Diversity transmission method and device in satellite-based communication system

Abstract

A satellite communication system is provided that uses a plurality of optical feeder links between its ground segment and its spatial segment and employs spatial diversity transmissions that split individual user data streams into substreams that are transmitted across two or more of the optical feeder links, thus, it is possible to restore the complete flow at the receiving end despite impairments that affect the individual feeder links on which the flow is split. Further, the system applies beamforming individually with respect to the feeder link, which means that there is no need for transmission time alignment between respective ones of the substreams. The spatial diversity transmission occurs in a forward direction or a return direction, or both, and may be employed on a conditional basis, and may be dynamically adjusted with respect to individual user terminals, groups of user terminals, or a population of user terminals throughout.

Description

Technical Field

[0001] Satellite communication systems employ multiple free-space optical links supported by corresponding ground stations to provide spatial diversity transmission of user data streams in one or both of the forward and return link directions.

[0002] background

[0003] In the context of designing, deploying, and operating satellite communication networks, a variety of challenges have emerged. Capacity limitations and spectrum efficiency represent recurring issues with no easy solutions. These problems are exacerbated by the increased data rates required to deliver richer media and the expectation of reducing latency.

[0004] One approach to addressing bandwidth limitations involves using free-space optical "feeder links" between satellites and ground gateway stations, which send forward traffic to the satellites and receive return traffic from them. Some satellite communication systems also use optical links for inter-satellite communication, which improve overall capacity or provide additional coverage and service routing flexibility.

[0005] Although optical feeder links offer significant bandwidth gain and the resulting increase in feeder link capacity compared to radio frequency (RF) feeder links, they are susceptible to damage due to cloud cover and atmospheric effects such as beam drift and scintillation. Scintillation is caused by refractive index fluctuations resulting from small temperature variations in the propagation medium, leading to variations in received optical power. Due to these factors, optical feeder links are more prone to severe signal degradation or complete signal loss than RF feeder links.

[0006] Using diversity optical links improves upon the problems encountered when using a single optical link, but diversity transmission over multiple optical links presents challenges in terms of how to use multiple links to transmit the information in question. Further challenges arise in the context of underlying technologies such as terrestrial beamforming, in which the ground segment of the satellite communication system performs or controls signal weighting to form forward or return beams for serving user terminals in different locations. Summary of the Invention

[0007] This invention provides a satellite communication system that uses multiple optical feeder links between its ground segment and its space segment and employs spatial diversity transmission. This spatial diversity transmission splits individual user data streams into sub-streams transmitted across two or more optical feeder links, making it possible to recover the complete stream at the receiving end despite impairments to the individual feeder links affecting the split streams. Furthermore, the system applies beamforming individually with respect to each feeder link, meaning that time alignment between corresponding sub-streams within the sub-streams is not required. Spatial diversity transmission occurs in the forward or return direction, or both, and can be employed conditionally and dynamically adjusted with respect to individual user terminals, user terminal groups, or the entire user terminal population.

[0008] One example embodiment includes a method operated by the ground segment of a satellite communication system comprising a ground segment and a space segment. The method includes: providing a plurality of forward user beams for transmitting forward user services to corresponding user terminals. Each forward user beam has a corresponding forward user beam coverage area, and at least one subset of the forward user beams is arranged as a forward spatial diversity beam subset, the forward spatial diversity beam subset comprising two or more forward user beams having unique combinations of signal frequencies and polarizations and corresponding forward user beam coverage areas overlapping by more than a threshold amount. The method further includes, for each forward spatial diversity beam subset: transmitting forward user services mapped to each forward user beam included in the forward spatial diversity beam subset from the ground segment to the space segment via different optical forward uplink signals originating from a different ground station among two or more geographically distributed ground stations.

[0009] Furthermore, for at least one user terminal located in the overlapping forward beam coverage area of ​​a given forward spatial diversity beam subset, the method includes employing diversity forward transmission by: (a) dividing the incoming user data stream for the user terminal into two or more forward user data substreams by block coding the incoming user data stream and partitioning the resulting coded blocks, such that each forward user data substream carries a different subset of coded data from the coded blocks; and (b) mapping each forward user data substream to a different forward user beam included in the given forward user beam subset of the forward spatial diversity beam. In this manner, each forward user data substream undergoes ground-based beamforming separately from the other substreams, such that coherent beamforming does not require transmission time alignment between the corresponding substreams across the involved ground stations.

[0010] A method according to a further embodiment includes: receiving incoming user data streams at a processing node in a ground segment, each incoming user data stream targeting a corresponding user terminal served by a satellite communication system, wherein the method further includes: employing forward spatial diversity transmission on one or more incoming user data streams.

[0011] The forward space diversity transmission method includes, for each such incoming user data stream: forming corresponding sets of two or more forward user data substreams by block coding the incoming user data stream and dividing each coded data block into different coded data subsets; mapping each forward user data substream to a corresponding forward beam signal among two or more forward beam signals, the two or more forward beam signals respectively corresponding to two or more forward user beams of a satellite communication system, the two or more forward user beams having corresponding forward user beam coverage areas covering the location of the user terminal to which the incoming user data stream is targeted; and transmitting each forward beam signal from the ground segment to the space segment via different optical forward uplink signals originating from different ground stations among a plurality of geographically distributed ground stations included in the ground segment. Each such forward uplink signal multiplexes multiple forward optical channel signals, which convey corresponding copies of a forward beam signal that is weighted for beamforming transmission from corresponding antenna elements in a target antenna array in the space segment to achieve far-field formation of the corresponding forward user beam.

[0012] In the context of the aforementioned method, a satellite communication system provides multiple forward user beams via one or more satellites included in a space segment, each forward user beam being based on a corresponding forward user beam signal and having a corresponding combination of downlink signal frequency and polarization. Accordingly, the method may further include receiving two or more forward beam signals at each of one or more ground stations among a plurality of ground stations, the two or more forward beam signals corresponding to two or more forward user beams having the same corresponding combination of downlink signal frequency and polarization. For each such ground station, the method includes: (a) forming a corresponding set of forward beam element signals for each of the two or more forward beam signals by generating a set of radio frequency signals and weighting each radio frequency signal with a corresponding forward beam weight from a corresponding set of forward beam weights, each radio frequency signal corresponding to an antenna element in a target satellite antenna array and modulated by a forward beam signal, the forward beam weight being calculated such that the set of forward beam element signals transmitted simultaneously from the target satellite antenna forms a corresponding forward beam in the far field. (a) User beam; (b) Combining the corresponding sets of forward beam element signals to form a set of combined forward beam element signals; (c) Modulating each of the multiple optical carriers at different wavelengths with a corresponding combined forward beam element signal from the set of combined forward beam element signals to obtain multiple forward optical channel signals; (d) Multiplexing the multiple forward optical channel signals in the optical domain to form a corresponding optical forward uplink signal; and (e) Transmitting the corresponding optical forward uplink signal toward a satellite having a target satellite antenna array.

[0013] The aforementioned ground station processing can occur for more than one set of forward beam signals, where each set represents a corresponding set of forward user beams. For each set of forward beam signals, the ground station forms a set of combined forward beam element signals and modulates the corresponding set of optical carriers to obtain a corresponding set of forward optical channel signals. Each set of forward optical channel signals resides in a different spectral band, allowing multiple sets of forward optical channel signals to be "stacked" in the optical domain to form a corresponding optical forward uplink signal with a total bandwidth spanning the respective spectral blocks occupied by the various sets of forward optical channel signals.

[0014] Another embodiment includes a method operated by a satellite communication system comprising a ground segment and a space segment, wherein the method includes: receiving two or more return user data substreams via one or more satellites included in the space segment. The two or more return user data substreams are transmitted by the same user terminal, which performs block coding on the return user data streams and divides the resulting block-coded data into two or more return user data streams, wherein each return user data substream conveys a different portion of the coded data from each coded block. The method further includes: delivering each return user data substream to the ground segment via different optical return downlink signals, each optical return downlink signal being received at a different ground station among a plurality of geographically distributed ground stations included in the ground segment; and receiving each of the two or more return user data substreams from a corresponding ground station that has received one of the two or more return user data substreams at a processing node in the ground segment. The method further includes: the processing node reassembling the return user data streams from the return user data streams for forwarding toward a target destination. In one or more embodiments or variations, such operation includes performing return beamforming in the ground segment to enhance the return uplink signal relative to some or all of the return user beam coverage areas that may correspond to some or all of the forward user beam coverage areas.

[0015] Of course, the present invention is not limited to the features and advantages described above. In fact, those skilled in the art will recognize additional features and advantages after reading the following detailed description and reviewing the accompanying drawings. Attached Figure Description

[0016] Figure 1 This is a block diagram of a satellite communication system according to one embodiment, which provides space transmission diversity via a free-space optical link between a ground station and a satellite.

[0017] Figure 2 This is a block diagram illustrating example details of a spatial diversity emission processing arrangement according to one embodiment.

[0018] Figure 3 and Figure 4 This is a block diagram illustrating example details of a ground station according to one embodiment.

[0019] Figure 5 This is a block diagram illustrating example details of a light emitter according to one embodiment.

[0020] Figure 6 This is an illustration of example multiplexing in the optical domain according to one embodiment.

[0021] Figure 7 This is a block diagram illustrating example details of a light emitter according to one embodiment.

[0022] Figure 8 This is a block diagram illustrating example details of a satellite according to one embodiment.

[0023] Figures 9 to 11 This is a block diagram illustrating example details of a user terminal according to one embodiment.

[0024] Figure 12 yes Figure 1 A block diagram illustrating further examples and details of the satellite communication system described in the text.

[0025] Figure 13 This is a logic flowchart of a method for operating a satellite communication system according to an example embodiment.

[0026] Figure 14 and Figure 15 This is a logic flowchart of a method for operation by a user terminal according to an example embodiment. Detailed Implementation

[0027] Figure 1 A satellite communication system (SCS) 10 is illustrated, which provides multiple forward user beams 12, each having a corresponding forward user beam coverage area 14 and generated by beamforming transmission of a corresponding forward downlink signal 16. Each forward downlink signal 16 conveys scheduled forward user services for user terminals (UTs) 18 served by the corresponding forward user beam 12. For example, each forward downlink signal 16 carries forward user services scheduled for multiple UTs 18 according to a Time Division Multiple Access (TDMA) arrangement.

[0028] The overall aggregation of the forward user beam coverage area 14 corresponds to a potentially large geographical area (aggregated coverage area 20) where SCS 10 provides communication services. For example, aggregated coverage area 20 may span at least a portion of North America or another geographical region. Aggregated coverage area 20 may be referred to as a satellite service area.

[0029] Among the plurality of forward user beams 12, there are one or more forward spatial diversity beam subsets 22. Each forward spatial diversity beam subset 22 includes a subset of two or more forward user beams 12 having a corresponding forward user beam coverage area 14 that overlaps by more than a threshold amount (i.e., an intentional overlap such that SCS 10 can serve UT 18 in the overlapping coverage area via two or more forward user beams 12).

[0030] Serving UT 18 via more than one forward user beam 12 is based on dividing the forward user traffic for UT 18 onto two or more forward downlink signals 16, which are beamformed to generate corresponding forward user beams 12, each of which provides coverage with respect to the location of UT 18. The corresponding beam coverage area 14 can be defined according to the effective isotropic radiated power (EIRP) contour (e.g., the corresponding 3dB contour).

[0031] The forward user beams 12 in each forward spatial diversity beam subset 22 have co-extended or substantially overlapping forward beam coverage areas 14, for example, more than fifty percent overlap. In at least one embodiment, the forward user beams 12 in the forward spatial diversity beam subset 22 have the same nominal forward user beam coverage area 14, but there may be differences in the actual coverage areas.

[0032] To achieve beam signal separability within overlapping forward beam coverage areas 14 of a given forward spatial diversity beam subset 22, the forward user beams 12 within a given forward spatial diversity beam subset 22 are located in different downlink frequency bands or have different polarizations, or both. In other words, any forward user beam 12 included in a given forward spatial diversity beam subset 22 has a unique combination of downlink signal frequencies and polarizations. Of course, in one or more embodiments, the SCS 10 employs frequency and polarization reuse across aggregation areas 20 and can assign frequencies and polarizations to corresponding forward user beams 12 according to a reuse pattern that avoids or minimizes inter-beam interference within aggregation coverage areas 20. Therefore, among the multiple forward user beams 12 provided by the SCS 10, there may be multiple forward user beams 12 using the same combination of downlink signal frequencies and polarizations, but these beams do not overlap. Conversely, the forward user beams belonging to the forward spatial diversity beam subset 22 overlap at least to some extent, but are distinguished from each other according to their respective frequency / polarization combinations. The same arrangement can be used in the return user beam coverage area for subdivided satellite service areas.

[0033] SCS10 can provide forward spatial diversity coverage over all portions of aggregation region 20. Alternatively, some portions of aggregation region 20 may have forward spatial diversity coverage via corresponding forward spatial diversity beam subsets 22, while other portions may only have non-diversity coverage provided by a corresponding single forward user beam 12.

[0034] The SCS10 is communicatively coupled to one or more external networks 24, such as the public switched telephone network and the Internet or other packet data networks. User traffic entering the SCS10 for transmission to the corresponding UT 18 includes, for example, corresponding incoming user data streams 26. Each incoming user data stream 26 includes, for example, data packets with a destination address identifying the target UT 18. In turn, the SCS10 maintains information indicating the location of each UT 18 or additionally indicating which forward user beam(s) 12 have been used or are available to serve each UT 18. Therefore, the SCS10 knows which forward user beam(s) 12 are available to convey forward user traffic for a given UT 18, and it uses this knowledge to map the scheduled forward user traffic for the corresponding UT 18 to the corresponding forward user beam among the multiple forward user beam(s) 12 provided by the SCS10.

[0035] In one or more embodiments, an advantageous processing function performed by SCS10 with respect to the incoming user data stream 26 is to determine whether to use forward spatial diversity transmission. Further, in at least one embodiment, SCS10 determines the “degree” of forward spatial diversity to be applied, where “degree” refers to the number of forward user beams 12 to be used for forward spatial diversity transmission for a particular incoming user data stream 26. Two forward user beams 12 represent the lowest degree of diversity, and three, four, or more beams represent a higher degree. For each incoming user data stream 26 using forward spatial diversity transmission, the incoming user data stream 26 is divided into as many forward user data substreams as the number of forward user beams 12 used for diversity.

[0036] For example, suppose an incoming user data stream 26 is targeted at UT 18 located at a position covered by five forward user beams 12, each forward user beam at a different forward downlink frequency and / or polarization. Therefore, the “maximum” forward transmit diversity for a given incoming user data stream 26 is to divide the incoming user data stream 26 into five forward downlink signals 16 corresponding to the five forward user beams 12. Thus, for this user data stream 26, the SCS 10 can use forward non-diversity transmission (a single forward user beam 12 conveys the incoming user data stream 26 targeted at UT 18), or the SCS 10 can use forward spatial diversity transmission (two or more forward user beams 12 each conveying a corresponding forward user data substream formed by dividing the incoming user data stream 26). In the case of forward spatial diversity transmission, in one or more embodiments, the SCS 10 can dynamically select the number of forward user beams 12 to be included in the diversity forward transmission.

[0037] The decision to employ forward space diversity or forward non-diversity transmission can be made regarding individual incoming user data streams 26 or groups or categories of incoming user data streams 26. As an example, the decision per user data stream depends on the user subscription agreement or other service agreement. As a specific example, SCS10 uses forward diversity transmission for preferred or deemed more critical incoming user data streams 26 according to the subscription agreement. This decision may additionally or alternatively consider the communication service or service type involved, such as based on throughput requirements, criticality, or other quality of service (QoS) considerations. Additionally or alternatively, this decision depends on atmospheric conditions affecting the reliability of the forward uplink 30 connecting the ground segment 32 of SCS10 to the involved satellite.

[0038] In this respect, Figure 1 To simplify the discussion, a single satellite 34 providing multiple forward user beams 12 is shown. However, SCS 10 should be understood to include one or more satellites 34, each providing a potentially large number of forward user beams 12. In at least one embodiment, SCS 10 includes one or more constellations of satellites 34. In at least one embodiment, each such satellite 34 is a geostationary satellite, and the corresponding forward user beam coverage area 14 is at least nominally fixed. In one or more embodiments, each such satellite 34 is a bend satellite that relays user traffic in the forward and / or return directions using an unprocessed signal path. The “unprocessed” signal path may include conversion between the electrical and optical domains and may include filtering, amplification, and frequency shifting, but excludes demodulation and regeneration of user traffic.

[0039] If a given UT 18 is within the overlapping forward beam coverage area 14 of two or more forward user beams 12 (i.e., its location is within the coverage provided by the forward spatial diversity beam subset 22), then the SCS 10 may choose to serve the given UT 18 using a single forward user beam 12 or using two or more forward user beams 12.

[0040] A key aspect of forward spatial diversity (as the term is used herein) is that each forward user data substream, segmented from any given incoming user data stream 26, is transmitted from the ground segment of SCS10 to the space segment of SCS10 via a different optical feeder link 30. This approach, combined with the coding and segmentation used to form the respective forward user data substreams, allows the target UT 18 to recover the complete user data stream, even if the individual optical feeder links 30 involved in transmitting the respective forward user data substreams encounter temporary impairments. In this respect, since different ground stations 36 in the ground segment provide different optical feeder uplinks 30, and since the different ground stations 36 are geographically distributed, atmospheric-related impairments affecting one optical feeder uplink 30 are independent of atmospheric-related impairments affecting other optical feeder uplinks 30.

[0041] The ability to utilize forward spatial diversity offers numerous advantages, particularly in the context of using optical feeder uplinks 30 between satellite 34 and the corresponding ground station 36 of SCS10. Since free-space optical feeder uplinks 30 are individually vulnerable to temporary impairment, the problem of communication drops or interruptions is mitigated by distributing incoming user data streams 26 across multiple optical feeder uplinks 30 using a data partitioning method. This data partitioning method allows for full stream recovery based on forward error correction (FEC) at the target UT 18, even during periods when fewer than all forward user data substreams are successfully received.

[0042] exist Figure 1 In this designation, each ground station 36 is labeled “OGS” to indicate “Optical Ground Station”. Each ground station 36 includes one or more optical transmitters (“OT”) 38, wherein each optical transmitter 38 is anchored to a corresponding optical feeder uplink 30, wherein each optical feeder uplink 30 is targeted at a specific satellite 34. More specifically, each optical transmitter 38 in each ground station 36 transmits a corresponding optical forward uplink signal 40, which conveys one or more forward beam signals. Each forward beam signal carries a scheduled forward user service corresponding to a specific UT 18 served by a forward user beam 12 corresponding to that forward user beam signal.

[0043] Forward spatial diversity transmission means that each forward user data substream divided from a given incoming user data stream 26 is carried by a different forward beam signal, and further means that each forward user beam signal is transmitted by a different ground station 36, such that the optical impairment of the transmission of one forward beam signal interfering with the transmission of the other forward beam signals is independent of the optical impairment of the transmission of the other forward beam signals interfering with the transmission of the other forward beam signals. According to the foregoing definition, "forward feeder link spatial diversity" is an equivalent term describing the process of forward user data substreams divided from a given incoming user data stream 26 and transmitted from the ground segment to the space segment using different optical feeder uplinks 30 provided by different ground stations 36. Here, the geographical separation between ground stations 36 provides at least some "spatial diversity". Further spatial diversity occurs when different satellites 34 in the space segment are used to transmit different forward user beams 12 carrying the corresponding forward user data substreams.

[0044] The communication and control subsystem (CCS) 42 included in the ground segment 32 of SCS10 includes one or more computer servers or other physical computing platforms configured to perform certain forward transmission processes, including generating forward beam signals 44 to be distributed to the respective ground stations 36.

[0045] Therefore, CCS 42 can be understood to include processing nodes. The reference to "processing node" here should be interpreted broadly to cover single-node or multi-node embodiments, such as situations where physically separate but communicatively linked nodes cooperate. A processing node includes, for example, a processing circuitry system and one or more types of communication interfaces for exchanging signaling with other entities in SCS 10, such as the corresponding ground station 36. In at least one embodiment, CCS 42 includes one or more microprocessors specifically adapted for executing the CCS functions described herein based on the execution of stored computer program instructions. In such embodiments, CCS 42 includes a storage device comprising one or more types of computer-readable media for storing computer program instructions.

[0046] Each ground station 36 corresponds to a specific combination of forward and downlink frequencies and polarizations. More specifically, each ground station 36 transmits one or more sets of forward beam signals in each of its transmitted optical forward uplink signals 40. Each set of or more forward beam signals corresponds to one or more sets of forward user beams 12 having the same downlink signal frequency and polarization, and is carried in different segments of the overall spectrum occupied by the forward uplink signal 40. Although the same reference numeral "44" is used for all forward beam signals for clarity, it should be understood that the user service carried in one forward beam signal 44 is different from the user service carried in another forward beam signal, and each forward beam signal 44 corresponds to a different beam among the overall multiple forward user beams 12 provided by the SCS 10.

[0047] According to the embodiment shown in SCS10, CCS 42 receives incoming user data stream 26 from external network 26 and performs forward diversity processing. This processing includes deciding whether to use forward spatial diversity transmission or forward non-diversity transmission. In at least one such embodiment, the decision-making process further includes deciding the degree of forward spatial diversity to be used. These decisions may be made on a stream-by-stream basis, or for a group of incoming user data streams 26, or with respect to all incoming user data streams 26.

[0048] CCS 42 can make decisions based on current conditions, such as whether weather damage has been detected or anticipated for one or more optical forward uplinks 30. For example, in at least one embodiment, SCS 10 operates in a mode-dependent manner by selecting between a diversity mode and a non-diversity mode, in which forward spatial diversity is employed for at least some of the incoming user data streams 26, and in a non-diversity mode, which does not employ forward spatial diversity. Further, in at least one embodiment, SCS 10 omits the decision operation and employs forward spatial diversity for all incoming user data streams 26. Therefore, the statement that SCS 10 "employs forward spatial diversity for at least one incoming user data stream 26" should be understood to mean that under at least some conditions or in at least one embodiment, SCS 10 employs forward spatial diversity to transmit one or more incoming user data streams 26.

[0049] according to Figure 1For example, for any incoming user data stream 26 not transmitted using forward spatial diversity, the CCS 42 passes it as a forward user data stream 46 to the forward beam mapping function implemented via the processing circuitry of the CCS 42. The incoming user data stream 26 to be transmitted using forward spatial diversity is divided into corresponding forward user data substreams 48, which are then passed to the forward beam mapping function. It should be noted here that the forward user data stream 46 may include block-coded versions of the corresponding incoming user data stream, which are based on application-defined block codes with defined block lengths, and for any incoming user data stream 26 to be transmitted using forward spatial diversity, the corresponding forward user data stream 46 may be divided such that different portions of the coded data from each coded block form corresponding forward user data substreams 48.

[0050] Each forward user data stream 46 targets a specific UT 18 and is mapped to a forward user beam 12 for serving that UT 18. Similarly, each forward user data substream 48 is mapped to a corresponding forward user beam 12 in the forward spatial diversity subset 22 associated with serving the target UT 18. Each forward user beam 12 may carry a mixture of forward user data streams 48 for serving UT 18 via non-diversity forward transmission and forward user data substreams 48 for serving UT 18 via diversity forward transmission. In a general sense, all such traffic may be referred to as forward user traffic or scheduled forward user traffic, but it should be understood that forward user traffic is beam-specific. It is noteworthy that the corresponding forward user data substreams 48 for serving any particular UT 18 via forward spatial diversity are each conveyed by a different forward user beam 12, meaning that these forward user data substreams are mapped from the ground segment to different forward beam signals 44.

[0051] Service-to-beam mapping occurs continuously with respect to the data streams constituting each incoming user data stream 26, and the forward beam mapping function of CCS 42 logically groups these forward user data streams and these forward user data substreams according to the corresponding forward user beams 12 in which the forward user data streams 46 and forward user data substreams 48 are transmitted. Based on this, the forward user scheduling function performs continuous multiplexing of the forward user data streams 46 and forward user data substreams 48 for each forward user beam 12 according to a user scheduling algorithm.

[0052] The forward beam signal generation function, implemented via the processing circuitry of CCS 42, generates multiple forward beam signals 44, wherein these individual forward beam signals 44 are graphically represented by signal lines "44" output from the forward beam signal generation function. Each forward beam signal 44 corresponds to a specific forward user beam in the forward user beam 12. That is, each forward downlink signal 16 is generated by beamforming transmission of the corresponding forward beam signal in the forward beam signals 44. Here, “beamforming” transmission refers to the transmission of a set of forward beamforming element signals from a target satellite antenna array, each of which is modulated according to the forward beam signal 44 in question and weighted according to a corresponding set of forward beam weights for transmission from the corresponding antenna element in the antenna array. These forward beam weights are calculated based on channel state information (CSI) (e.g., propagation channel estimates that describe the forward path from the target antenna array to one or more UT 18s in the forward user beam coverage area 14 corresponding to the forward user beam 12 of the forward beam signal 44).

[0053] For each forward beam user signal 44, the simultaneous transmission of the corresponding set of forward beam element signals from the target satellite antenna array can be understood as the beamforming transmission of the corresponding forward downlink signal 16, and the element signal weighting generates a constructive and destructive superposition pattern of the forward downlink signal 16 in the far field, which generates the corresponding forward user beam 12 (here, "far field" refers to the electromagnetic field region where radiation behavior is dominant).

[0054] Figure 1 The foregoing details are illustrated by depicting each forward beam signal 44 as a corresponding set with forward beam weights 50, which are determined by a forward beam weight calculation function implemented via the processing circuitry system of the CCS 42. It should be noted that... Figure 1 The use of the reference numeral "50" in the figures is plural, meaning that each forward beam signal 44 has a set of forward beam weights 50. The forward beam weights 50 are calculated with respect to each forward user beam 12 using, for example, channel feedback from one or more UTs 18 operating in the corresponding forward user beam coverage area 14. Therefore, in one or more embodiments, the forward beam weight calculation function uses forward channel estimation to calculate the corresponding set of forward beam weights 50 for each forward beam signal 44.

[0055] The forward beam signal distribution function, implemented via the processing and communication interface circuitry of CCS 42, distributes the forward beam signal 44 and additional corresponding information (such as a set of forward beam weights 50) to the corresponding ground station 36. Figure 1Reference numeral 52 is used to denote the distribution of forward beam signals 44 and the corresponding information therein. That is, each “signal 52” should be understood as one or more sets of forward beam signals 44, together with the corresponding set of forward beam weights 50. Again, each “set” of forward beam signals 44 sent to the corresponding ground station 36 represents one or more forward user beams 12 having the same downlink signal frequency and polarization and transmitted from the same satellite antenna array.

[0056] In one example arrangement, each ground station 36 processes one or more sets of forward beam signals 44 corresponding to one or more sets of forward user beams 12 among the overall plurality of forward user beams 12 provided by the SCS 10. The CCS 42 may distribute the corresponding forward beam signals 44 to the ground station 36 based on such associations. However, such associations may change from time to time (e.g., to account for a failed ground station 36 or maintenance, or other availability or load balancing considerations), and the distribution may be updated to reflect these changes. However, for any given forward spatial diversity beam subset 22, at least when using forward spatial diversity, each included forward beam 12 is processed by a different ground station 12.

[0057] In at least one embodiment, one or more ground stations in ground station 36 may use corresponding optical transmitters 38 to transmit more than one optical forward uplink signal 40. In any case, each optical forward uplink signal 40 conveys one or more sets of forward beam signals 44, wherein each such set represents a corresponding set of forward user beams 12 and is carried within a corresponding segment of the overall spectrum traversed by the forward uplink signal 40. More specifically, in at least one embodiment, each “set” of forward beam signals 44 conveyed in any given optical forward uplink signal 40 transmitted by any given ground station 36 corresponds to a forward user beam 12 having the same downlink signal frequency and polarization. Furthermore, each such set of forward beam signals 44 targets the same antenna array airborne on the satellite to which the forward uplink signal 40 is directed and is carried within a corresponding segment of the overall spectrum of the forward uplink signal 40. This approach reduces beamforming complexity in ground station 36 and simplifies electro-optical conversion and multiplexing for forming optical forward uplink signals 40. The optical bandwidth of each forward uplink signal 40 means that each forward uplink signal 40 can carry multiple sets of forward beam signals 44 corresponding to possibly many forward user beams 12 (e.g., hundreds of forward user beams 12).

[0058] Figure 2An implementation of forward diversity processing using CCS 42 in one embodiment is shown. This diagram illustrates processing for a given incoming user data stream 26. It should be understood that CCS 42 includes additional signaling paths and processing to apply the same processing to all incoming user data streams 26. In other words, CCS 42 is configured to process multiple incoming user data streams 26 in parallel.

[0059] Forward diversity controller 100 determines whether to apply forward spatial diversity to the incoming user data stream 26 and routes each incoming user data stream 26 to either non-diversity processing path 102 or diversity processing path 104 accordingly. Diversity processing path 104 includes block encoder 106, which performs block encoding on the incoming user data stream 26 and outputs the corresponding forward stream with encoded blocks 108.

[0060] Divider 110 divides each coded block 108 into corresponding sub-blocks, each sub-block containing a different subset of the coded data included in the coded block 108. This operation produces corresponding streams of sub-blocks 112, each containing different coded data, wherein these streams of sub-blocks 112 include forward user data sub-streams 48 for forward spatial diversity transmission of the associated incoming user data stream 26. The number of forward user data sub-streams 48 formed from a given incoming user data stream 26 represents the degree of diversity, i.e., the number of individual forward user beams 12 used to transmit the incoming user data stream 26 to the target UT 18.

[0061] In at least one embodiment, CCS 42 applies the same block coding to each incoming user data stream 26, regardless of whether the incoming user data stream 26 is transmitted using forward spatial diversity. That is, CCS 42 performs block coding on each incoming user data stream 26 to form a corresponding forward user data stream 46, and then, for each forward user data stream 46 transmitted using forward spatial diversity, CCS 42 performs coded block partitioning to produce a corresponding set of forward user data substreams 48. Therefore, the forward diversity processing performed by CCS 42 outputs forward user data streams 46 for non-diversity transmitted incoming user data streams 26, and outputs corresponding sets of forward user data substreams 48 for diversity transmitted incoming user data streams 26.

[0062] Figure 3 An example arrangement of ground station 36 is shown, which includes a communication interface 120 configured to receive signals 52 from CCS 42, the signals including one or more sets of forward beam signals 44 and corresponding sets of forward beam weights 50. Ground station 36 may include more than one optical transmitter 38, and the signals 52 received from CCS 42 may include one or more sets of forward beam signals 44 for transmission from each respective optical transmitter 38.

[0063] Communication interface 120 includes a physical layer receiver circuitry, along with timing and communication processing, and outputs forward beam signals 44 to be transmitted via a specific optical transmitter 38 to a corresponding forward path circuitry 122. There exists a set of forward path circuitry 122 associated with each optical transmitter 38 included in the ground station, wherein the circuitry is configured to provide signal processing for a specific set of one or more forward beam signals 44 to be transmitted by the associated optical transmitter 38. The set of forward path circuitry 122 associated with each optical transmitter 38 generates a set of combined forward beam element signals 124 for each set of forward beam signals 44 to be conveyed in the forward signals 40 output by the optical transmitter 38. Therefore, it should be understood that each set of forward path circuitry 122 receives one or more sets of forward beam signals 44, wherein each such set contains at least one forward beam signal 44, and wherein a corresponding set of forward beam weights 50 is received for each forward beam signal 44.

[0064] Figure 4 Example details of the forward path circuitry 122 associated with each optical emitter 38 according to one embodiment are shown. More specifically, Figure 4 A circuit system is shown for a corresponding set of forward beam signals 44 to be transmitted in the same forward uplink signal 40. For each forward beam signal 44 in each set, there is a forward beam element signal generator 126. Although Figure 4 Three forward beamforming element signal generators 126 are presented for an example set of three individual forward beam signals 44, but it should be understood that, with respect to each optical transmitter 38 included in each ground station 36, there may be a defined number of forward beamforming element signal generators 126 corresponding to the maximum number of forward beam signals 44 that can be transmitted via the corresponding forward uplink signal 40.

[0065] Each forward beamforming element signal generator 126 operates on a corresponding forward beam signal 44 in the associated set and includes multiple radio frequency modulators 128, or equivalently, one RF modulator and one signal splitter. Each forward beamforming element signal generator 126 is configured to output a set of RF signals 130. Each RF signal 130 corresponds to a corresponding antenna element in the target satellite antenna array, which is used to form a forward user beam 12 corresponding to the forward beam signal 44 being processed. The RF signals 130 are formed by modulating an RF carrier according to the forward beam signal 44, and they can all be at the same frequency, for example, a given intermediate frequency. A weighting circuit system 132 applies a corresponding set of forward beam weights 50 to the set of RF signals 130 to form the set of forward beamforming element signals 134. The corresponding set of forward beam weights 50 is calculated such that the set of forward beam element signals 134 transmitted simultaneously from the corresponding antenna elements in the target satellite antenna array produces a signal superposition that forms the corresponding forward user beam 12 in the far field.

[0066] As shown in the figure, for each set of forward beam signals 44 to be transmitted by the optical transmitter 38, a set of forward beam element signals 134 is generated. The combination circuit system 136 combines corresponding forward beam element signals from the corresponding sets of forward beam element signals 134 to obtain corresponding sets of combined forward beam element signals 124. Combination occurs on an element-by-element basis, such that forward beam element signals 134 from each set of the same antenna element mapped to the target antenna array are combined. These linear combinations are possible because all forward beam signals 12 corresponding to the combined sets of forward beam element signals 134 have the same downlink signal frequency and polarization.

[0067] For example, suppose that ground station 36 is processing a given set of forward beam signals 44 for a specific optical transmitter 38 in ground station 36, and there are four forward beam signals 44, and there are one hundred antenna elements in the target satellite antenna array. Based on the corresponding set of one hundred forward beam weights 50, ground station 36 generates one hundred forward beam element signals 134 for each forward beam signal 44 being processed. For the i-th antenna element in the target satellite antenna array, there are four i-th forward beam element signals 134, one forward beam signal for each of the forward beam signals 44, and these four forward beam element signals 134 are added together to produce the corresponding combined forward beam element signal 124 for the i-th antenna element. Of course, if there is only one forward beam signal 44 in the "set" of forward beam signals 44, then the set of forward beam element signals 124 output from the combination circuit system 136 is only a set of forward beam element signals 134 generated for that one forward beam element signal 44.

[0068] from Figure 4 As can be seen, each forward uplink signal 40 then conveys one or more sets of forward beam signals 44. Each such set of forward beam signals 44 is represented by a set of combined forward beam element signals 124. This set of combined forward beam element signals 124 is obtained by combining the respective sets of forward beam element signals 134 generated for the respective forward beam signals 44 included in the set of forward beam element signals 44.

[0069] Figure 5 An optical transmitter 38 according to one embodiment is shown. For ease of illustration, the diagram assumes three sets of forward beam signals 44 to be transmitted, each such set being represented by a corresponding set of combined forward beam element signals 124 input to the optical transmitter 38. Of course, many such sets of forward beam signals 44 may exist, each set containing one or more forward beam signals 44, thereby efficiently utilizing the overall spectrum of the forward uplink signal 40.

[0070] Each set of combined forward beamforming signals 124 is fed into a corresponding set of optical modulators 144. Within each such optical modulator 144, each combined forward beamforming signal 124 modulates a corresponding optical carrier 142 among a plurality of optical carriers 142 provided by a plurality of light sources 140. With respect to each set of combined forward beamforming signals 124, the corresponding set of optical carriers 142 is at a different optical wavelength defining a corresponding optical channel. Furthermore, each corresponding set of light sources 140 outputs its corresponding set of optical carriers 142 in a different portion of the spectrum; that is, each set of optical carriers 142 corresponds to a different set of optical channels. Therefore, each set of forward beamforming signals 44 being transmitted is represented by a different set of combined forward beamforming signals 124, wherein each such set of combined forward beamforming signals 144 is carried within a different set of optical channel signals 146.

[0071] Each optical channel signal 146 in each set of optical channel signals 146 conveys a corresponding combined forward beamforming signal from the corresponding set of combined forward beamforming signals 124 used to generate the optical channel signal. Since the combined forward beamforming signals 124 are RF signals, one approach is to intensity modulate the optical carriers 142 such that intensity variations in each resulting forward optical channel signal 146 convey the corresponding combined forward beamforming signal 124. In at least one embodiment, phase modulation is used, wherein the phase of each optical carrier 142 is modulated according to the corresponding combined forward beamforming signal 124. More broadly, each forward optical channel signal 146 conveys user services contained in the forward beamforming signals 44 for which it forms the corresponding combined forward beamforming signal 124.

[0072] Figure 6 An example arrangement for forming a forward uplink signal 40 into a multiplexed optical signal is illustrated. This example assumes three sets of forward beam signals 44 to be transmitted in the forward uplink signal 40, each such set comprising one or more forward beam signals 44, and including that the forward beam signals 44 in each such set correspond to forward user beams 12 having the same downlink signal frequency and polarization. Each set of forward beam signals 44 is used to generate a corresponding set of combined forward beam element signals 124, and each set of combined forward beam element signals 124 is transmitted in a corresponding set of forward optical channel signals 146.

[0073] To be more detailed, Figure 6The spectrum shown in the image includes a first set of forward optical channel signals 146, which are transmitted via a first set of combined forward beamforming element signals 124. This first set of combined forward beamforming element signals corresponds to a first set of forward beamforming signals 44 representing a first set of forward user beam 12. The spectrum also includes a second set of forward optical channel signals 146, which are transmitted via a second set of combined forward beamforming element signals 124. This second set of combined forward beamforming element signals corresponds to a second set of forward beamforming signals 44 representing a second set of forward user beam 12. The spectrum further includes a third set of forward optical channel signals 146, which are transmitted via a third set of combined forward beamforming element signals 124. This third set of combined forward beamforming element signals corresponds to a third set of forward beamforming signals 44 representing a third set of forward user beam 12. There may be many additional sets of forward optical channel signals 146 that match the total span of the spectrum allocated for the forward uplink signal 40.

[0074] Therefore, the forward uplink signal 40 effectively “stacks” corresponding sets of combined forward beamforming element signals 124 in the optical frequency domain using dense wavelength division multiplexing (DWDM). This method allows, but does not require, all combined forward beamforming element signals 124 in each such set to be at the same RF frequency, which can be the downlink signal frequency used by the forward user beam 12 represented in the set of combined forward beamforming element signals 124, or it can be a certain intermediate frequency, such as 3.5 GHz.

[0075] like Figure 5 As shown, the optical multiplexer 148 in the optical transmitter 38 aggregates the forward uplink signal 40 into a set of such a collection as the forward optical channel signal 146, and the optical head unit 150 focuses or otherwise directs the forward uplink signal 40 for transmission toward the target satellite 34. As noted above, the head unit 150 focuses or otherwise directs the forward uplink signal 40 for free-space transmission toward the optical receiver of the target satellite 34. As an example, the head unit 150 includes one or more mirrors. As another example, the head unit includes one or more prisms. In at least one embodiment, the head unit 150 is capable of turning in response to a turning command signal, wherein turning allows adjustment of the head unit 150 to align with the target optical receiver on the target satellite 34.

[0076] Figure 7 Further example details of a light emitter 38 according to one embodiment are shown. Figure 7The implementation details are simplified to show a single set of combined forward beamforming signals 124, which carries a corresponding set of forward beaming signals 44 to be conveyed in the forward uplink signal 40 output from the optical transmitter 38. However, it should be understood that the optical transmitter 38 includes modulation circuitry for each set of combined forward beamforming signals 124 processed by the optical transmitter 38.

[0077] exist Figure 7 In the diagram, the first combined forward beamforming signal of the combined forward beamforming signal 124 is used as the modulation input of the first optical modulator 144-1, the second combined forward beamforming signal of the combined forward beamforming signal 124 is used as the modulation input of the second optical modulator 144-2, and so on. Each optical modulator 144 includes, for example, a bias circuit 152 for applying a DC bias to the corresponding combined forward beamforming signal 124 input thereto, and then applying the DC bias signal to the modulator 154. The modulator 154 is, for example, a Mach-Zehnder modulator (MZM) that modulates an optical carrier 142 output from a light source 140 (such as a laser diode that outputs light of a specific wavelength). As noted above, in one or more embodiments, the modulation is phase modulation. Intensity modulation may also be used.

[0078] Back Figure 1 Each satellite 34 carries one or more optical receivers (“OR”) 200. Each optical receiver 200 is configured to receive a corresponding forward uplink signal 40 from a corresponding optical transmitter 38 at a corresponding ground station 36. Like the optical transmitter 38, the optical receiver 200 is steerable in one or more embodiments, and it should be understood that a given optical receiver 200 on a given satellite 34 may be aligned with a different optical transmitter 38 at the same or different ground stations 36 at different times. Steerability may be used for load balancing or to accommodate ground station maintenance or failure or current weather conditions, or for other reasons.

[0079] Each optical receiver 200 outputs a set of recovered RF signals 202, which corresponds to each set of combined forward beamforming signals 124 transmitted in the received forward uplink signal 40. That is, for each set of forward beamforming signals 44 transmitted in the forward beamforming signals 44, the optical receiver 200 recovers a corresponding set of RF signals 202, which includes a recovered version of the combined forward beamforming signals 124 generated in the transmitter from the set of forward beamforming signals 44. Figure 1 Each signal line marked "202" should be understood as representing a set of recovered RF signals 202.

[0080] This operation is based on multiplexing the received forward uplink signal 40 in the optical domain to recover the corresponding set of forward optical channel signals 146 conveyed by the forward uplink signal 40. Each recovered forward optical channel signal 146 is then demodulated (e.g., using a photodetector to track, for example, the phase modulation of the recovered forward optical channel signal 146) to generate a corresponding recovered RF signal in the recovered RF signal 202. The use of reference numeral 202 in the receiver background, rather than reference numeral 124 in the transmitter background, is merely for emphasis. In the absence of interference or damage, each set of RF signals 202 recovered from the received forward uplink signal 40 is identical in information content to the corresponding set of combined forward beamforming element signals 124 multiplexed into the forward uplink signal 40 at the respective optical transmitter 38.

[0081] Forward transmit (TX) subsystem 204 couples each set of recovered RF signals 202 to one of one or more antenna arrays 210 mounted on satellite 34. Each forward TX subsystem 204 receives a corresponding set of recovered RF signals 202 and outputs a corresponding set of forward antenna element signals 206. Figure 1 Each signal line marked "206" should be understood as representing a set of forward antenna element signals 206.

[0082] Each set of forward antenna element signals 206 differs from its corresponding set of recovered RF signals 202 in one or more aspects of amplification, filtering, and frequency conversion. In at least one embodiment, each set of recovered RF signals 202 is in IF mode, and the forward TX subsystem 204 corresponding to each such set converts these signals to downlink signal frequencies for the forward user beam 12 represented in that set. Thus, in one or more embodiments, each forward TX subsystem 204 is associated with a particular antenna array 210 and / or a particular set of antenna input feeds having associated downlink signal frequencies and polarizations, wherein each forward TX subsystem 204 includes a set of forward analog signal paths that provide power amplification, at least for the corresponding set of recovered RF signals 202, to transmit these signals from the corresponding array elements in the associated antenna array 210.

[0083] Satellite 34 may have a single antenna array 201 with different sets of input feeds associated with different downlink signal frequencies and polarizations, such that forward user beams 12 with different downlink signal frequencies and polarizations are transmitted from the same antenna array 210. For example, each optical receiver 200 receives a corresponding forward uplink signal 40 conveying one or more sets of forward beam signals 44, each such set associated with one or more forward user beams 12 having a specific combination of downlink signal frequencies and polarizations, wherein all forward TX subsystems 204 apply corresponding sets of forward antenna element signals 206 to different sets of input feeds of the same antenna array 210. Alternatively, satellite 34 includes multiple antenna arrays 210, each associated with one or more specific combinations of downlink signal frequencies and polarizations, wherein a corresponding forward TX subsystem 204 is associated with a corresponding antenna array within antenna array 210 according to frequency and polarization relationships.

[0084] In a general sense, since each set of forward antenna element signals 206 corresponds to one or more forward user beams 12 with a specific downlink carrier frequency and / or polarization, each forward TX subsystem 204 couples its output set of forward antenna element signals 206 to an antenna feed set corresponding to that specific frequency and / or polarization.

[0085] Figure 8 Example details of a given optical receiver 200, airborne on a given satellite 34, for receiving a corresponding forward uplink signal 40 are shown. An optical head 220 (e.g., one or more lenses and / or mirrors) receives the forward uplink signal 40 from a corresponding ground station 36, and an optical demultiplexer 222 uses wavelet demultiplexing to recover one or more sets of forward optical channel signals 224 corresponding to the set of forward optical signals 146 multiplexed in the received forward uplink signal 40. For simplicity, Figure 8 The recovery of a single set of forward optical channel signals 224 corresponding to a set of combined forward beamforming element signals 124 is shown, wherein the set of combined forward beamforming element signals 124 represents a set of forward beamforming signals 44.

[0086] about Figure 6 It shows multiple spectral bands of the corresponding set of forward optical channel signals 146 contained within the forward uplink signal 40. Figure 8This can be understood as demonstrating the recovery and demultiplexing of such a set. Accordingly, it should be understood that additional similar circuitry within the optical receiver 200 and the additional forward TX subsystem 204 is used to recover an additional set of forward optical channel signals 146 from the received forward uplink signal 40, and correspondingly recover a corresponding set of RF signals 202 and generate a corresponding set of forward antenna element signals 206. Each set of forward antenna element signals 206 represents a corresponding set of one or more forward user beams 12, wherein each such beam conveys the service contained in the corresponding forward beam signal 44.

[0087] Regarding the forward optical channel signal 146, the reference numeral "224" is used in the receiver background instead of "146" merely to emphasize the difference between the receiver background and the transmitter background. In the absence of interference or damage, each set of the forward optical channel signals 224 demultiplexed at the optical receiver 200 is identical in information content to the corresponding set of the forward optical channel signals 146 multiplexed at the corresponding optical transmitter 38.

[0088] Secondary lenses or mirrors 226 can be used to guide the corresponding optical channel signals 224 to the corresponding photodiodes 228. For example, the first optical channel signal in the optical channel signal 224 is guided to photodiode 228-1 via lens 226-1, the second optical channel signal in the optical channel signal 224 is guided to photodiode 228-2 via lens 226-2, and so on. Each photodiode 228 outputs an electrical signal in response to the phase or intensity of the corresponding optical channel signal. These output electrical signals are the recovered RF signals 202 described above.

[0089] The forward TX subsystem 204 in the depicted embodiment includes an analog forward signal path for each RF signal 202. Each forward signal path includes, for example, a low-noise amplifier (LNA) 230, a frequency converter (FC) 232, and a power amplifier (PA) 234. The FC 232 converts the RF signal 202 from an intermediate frequency (IF) to a downlink carrier frequency associated with the target forward user beam 12. The FC 232 can be implemented as an upconverter or a downconverter, depending on the frequency involved.

[0090] PA 234 provides power amplification for the frequency-converted RF signal 202, wherein the power-amplified signal output from PA 234 is referred to as the set of forward antenna element signals 206. The set of forward antenna element signals 206 is applied to the set of input feeds 236 of the antenna array 210 on the satellite 34, wherein each input feed corresponds to a corresponding antenna element 238 in the antenna array 210. Each antenna element 238 radiates a corresponding forward beam element signal 206 applied to its corresponding input feed 236, and the collective transmission of these element-wise signals can be regarded as the transmission of the corresponding forward downlink signal 16, wherein the far-field superposition of the signals of each element produces the corresponding forward user beam 12.

[0091] To understand these results, recall that the forward uplink signal 40 received by optical receiver 200 conveys one or more sets of combined forward beamforming element signals 124, each set of the combined forward beamforming element signals 124 being formed by combining two or more sets of forward beamforming element signals 134. Each such set of forward beamforming element signals 134 is weighted by a corresponding set of forward beamweights 50, which is calculated such that the simultaneous transmission of the sets of forward beamforming element signals 134 from the corresponding antenna elements 238 of the target satellite antenna array 210 produces far-field signal superposition, which forms a specific forward user beam in the forward user beam 12 provided by SCS 10. Therefore, transmitting the set of forward antenna element signals 206 formed by the satellite-recovered version of the combined forward beamforming element signals 124 produces the corresponding forward user beam 12 represented by the combined forward beamforming element signals 124.

[0092] Figure 9 A UT 18 according to an example embodiment is depicted, wherein the UT 18 includes one or more transmit / receive antennas 240 and associated communication circuitry 242. The communication circuitry 242 includes two or more transceiver signal chains 244, each transceiver signal chain including a satellite radio receiver or transmitter or both, together with a baseband processor 246 providing transmit and receive signal processing and control. The example UT 18 further includes a system processor 248 that governs the overall operation of the UT and, for example, executes one or more applications to produce the intended functionality of the UT 18. Example functions include telecommunications services, broadband multimedia delivery, etc. The UT 18 may include additional circuitry 250 to support its intended functionality.

[0093] System processor 248 and / or baseband processor 246 implement substream processing function 252, which provides processing of forward user data substreams in a diversity forward transmission context, and / or processing of return user data substreams in a diversity return transmission context, or both. System processor 248 and baseband processor 246 include one or more microprocessors, digital signal processors, FPGAs, ASICs, SoCs or other digital processing circuits, as well as supporting clock circuitry systems, computer-readable storage media, etc.

[0094] Figure 10 Example substream processing at UT 18 demonstrates the diversity forward pass scenario, while Figure 11 Example substream processing at UT 18 shows the diversity return transmission situation.

[0095] Figure 10 Using the example of a forward user data stream 46 targeted at UT 18, this forward user data stream has been divided into three forward user data substreams 48, shown as 48-1, 48-2, and 48-3. For reference... Figure 1 As a reminder, the forward user data stream 46 can be understood as the encoded, beam-mapped and scheduled forward user service from the incoming user data stream 26.

[0096] In one or more embodiments, example UT 18 uses separate receiver circuitry systems RX1, RX2, and RX3 to receive three distinct forward downlink signals 16, shown as 16-1, 16-2, and 16-3. Each forward downlink signal 16-1, 16-2, and 16-3 is at a different downlink signal frequency and / or polarization, and each forward downlink signal 16 conveys a corresponding forward user data substream of forward user data substreams 48-1, 48-2, and 48-3. Each forward downlink signal 16 is beamformed to generate a corresponding forward user beam 12.

[0097] In one or more other embodiments, some or all of the receiver circuitry within the receiver chain of UT 18 may be shared. For example, for UT 18 to receive two diversity carriers at different frequencies (e.g., 18 GHz and 19 GHz), UT 18 may use the same LNA, RF converter, analog-to-digital converter (ADC), etc., and then demodulate the “combined” signals of the two carriers separately in the digital domain. Furthermore, at least some of the DSP or ASIC resources, such as buffers, demodulators, etc., used for demodulation and other signal processing of the different received diversity carriers may be shared. Because this processing ultimately produces information extracted separately from each received diversity carrier, UT 18 can still be considered to have functionally independent receiver chains for the respective diversity carriers, despite sharing some or all of the physical circuitry for receiving two or more diversity carriers (i.e., different forward and downlink signals 16).

[0098] although Figure 10 Not shown, but it should be understood that the forward user beam 12-1, which is formed by the transmission of forward downlink signal 16-1 by satellite 34, forms a forward user beam coverage area 14-1 covering the location of UT 18; the forward user beam 12-2, which is formed by the transmission of forward downlink signal 16-2, forms a forward user beam coverage area 14-2 covering the location of UT 18; and the forward user beam 12-3, which is formed by the transmission of forward downlink signal 16-3, forms a forward user beam coverage area 14-31 covering the location of UT 18. In other words, UT 18 is located in the overlapping coverage area formed by the three forward user beams 12-1, 12-2, and 12-3, which act as a forward spatial diversity beam subset 22 of UT 18.

[0099] One or more forward user data substreams in forward user data substream 48 carry header information indicating the reassembly order of forward user data substream 48 for recovering the corresponding encoded block stream. UT 18 uses the header information to perform encoded block reassembly, and thus can be understood as recovering forward user data stream 46. UT 18 performs block decoding to recover the original incoming user data stream 26 and provides it to higher-level processing, such as application layer processing at UT 18. This is performed via the configuration processing circuitry system. Figure 10 All the functions shown in the document, such as the baseband processor 246 and / or the system processor 248.

[0100] It should be noted that UT 18 may additionally or alternatively use non-diversity forward transmission for service, meaning that it uses a single forward user beam 12 in the forward direction, which is generated by beamforming transmission of a single forward downlink signal 16 carrying a single forward user data stream 46 for UT 18. In such cases, reception processing at UT 18 relies on a single receiver circuit.

[0101] Figure 11 An example configuration of UT 18 in a reverse transmission context is illustrated. Advanced processing in UT 18 generates an outgoing user data stream 258 for return transmission to CCS 42. UT 18 performs block encoding on the outgoing user data stream 258 (e.g., according to a defined transport block size) to obtain a corresponding return user data stream 260. In at least one embodiment, the processing circuitry of UT 18 is configured to determine whether to use return spatial diversity processing for the return user data stream 260. If return spatial diversity is not used, UT 18 transmits the return user data stream 260 via a corresponding return uplink signal 264, which is a radio transmission at a defined return uplink frequency.

[0102] If UT 18 employs return space diversity, then the return user data stream 260 is divided on a block-by-block basis to form two or more return user data substreams 262, where Figure 11 An example scenario of three return user data substreams 262-1, 262-2, and 262-3 is illustrated. Separate transmit signal chains TX1, TX2, and TX3 are used to transmit the respective return user data substreams 262-1, 262-2, and 262-3 in the corresponding return uplink signals 264-1, 264-2, and 264-3. At least in the case of simultaneously transmitting multiple return user data substreams 262, the multiple return uplink signals 264 are distinguished from each other in terms of signal frequency and / or polarization.

[0103] The “TX” block shown should be understood as including the transmission circuitry system for modulation, up-conversion, and amplification. As previously discussed regarding the possibility of a shared circuitry system receiving different diversity carriers, at least some of the transmission circuitry systems (including in the digital and / or analog domains) can be shared for transmitting diversity return carriers. Here, “return carrier” refers to the return uplink signal 264 transmitted by UT 18 using a specific carrier signal frequency and / or polarization.

[0104] In some embodiments, UT 18 determines whether to use return spatial diversity transmission for the return user data stream 260 based on, for example, control signaling sent to it from SCS 10. When return spatial diversity is used, UT 18 embeds header information into one or more return user data substreams 262 formed by the return user data stream 260 in order to reassemble the return user data stream 260 at CCS 42.

[0105] Figure 12 SCS10 is depicted in the background of the return direction. The aggregated coverage area 20 can be divided using multiple return user beams 300 with corresponding return user beam coverage areas 302. That is, the entire satellite service area can be logically subdivided into multiple return user beam coverage areas, where each return user beam coverage area 302 represents a corresponding return user beam 300. One or more return space diversity subsets 304 may exist, each comprising two or more return user beams 300 having corresponding return user beam coverage areas 302 that overlap by more than a threshold amount, such that UT 18 in the overlapping area can be served in the return direction via two or more of the associated return user beams 300. Regarding this service, SCS10 can be understood as providing return space transmit diversity.

[0106] Each UT 18 covered by the return spatial diversity subset 304 does not necessarily operate in return spatial diversity transmission mode. In practice, individual UT 18s or groups thereof can be controlled to operate in return spatial diversity transmission mode, while other UT 18s located within the same return user beam coverage overlap can be controlled individually or as a group to operate in return non-spatial diversity transmission mode. A UT 18 operating in return spatial diversity transmission mode subdivides the data constituting a return user data stream into a set of two or more return user data substreams, where each return user data substream is transmitted as a unique radio transmission using the uplink signal frequency and / or polarization associated with the corresponding return user beam 300 in the return spatial diversity subset 304 associated with the location of the UT 18. A UT 18 operating in return non-spatial diversity transmission mode does not subdivide any of its transmitted return user data streams.

[0107] In one or more embodiments, the return user beam 300 is implemented retrospectively based on return beamforming in CCS 42 rather than on any transmit beamforming performed by UT 18 or any receive beamforming applied in satellite 34. Therefore, although Figure 12The return user beam 300 in free space is shown, but such a beam may exist only in a signal processing sense based on the signal weighting of the recovered signal applied in the CCS 42. Specifically, in one or more embodiments, the CCS 42 calculates a set of return beam weights representing each return user beam coverage area 302, wherein this set of return beam weights is calculated to maximize the signal-to-noise ratio (SNR) of the return uplink signal 264 originating from the UT 18 operating within that return user beam coverage area 302. In this way, the CCS 42 generates corresponding return user beam signals, wherein each return user beam signal corresponds to a specific return user beam in the return user beam 300 and conveys the return uplink signal 264 transmitted by the UT 18 located within the return user beam coverage area 302 corresponding to that specific return user beam 300.

[0108] The return beam coverage area 302 and the forward beam coverage area 14 may be the same or different. However, in at least one embodiment, the return beam coverage area 302 and the forward beam coverage area 14 are at least nominally the same.

[0109] One or more antenna arrays 320 on satellite 34 receive incoming return uplink signals 264 from the corresponding UTs in UT 18. One or more antenna arrays 320 can interact with... Figure 1 One or more antenna arrays 210 shown may be the same or different.

[0110] Each antenna element in each antenna array 320 receives a superposition of return uplink signals 264 from multiple UTs 18, which may originate from multiple return beam coverage areas 302. The corresponding return uplink signals 264 from different UTs 18 are transmitted according to return link service scheduling performed by CCS 42. UTs operating with spatial diversity return transmission each transmit multiple return uplink signals 264. Each of the multiple return uplink signals 264 corresponds to a different return user beam 300, wherein the different beams differ in uplink signal frequency and / or polarization, and wherein each such return user beam 300 conveys a return user data substream 262 partitioned from the corresponding return user data stream 260. UTs operating with non-diversity return transmission transmit return uplink signals 264 conveying return user data streams 260 that are not partitioned.

[0111] One or more antenna arrays 320 on the satellite 34 output corresponding sets of return antenna element signals 322, each such set corresponding to a different combination of return uplink signal frequency and polarization. Figure 12Each signal line marked "322" should be understood as representing a corresponding set of return antenna element signals 322. For an associated combination of return uplink signal frequencies and polarizations, each return antenna element signal 322 within each set of return antenna element signals 322 can be understood as a synthesis of the return uplink signals 264 received on the corresponding antenna element.

[0112] Each of the two or more return TX subsystems 324 onboard on satellite 34 receives a corresponding set of return antenna element signals 322 and outputs a corresponding set of combined return beam element signals 326. Figure 12 Each signal line marked "326" should be understood as representing a set of combined return beamforming element signals 326. Each set of combined return beamforming element signals 326 contains a corresponding return uplink signal 264 received via antenna array 320 for a combination of corresponding uplink signal frequencies and polarizations, and represents one or more return user beams 300 using that combination of frequencies and polarizations. In at least one embodiment, each set of combined return beamforming element signals 326 is a set of radio signals that have been amplified, filtered, and frequency-shifted compared to a corresponding set of return antenna element signals 322.

[0113] To achieve return space diversity, satellite 34 has two or more optical transmitters 328. The return signal paths and processing within satellite 34 are arranged such that the return uplink signal 264 associated with each corresponding return user beam 300 included in a given return diversity beam subset is relayed to the ground segment 32 of SCS10 using a separate optical transmitter 328, each optical transmitter targeting a different ground station among ground stations 36. That is, at least one subset of the return user beams 300 is arranged as a return space diversity beam subset comprising two or more return user beams 300 having unique combinations of signal frequencies and polarizations and corresponding return user beam coverage areas 302 overlapping by more than a threshold amount.

[0114] Each optical transmitter 328 is coupled to a different ground station 36 via a corresponding optical return feeder link 330. Therefore, for example, for a UT 18 that divides the return user data stream 260 into three return user data substreams 262 and transmits each such return user data substream 262 in a different return uplink signal 264, each such return uplink signal 264 will be carried back to the CCS 42 via a different optical return feeder link 330. This arrangement provides spatial diversity in the return direction for the different return user data substreams 262 and allows the CCS 42 to recover the return user data stream 260 even during temporary fading or interruption of the individual optical return feeder links 330 used in the return spatial diversity transmission.

[0115] Therefore, each optical transmitter 328 onboard the satellite 34 targets a different ground station 36 and transmits an optical return downlink signal 332 comprising multiplexed return optical channel signals, wherein each such return optical channel signal is modulated according to a corresponding combined return beamforming element signal from the set of transmitted combined return beamforming element signals 326. Each optical transmitter 328 may be similar to the optical transmitter 38 described for the ground station 36 (see [reference]). Figure 7 The arrangement can be optimized, but weight reduction features can be adopted for satellite use. The multiplexing used for the optical return downlink signal 332 can be structured similarly to the multiplexing shown and detailed for the forward uplink signal 40. For example, any given optical transmitter 328 is used to transmit one or more sets of recovered RF signals 202 based on a corresponding set forming the return optical channel signal (each set occupying a corresponding spectral band). Each optical channel signal in each such set of return optical channel signals is modulated with a corresponding signal from the corresponding set of RF signals 202, and the corresponding sets of return optical channel signals are aggregated via DWDM to form the corresponding optical return downlink signal 332.

[0116] Each ground station 36 includes one or more optical receivers 334, wherein each optical receiver receives a return downlink signal 332 from a corresponding optical transmitter 328 onboard the respective satellite 34 at any given time. Each such optical receiver 334 may be similar to the optical receiver 200 onboard the satellite 200 (see [link to satellite 200]). Figure 8 The optical receiver 334 is arranged such that each optical receiver 334 demultiplexes the return optical channel signal from the received return downlink signal 332, wherein each return optical channel signal is at a different optical wavelength, and the demultiplexing is based on wavelength-based filtering to recover the individual return optical channel signals.

[0117] At ground station 36, corresponding photodetectors (such as photodiodes) are used to demodulate each return optical channel signal to recover the corresponding combined return beamforming element signal 326 transmitted therefrom. That is, the photodetectors output analog domain radio signals, which serve as the recovered version of the corresponding combined return beamforming element signal 326. In other words, each optical receiver 334 includes an optical demultiplexer for recovering each set of return optical channel signals multiplexed in the received return downlink signal 332, and includes multiple photodetectors for demodulating each recovered set of return optical channel signals to recover the corresponding set of combined return beamforming element signals 326 transmitted by the return downlink signal 332. Such operation occurs within each ground station 36 for each included optical receiver 334, or at least with respect to each included optical receiver 334 that is in active operation and receiving the corresponding return downlink signal 334.

[0118] Each ground station 36 sends a return signal 336 to the CCS 42, which conveys a recovered set of combined return beamforming signals obtained by the ground station 36. Since each recovered set of combined return beamforming signals corresponds to one or more return user beams 300 with a specific return uplink signal frequency and polarization, the CCS 42 performs return beamforming on each such set. Specifically, for each recovered set of combined return beamforming signals, the CCS 42 applies a corresponding set of return beam weights 338 individually. Individual application means applying each set of return beam weights 338 independently to a separate copy of the recovered set of combined return beamforming signals. Each such weight set is calculated to produce directional sensitivity (enhanced SNR) for the return uplink signal 264 originating from UT 18 in the return user beam coverage area 302 corresponding to the return user beam 300 for which its weight set is calculated.

[0119] CCS 42 applies this processing to each recovered set of combined return beam element signals received from ground station 36 to CCS 42, resulting in the generation (on a continuous basis) of a corresponding return beam signal 340. Each return beam signal 340 corresponds to one of the return user beams 300, and CCS 42 recovers the return user data stream 260 conveyed in each return beam signal 340, for example, for forwarding the return user data stream as outgoing user traffic 342 via one or more external networks 24 toward their target destination address.

[0120] For each UT 18 using diversity return transmission, the recovery of the corresponding return user data stream 260 is based on the reassembly of multiple return user data substreams 262 by CCS 42, for example, using reassembly information carried in one or more of the multiple return user data substreams 262. The reassembly produces a block-coded version 260 of the return user data stream, and CCS 42 performs block decoding to obtain the return user data stream 260.

[0121] Figure 13 An overall method 1300 for operation by an SCS10 according to an example embodiment is shown. Method 1300 is performed on a cyclical or continuous basis, that is, one or more operations shown reflect continuous actions taken with respect to the data stream incoming to the SCS10 for transmission.

[0122] Method 1300 includes SCS10 receiving (box 1302) incoming user data streams 26, each incoming user data stream targeting a specific UT 18. Method 1300 further includes stream-by-stream processing (box 1304), which includes, for each incoming user data stream 26, determining (box 1304A) whether forward spatial diversity is used. If forward spatial diversity is used ("yes" from box 1304A), method 1300 optionally includes determining (box 1304B) the degree of forward spatial diversity, and further includes: splitting (box 1304C) the incoming user data stream into two or more forward user data substreams 48, mapping (box 1304D) each forward user data substream 48 to a corresponding forward beam signal 44 corresponding to a corresponding forward user beam 12 covering the location of the target UT 18.

[0123] If the result is "No" from box 1304A, forward spatial diversity transmission is not used for the incoming user data stream 26, and processing is performed to map the forward user data stream 48 corresponding to the incoming user data stream 26 into the corresponding forward beam signal 44 corresponding to the forward user beam 12 at the location of the coverage target UT 18. This processing includes, for example, block coding of the incoming user data stream 26, and the selection of a specific forward user beam 12 as part of a load balancing or user scheduling operation.

[0124] Further operations in method 1300 include performing (block 1306) the continuous distribution of the forward beam signal 44 to the corresponding ground station 36. Block 1308 relates to operations per ground station, which includes: in each ground station 36, (A) forming a set of forward beam element signals 134 for each forward beam signal 44 transmitted by the ground station 36; (B) multiplexing the forward beam element signals 134 onto an optical carrier; and (C) transmitting the resulting optical forward uplink signal 40 to the target satellite 34. Now refer back to Figure 4 Ground station 36 forms a corresponding forward uplink signal 40 for transmitting one or more sets of forward beam signals 44.

[0125] Such operations include, for each set of forward beam signals 44 to be transmitted in the forward uplink signal 40: forming a set of forward beam element signals 134 for each forward beam signal in that set, and combining these sets of forward beam element signals 134 to form a set of combined forward beam element signals 124. Each set of combined forward beam element signals 124 is used to modulate a corresponding set of optical carriers 142 to form a corresponding set of forward optical channel signals 146, which are multiplexed to form the optical forward uplink signal 40.

[0126] Box 1310 relates to satellite-based operations. Such operations include: (A) recovering one or more sets of combined forward beaming element signals 124 from each received forward uplink signal 40; and (B) transmitting the corresponding set of forward antenna element signals 206 to form the corresponding forward user beam 12.

[0127] Figure 14 A method 1400 of operation performed by UT 18 according to one embodiment is illustrated. The illustration assumes forward spatial diversity reception at UT 18, wherein SCS 10 generates forward user data stream 46 based on block coding of incoming user data stream 26 for transmission, and divides each coded block into a unique subset of coded data to form two or more forward user data substreams 48, which are transmitted by SCS 10 in the forward direction using corresponding forward user beams 12 corresponding to forward beam signals 44 transmitted via corresponding forward uplink signals 40 on geographically separated forward optical feed uplinks 30.

[0128] Therefore, method 1400 includes UT 18 receiving (box 1402) two or more forward user data substreams 48 on different forward user beams 12. UT 18 reassembles (box 1404) the forward user data streams from the received forward user data substreams 48, including recovering missing information associated with temporary interruptions in the respective forward user data substreams 48 based on forward error correction (FEC) decoding applied when generating the forward user data stream 46. Further, method 1400 includes higher-level processing of passing the recovered incoming user data stream 26 to UT 18.

[0129] Figure 15A method 1500 regarding return spatial diversity, performed by UT 18 in one embodiment, is illustrated. Processing begins with receiving (box 1502) outgoing user data stream 258. For example, an application executing on UT 18 generates outgoing packet data for a remote device or system. Therefore, "receiving" here refers to internal operations within UT 18, where UT 18 determines whether to employ return spatial diversity for outgoing user data stream 258. If return spatial diversity is not employed ("No" from box 1504), processing continues with UT 18 obtaining (box 1506) return user data stream 260 by encoding the outgoing user data stream and transmitting return user data stream 260 via return uplink signal 264, which is associated with a single return user beam 300 and carried to CCS 42 via a single optical return feeder link 330.

[0130] If UT 18 employs return spatial diversity ("Yes" from box 1504), the processing continues to determine the degree of diversity (box 1508) in at least one embodiment, meaning determining how many return user data streams 260 will be split into return user data substreams 262. In other embodiments or other operational scenarios, the number of return user data substreams 262 is a default or predefined number. In at least some embodiments, SCS 10 is configured to determine the degree of return spatial diversity employed by individual UT 18s, groups of UT 18s, or the entire group of UT 18s. Such decisions are made, for example, based on load, such as the number of UT 18s supported (e.g., on a per-return user beam basis), the amount or type of traffic originating from individual UT 18s or groups of UT 18s (e.g., within the corresponding return user beam coverage area 302). Control signaling sent by SCS 10 to UT 18 configures whether a given UT 18 uses return spatial diversity and to what extent.

[0131] The processing continues by splitting the return user data stream 260 (box 1510) into two or more return user data substreams 262 using UT 18. Splitting refers to dividing each coded block included in the return user data stream 260 into a unique subset of coded data, where the resulting data subset stream is the corresponding return user data substream 262. Each return user data substream 262 is transmitted via different return uplink signals 264 (box 1512). Each return uplink signal 264 corresponds to a different return user beam 300 and is transmitted back to CCS 42 via a different optical return feeder link 330.

[0132] It is worth noting that, benefiting from the teachings presented in the foregoing description and related drawings, those skilled in the art will conceive of modifications and other embodiments of the disclosed invention. Therefore, it should be understood that the invention is not limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of this disclosure. Although specific terminology may be used herein, it is used only in a general and descriptive sense and not for limiting purposes.

Claims

1. A method for operating the ground segment of a satellite communication system comprising a ground segment and a space segment, the method comprising: Incoming user data streams are received at one or more processing nodes on the ground segment, each incoming user data stream targeting a corresponding user terminal served by the satellite communication system; as well as Forward spatial diversity transmission is performed for each of the incoming user data streams by performing the following operations on one or more of the incoming user data streams: By block encoding the incoming user data stream and dividing each encoded data block into different encoded data subsets, corresponding sets of two or more forward user data substreams are formed. as well as Each forward user data substream is mapped to a corresponding forward beam signal among two or more forward beam signals, the two or more forward beam signals respectively corresponding to two or more forward user beams of the satellite communication system, the two or more forward user beams having a corresponding forward user beam coverage area covering the location of the user terminal to which the incoming user data stream is targeted; as well as Each forward beam signal is sent to different ground stations among multiple geographically distributed ground stations, each of which uses its corresponding optical forward uplink signal to transmit to the space segment.

2. The method according to claim 1, further comprising: At each of the plurality of geographically distributed ground stations, a corresponding forward uplink signal is formed by multiplexing a plurality of forward optical channel signals, the plurality of forward optical channel signals conveying a corresponding copy of the forward beam signal received by the ground station, the forward beam signal being weighted for beamforming transmission from a corresponding antenna element in a target antenna array in the space segment to achieve far-field formation of the corresponding forward user beam.

3. The method according to claim 1 or 2, wherein the method further comprises: For each incoming user data stream that employs forward spatial diversity, stream reassembly information is embedded in at least one of the forward user data substreams in the corresponding set of two or more forward user data substreams, the reassembly information providing an ordered reassembly of the incoming user data stream at the target user terminal.

4. The method according to any one of claims 1 to 3, wherein forward spatial diversity transmission is employed on a selective basis, and wherein the method further comprises: For any incoming user data stream that does not employ forward spatial diversity transmission, forward non-diversity transmission is used, in which the incoming user data stream is block-coded and mapped to a single forward beam signal corresponding to the respective forward user beam.

5. The method according to any one of claims 1 to 4, wherein the satellite communication system provides a plurality of forward user beams via one or more satellites included in the space segment, wherein one or more forward spatial diversity beam subsets are present among the plurality of forward user beams, each forward spatial diversity beam subset comprising two or more forward user beams having a unique combination of signal frequencies and polarizations and having corresponding forward user beam coverage areas overlapping by more than a threshold amount, and wherein forward spatial diversity transmission for the one or more incoming user data streams in the incoming user data stream comprises: For each such incoming user data stream, the corresponding two or more forward user data substreams are mapped to a corresponding forward beam signal that corresponds to a forward user beam, which is a member of a forward spatial diversity beam subset that provides coverage with respect to the location of the corresponding user terminal.

6. The method of claim 5, wherein forward user services mapped to each forward user beam included in each forward spatial diversity beam subset are transmitted from the ground segment to the space segment via different optical forward uplink signals, the different optical forward uplink signals originating from one of two or more geographically distributed ground stations.

7. The method according to any one of claims 1 to 6, the method further comprising: The decision to use forward spatial diversity transmission for any one or more incoming user data streams is based on the corresponding user subscription protocol, such that forward spatial diversity transmission is used for a given incoming user data stream according to the corresponding user subscription protocol.

8. The method according to any one of claims 1 to 6, the method further comprising: On a continuous basis, a decision is made as to whether to use forward spatial diversity transmission for any one or more of the incoming user data streams, the decision being based on any one or any combination of the following: the number of ground stations available for transmitting forward beam signals to the space segment; detected impairments in any one or more of the optical forward uplink signals used to transmit the forward beam signals from the ground segment to the space segment; and the load of the corresponding forward user beam.

9. The method according to any one of claims 1 to 8, wherein the satellite communication system provides a plurality of forward user beams via one or more satellites included in the space segment, each forward user beam being based on a corresponding forward user beam signal and having a corresponding combination of downlink signal frequency and polarization, and wherein the method comprises: At each of one or more of the plurality of ground stations, two or more forward beam signals are received, the two or more forward beam signals corresponding to two or more forward user beams having the same combination of corresponding downlink signal frequencies and polarizations, and at each such ground station: By generating a set of radio frequency signals and using the corresponding set of forward beam weights from the forward beam weights... The beam weights are applied to each radio frequency (RF) signal to form a corresponding set of forward beam element signals for each of the two or more forward beam signals, each RF signal corresponding to an antenna element in the target satellite antenna array and modulated by the forward beam signal. The forward beam weights are calculated such that the set of forward beam element signals is simultaneously transmitted from the target satellite antenna in the far field to form a corresponding forward user beam. The corresponding sets of forward beamforming element signals are combined to form a set of combined forward beamforming element signals; Each optical carrier of multiple optical carriers at different wavelengths is modulated using a corresponding one of the combined forward beamforming signals in the set of combined forward beamforming signals to obtain multiple forward optical channel signals. The multiple forward optical channel signals are multiplexed in the optical domain to form corresponding optical forward uplink signals; as well as The corresponding optical forward uplink signal is transmitted toward the satellite with the target satellite antenna array.

10. A satellite communication system, the satellite communication system comprising a ground segment, the ground segment comprising: An interface circuit system configured to receive incoming user data streams, each of which is targeted at a corresponding user terminal served by the satellite communication system. as well as A processing circuitry system, configured to perform forward spatial diversity transmission for each of the incoming user data streams based on being configured to perform the following operations for one or more of the incoming user data streams: By block encoding the incoming user data stream and dividing each encoded data block into different encoded data subsets, corresponding sets of two or more forward user data substreams are formed. as well as Each forward user data substream is mapped to a corresponding forward beam signal among two or more forward beam signals, the two or more forward beam signals respectively corresponding to two or more forward user beams of the satellite communication system, the two or more forward user beams having a corresponding forward user beam coverage area covering the location of the user terminal to which the incoming user data stream is targeted; as well as Each forward beam signal is sent to different ground stations among a plurality of geographically distributed ground stations, each ground station being configured to transmit to the space segment of the satellite communication system using a corresponding optical forward uplink signal.

11. The satellite communication system according to claim 10, wherein the satellite communication system further comprises: The plurality of geographically distributed ground stations, each of which is configured to form a corresponding forward uplink signal by multiplexing a plurality of forward optical channel signals, the plurality of forward optical channel signals conveying a corresponding copy of the forward beam signal received by the ground station, the forward beam signal being weighted for beamforming transmission from a corresponding antenna element in a target antenna array in the space segment to achieve far-field formation of the corresponding forward user beam.

12. The satellite communication system of claim 10 or 11, wherein for each incoming user data stream employing forward spatial diversity, the processing circuitry in the ground segment is configured to embed stream reassembly information into at least one of the forward user data substreams in the corresponding set of two or more forward user data substreams, the reassembly information providing an ordered reassembly of the incoming user data stream at the target user terminal.

13. The satellite communication system according to any one of claims 10 to 12, wherein forward spatial diversity transmission is employed on a selective basis, and includes a processing circuitry system in the ground segment configured to employ forward non-diversity transmission for any incoming user data stream for which forward spatial diversity transmission is not employed, wherein the incoming user data stream is block-coded and mapped to a single forward beam signal corresponding to the respective forward user beam.

14. The satellite communication system according to any one of claims 10 to 13, wherein the satellite communication system provides a plurality of forward user beams via one or more satellites included in the space segment, wherein one or more forward spatial diversity beam subsets exist among the plurality of forward user beams, each forward spatial diversity beam subset comprising two or more forward user beams having a unique combination of signal frequencies and polarizations and having corresponding forward user beam coverage areas overlapping by more than a threshold amount, and wherein, in order to employ forward spatial diversity transmission for the one or more incoming user data streams in the incoming user data streams, the processing circuitry system in the ground segment is configured to, for each such incoming user data stream, map the corresponding two or more forward user data substreams to a corresponding forward beam signal corresponding to a forward user beam, the forward user beam being a member of the forward spatial diversity beam subset providing coverage with respect to the location of the corresponding user terminal.

15. The satellite communication system of claim 14, wherein the ground segment is configured such that forward user services mapped to each forward user beam included in each forward space diversity beam subset are transmitted from the ground segment to the space segment via different optical forward uplink signals, the different optical forward uplink signals originating from a different ground station among two or more geographically distributed ground stations.

16. The satellite communication system according to any one of claims 10 to 15, wherein the processing circuitry in the ground segment is configured to determine, based on a corresponding user subscription protocol, whether to use forward spatial diversity transmission for any one or more of the incoming user data streams, such that forward spatial diversity transmission is used for a given incoming user data stream according to the corresponding user subscription protocol.

17. The satellite communication system according to any one of claims 10 to 16, comprising a processing circuitry system in the ground segment configured to continuously determine whether to use forward space diversity transmission for any one or more of the incoming user data streams, the determination being based on any one or any combination of: the number of ground stations available for transmitting forward beam signals to the space segment; detected impairments in any one or more of the optical forward uplink signals for transmitting the forward beam signals from the ground segment to the space segment; and the load of the corresponding forward user beam.

18. The satellite communication system according to any one of claims 10 to 17, wherein the satellite communication system provides a plurality of forward user beams via one or more satellites included in the space segment, each forward user beam being based on a corresponding forward user beam signal and having a corresponding combination of downlink signal frequency and polarization, and wherein each ground station comprises: An interface circuitry system configured to receive two or more forward beam signals, the two or more forward beam signals corresponding to two or more forward user beams having the same combination of corresponding downlink signal frequencies and polarizations; and Processing and transmission circuitry system, the processing and transmission circuitry system being configured to: A set of forward beam element signals is formed for each of the two or more forward beam signals by generating a set of radio frequency (RF) signals and weighting each RF signal with a corresponding forward beam weight from a corresponding set of forward beam weights, each RF signal corresponding to an antenna element in the target satellite antenna array and modulated by the forward beam signal, the forward beam weights being calculated such that the set of forward beam element signals is simultaneously transmitted from the target satellite antenna array in the far field to form a corresponding forward user beam; The corresponding sets of forward beamforming element signals are combined to form a set of combined forward beamforming element signals; Each optical carrier of multiple optical carriers at different wavelengths is modulated using a corresponding one of the combined forward beamforming signals in the set of combined forward beamforming signals to obtain multiple forward optical channel signals. The multiple forward optical channel signals are multiplexed in the optical domain to form corresponding optical forward uplink signals; as well as The corresponding optical forward uplink signal is transmitted toward the satellite having the target satellite antenna array.

19. A method operated by a processing node of a satellite communication system, the method comprising: Receive multiple return signals, each return signal being received from a corresponding ground station among a plurality of geographically separated ground stations included in the ground segment of the satellite communication system, wherein each return signal originates from a corresponding optical return downlink signal received by the corresponding ground station from the space segment of the satellite communication system, and wherein each return signal carries return user services transmitted by user terminals in one or more corresponding return user beam coverage areas associated with the return signal; For each return signal, a return beam signal is formed for each of the one or more corresponding return user beam coverage areas associated with the return signal by applying a corresponding set of return user beam weights to the return signal. The corresponding set of return user beam weights represents the return user beam corresponding to the corresponding return user beam coverage area and is calculated to minimize the signal-to-noise ratio (SNR) of the return uplink signal transmitted by the user terminal located in the corresponding return user beam coverage area. Two or more return user data substreams are recovered, the two or more return user data substreams together forming a set of return user data substreams, the set of return user data substreams being transmitted by a user terminal located at a location covered by two or more return user beam coverage areas and relayed by the satellite communication system using return space diversity transmission, wherein each return user data substream is relayed to a different ground station among the plurality of ground stations using a corresponding optical return downlink signal, such that each return user data substream in the set of return user data substreams is recovered from the return signal received from a different ground station among the plurality of geographically separated ground stations, and corresponds to a corresponding return user beam among the return user beams corresponding to the two or more return user beam coverage areas covering the location of the user terminal; Reassemble the set of returned user data substreams to obtain the corresponding returned user data stream; as well as The outgoing user data stream corresponding to the returned user data stream is transmitted toward the external network.

20. The method of claim 19, wherein reassembling the returned user data substream includes using reassembly information included by the user terminal in at least one of the two or more returned user data substreams.

21. The method of claim 19 or 20, wherein each returned user data substream is transmitted by the user terminal using a different combination of returned uplink signal frequencies and polarizations, wherein each such combination corresponds to a corresponding returned user beam coverage area among the two or more returned user beam coverage areas covering the location of the user terminal.

22. The method according to any one of claims 19 to 21, wherein the satellite communication system serves a group of user terminals in a satellite service area, the satellite service area being logically divided into a plurality of return user beam coverage areas, wherein each return user beam coverage area is associated with a corresponding combination of return uplink signal frequency and polarization, wherein each return signal conveys a unique set of combined return beam element signals representing one or more non-overlapping return user beams having the same corresponding combination of return uplink signal frequency and polarization, and each combined return beam element signal in each unique set of combined return beam element signals corresponds to a corresponding element in a corresponding satellite antenna array for receiving return uplink signals transmitted by the group of user terminals.

23. The method of claim 22, wherein the method comprises: For each return signal, a return beam signal is formed for each return user beam represented by the unique set of combined return beam element signals conveyed by the return signal.

24. The method of claim 23, further comprising: The corresponding return user beam weights are calculated using channel state information (CSI) determined about one or more reference user terminals in each return user beam coverage area, in order to form the corresponding return user beam signal based on the CSI.

25. The method according to any one of claims 19 to 24, wherein the satellite service area is logically divided into a plurality of return user beam coverage areas, each return user beam coverage area representing a corresponding return user beam among the plurality of return user beams, wherein one or more return space diversity beam subsets exist among the plurality of return user beams, each return space diversity beam subset comprising two or more return user beams having a unique combination of signal frequencies and polarizations and having a corresponding return user beam coverage area with an overlap exceeding a threshold amount, and wherein the location of the user terminal is within the overlap of one of the return space diversity beam subsets, and the use of return space diversity transmission for the user terminal comprises: Each return user data substream corresponding to the return user data stream is transmitted from the space segment to the ground segment via different return optical downlink signals received at one of the different ground stations in the ground segment.

26. The method according to any one of claims 19 to 25, the method further comprising: At each ground station, the corresponding optical return downlink signal is received, the corresponding optical return downlink signal is optically demultiplexed to obtain multiple optical channel signals at the corresponding optical wavelength, and a unique set of combined return beam element signals conveyed by the return signal output from the ground station is generated from the multiple optical channel signals.

27. The method according to any one of claims 19 to 26, the method further comprising: The user terminal is controlled to selectively operate in a return spatial diversity transmission mode rather than a return non-spatial diversity transmission mode, in which the user terminal transmits the return user data stream instead of forming and transmitting the set of return user data substreams.

28. The method of claim 27, wherein controlling the user terminal to selectively operate in the return space diversity transmission mode comprises: The user terminal, whether operating as a standalone user terminal or as part of a larger group of user terminals, is determined based on any one or any combination of the following: the number of ground stations available to receive the corresponding optical return downlink signal; detected impairments to any one or more optical return downlink signals; and the load of the corresponding return user beam.

29. A satellite communication system, the satellite communication system comprising: Processing nodes, the processing nodes include: An interface circuit system configured to receive multiple return signals, each return signal received from a corresponding ground station among multiple geographically separated ground stations, wherein each return signal originates from a corresponding optical return downlink signal received by the corresponding ground station from a corresponding satellite, and wherein each return signal carries return user services transmitted by user terminals in one or more corresponding return user beam coverage areas associated with the return signal; and Processing circuitry system, the processing circuitry system being configured to: For each return signal, a return beam signal is formed for each of the one or more corresponding return user beam coverage areas associated with the return signal by applying a corresponding set of return user beam weights to the return signal. The corresponding set of return user beam weights represents the return user beam corresponding to the corresponding return user beam coverage area and is calculated to minimize the signal-to-noise ratio (SNR) of the return uplink signal transmitted by the user terminal located in the corresponding return user beam coverage area. Two or more return user data substreams are recovered, forming a set of return user data substreams. This set of return user data substreams is transmitted by user terminals located within the coverage areas of two or more return user beams and relayed by the satellite communication system using return space diversity transmission. Each return user data substream is relayed to a different ground station among the plurality of ground stations using a corresponding optical return downlink signal, such that each return user data substream in the set receives the return signal from the different ground stations among the plurality of geographically separated ground stations. Restored, and corresponding to one of the return user beams that corresponds to the two or more return user beam coverage areas covering the location of the user terminal; Reassemble the set of returned user data substreams to obtain the corresponding returned user data stream; and The outgoing user data stream corresponding to the returned user data stream is transmitted toward the external network.

30. The satellite communication system of claim 29, wherein the processing circuitry is configured to reassemble the set of returned user data substreams using reassembly information included by the user terminal in at least one of the two or more returned user data substreams.

31. The satellite communication system of claim 29 or 30, wherein each returned user data substream is transmitted by the user terminal using a different combination of returned uplink signal frequencies and polarizations, wherein each such combination corresponds to a corresponding returned user beam coverage area among the two or more returned user beam coverage areas covering the location of the user terminal.

32. The satellite communication system according to any one of claims 29 to 31, wherein the satellite communication system serves a group of user terminals in a satellite service area, the satellite service area being logically divided into a plurality of return user beam coverage areas, wherein each return user beam coverage area is associated with a corresponding combination of return uplink signal frequency and polarization, wherein each return signal conveys a unique set of combined return beam element signals representing one or more non-overlapping return user beams having the same corresponding combination of return uplink signal frequency and polarization, and each combined return beam element signal in each unique set of combined return beam element signals corresponds to a corresponding element in a corresponding satellite antenna array for receiving return uplink signals transmitted by the group of user terminals.

33. The satellite communication system of claim 32, wherein the processing circuitry is configured to form a return beam signal for each return user beam represented by the unique set of combined return beam element signals conveyed by the return signal for each return signal.

34. The satellite communication system of claim 33, wherein the processing circuitry is configured to use channel state information (CSI) determined with respect to one or more reference user terminals in each return user beam coverage area to calculate corresponding return user beam weights for forming corresponding return user beam signals based on the CSI.

35. The satellite communication system according to any one of claims 29 to 34, wherein the satellite service area is logically divided into a plurality of return user beam coverage areas, each return user beam coverage area representing a corresponding return user beam among the plurality of return user beams, wherein one or more return space diversity beam subsets exist among the plurality of return user beams, each return space diversity beam subset comprising two or more return user beams having a unique combination of signal frequencies and polarizations and having a corresponding return user beam coverage area with an overlap exceeding a threshold amount, and wherein the location of the user terminal is within the overlap of one of the return space diversity beam subsets, and the satellite communication system employs return space diversity transmission for the user terminal by transmitting each return user data substream corresponding to the return user data stream from the space segment to the ground segment via different return optical downlink signals received at a different ground station in the ground station.

36. The satellite communication system according to any one of claims 29 to 35, the satellite communication system further comprising the plurality of geographically separated ground stations, wherein each ground station is configured to receive the corresponding optical return downlink signal, optically demultiplex the corresponding optical return downlink signal to obtain a plurality of optical channel signals at a corresponding optical wavelength, and generate from the plurality of optical channel signals the unique set of combined return beam element signals conveyed by the return signal output from the ground station.

37. The satellite communication system according to any one of claims 29 to 36, wherein the processing circuitry is configured to control the user terminal to selectively operate in a return spatial diversity transmission mode rather than a return non-spatial diversity transmission mode, in which the user terminal transmits the return user data stream rather than forming and transmitting the set of return user data substreams.

38. The satellite communication system of claim 37, wherein the processing circuitry is configured to determine whether a user terminal, as a standalone user terminal or as part of a larger group of user terminals, operates in the return spatial diversity mode or the return non-spatial diversity mode based on any one or any combination of the following: the number of ground stations available to receive the corresponding optical return downlink signal; detected impairments to any one or more optical return downlink signals; and the load of the corresponding return user beam.

39. A method operated by a satellite of a satellite communication system, the method comprising: Two or more return user substreams are received from a user terminal located in a location covered by two or more return user beam coverage areas, each return user substream being received as a unique radio transmission from the user terminal and subdivided from the return user data stream at the user terminal; as well as Each return user substream is transmitted to the ground segment of the satellite communication system via a corresponding optical return downlink signal, which is received at a different ground station among a plurality of geographically separated ground stations included in the ground segment of the satellite communication system.

40. The method of claim 39, wherein each returned user data substream is received as a corresponding returned uplink signal, and wherein the corresponding two or more returned uplink signals have a unique combination of returned uplink signal frequency and polarization.

41. The method of claim 40, wherein the two or more return user uplink signals are received via corresponding antenna arrays on the satellite, the corresponding antenna arrays comprising a plurality of antenna elements and having a plurality of antenna outputs for outputting corresponding array element signals.

42. The method of claim 40 or 41, wherein the corresponding antenna array is identical for each returned user data substream, and wherein the corresponding antenna array has a corresponding plurality of antenna outputs for each unique combination of returned uplink signal frequency and polarization.

43. The method according to claim 41 or 42, wherein the method further comprises: Each optical return downlink signal is formed by modulating a corresponding optical channel carrier among multiple optical channel carriers at a corresponding optical wavelength according to the corresponding array element signal among the corresponding multiple array element signals, and then multiplexing the resulting multiple optical channel signals in the frequency domain to form the optical return downlink signal.

44. The method according to any one of claims 39 to 43, wherein transmitting each return user substream to the ground segment of the satellite communication system via a corresponding optical return downlink signal comprises: Each optical return downlink signal is transmitted toward one of the corresponding ground stations among the plurality of geographically separated ground stations.

45. The method according to any one of claims 39 to 44, the method further comprising: The satellite receives control signaling that controls which ground stations it will target for receiving the corresponding optical return downlink signals.

46. ​​The method according to any one of claims 39 to 45, wherein the satellite is a curved satellite comprising an unprocessed return signal path.

47. A method operated by a satellite of a satellite communication system, the method comprising: Receive two or more optical forward uplink signals, each optical forward uplink signal being received from a corresponding ground station among two or more geographically separated ground stations in the ground segment of the satellite communication system, wherein each optical forward uplink signal comprises a corresponding forward user data sub-stream in a set of two or more forward user data sub-streams subdivided from the forward user data stream in the ground segment, the forward user data stream being directed to a user terminal located in a location covered by two or more forward user beam coverage areas; as well as Each forward user substream is transmitted to the user terminal via a corresponding forward user beam from one of the two or more forward user beams that correspond to the coverage area of ​​the two or more forward user beams.

48. The method of claim 47, wherein transmitting each forward user substream to the user terminal via a corresponding forward user beam of the two or more forward user beams corresponding to the coverage area of ​​the two or more forward user beams comprises: For each forward user substream, corresponding antenna element signals are transmitted from corresponding antenna elements in the corresponding antenna array on the satellite, wherein the antenna element signals are weighted such that the far-field superposition of the antenna element signals forms a corresponding forward user beam.

49. The method of claim 48, wherein the method comprises: Each optical forward uplink signal is demultiplexed to obtain multiple corresponding optical channel signals at different optical wavelengths. Each optical channel signal conveys a corresponding combined forward beamforming signal from the set of combined forward beamforming signal. Each combined forward beamforming signal is weighted for beamforming transmission from a corresponding element of the corresponding antenna array. The corresponding multiple antenna element signals are either the set of combined forward beamforming signals or originate from the set of combined forward beamforming signals.

50. The method of claim 49, wherein each set of combined forward beam element signals conveys forward user services for a user terminal associated with one or more of a plurality of forward user beams defined by a satellite communication system, and wherein the one or more forward user beams do not overlap and have the same user downlink signal frequency and polarization.

51. The method according to any one of claims 47 to 50, the method further comprising: The satellite receives control signaling, which controls which ground stations it receives the corresponding optical forward uplink signals from.

52. The method according to any one of claims 47 to 51, wherein the satellite is a curved satellite comprising an unprocessed return signal path.

53. A satellite configured for operation in a satellite communication system, the satellite comprising: One or more antenna arrays configured to receive two or more return user substreams from a user terminal located at a location covered by two or more return user beam coverage areas, each return user substream being received as a unique radio transmission from the user terminal and subdivided from the return user data stream at the user terminal; as well as Two or more optical transmitters, each configured to transmit each return user substream to the ground segment of the satellite communication system via a corresponding optical return downlink signal received at a different ground station among a plurality of geographically separated ground stations included in the ground segment of the satellite communication system.

54. The satellite of claim 53, wherein each returned user data substream is received as a corresponding returned uplink signal, and wherein the corresponding two or more returned uplink signals have a unique combination of returned uplink signal frequency and polarization.

55. The satellite of claim 54, wherein the one or more antenna arrays comprise an antenna array having a plurality of array elements for receiving the unique radio transmission.

56. The satellite of claim 55, wherein for each unique combination of return uplink signal frequency and polarization, the antenna array has a corresponding plurality of antenna outputs.

57. The satellite according to claim 55 or 56, wherein each optical transmitter is configured to form the corresponding optical return downlink signal by modulating a corresponding optical channel carrier among a plurality of optical carriers at a corresponding optical wavelength according to a corresponding array element signal among the corresponding plurality of array element signals, and then multiplexing the resulting plurality of optical channel signals in the frequency domain to form the optical return downlink signal.

58. The satellite according to any one of claims 53 to 57, wherein the satellite is configured to transmit each optical return downlink signal toward a corresponding ground station among the plurality of geographically separated ground stations.

59. The satellite according to any one of claims 53 to 58, wherein the satellite is configured to receive control signaling for controlling which ground stations the satellite will target for receiving the corresponding optical return downlink signal.

60. The satellite according to any one of claims 53 to 59, wherein the satellite is a curved-tube satellite, the curved-tube satellite including an unprocessed return signal path coupling the one or more antenna arrays to the two or more optical transmitters.

61. A satellite configured for operation in a satellite communication system, the satellite comprising: Two or more optical receivers, each configured to receive a corresponding optical forward uplink signal among two or more optical forward uplink signals, each optical forward uplink signal being received from a corresponding ground station among two or more geographically separated ground stations in the ground segment of the satellite communication system, and wherein each optical forward uplink signal comprises a corresponding forward user data sub-stream in the ground segment of a set of two or more forward user data sub-streams subdivided from a forward user data stream, the forward user data stream being directed to a user terminal located in a location covered by two or more forward user beam coverage areas; as well as A radio frequency (RF) transmission circuitry system associated with one or more antenna arrays, the RF transmission circuitry system being configured to transmit each forward user substream to the user terminal via a corresponding forward user beam of two or more forward user beams corresponding to the coverage areas of the two or more forward user beams.

62. The satellite of claim 61, wherein, in order to transmit each forward user substream to the user terminal via a corresponding forward user beam of the two or more forward user beams corresponding to the coverage area of ​​the two or more forward user beams, the satellite is configured to transmit corresponding plurality of antenna element signals from corresponding plurality of antenna elements in corresponding antenna arrays on the satellite, wherein the antenna element signals are weighted such that the far-field superposition of the antenna element signals forms a corresponding forward user beam.

63. The satellite of claim 62, wherein each optical receiver is configured to demultiplex the optical forward uplink signal received by the optical receiver to obtain a plurality of corresponding optical channel signals at different optical wavelengths, each optical channel signal conveying a corresponding combined forward beamforming signal from a set of combined forward beamforming signal, each combined forward beamforming signal being weighted for beamforming transmission from a corresponding element of the corresponding antenna array, and wherein the corresponding plurality of antenna element signals are the set of combined forward beamforming signals or originate from the set of combined forward beamforming signal.

64. The satellite of claim 63, wherein each set of combined forward beam element signals conveys forward user services for a user terminal associated with one or more of a plurality of forward user beams defined by the satellite communication system, and wherein the one or more forward user beams do not overlap and have the same user downlink signal frequency and polarization.

65. The satellite according to any one of claims 61 to 64, wherein the satellite is configured to receive control signaling and accordingly align the two or more optical receivers to control from which ground stations the satellite receives corresponding optical forward uplink signals.

66. The satellite according to any one of claims 61 to 65, wherein the satellite is a curved-tube satellite, the curved-tube satellite comprising an unprocessed return signal path coupling the two or more optical receivers to the one or more antenna arrays.

67. A method for operating a satellite communication system comprising a ground segment and a space segment: The system receives two or more return user data substreams via one or more satellites included in the space segment, the two or more return user data substreams being transmitted by the same user terminal, the user terminal performing block coding on the return user data streams and dividing the resulting block-coded data into the two or more return user data streams, wherein each return user data substream conveys a different portion of the coded data from each coded block; Each return user data substream is delivered to the ground segment via different optical return downlink signals, and each optical return downlink signal is received at a different ground station among a plurality of geographically distributed ground stations included in the ground segment; as well as At the processing node of the ground segment, each of the two or more returned user data substreams is received from the respective ground station that has received one of the returned user data substreams; as well as The returned user data stream is reassembled from the returned user data stream for forwarding toward the target destination.

68. A satellite communication system, the satellite communication system comprising: The ground segment includes multiple geographically distributed ground stations and further includes an interface and processing circuitry system configured to: Incoming user data streams are received at the processing nodes of the ground segment, each incoming user data stream targeting a corresponding user terminal served by the satellite communication system; and Forward spatial diversity transmission is performed for each of the incoming user data streams by performing the following operations on one or more of the incoming user data streams: By block encoding the incoming user data stream and dividing each encoded data block into different encoded data subsets, corresponding sets of two or more forward user data substreams are formed. as well as Each forward user data substream is mapped to a corresponding forward beam signal among two or more forward beam signals, the two or more forward beam signals respectively corresponding to two or more forward user beams of the satellite communication system, the two or more forward user beams having a corresponding forward user beam coverage area covering the location of the user terminal to which the incoming user data stream is targeted; as well as Each forward beam signal is transmitted from the ground segment to the space segment via different optical forward uplink signals originating from different ground stations among the plurality of geographically distributed ground stations. Each forward uplink signal multiplexes multiple forward optical channel signals, which convey corresponding copies of the forward beam signal. The forward beam signal is weighted for beamforming transmission from corresponding antenna elements in the target antenna array in the space segment to achieve far-field formation of the corresponding forward user beam.

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