Method and apparatus for improved availability via multi-satellite diversity

Abstract

A satellite communications network (SCN) advantageously features selective use of a diversity service mode and a non-diversity service mode for providing service to individual user terminals (UTs) using a constellation of non-geosynchronous satellites included in the SCN. For example, for providing service to any given UT, the SCN may switch from the non-diversity service mode to the diversity service mode in response to determining that the non-diversity service includes one or more constrained view angles. The constrained view angles may be learned for the UT's location based on past monitoring by the SCN or may be estimated from view angle constraints learned for one or more locations in the vicinity of the UT's location.

Description

[Technical Field]

[0001] In the context of a satellite communications network including a constellation of non-geosynchronous satellites, the disclosed method and apparatus relate to selectively using a non-diversity service mode or a diversity service mode to provide service to each user terminal supported by the network. [Background technology]

[0002] Any given user terminal (UT) has a nominal "line of sight," which refers to the nominal range of angles over which the terminal can see and communicate with satellites. For example, by design, a UT has a nominal range of elevation angles over which it can establish and maintain communication with satellites.

[0003] In a constellation of non-geosynchronous orbit (NGSO) satellites, each satellite moves relative to the Earth's surface. That is, each satellite provides a moving coverage area whose ground footprint follows a terrestrial orbit corresponding to the satellite's orbit. Satellites in the constellation are candidates to serve a given UT to the extent that the UT's view overlaps with the satellite's coverage area. "Serving" in this context means providing communications services to the UT.

[0004] In a typical approach, an SCN based on a constellation of NGSO satellites serves UTs without diversity, meaning that a given satellite in the constellation serves only one UT at a time. The serving satellite switches as different satellites in the constellation move in and out of view of a given UT. The switch in serving satellite is called a UT's "handover."

[0005] Providing service to UTs without diversity offers several advantages, such as simplified scheduling and corresponding management of forward and / or return data flows within the ground and space segments of the SCN for individual terminals. However, non-diversity service situations result in reduced availability, or at least an increased risk of reduced availability. "Availability" in this context refers to the degree to which the SCN is accessible and able to provide reliable connectivity to user terminals. However, addressing the availability issue involves a wide range of considerations, including, but not limited to, the complexity of traffic scheduling, network throughput, resource utilization efficiency, and how to make intelligent decisions about whether and when to use diversity techniques to provide service to a given UT. Summary of the Invention

[0006] A satellite communications network (SCN) advantageously features selective use of a diversity service mode and a non-diversity service mode for providing service to individual user terminals (UTs) using a constellation of non-geosynchronous satellites included in the SCN. For example, for providing service to any given UT, the SCN may switch from the non-diversity service mode to the diversity service mode in response to determining that the non-diversity service includes one or more constrained view angles. The constrained view angles may be learned for the UT's location based on past monitoring by the SCN or may be estimated from view angle constraints learned for one or more locations near the UT's location.

[0007] One embodiment includes a method performed by a controller operating in an SCN including a constellation of non-geosynchronous satellites moving along respective orbital paths. The method includes the SCN learning view angle constraints for corresponding geographic locations based on collecting connectivity metrics over time for a given UT operating at the corresponding locations, the collected connectivity metrics for each such location indicating view angles characteristically associated with reduced connectivity. The method further includes the SCN serving the UT in a non-diversity service mode in which a single serving satellite is present in the constellation for the UT at a time, and predicting, based on the learned view angle constraint, that the UT will experience a connectivity degradation. The method further includes, in response to the prediction, the SCN determining to switch from serving the UT in the non-diversity service mode to serving the UT in a diversity service mode in which two or more serving satellites are present in the constellation for the UT simultaneously, and serving the UT in the diversity service mode.

[0008] A related embodiment includes a controller configured to operate in an SCN including a constellation of non-geosynchronous satellites moving along respective orbital paths, the controller including a communications interface circuit and a processing circuit configured to learn view angle constraints for corresponding geographic locations based on collecting connectivity metrics over time for given user terminals (UTs) operating at the corresponding locations, the collected connectivity metrics for each such location indicating view angles characteristically associated with reduced connectivity.

[0009] The processing circuitry of the diversity controller is further configured to serve the UT in a non-diversity service mode in which a single serving satellite is present in a constellation for the UT at a time and to predict that the UT will experience reduced connectivity based on the learned view angle constraint, and in response to the prediction, the processing circuitry is configured to determine to switch from serving the UT in the non-diversity service mode to serving the UT in a diversity service mode in which two or more serving satellites are present in a constellation for the UT at a time, and to serve the UT in the diversity service mode.

[0010] Another embodiment includes a method of operation by a UT configured to be served by an SCN including a constellation of non-geosynchronous satellites moving along respective orbital paths. The method includes the UT operating in a non-diversity service mode (wherein the SCN serves the UT via a single serving satellite in the constellation at a time), the UT receiving a control signal from the SCN indicating a switch from the non-diversity service mode to a diversity service mode (wherein the SCN serves the UT via two or more serving satellites in the constellation at a time), and the UT switching from operating in the non-diversity service mode to operating in the diversity service mode. The UT switches in response to either receiving the control signal or satisfaction of a diversity mode trigger condition indicated by the control signal.

[0011] A related embodiment includes a UT configured to be served by an SCN including a constellation of non-geosynchronous satellites moving along respective orbital paths. The UT includes a communications interface circuit configured to communicate with the SCN via an exchange of radio signals with one or more satellites in the constellation. The UT further includes processing circuitry operatively associated with the communications interface circuit and configured to: operate in a non-diversity service mode in which the SCN serves the UT via a single serving satellite in the constellation at a time; receive a control signal from the SCN indicating a switch from the non-diversity service mode to a diversity service mode in which the SCN serves the UT via two or more serving satellites in the constellation at a time; and switch from operating in the non-diversity service mode to operating in the diversity service mode in response to one of receiving the control signal or satisfaction of a diversity mode trigger condition indicated by the control signal.

[0012] It is to be understood that the present invention is not limited to the above-described features and advantages. Indeed, those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram of a satellite communications network (SCN) in accordance with an exemplary embodiment. [Figure 2] FIG. 2 is a logic flow diagram of a method of operation by a diversity controller in an SCN, according to an exemplary embodiment. [Figure 3] FIG. 3 is a logic flow diagram of another method of operation by a diversity controller, according to an exemplary embodiment. [Figure 4] FIG. 4 is a block diagram of a diversity control unit in accordance with an exemplary embodiment. [Figure 5]FIG. 5 is a block diagram of a machine learning (ML) model instantiated in a runtime environment for diversity control decisions according to one embodiment. [Figure 6] FIG. 6 is a block diagram of a circuit configured to split a data stream into two or more data substreams for diversity transmission, according to an exemplary embodiment. [Figure 7] FIG. 7 shows examples of UT viewing angles at given locations, including constrained viewing angles. [Figure 8] FIG. 8 shows examples of UT viewing angles at given locations, including constrained viewing angles. [Figure 9] FIG. 9 is a diagram of an example satellite coverage area that includes several locations characterized by viewing angle constraints by the SCN. [Figure 10] FIG. 10 is a block diagram of an exemplary database structure that may be used to hold data indicating learned viewing angle constraints for a potentially large number of positions. [Figure 11] FIG. 11 is a logic flow diagram of a method of operation by a UT, according to an exemplary embodiment. [Figure 12] FIG. 12 is a block diagram of a UT in accordance with an exemplary embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] One approach to improving the availability of satellite communication networks (SCNs) relies on cooperative beamforming from multiple (two or more) satellites. Various techniques can be used to perform beamforming by selecting a specific satellite from among multiple satellites for beamforming and / or adaptively incorporating signals from two or more satellites for beamforming.

[0015] In some embodiments, diversity may provide service to a user terminal (UT) by one or more of the following: (a) polarization combining from a single satellite, including (i) selecting the best of two polarizations in a fading environment or (ii) adaptively and optimally combining two polarizations; (b) diversity selection, including (i) selecting the best satellite based on, for example, signal strength or (ii) adaptively monitoring multiple satellites and dynamically selecting the best one; and (c) diversity combining, including (i) adaptively and optimally combining signals from multiple satellites and (ii) performing interference cancellation based on the use of channel sounding.

[0016] Diversity combining may also include interleaving or applying forward error correction (FEC) coding to data to be relayed via multiple satellites. In a forward downlink example, a participating UT receives a respective signal from each of multiple satellites, demodulates the data from each such signal, and combines and orders the data according to the FEC coding. Each signal may use any one or more of the following: a different CDMA code, a different polarization, a different frequency, or a different time slot.

[0017] One notable aspect herein is the selective use of diversity from multiple non-geosynchronous orbit (NGSO) satellites to improve SCN availability to handsets operating in the L-band. Of course, the disclosed methods and apparatus apply directly to other frequency bands and other types of satellite receivers. While improved availability through diversity is a key advantage, the use of diversity may also improve link budget and / or throughput. Unless otherwise specified or apparent from the context, the term "satellite" means an NGSO satellite, and any reference to a "constellation" may be understood to refer to a constellation of NGSO satellites, unless otherwise specified or apparent from the context.

[0018] One or more embodiments disclosed herein are based on the assumption that the position and velocity of each satellite in a constellation are known reasonably accurately to a ground station that provides forward traffic for relay through the satellite in the constellation. In a particular example involving selective use of diversity or non-diversity services, a constellation of NGSO satellites has at least two candidate satellites that serve a given UT, e.g., a handset. The involved SCN includes one or more ground stations (also called base stations) that are communicatively coupled, directly or indirectly, to two or more candidate satellites in the constellation to relay forward traffic (user data) to the given UT via a forward link and / or relay return traffic from the UT via a return link. Unless otherwise specified or apparent from the context, "satellite" as used herein refers to an NGSO satellite.

[0019] If there are two or more candidate satellites, the SCN may choose to serve the UT in a non-diversity service mode, meaning that the UT is served by one satellite in the constellation at a time, or in a diversity service mode, meaning that the UT is served by multiple (two or more) satellites in the constellation at a time.

[0020] Diversity service mode improves availability because multiple serving satellites mean that service can continue, albeit with reduced throughput or other degradation, even if the UT experiences fading relative to one of the multiple serving satellites. Availability is generally reduced for a given serving satellite due to nearby problems, such as: (a) shadowing caused by large objects such as hills or large structures. Such shadowing can be persistent and affect all or most propagation paths between the UT and the serving satellite; (b) shading caused by thin objects such as trees and leaves. Such shading can be persistent but affect a limited number of propagation paths between the UT and the serving satellite; and (c) scattering. Satellite signals often bounce off objects, causing multipath; scattering is only an issue when the serving satellite is at a low elevation angle and the ground near the UT is highly reflective.

[0021] All of these issues can be understood as reducing connectivity between a given UT and its serving satellite. In most cases, a given UT's connectivity is very good even using a single serving satellite, as the signal(s) travel through space with a clear line of sight and minimal scattering. However, the combination of terminal location and satellite location can result in occlusion, shadowing, and reflections. In other words, a given UT may be operating safely within the nominal viewing angle range, yet experience reduced connectivity due to the local environment. Reduced connectivity translates to reduced availability.

[0022] In one or more embodiments, the increased availability is based on the following operational logic in the SCN: (a) if a UT operating in a non-diversity service mode experiences a decrease in availability or if the SCN predicts that it will experience a decrease in availability, the SCN switches the UT to a new serving satellite, assuming there are other satellites in the constellation that are currently candidates to serve the UT; and (b) if there are no other satellites that are currently candidates to serve the UT, or if the UT experiences or is predicted to experience a decrease in availability with respect to all candidate satellites, the SCN performs one of two actions: (i) suspends traffic scheduling for the UT to avoid transmitting user traffic to (or receiving user traffic from) the UT during the time period corresponding to the decrease in availability, or (ii) selects a diversity service mode to serve the UT from multiple satellites in the constellation.

[0023] One approach involves the SCN creating and maintaining a short-term history (database) of UTs and using it to predict locations where availability is or may be reduced. This database thus represents a type of short-term spatial database. If one satellite is having problems serving a UT, a scheduling algorithm switches serving satellites. If all candidate satellites for a UT are experiencing problems, two options exist: one is to delay communication until one of the candidate satellites moves into a better position. Delays are effective for certain types of communication services, such as low-priority data transfers, such as software downloads or text transfers. For other, more delay-sensitive types of communication services, the SCN activates diversity techniques. This decision-making process can use machine learning to better understand when diversity is needed. Selectively utilizing diversity services has several advantages, including the SCN not unnecessarily tying up two satellites when it is not necessary for good availability.

[0024] For diversity services in the return link direction, where traffic travels from the UT to one or more satellites in the constellation and then downlinks to the SCN's terrestrial network, the return link signals carrying such traffic may be received at multiple base stations, and the SCN then forwards the physical (PHY) layer data (either sampled analog-to-digital conversion (ADC) data or data that has been downsampled and processed to some level) over the terrestrial network and / or external network links for aggregation at a common processing entity. Once the data is aggregated, the SCN can use various techniques to reliably recover the data. These techniques include one or a combination of: (a) estimating the gain and phase of each channel and using the estimates to implement a best-fit combining technique; or (b) independently attempting to receive the return data via any of the multiple serving satellites.

[0025] In the forward direction, from the terrestrial network to the constellation and from there to the UT, one diversity technique is optimal single-channel multiple-input-single-output (MISO) or multiple-input-multiple-output (MIMO) transmission. "Multiple-input" here refers to transmissions from two or more satellites in the constellation. Using MIMO or MISO transmission for forward diversity means transmitting from two or more satellites with precise timing and predetermined gain and phase adjustments so that the two or downlink signals are optimally combined when received at the UT. This operation can be understood as coordinated beamforming between two or more satellites participating in the MIMO or MISO transmission.

[0026] Consider the case of forward MISO, where the SCN's terrestrial network includes two satellite access nodes (SANs), each associated with a corresponding satellite in a constellation, each serving a given UT. In one embodiment, both SANs transmit the same fundamental signal, but with different frequencies, gains, phases, and delays so that the downlink signals from the two satellites add constructively at the given UT. While MISO is in some respects a known technique, adopting it for diversity service in a satellite environment requires the innovative use of ephemeris and corresponding dynamic adjustment of the involved channel estimates as a function of the relative motion between the multiple serving satellites and the given UT. This channel estimate may be obtained via channel sounding, in which sounding signals are transmitted and received via two or more satellites to estimate the physical channel between the UT and the SCN, from or via each of the serving satellites. For example, the SCN transmits different orthogonal signals from each ground station, allowing the UT to estimate the channel and send back the estimate, and the SCN dynamically adjusts the channel estimate to account for the satellite motion.

[0027] Regarding dynamic adjustment of channel estimates, in one or more embodiments, the SCN dynamically adjusts past channel estimates to predict new estimates. The SCN may use, for example, a linear channel estimator or a maximum likelihood channel estimator to predict future channels. Furthermore, at future times, the SCN may use current / recent sounding information to estimate the error in the corresponding predicted estimate. By repeating this process, the SCN can refine not only past estimates but also future estimates. This may take the form of estimating the rate of change of channel phase and gain, or the rate of change of channel delay. Once the estimation circuitry used in the CN is trained, it enables the SCN to transmit diversity signals that optimally or near-optimally couple to a given UT.

[0028] Another technique is MISO with time offset. This technique involves transmitting the same signal for the UT from each of several serving satellites, but with a defined delay between the signals. If the delay is large enough, the UT can combine the two signals using a rake-receiver-type structure. Such a receiver adjusts the frequency, gain, and phase of the two or more received signals so that they add constructively. One challenge with this structure is avoiding increased self-interference caused by the delay. One way to mitigate this problem is to make the delay(s) long enough so that only one of the two or more serving satellites is transmitting at the UT's exact location at a time. Of course, the serving satellites can transmit at other locations as well. Another way to mitigate this problem is to make the delay long compared to the symbol rate and use a maximum likelihood decoding algorithm, which effectively ignores the effect of the delayed signal(s). A third way to mitigate this problem is to use direct-sequence spread-spectrum techniques to make the delayed signal nearly orthogonal to the non-delayed signal.

[0029] Frequency diversity is another example of a forward diversity technique. In frequency diversity, each serving satellite transmits to the UT using a different frequency. The multiple downlink signals may overlap, e.g., each diversity downlink signal carries the same content (same traffic). The UT can use any one of a variety of techniques to recover the content, including best signal selection and / or multiple signal combining. Advantageously, this approach is simple but uses more signal bandwidth.

[0030] Another forward diversity technique is message diversity. In message diversity, multiple serving satellites transmit the same message intended for the UT, but at different times and possibly using different frequencies. The advantage is that message diversity can be implemented at various levels of the communications protocol stack, offering a relatively simple implementation but using more capacity. Or, stated another way, message diversity is less efficient because it transmits the same message multiple times.

[0031] FIG. 1 illustrates an SCN 10 according to an exemplary embodiment, which includes a constellation 12 of NGSO satellites 14. By way of example, the satellites 14 are LEO or Medium Earth Orbit (MEO) satellites. Additionally, the SCN 10 includes a terrestrial network 16, which includes a core network (CN) 18. Of particular interest here is that the terrestrial network 16 is configured to employ diversity on a selective basis (dynamic decision-based) with respect to individual UTs 20 served by the SCN 10. While FIG. 1 illustrates a single UT 20 for ease of illustration and discussion, it should be understood that the SCN 10 is operable to serve a potentially large number of UTs 20, such as a collection of UTs 20 spread across a wide geographic area covered by the constellation 12.

[0032] In dynamic diversity, the SCN 10 decides whether and when to serve a given UT 20 using a non-diversity service mode or a diversity service mode. The diversity service mode itself can use a specific selection of two or more diversity techniques. That is, there may be a variety of selectable techniques for operation in the diversity service mode, depending, for example, on whether diversity is used in the forward or return direction, or both. Other variables that influence the particular diversity technique used include the configuration and capabilities of the SCN 10 and the involved UT(s) 20, and, in some cases, the type of communication service involved.

[0033] In the illustrated embodiment, the CN 18 includes a diversity controller 22 configured to determine whether the SCN 10 will serve a given UT 20 in a non-diversity service mode or in a diversity service mode. The diversity controller 22 is communicatively coupled to or integrated within a communications processing system (CPS) 24, which performs user scheduling of forward and return user traffic for each UT 20 within the population of UTs 20 served by the SCN 10. In particular, the CPS 24 is configured to interface with one or more external networks 26, such as the Internet, and to support routing of user data streams between one or more types of remote devices or systems 28 and each of the UTs 20 supported by the SCN 10. In this regard, the SCN 10 should be understood to provide one or more types of communications services to each UT 20, such as mobile broadband service or other types of data and / or voice connectivity.

[0034] CPS 24 comprises hardwired circuitry or programmable circuitry, or a combination of both. In one or more embodiments, CPS 24 comprises one or more computer servers, each such server comprising one or more microprocessors or other types of digital processors, a communications interface such as an Ethernet or other data network interface, and memory and / or storage containing computer program instructions that, when executed by the one or more microprocessors or other types of digital processors, cause CPS 24 to perform user scheduling and configure such processor(s) to interact with (or implement) diversity controller 22. User scheduling, as described above, involves scheduling forward and / or return traffic for individuals among the population of UTs 20 served by SCN 10.

[0035] Of course, due to the relative movement of the satellites 14 and the UTs 20, scheduling user traffic involves mapping respective traffic flows to different satellites 14 at different times, depending on which satellite(s) 14 in the constellation 12 are candidates for serving a particular UT 20 at any given time. To that end, the terrestrial network 16 includes multiple geographically dispersed satellite access nodes 30.

[0036] Forward traffic destined for an individual UT 20 flows from one or more SANs 30 into the constellation 12, and the satellites 14 in the constellation 12 may participate in mesh routing of that traffic for downlink transmission by the particular satellite(s) 14 serving the intended UT 20. Generally, the CPS 24 has network links 32 to each SAN 30 so that, at any given time, user traffic for any given UT 20 may be sent to or received from one or more SANs 30 for subsequent direct or meshed transmission to the satellite(s) 14 serving the given UT 20.

[0037] Correspondingly, each SAN 30 includes optical and / or radio frequency (RF) transceivers for transmitting one or more feeder uplink signals 34 to and receiving one or more downlink signals 36 from within-coverage satellite(s) 14. These feeder link signals generally carry the traffic of multiple UTs 20 according to a defined multiplexing scheme.

[0038] 1 includes an illustration of the beams 40, with each beam 40's directional direction and size defining the coverage area of ​​each satellite 14. The illustrated beams 40 may be associated with the coverage area of ​​each satellite 14 in the forward and / or return paths, with each beam 40 having a beam footprint 42 that moves along a ground track on the Earth's surface corresponding to the orbital path of the corresponding satellite 14. As previously mentioned, cooperative beamforming may be used to serve a given UT 20 in a diversity service mode, such that the respective beams 40 from two serving satellites 14 are cooperatively controlled in terms of phase, timing, frequency, etc. to generate a constructive combination of beams at a particular location of the given UT 20.

[0039] Additionally, satellite 14 may simultaneously support the formation of multiple beams 40, e.g., at different frequencies and / or polarizations. Thus, Figure 1 is merely an illustration of a satellite coverage area for transmitting user downlink signals 44 carrying forward user traffic to each UT 20 and receiving user uplink signals 46 carrying return user traffic from each UT 20. In one or more embodiments, satellite 14 further includes inter-satellite links 48 for routing user traffic between serving and non-serving satellites 14 in constellation 12 on a mesh basis for a given traffic flow.

[0040] In one or more embodiments, the relative beam orientation of each satellite 14 is fixed or otherwise controlled on an open-loop basis. In one or more other embodiments, the satellites 14 have closed-loop control of their own beamforming. An example of closed-loop beamforming is when two or more satellites 14 participate in cooperative beamforming to serve a UT 20 using multiple-input multiple-output (MIMO) or multiple-input single-output (MISO) diversity, where MIMO and MISO are examples of diversity techniques used by the SCN 10 when serving a UT 20 in a diversity service mode.

[0041] In at least one embodiment, the SCN 10 supports two or more diversity techniques, and a given UT 20 served in a diversity service mode is not necessarily served using the same diversity technique. For example, the particular diversity technique used may be based on known or estimated channel conditions and / or the particular type or priority of the communication service involved. Thus, in one or more embodiments, the SCN 10 may use different diversity techniques at different times, such as for different UTs 20 experiencing different conditions or using different communication services.

[0042] 2 illustrates an example of method 200 in operation by diversity controller 22. For example, diversity controller 22 may comprise a computer server having a memory that stores computer program instructions that, when executed by a microprocessor of the computer server, cause the computer server to perform method 200.

[0043] Method 200 includes learning view angle constraints for corresponding geographic locations based on collecting connectivity metrics over time for given UTs operating at the corresponding locations (block 202), the connectivity metrics collected for each such location indicating view angles characteristically associated with connectivity degradation. It should be understood that learning step 202 may be performed one or more times, and that learning may be continuous or may occur on an iterative basis based on ongoing observation of connectivity metrics, such as received signal quality or strength, or error rates, or dropped connections, or other such metrics indicative of instances of connectivity degradation between given UTs 20 and their serving satellites 14.

[0044] Method 200 further includes serving UT 20 in a non-diversity service mode in which there is a single serving satellite 14 in constellation 12 for UT 20 at a time (block 204), and predicting that UT 20 will experience reduced connectivity based on the learned view angle constraint (block 206). Method 200 further includes responding to the prediction by determining to change from serving UT 20 in a non-diversity service mode to serving UT 20 in a diversity service mode in which there is more than one serving satellite in constellation for UT 20 at a time, and serving UT 20 in the diversity service mode (block 208).

[0045] In one or more embodiments, predicting that the UT 20 will experience connectivity degradation is based on learned view angle constraints, the UE's location, and the serving satellite's ephemeris, from which it is determined that providing service to the UT in a non-diversity service mode will involve a constrained view angle. For example, over one or more observation intervals, the SCN 10 collects connectivity metrics for a given UT 20 operating in many different locations, and the collected metrics are used to identify, for each of the one or more locations, a view angle characteristically associated with connectivity degradation.

[0046] In particular embodiments, the learned view angle constraints are represented in a database that associates each of a plurality of respective locations with a corresponding view angle constraint learned for the respective location. Here, predicting that the UT will experience connectivity degradation includes referencing an index of the database as a function of the UT's location to determine the view angle constraints applicable to the UT's location, and determining from the serving satellite ephemeris that the UT 20 will experience one or more constrained view angles. In other words, as an example of predicting connectivity degradation, diversity controller 22 determines that the UT 20's serving satellite 14 is at or passing through a location corresponding to a view angle from the UT 20's location where connectivity is known or predicted to be degraded.

[0047] The location of the UT 20 may not match any location in the database for which the view angle constraints were learned. However, one or more embodiments of method 200 include determining the view angle constraints applicable to the location of the UT by interpolating or extrapolating the view angle constraints corresponding to one or more locations in the database that are closest to the location of the UT 20. This determination may take into account the vector relationship (distance and direction) between the closest database location(s) and the UT location to determine the constrained view angle applicable to the UT location. Additionally or alternatively, the database may include information regarding the location and direction of estimated obstacles, and such information may be used to estimate the constrained view angle for locations not represented in the database.

[0048] Alternatively, in one or more embodiments of the method, the learned view angle constraints are represented by a trained machine learning (ML) model that outputs view angle constraints applicable to an input location, where predicting that the UT 20 will experience reduced connectivity includes inputting the UT location into the trained ML model, and evaluating the ephemeris of the servicing satellite to determine whether the UT 20 will experience a constrained view angle as indicated by the applicable view angle constraints output by the trained ML model.

[0049] As mentioned above, any given viewing angle includes an azimuth angle (Az) and an elevation angle (E1). Thus, viewing angle constraints can be expressed as individual viewing angles or ranges of viewing angles. Furthermore, constrained viewing angles can be implicitly and dynamically specified, rather than by explicit or fixed criteria. For example, connectivity metrics collected over time for a particular location can reveal characteristic channel qualities for different viewing angles or ranges. By incorporating such data into a database, viewing angles considered restricted can be dynamically defined by specifying minimum characteristic channel qualities, with such minimum values ​​varying for different communication services. Similarly, collected metrics can be used to assign a grade or other ranking to a given viewing angle or range of viewing angles for a given location, with whether a viewing angle or range of viewing angles is considered restricted depending on the minimum acceptable grade. Again, the acceptable grade can be varied as a function of SCN loading and / or the type of communication service involved to bias diversity decision control toward or away from the diversity service.

[0050] Additionally, in the context of method 200, serving UT 20 in a diversity service mode includes serving UT 20 in one or both of a forward diversity service mode and a return diversity service mode. Serving UT 20 in a return diversity service mode includes, for example, attempting to receive an uplink transmission from UT 20 on each of two or more satellites 14 in constellation 12 such that, upon successful reception of an uplink transmission on one or more of the two or more satellites 14, SCN 10 receives corresponding return traffic from UT 20.

[0051] Providing service to the UT 20 in a forward diversity service mode includes, for example, using MIMO or MISO forward downlink transmissions to provide forward data to the UT 20. The MIMO or MISO forward downlink transmissions include, for example, cooperative beamforming transmissions from two or more satellites 14 in the constellation 12. The cooperative beamforming includes cooperatively setting any one or more of the transmit carrier frequency, transmit carrier amplitude, transmit carrier phase, or transmit carrier timing offset across the two or more satellites 14 to produce a constructive combination at the UT 20 of the respective downlink transmission signals from the two or more satellites 14.

[0052] In at least one such embodiment of method 200, the method further includes performing beamforming updates for cooperative beamforming according to a beam update rate that is faster than a channel sounding rate, where the channel sounding rate determines the rate at which the SCN 10 obtains updated channel state information (CSI) based on transmissions of reference signals on physical propagation channels linking each UT 20 to the SCN 10, and the SCN 10 supports the faster beam update rate by predicting changes in CSI between CSI updates. More generally, in one or more embodiments using cooperative beamforming, the method includes updating channel estimates used for cooperative beamforming to account for relative changes in position between two or more satellites 14 participating in cooperative beamforming.

[0053] In one or more embodiments, deciding to switch from serving the UT 20 in a non-diversity service mode to serving the UT 20 in a diversity service mode includes making the decision further dependent on a delay tolerance associated with the communication service provided to the UT 20 via the SCN 10. Making the decision dependent on a delay tolerance associated with the communication service provided to the UT 20 via the SCN 10 includes, for example, deciding to change to a diversity service mode in response to stored configuration information that identifies the communication service as being delay sensitive. In the opposite case, i.e., if the stored information indicates that the communication service involved is not delay sensitive, diversity controller 22 may decide not to switch from a non-diversity service mode to a diversity service mode despite predicting that the UT 20 will experience a degradation in connectivity.

[0054] 3 illustrates a method 300 that may be performed by diversity controller 22, for example, as part of or in support of performing method 200. Method 300 includes diversity controller 22 collecting (block 302) connectivity metrics over time for given UTs served by an SCN. Examples of metrics include QoS values, SINR, received signal strength, etc.

[0055] Method 300 continues with diversity controller 22 identifying, for each of one or more locations, a viewing angle characteristically associated with reduced connectivity for UTs 20 operating at that location (block 304). The results of the identification are stored as a database (block 306) for use by diversity controller 22 in making live diversity control decisions for a given UT 20.

[0056] 4 illustrates an example implementation of diversity controller 22, which may be configured to perform the operations included in methods 200 and 300, along with any one or more of the extensions and variations described herein. The example diversity controller 22 is configured to operate within SCN 10 and includes a communications interface circuit 60 and a processing circuit 62 operatively associated with communications interface circuit 60.

[0057] In implementations in which diversity controller 22 is implemented separately from CPS 24, communication interface circuit 60 comprises, for example, an Ethernet interface or other data network interface through which processing circuit 62 exchanges control signals with CPS 24. Such signaling indicates a diversity / non-diversity decision made by processing circuit 62 to initiate or otherwise control configuration of SCN 10 to selectively serve a given UT 20 using a diversity service mode or a non-diversity service mode. For example, reference to diversity controller 22 "serving" a UT 20 in a non-diversity service mode or a diversity service mode can be understood to mean that diversity controller 22 outputs control signals to cause SCN 10 to perform such operation.

[0058] In another implementation, diversity controller 22 is integrated with CPS 24. In such a case, communication interface circuit 60 may comprise a data bus interface or other inter-processor interface within a computer server or other node that includes CPS 24.

[0059] Processing circuitry 62 may comprise, for example, one or more microprocessors 70 specially adapted to perform methods 200 and / or 300 based on the execution of computer program instructions carried on a computer-readable medium. Thus, FIG. 4 illustrates memory or other storage device 64 storing computer program instructions 66 for execution by one or more microprocessors 70. The same storage device 64 may also store data 68, such as configuration data governing the diversity / non-diversity decisions made by diversity controller 22. In at least one embodiment, data 68 includes a database, such as database 50 shown in FIG. 1. Database 50 contains information indicating learned viewing angle constraints for one or more positions. In at least one embodiment, data 68 includes training data and parameter data for a machine learning (ML) model 80, such as that shown in FIG. 5.

[0060] 5 , processing circuitry 62 provides a runtime environment 82 in which ML model 80 is trained and instantiated for subsequent use as a trained ML model. In at least one embodiment, diversity controller 22 uses collected training data 84 (e.g., raw or filtered connectivity metrics collected over one or more collection intervals) to train ML model 80. Once trained, ML model 80 takes in an input location and outputs a viewing angle constraint associated with the input location. The input location need not match a specific one of the locations represented in collected training data 84.

[0061] In general, whether implemented as shown in Figure 4 or Figure 5, an exemplary SCN 10 includes control circuitry configured to determine whether or when to serve individual UTs 20 or groups of UTs 20 supported by the SCN 10 using a diversity service mode or a non-diversity service mode. In at least one embodiment, the CPS 24 includes stream splitting / encoding circuitry 90 as shown in Figure 6. In an exemplary scenario, the control circuitry determines to change from serving a UT 20 in a non-diversity service mode to serving a UT 20 in a diversity service mode and sends corresponding control signals to the CPS 24 and / or elsewhere in the SCN 10 to initiate or otherwise time the switch.

[0062] In an exemplary forward diversity technique used to serve UT 20 in diversity service mode, a forward data stream, such as an IP packet flow, is targeted for delivery to UT 20 via SCN 10. For diversity transmission of the forward data stream, circuitry 90 divides the forward data stream into a number of data substreams equal to the number of satellites 14 used to serve UT 20 in diversity service mode. Each satellite 14 transmits a respective one of the data substreams, and circuitry 90 in one or more embodiments is configured to apply forward error correction (FEC) coding to the data substreams so that UT 20 can recover the complete data stream even in the presence of an impairment affecting any given one or more of the data substreams.

[0063] Figures 7 and 8 provide a detailed example to aid in understanding view angle constraints. In Figure 7, a UT 20 is located at a predetermined location 100 on the Earth's surface and is served by a single serving satellite 14. The UT 20 experiences different view angles 102 as the serving satellite 14 moves along its orbit 104. The figure suggests such movement by showing the serving satellite at three different positions relative to the UT 20: a first position at time t1, a second position at time t2, and a third position at time t3. While the UT 20 enjoys clear LoS to the satellite 14 over a range of view angles, it can be seen that a nearby obstacle 106 obstructs the view angle 102 over a corresponding range. In the figure, the unobstructed view angle 102 is depicted using a solid line, and the view angle 102 obstructed by the obstacle 106 is depicted using a dashed line. As FIG. 8 repeatedly shows, any given view angle can be understood to correspond to a line of direction from the UT 20 towards the satellite 14 and can be expressed as a pair of values ​​for Az and El.

[0064] FIG. 9 illustrates a satellite coverage area 120, which may be a large geographic region. Certain locations 122 within the satellite coverage area 120 are characterized in terms of constrained viewing angles. These characterized locations 122 are shown as solid ellipses within the satellite coverage area 120. To determine the viewing angle constraints applicable to an uncharacterized location 124, diversity controller 22 may extrapolate or otherwise infer the restrictions from the nearest characterized location, shown as location 122A in the figure, or may interpolate or otherwise infer the restrictions using two (or more) nearest neighbors, e.g., characterized locations 122A and 122B shown in FIG. 9.

[0065] FIG. 10 illustrates example contents of a database 50 containing information indicating or otherwise representing learned viewing angle constraints for multiple locations. Each entry in the database represents a location, which may be a "spot" or "zone" rather than simply a pinpoint location. Associated data stored at each location may include vector data representing restricted or unrestricted viewing angles, channel quality data organized by viewing angle, etc. Such data may be expressed not for individual, discrete viewing angles, but for different discretized ranges of viewing angles within an overall nominal range of viewing angles.

[0066] 11 illustrates a method 1100 in operation by a UT 20. The method 1100 includes the UT 20 operating in a non-diversity service mode (block 1102), with the SCN 10 serving the UT 20 via a single serving satellite 14 at a time in a constellation 12 of satellites 14. The method 1100 further includes the UT 20 receiving a control signal from the SCN 10 indicating a change from the non-diversity service mode to a diversity service mode in which the SCN serves the UT via two or more serving satellites 14 at a time in the constellation 12 (block 1104). Furthermore, the method 1100 includes the UT 20 changing from operating in the non-diversity service mode to operating in the diversity service mode in response to one of receiving the control signal or satisfaction of a diversity mode trigger condition indicated by the control signal (block 1106). The method 1100 may further include later returning the UT 20 to operating in the non-diversity service mode (block 1108).

[0067] In one example, the change to diversity operation occurs in response to a diversity mode trigger condition. As a particular example, the diversity mode trigger condition is a time indicated in the control signal that is associated with the UT experiencing a viewing angle determined by the SCN 10 as being limited. In another example, the diversity mode trigger condition is a handover of the UT to a particular satellite 14 in the constellation 12 as the new serving satellite 14.

[0068] Operating in a diversity service mode includes, for example, the UT 20 receiving a forward data stream as two or more forward data substreams transmitted from respective ones of two or more serving satellites 14. Receiving a forward data stream transmitted as two or more forward data substreams includes, for example, the UT 20 receiving a MIMO or MISO transmission from two or more serving satellites 14. Receiving a MIMO or MISO transmission includes, for example, the UT 20 receiving a MIMO or MISO transmission using a single radio front end.

[0069] In at least one embodiment, UT 20 receiving the forward data stream as two or more forward data substreams includes UT 20 receiving each forward data substream at a respective frequency or polarization or at a respective transmission time.

[0070] In at least one embodiment, to serve the UT 20 in a diversity service mode, the SCN 10 transmits the same forward data stream from each of two or more serving satellites 14, with successful transmission being based on successful reception at the UT 20 from any one or more of the two or more serving satellites 14.

[0071] In at least one embodiment, with respect to operation of UT 20 in a diversity service mode, method 1100 includes UT 20 splitting a return data stream into two or more return data substreams, each return data substream being received by a respective one of two or more serving satellites 14.

[0072] In at least one embodiment, the return to the non-diversity service mode by the UT 20 occurs in response to a return trigger condition, such as a handover to the next serving satellite, or after the expiration of a timer. As another example, the return is based on receiving further control signals at the UT 20 from the SCN 10.

[0073] 12 illustrates an exemplary UT 20 comprising one or more antennas 130 and an associated antenna interface 132 that couples the antenna(s) 130 to a communications interface circuit 134. The communications interface circuit 134 is configured to communicate with the SCN 10 via an exchange of wireless signals with one or more satellites 14 in the constellation 12.

[0074] In the exemplary depiction, the communications interface circuitry includes a transmitter 136 having a transmitter (TX) front end 138. The TX front end 138 includes analog circuitry for upconversion and amplification of signals for transmission from the antenna(s) 130 as uplink signals for reception by one or more satellites 14 in the constellation 12. The communications interface circuitry 134 further includes a receiver 140 having a receiver (RX) front end 142. The RX front end 142 comprises analog circuitry configured for filtering, amplification, and downconversion of downlink signals received at the antenna(s) 130 from one or more satellites 14 in the constellation 12.

[0075] In one or more embodiments, the RX front end 142 has a wide bandwidth to support simultaneous reception of two or more downlink signals at different downlink carrier frequencies, provided that each of the downlink carrier frequencies is within the radio frequency spectrum spanned by the receive bandwidth of the RX front end 142. Such simultaneous reception may be used, for example, to support simultaneous reception for MIMO or MISO transmissions of forward diversity services, or more generally, to support simultaneous reception of different data substreams or overlapping streams transmitted simultaneously from different satellites 14 at different downlink carrier frequencies.

[0076] Baseband processing of transmit and receive signals may be performed by a baseband processor included within the communications interface circuitry 134 or within processing circuitry 144 operatively associated with the communications interface circuitry 134 .

[0077] In one or more embodiments, processing circuitry 144 is configured to operate UT 20 in a non-diversity service mode in which SCN 10 serves UT 20 via a single serving satellite 14 at a time in constellation 12. Additionally, processing circuitry 144 is configured to receive a control signal from the SCN (via communications interface circuitry 134), the control signal indicating a change from the non-diversity service mode to a diversity service mode in which SCN 10 serves UT 20 via two or more serving satellites 14 at a time in constellation 12. Still further, processing circuitry 144 is configured to change UT 20 from operating in the non-diversity service mode to operating in the diversity service mode in response to one of receiving the control signal or satisfaction of a diversity mode trigger condition indicated by the control signal.

[0078] More generally, processing circuitry 144 in one or more embodiments is configured to perform any one or more of the operations of method 1100, or extensions and variations thereof. In at least one embodiment operating in a diversity service mode, processing circuitry 144 is configured to perform a return path diversity transmission that splits the return path data stream into two or more return path data substreams that are transmitted to respective ones of two or more serving satellites 14 in constellation 12. Correspondingly, processing circuitry 144 in such embodiments includes stream splitting and encoding circuitry, such as that depicted in FIG. 6, for splitting the return path data stream into substreams and applying FEC coding to the substreams.

[0079] Processing circuitry 144 comprises hardwired circuitry, programmable circuitry, or a mixture of both. In at least one embodiment, processing circuitry comprises one or more microprocessors, digital signal processors, or other digital processors specially adapted to perform the operations described herein for UT 20 based on execution of computer program instructions stored in the memory of UT 20.

[0080] It should be noted that modifications and other embodiments of the disclosed invention(s) will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. It is therefore to be understood that the invention(s) is not limited to the particular embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the present disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. 1. A method performed by a controller operating within a satellite communications network (SCN) including a constellation of non-geosynchronous satellites moving along respective orbital paths, the method comprising: learning view angle constraints for corresponding geographic locations based on collecting connectivity metrics over time for given user terminals (UTs) operating at said corresponding geographic locations, wherein the collected connectivity metrics for each such location indicate view angles characteristically associated with reduced connectivity; Serving a user terminal (UT) in a non-diversity service mode in which there is a single serving satellite in the constellation at a time for said UT; predicting that the UT will experience a decrease in connectivity based on the learned viewing angle constraints; In response to the prediction, determining to change from serving the UT in the non-diversity service mode to serving the UT in a diversity service mode in which there is more than one serving satellite in the constellation at a time to the UT; providing service to the UT in a diversity service mode; A method comprising:

2. 2. The method of claim 1, wherein predicting that the UT will experience connectivity degradation includes determining, based on learned view angle constraints, a UE's location, and serving satellite ephemeris, that serving the UT in the non-diversity service mode will involve a constrained view angle.

3. 3. The method of claim 1 or 2, wherein the learned view angle constraints are represented in a database that associates each of a plurality of respective locations with a corresponding view angle constraint learned for the respective location, and predicting that the UT will experience reduced connectivity includes: referencing an index of the database as a function of the location of the UT to determine view angle constraints applicable to the location of the UT; and determining from a servicing satellite ephemeris that the UT will experience one or more constrained view angles.

4. 4. The method of claim 3, wherein determining the view angle constraints applicable to the location of the UT includes interpolating or extrapolating view angle constraints corresponding to one or more locations in the database that are closest to the location of the UT.

5. 3. The method of claim 1 or 2, wherein the learned view angle constraints are represented in a trained machine learning (ML) model that outputs view angle constraints applicable to an input location, and predicting that the UT will experience reduced connectivity comprises inputting the location of the UT into the trained ML model and evaluating a servicing satellite ephemeris to determine whether the UT will experience a constrained view angle as indicated by the applicable view angle constraints output by the trained ML model.

6. The method of any one of claims 1 to 5, wherein any predetermined viewing angle comprises an azimuth angle (Az) and an elevation angle (El), and the viewing angle constraint comprises an individual viewing angle or a range of viewing angles.

7. 7. The method of claim 1, wherein serving the UT in a diversity service mode comprises serving the UT in one or both of a forward diversity service mode and a return diversity service mode.

8. 8. The method of claim 7, wherein serving the UT in the return diversity service mode includes attempting to receive an uplink transmission from the UT on each of two or more satellites in the constellation, and wherein the SCN receives corresponding return traffic from the UT upon successful reception of the uplink transmission on one or more of the two or more satellites.

9. 8. The method of claim 7, wherein serving the UT in the forward diversity service mode includes using multiple-input multiple-output (MIMO) or multiple-input single-output (MISO) forward downlink transmission to provide forward data to the UT.

10. 10. The method of claim 9, wherein the MIMO or MISO forward downlink transmission comprises cooperative beamforming transmission from two or more satellites in the constellation, the cooperative beamforming comprising cooperatively setting one or more of a transmit carrier frequency, a transmit carrier amplitude, a transmit carrier phase, or a transmit carrier timing offset across the two or more satellites to generate a constructive combination of the respective downlink transmit signals from the two or more satellites at the UT.

11. 11. The method of claim 10, further comprising: performing beamforming updates for the cooperative beamforming according to a beam update rate that is faster than a channel sounding rate, the channel sounding rate determining a rate at which the SCN obtains updated channel state information (CSI) based on transmission of reference signals on physical propagation channels linking each UT to the SCN; and the SCN supporting the faster beam update rate by predicting changes in the CSI between CSI updates.

12. 11. The method of claim 10, further comprising updating channel estimates used in the cooperative beamforming to account for changes in relative locations between the two or more satellites participating in the cooperative beamforming.

13. 13. The method of claim 1, wherein deciding to change from providing service to the UT in the non-diversity service mode to providing service to the UT in the diversity service mode comprises making the decision further dependent on a delay tolerance associated with a communication service provided to the UT via the SCN.

14. 14. The method of claim 13, wherein making the determination dependent on the delay tolerance associated with the communication service provided to the UT via the SCN comprises determining to change to the diversity service mode in response to stored configuration information that identifies the communication service as latency sensitive.

15. 1. A controller configured to operate within a satellite communications network (SCN) including a constellation of non-geosynchronous satellites moving along respective orbital paths, the controller comprising: a communication interface circuit; A processing circuit, learning view angle constraints for corresponding geographic locations based on collecting connectivity metrics over time for given user terminals (UTs) operating at said corresponding geographic locations, wherein the collected connectivity metrics for each such location indicate view angles characteristically associated with reduced connectivity; Serving a user terminal (UT) in a non-diversity service mode in which there is a single serving satellite in the constellation at a time for said UT; predicting that the UT will experience a decrease in connectivity based on the learned viewing angle constraints; In response to the prediction, determining to change from serving the UT in the non-diversity service mode to serving the UT in a diversity service mode in which there is more than one serving satellite in the constellation at a time to the UT; providing service to the UT in the diversity service mode; and a processing circuit configured to: A control device comprising:

16. 16. The control device of claim 15, wherein, with respect to predicting that the UT will experience reduced connectivity, the processing circuitry is configured to determine, based on the learned view angle constraints, the location of the UE, and ephemeris of serving satellites, that providing service to the UT in a non-diversity service mode will involve a constrained view angle.

17. 17. The control device of claim 15 or 16, wherein the learned view angle constraints are represented in a database that associates each of a plurality of respective locations with a corresponding view angle constraint learned for the respective location, and wherein, with respect to predicting that the UT will experience reduced connectivity, the processing circuitry is configured to: reference an index of the database as a function of the location of the UT to determine view angle constraints applicable to the location of the UT; and determine from a servicing satellite ephemeris that the UT will experience one or more constrained view angles.

18. 18. The control device of claim 17, wherein the processing circuitry is configured to determine the field of view constraints that apply to the location of the UT by interpolating or extrapolating field of view constraints that correspond to one or more locations in the database that are closest to the location of the UT.

19. 17. The control device of claim 15 or 16, wherein the learned limitations on view angles are represented in a trained machine learning (ML) model that outputs view angle constraints applicable to an input location, and wherein, with respect to predicting that the UT will experience reduced connectivity, the processing circuitry is configured to input the location of the UT into the trained ML model and evaluate a servicing satellite ephemeris to determine whether the UT will experience a constrained view angle as indicated by the applicable view angle constraints output by the trained ML model.

20. The control device of any one of claims 15 to 19, wherein any predetermined viewing angle comprises an azimuth angle (Az) and an elevation angle (El), and the viewing angle constraint comprises an individual viewing angle or a range of viewing angles.

21. A control device as claimed in any one of claims 15 to 20, wherein the diversity service mode comprises providing service to the UT in one or both of a forward diversity service mode and a return diversity service mode.

22. 22. The control device of claim 21, wherein with respect to serving the UT in the return diversity service mode, the processing circuitry is configured to control the SCN to attempt to receive an uplink transmission from the UT on each of two or more satellites in the constellation, and the SCN receives corresponding return traffic from the UT upon successful reception of the uplink transmission on one or more of the two or more satellites.

23. 22. The control device of claim 21, wherein, with respect to providing service to the UT in the forward diversity service mode, the control device is configured to initiate multiple-input multiple-output (MIMO) or multiple-input single-output (MISO) forward downlink transmissions to provide forward data to the UT.

24. 24. The controller of claim 23, wherein the MIMO or MISO forward downlink transmission comprises coordinated beamforming transmission from two or more satellites in the constellation, the coordinated beamforming comprising coordinately setting one or more of a transmit carrier frequency, a transmit carrier amplitude, a transmit carrier phase, or a transmit carrier timing offset across the two or more satellites to generate a constructive combination of the respective downlink transmission signals from the two or more satellites at the UT.

25. 25. The control device of claim 24, wherein the processing circuitry is configured to perform beamforming updates for the cooperative beamforming according to a beam update rate that is faster than a channel sounding rate, the channel sounding rate determining a rate at which the processing circuitry obtains updated channel state information (CSI) based on transmission of a reference signal over the physical propagation channel linking each UT to the SCN, and the control device supports the faster beam update rate by predicting changes in the CSI between CSI updates.

26. 25. The controller of claim 24, wherein the controller is configured to update channel estimates used in the cooperative beamforming to account for relative changes in position between the two or more satellites participating in the cooperative beamforming.

27. 27. The control device of claim 15, wherein, with regard to deciding to change from providing service to the UT in a non-diversity service mode to providing service to the UT in the diversity service mode, the processing circuitry is configured to make the decision further dependent on a delay tolerance associated with communication services provided to the UT via the SCN.

28. 28. The control device of claim 27, wherein with respect to making the decision further dependent on the delay tolerance, the processing circuitry is configured to decide to change to the diversity service mode in response to stored configuration information that identifies the communication service as delay sensitive.

29. 1. A method of operation by a user terminal (UT) configured to be served by a satellite communications network (SCN) including a constellation of non-geosynchronous satellites moving along respective orbital paths, said method comprising: operating in a non-diversity service mode in which the SCN serves the UT via a single serving satellite in the constellation at a time; receiving a control signal from the SCN indicating a change from the non-diversity service mode to a diversity service mode in which the SCN serves the UT via more than one serving satellite at a time in the constellation; changing from operating in the non-diversity service mode to operating in the diversity service mode in response to either receiving the control signal or satisfaction of a diversity mode trigger condition indicated by the control signal; A method comprising:

30. 30. The method of claim 29, wherein the diversity mode trigger condition is a time indicated in the control signal, the time being associated with the UT experiencing a viewing angle determined by the SCN as being limited.

31. 30. The method of claim 29, wherein the diversity mode trigger condition is a handover of the UT to a particular satellite in the constellation as a new serving satellite.

32. 32. The method of any one of claims 29 to 31, wherein operating in the diversity service mode includes the UT receiving a forward data stream as two or more forward data sub-streams transmitted from respective ones of the two or more serving satellites.

33. 33. The method of claim 32, wherein the UT receiving the forward data stream transmitted as the two or more forward data substreams comprises the UT receiving a multiple-input multiple-output (MIMO) or multiple-input single-output (MISO) transmission from the two or more serving satellites.

34. 34. The method of claim 33, wherein receiving the MIMO or MISO transmission comprises the UT receiving the MIMO or MISO transmission using a single radio front end.

35. 33. The method of claim 32, wherein receiving the forward data stream as two or more forward data sub-streams comprises receiving each forward data sub-stream at a respective frequency or polarization or at a respective transmission time.

36. 32. The method of claim 29, wherein, to serve the UT in the diversity service mode, the SCN transmits the same forward data stream from each of two or more serving satellites, such that successful transmission is based on successful reception at the UT from any one or more of the two or more serving satellites.

37. 37. The method of any one of claims 29 to 36, wherein, with respect to operation of the UT in the diversity service mode, the method includes the UT splitting a return data stream into two or more return data substreams, each return data substream for reception by a respective one of the two or more serving satellites.

38. 1. A user terminal (UT) configured to be served by a satellite communications network (SCN) including a constellation of non-geosynchronous satellites moving along respective orbital paths, said UT comprising: a communications interface circuit configured to communicate with the SCN via an exchange of radio signals with one or more satellites in the constellation; a processing circuit operatively associated with said communication interface circuit, the SCN operating in a non-diversity service mode serving the UT via a single serving satellite in the constellation at a time; receiving a control signal from the SCN indicating a change from the non-diversity service mode to a diversity service mode in which the SCN serves the UT via more than one serving satellite at a time in the constellation; changing from operation in the non-diversity service mode to operation in the diversity service mode in response to either receiving the control signal or satisfaction of a diversity mode trigger condition indicated by the control signal; configured to: processing circuitry, Including, UT.

39. 39. The UT of claim 38, wherein the diversity mode trigger condition is a time indicated in the control signal, the time being associated with the UT experiencing a viewing angle determined by the SCN as being limited.

40. 39. The UT of claim 38, wherein a trigger condition for the diversity mode is a handover of the UT to a particular satellite in the constellation as a new serving satellite.

41. 41. A UT as described in any one of claims 38 to 40, wherein, with respect to operation in the diversity service mode, the processing circuitry is configured to receive, using the communications interface circuitry, a forward data stream as two or more forward data substreams transmitted from respective ones of the two or more serving satellites.

42. 42. The UT of claim 41, wherein the processing circuitry is configured to receive the forward data stream via multiple-input multiple-output (MIMO) or multiple-input single-output (MISO) transmission from the two or more serving satellites.

43. 43. The UT of claim 42, wherein the processing circuitry is configured to receive the MIMO or MISO transmission using a single radio front end of the communications interface circuitry.

44. 42. The UT of claim 41, wherein each forward data substream uses a respective frequency or polarization or a respective transmission time.

45. A UT as described in any one of claims 38 to 40, wherein to provide service to the UT in the diversity service mode, the SCN transmits the same forward data stream from each of two or more serving satellites, and the processing circuit considers reception of the forward data stream to be successful based on reception of the forward data stream from any one or more of the two or more serving satellites.

46. 46. ​​A UT as described in any one of claims 38 to 45, wherein, with respect to operation of the UT in the diversity service mode, the processing circuitry is configured to split a return data stream into two or more return data substreams, each return data substream being received by a respective one of the two or more serving satellites.

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