426 (of the first user link antenna subsystem 3420) or via a second set of LNAs 3705 to a second user link component receiving element 3426 (of the second user link antenna subsystem 3420). For example, in a first switch mode, the return link transponder 3440 effectively forms a signal path between the first user link component receiving element 3426 and the feeder link component transmitting element 3419; and in a second switch mode, the return link transponder 3440 effectively forms a signal path between the second user link component receiving element 3426 and the same feeder link component transmitting element 3419. The switch 4010 can be implemented using any suitable switching device such as an electromechanical switch, a relay, a transistor, etc. Although shown as a switch 4010, other embodiments can also use any other suitable device to selectively couple the input of the forward link transponder 3430 to multiple outputs. For example, the amplifier 3705 can be used as a switch (e.g., providing high gain when "on" and zero gain (or loss) when "off").

[0305] An example of an end - to - end repeater 3403 may include a switch controller 4070 to selectively switch some or all of the switches 4010 (or other suitable selective coupling devices) according to a switching schedule. For example, the switching schedule can be stored in a storage device on the end - to - end repeater 3403. In some cases, the switching schedule effectively selects which user link antenna subsystem 3420 (e.g., which user beam set to illuminate) will be activated in each of multiple 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 achieve capacity sharing goals. For example, one user link antenna subsystem 3420 can be associated with a higher - demand user and can be allocated a larger time portion in the schedule, while another user link antenna subsystem 3420 can be associated with a lower - demand user and can be allocated a smaller time portion in the schedule.

[0306] Fig.48A and Fig.48BAn example of end - to - end repeater 3403 coverage areas 4100 and 4150 including multiple selectively - activated user coverage areas 3460a, 3460b is shown. Exemplary end - to - end repeater 503 is similar to those in Fig.38 and Fig.39 , except having a different antenna subsystem. In this example, 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 shown in Fig.47A and 47B ). For example, during a first time interval, as shown in Fig.48A , user coverage area 3460a includes five hundred and ninety active user - beam coverage areas 519. The active user - beam coverage areas 519 effectively cover half of the western United States. AN coverage area 3450 (AN field) is the same as that in Fig.38 and Fig.39 : an area in the eastern United States with 597 ANs 515 distributed. During the first time interval, AN coverage area 3450 does not overlap with the active user coverage area 3460. During a second time interval, as shown in Fig.48B , user coverage area 3460a includes another five hundred and ninety active user - beam coverage areas 519. The active user - beam coverage areas 519 effectively cover half of the eastern United States during the second time interval. AN coverage area 3450 does not change. However, during the second time interval, AN coverage area 3450 completely overlaps with the active user coverage area 3460 (is a subset of the active user coverage area). Capacity can be flexibly allocated to individual regions (e.g., between the eastern user coverage area and the western user coverage area) by dynamically adjusting the time ratio allocated to the corresponding user - link antenna subsystem.

[0307] Although the previous example illustrates two user coverage areas of similar size, other numbers of user coverage areas (e.g., three or more) can be provided and can have different sizes (e.g., earth coverage, continental United States only, United States only, region only, etc.). In the case of multiple user coverage areas 3460, the user coverage areas 3460 can have any suitable geographical relationship. In some cases, the first user coverage area and the second user coverage area 3460 partially overlap (e.g., as shown in Fig.48A and Fig.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 Fig.45 and Fig.46 ). In other cases, the first user coverage area and the second user coverage area do not overlap (e.g., are disjoint).

[0308] FIG. 47A to FIG. 47B Signal path selection on the user link side is described. However, alternatively or additionally, some scenarios include signal path switching on the feeder link side. Fig.49 An exemplary forward signal path 4200 with selective activation of multiple user link antenna subsystems 3420 and multiple feeder link antenna subsystems 3410 is shown. The signal path has a forward link transponder 3430 coupled between the constituent antenna elements. As described above, the forward link transponder 3430 may include some or all of the following: an LNA 3705, a frequency converter and associated filter 3710, a channel amplifier 3715, a phase shifter 3720, a power amplifier 3725, and a harmonic filter 3730. The input side of the forward link transponder 3430 is selectively coupled to one of two feeder link constituent receiving elements 3416 (e.g., using switches 4010a and 4010b, or any other suitable path selection device). Each feeder link constituent receiving element 3416 can be part of a separate feeder link antenna subsystem 3410 (e.g., each part of a separate array of cooperating feeder link constituent receiving elements 3416). The output side of the forward link transponder 3430 is selectively coupled to one of the two user link component transmit elements 3429 (e.g., using switches 4010c and 4010d, or any other suitable path selection device). Each user link component transmit element 3429 can be part of a separate user link antenna subsystem 3420 (e.g., each part of a separate array of user link component transmit elements 3429). One or more switching controllers (not shown) can be included in the end-to-end repeater 3403 for selecting between some or all of the four possible signal paths enabled by the forward link transponder 3430. Fig.47A , Fig.47B and Fig.49 The transponders are used to illustrate only some of the many possible situations. In addition, some situations may include path selection between more than two user link antenna subsystems 3420 and / or more than two feeder link antenna subsystems 3410. Similarly, additional path selection may be included in situations where the user link antenna subsystems 3420 and / or the feeder link assembly receiving element 3416 have separate transmit reflectors and receive reflectors, etc.

[0309] Multiple AN coverage areas may also be provided in a similar manner. For example, it may be desirable that services for a particular geographic area be terminated in their respective regions. For example, with or without Fig.49The end-to-end repeater 3403 of the shown transponder can serve the first AN coverage area 3450 and the first user coverage area 3460 in North America, as well as the second AN coverage area 3450 and the second user coverage area 3460 in South America. By using path selection (e.g., switching) in the transponder, a single end-to-end repeater 3403 (e.g., a single satellite) can use the AN 515 in the North American AN coverage area 3450 to serve the traffic associated with the North American user coverage area 3460, and use the AN 515 in the South American AN coverage area 3450 to serve the traffic associated with the South American user coverage area 3460. The capacity can be flexibly allocated to each region (e.g., between the North American user coverage area and the South American user coverage area) by dynamically adjusting the time ratio allocated to the corresponding antenna subsystem.

[0310] Generally speaking, Fig.41 The features of the described end-to-end repeater 3403 enable serving at least one user beam coverage area 519 different from at least one AN coverage area 3450. In some cases, different coverage area services can enable the use of the AN field to provide high capacity for a large user coverage area 3460. Fig.45 、 Fig.46 、 Fig.48A and Fig.48B show various examples of such AN field embodiments. Deploying a large number of AN 515s in a relatively small geographical area can provide multiple features. For example, it can be easier to ensure that more (even all) AN 515s are deployed closer to high-speed networks (e.g., in areas with good fiber connectivity to the CPS 505), within the boundaries of a single country or region, on land, etc., with less deviation from the ideal AN 515 distribution. Implementing different coverage area services through path selection (e.g., as shown in FIG. 47A to FIG. 47B ) can provide additional features. For example, as described above, a single AN field (and a single end-to-end repeater 3403) can be used to selectively serve multiple user coverage areas 3460. Similarly, a single end-to-end repeater 3403 can be used to distinguish and serve regional traffic.

[0311] In some cases, different coverage area services implemented through path selection can enable various interference management and / or capacity management features. For example, referring back to Fig.48A and Fig.48B , four types of communication links can be considered: the forward link communication from the AN field to the western active user coverage area 3460 of Fig.48A ("Link A"); the forward link communication from the AN field to the eastern active user coverage area 3460 of Fig.48B ("Link B"); from Fig.48AReturn link communication from the active user coverage area 3460 in the west to the AN field (“Link C”); and from Fig.48B Return link communication from the active user coverage area 3460 in the east to the AN field (“Link D”). During the first time interval, Fig.48B The eastern user coverage area 3460 is active, such that communication occurs via Link B and Link D. Since there is complete overlap between the AN coverage area 3450 and the eastern user coverage area 3460, interference may occur between Links B and D. Thus, during the first time interval, a first portion of the bandwidth (e.g., 2 GHz) may be allocated to Link B, and a second portion of the bandwidth (e.g., 1.5 GHz) may be allocated to Link D. During the second interval, Fig.48A The western user coverage area 3460 is active, such that communication occurs via Link A and Link C. Since there is no overlap between the AN coverage area 3450 and the western user coverage area 3460, Links A and C may use the full bandwidth (e.g., 3.5 GHz) of the end-to-end repeater 3403 during the second time interval. For example, during the first time interval, the forward uplink signal may be received using a first frequency range, and the return uplink signal may be received using a second frequency range different from the first frequency range. And during the second time interval, the forward uplink signal and the return uplink signal may be received using the same frequency range (e.g., the first, second, or other frequency range). In some cases, frequency reuse may occur during the first and second time intervals, where other interference mitigation techniques are used during the first time interval. In some cases, the path selection timing may be selected to compensate for this difference in bandwidth allocation during different time intervals. For example, the first time interval may be longer than the second time interval, such that Links B and D are allocated less bandwidth for more time, thereby compensating for Links A and C being allocated more bandwidth for a shorter time.

[0312] In some cases, the first return uplink signal is received by the multi-cooperating user link component receiving element 3426a from a first portion of the plurality of user terminals 517 geographically distributed within some or all of the first user coverage area (e.g., the eastern user coverage area 3460) during the first time interval, and the second return uplink signal is received by the multi-cooperating user link component receiving element 3426b from a second portion of the plurality of user terminals 517 geographically distributed within some or all of the second user coverage area (e.g., the western user coverage area 3460) during the second time interval. When the AN coverage area 3450 (AN field) is a subset of the first user coverage area (e.g., as Fig.48A and Fig.48BWhen as shown, the AN timing can be calibrated using the end-to-end repeater 3403 during the first time frame (e.g., when there is an overlap between the user coverage area 3460 and the AN coverage area 3450).

[0313] As described above, some cases may include determining corresponding relative timing adjustments for each of the multiple ANs 515 such that the associated transmissions from the multiple ANs 515 arrive at the end-to-end repeater 3403 in a synchronized manner (e.g., timed sufficiently in coordination relative to the symbol duration, which is typically a fraction of the symbol duration such as 10%, 5%, 2% or other suitable values). In such cases, the forward uplink signal is transmitted by the multiple ANs 515 according to the corresponding relative timing adjustments. In some such cases, at least some of the multiple ANs 515 receive a synchronization beacon signal (e.g., a PN signal generated by the beacon signal generator as described above) from the end-to-end repeater 3403 and determine the corresponding relative timing adjustments based on the synchronization beacon signal. In other such cases, some or all of the ANs 515 may receive a loopback transmission from the end-to-end repeater 3403 and determine the corresponding relative timing adjustments based on the loopback transmission. The various methods of calibrating the ANs 515 may depend on the ability of the ANs 515 to communicate with the end-to-end repeater 3403. Thus, some cases may calibrate the ANs 515 only during time intervals when the appropriate coverage areas are illuminated. For example, the loopback transmission can only be used 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 via 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 repeater 3403). In some cases, the appropriate calibration may further depend on some overlap between the feeder downlink frequency range and the user downlink frequency range.

[0314] in conclusion

[0315] Although the methods and apparatuses disclosed in the present invention have been described above in accordance with various examples, cases, and specific implementations, it should be understood that the specific features, aspects, and functions described in one or more of the individual examples may be applied to other examples. Accordingly, the breadth and scope of the claimed invention are not limited by any of the examples provided above, but are defined by the appended claims.

[0316] Unless otherwise expressly stated, the terms and phrases used in this document and their variants will be regarded as open-ended rather than restrictive. As examples of the foregoing: the term "comprising" is used to mean "including but not limited to", etc.; the term "example" is used to provide examples of instances of the item under discussion, rather than an exhaustive or restrictive list; the term "a" or "an" means "at least one / kind", "one / kind or more than one / kind", etc.

[0317] Throughout the specification, the term "coupled" or "coupled to" is used broadly to refer to a physical or electrical connection (including a 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 current block, an AC current block, etc.

[0318] A group of items joined by the conjunction "and" does not mean that each and every one of these items in the group is required to be present, unless otherwise specifically stated, but means including all or any subset of all. Similarly, a group of items joined by the conjunction "or" does not require mutual exclusivity within the group, and unless otherwise specifically stated, includes all or any subset of all. In addition, although the items, elements, or components of the methods and devices disclosed in the present invention may be described or claimed in the singular, the plural is considered to be within the scope of the present invention unless specifically limited to the singular.

[0319] In some cases, the presence of expansive words and phrases such as "one or more", "at least", or other similar phrases does not mean that a narrower situation is expected or required in cases where such expansive words may not be present.

[0320] Although the claims include reference numerals, these reference numerals are provided merely to make the claims more readily understandable, and the introduction (or omission) of reference numerals should not be regarded as limiting the scope of the subject matter protected by the claims.

Claims

1. A method of operating a satellite communication system, the method comprising: Receiving a plurality of combined return downlink signals, each combined return downlink signal provided from a respective one of a plurality of geographically distributed access nodes, each combined return downlink signal being a unique received superposition of return downlink signals transmitted by a respective one of a plurality of cooperating receive or transmit paths of a satellite of the satellite communication system, each return downlink signal transmitted by the satellite being a relayed version of a combined return uplink signal received by a corresponding receive or transmit path, and each combined return uplink signal being a unique received superposition of return uplink signals transmitted by a respective user terminal of a plurality of user terminals located within a user coverage area logically subdivided into a plurality of return user beam coverage areas; Calculating return beam weights based on an end-to-end return gain estimated from the phase and amplitude of known signals received from the access nodes, wherein one or more designated terminals in each return user beam coverage area transmit a respective one of the known signals for relayed transmission via a plurality of receive or transmit signal paths of the satellite to a plurality of access nodes; Applying the return beam weights to the plurality of combined return downlink signals to obtain a plurality of return user beam signals, each return user beam signal corresponding to a respective one of the return user beam coverage areas and increasing the signal-to-noise ratio of the return uplink signals originating from user terminals in the corresponding return user beam coverage area; And Recovering return user traffic originating from respective user terminals in each return user beam coverage area from the return user beam signals corresponding to the return user beam coverage areas.

2. The method according to claim 1, wherein applying the return beam weights to the plurality of combined return downlink signals to obtain the plurality of return user beam signals comprises forming each return user beam signal as a corresponding weighted combination of the plurality of combined return downlink signals.

3. The method according to claim 2, further comprising synchronizing the plurality of combined return downlink signals before combining the plurality of combined return downlink signals.

4. The method according to claim 3, wherein synchronizing the plurality of combined return downlink signals comprises taking into account respective path delay differences relative to the satellite among the plurality of geographically distributed access nodes.

5. The method according to claim 4, further comprising determining the respective path delay differences among the plurality of geographically distributed access nodes based on beacon signals received by one or more of the access nodes from the satellite.

6. The method according to claim 1, wherein calculating the return beam weights comprises calculating a set of return beam weights that take into account the multipath return channels from each designated terminal to each access node via the satellite.

7. The method according to claim 1, wherein the satellite comprises L cooperating receive or transmit paths, wherein there are K designated terminals, each designated terminal corresponding to a respective one of the K return user beam coverage areas, wherein there are M distributed access nodes, and wherein calculating the return beam weights comprises calculating an M×K return channel matrix that models L end-to-end return channels from each of the K designated terminals to each of the M distributed access nodes, and calculating the return beam weights from the M×K return channel matrix.

8. The method according to claim 7, wherein the M×K return channel matrix is calculated as C t ×E ret ×A r , where E ret is an L×L payload matrix representing L cooperative receive or transmit paths, A r is an L×K return uplink radiation matrix that associates each of the K specified terminals with each of the L cooperative receive or transmit paths, and C t is an M×L return downlink radiation matrix that associates each of the L cooperative receive or transmit paths with each of the M distributed access nodes.

9. The method according to claim 7, wherein the return beam weights comprise a K×M return beam weight matrix, each row corresponding to the k-th of the K return user beams, and each column corresponding to the m-th of the M distributed access nodes, and wherein obtaining a return beam signal corresponding to the k-th return user beam coverage area comprises weighting the combined return downlink signals from each of the M distributed access nodes by the matrix elements in the k-th row of the K×M return beam weight matrix.

10. A central processing system CPS of a satellite communication system, the CPS comprising: an interface configured to receive a plurality of combined return downlink signals, each combined return downlink signal provided by a respective one of a plurality of geographically distributed access nodes and being the uniquely received superposition of the return downlink signals transmitted by a respective one of the plurality of cooperating receive or transmit paths of the satellite of the satellite communication system, each return downlink signal transmitted by the satellite being a relayed version of a combined return uplink signal received by the corresponding receive or transmit path, and each combined return uplink signal being the uniquely received superposition of the return uplink signals transmitted by a respective user terminal among a plurality of user terminals located within a user coverage area logically subdivided into a plurality of return user beam coverage areas; and a processing circuit configured to: calculate return beam weights based on an end-to-end return gain estimated from the phase and amplitude of known signals received from the access nodes, wherein one or more designated terminals in each return user beam coverage area transmit a respective one of the known signals for relayed transmission via the plurality of receive or transmit signal paths of the satellite to the plurality of access nodes; apply the return beam weights to the plurality of combined return downlink signals to obtain a plurality of return user beam signals, each return user beam signal corresponding to a respective one of the return user beam coverage areas and increasing the signal-to-noise ratio of the return uplink signals originating from user terminals in the corresponding return user beam coverage area; and recover return user traffic originating from respective user terminals in each return user beam coverage area from the return user beam signals corresponding to the return user beam coverage areas.

11. The CPS according to claim 10, wherein, with respect to applying the returned beam weights to the plurality of synthesized return downlink signals to obtain the plurality of returned user beam signals, the processing circuit is configured to form each returned user beam signal as a corresponding weighted combination of the plurality of synthesized return downlink signals.

12. The CPS according to claim 11, wherein the processing circuit is configured to synchronize the plurality of synthesized return downlink signals before combining the plurality of synthesized return downlink signals.

13. The CPS according to claim 12, wherein the processing circuit is configured to synchronize the plurality of synthesized return downlink signals to account for corresponding path delay differences with respect to the satellite among the plurality of geographically distributed access nodes.

14. The CPS according to claim 13, wherein the processing circuit is configured to determine the corresponding path delay differences among the plurality of geographically distributed access nodes based on beacon signals received by one or more of the access nodes from the satellite.

15. The CPS according to claim 10, wherein, in order to calculate the returned beam weights, the processing circuit is configured to calculate a set of returned beam weights that account for multipath return channels from each designated terminal to each access node via the satellite.

16. The CPS according to claim 10, wherein the satellite includes L cooperative receive or transmit paths, there are K designated terminals, each designated terminal corresponding to a respective one of K returned user beam coverage regions, there are M distributed access nodes, and wherein, in order to calculate the returned beam weights, the processing circuit is configured to calculate an M×K return channel matrix that models L end-to-end return channels from each of the K designated terminals to each of the M distributed access nodes, and calculate the returned beam weights from the M×K return channel matrix.

17. The CPS according to claim 16, wherein the M×K return channel matrix is calculated as C t ×E ret ×A r , where E ret is an L×L payload matrix representing L cooperative receive or transmit paths, A r is an L×K return uplink radiation matrix that associates each of the K specified terminals with each of the L cooperative receive or transmit paths, and C t is an M×L return downlink radiation matrix that associates each of the L cooperative receive or transmit paths with each of the M distributed access nodes.

18. The CPS according to claim 16, wherein the returned beam weights include a K×M returned beam weight matrix, each row corresponding to the k-th of the K returned user beams, and each column corresponding to the m-th of the M distributed access nodes, and wherein, in order to obtain the returned beam signal corresponding to the k-th returned user beam coverage region, the processing circuit is configured to weight the synthesized return downlink signals from each of the M distributed access nodes by matrix elements in the k-th row of the corresponding K×M returned beam weight matrix and combine the resulting M weighted synthesized return downlink signals.

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