Method and apparatus for enhanced availability via multi-satellite diversity

Abstract

An advantage of the satellite communication network (SCN) of the present invention is characterized by selectively using a diversity service mode and a non-diversity service mode to serve individual user terminals (UTs) using constellations of non-geostationary satellites included in the SCN. For example, for any given UT, the SCN may switch from a non-diversity service mode to a diversity service mode in response to determining that the non-diversity service relates to one or more restricted perspectives. The restricted viewing angle of the UT location may be learned based on past monitoring by the SCN, or the restricted viewing angle may be estimated from viewing angle restrictions learned for one or more locations near the UT location.

Description

Technical Field

[0001] In the context of a satellite communications network including a constellation of non-geostationary satellites, the disclosed methods and apparatus relate to selectively employing either a non-diversity service mode or a diversity service mode to provide service to respective user terminals supported by the network. Background Art

[0002] Any given user terminal (UT) has a nominal "field of view," which is the nominal range of viewing angles within which the terminal can communicate with a satellite. For example, by design, a UT has a nominal range of elevation angles within which it can establish and maintain communication with a satellite.

[0003] In a constellation of non-geosynchronous orbit (NGSO) satellites, each satellite moves relative to the Earth's surface. This means each satellite provides a mobile coverage area whose ground footprint follows a ground track corresponding to the satellite's orbital path. To the extent that a given UT's field of view overlaps with a satellite's coverage area, the satellite in the constellation is a candidate for providing service to that UT. In this context, "providing service" refers to providing communications services to the UT.

[0004] In a typical approach, an SCN based on a constellation of NGSO satellites serves the corresponding UT without diversity, meaning that there is one satellite in the constellation serving any given UT at a time. The serving satellite changes as different satellites in the constellation move in and out of the field of view of a given UT. This change in serving satellite is referred to as a "handoff" for the UT.

[0005] Serving UTs without diversity offers many advantages, such as simplifying the scheduling and corresponding management of forward and / or reverse data flows within the terrestrial and space segments of the SCN for individual terminals. However, with non-diversity servicing, availability is degraded, or at least the risk of availability degradation increases. "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 availability involves multiple considerations. These include, but are not limited to, traffic scheduling complexity, network throughput, resource utilization efficiency, and how to make intelligent decisions about whether and when to use diversity techniques to serve a given UT. Summary of the Invention

[0006] An advantageous feature of a satellite communication network (SCN) of the present invention is the selective use of a diversity service mode and a non-diversity service mode to provide service to individual user terminals (UTs) using a constellation of non-geostationary satellites included in the SCN. For example, for any given UT, the SCN may switch from a non-diversity service mode to a diversity service mode in response to determining that non-diversity service involves one or more restricted viewing angles. The restricted viewing angles for the UT's location may be learned based on past monitoring by the SCN or estimated based on viewing angle constraints learned for one or more locations near the UT's location.

[0007] One embodiment includes a method performed by a control device operating in an SCN, the SCN including a constellation of non-geostationary satellites following respective orbital paths. The method includes: the SCN learning a view limit for a corresponding geographic location based on collecting connectivity metrics over time for a given UT operating in the corresponding location, wherein the connectivity metrics collected for each such location indicate a view that is characteristically associated with degraded connectivity. The method also includes: the SCN serving the UT in a non-diversity service mode, wherein there is a single serving satellite in the constellation at a time for the UT, and predicting based on the learned view limit that the UT will experience degraded connectivity. The method also includes: responsive to the prediction, the SCN deciding to change from serving the UT in the non-diversity service mode to serving the UT in a diversity service mode, wherein there are two or more serving satellites in the constellation at a time for the UT; and serving the UT in the diversity service mode.

[0008] A related embodiment includes a control apparatus configured to operate in a SCN including a constellation of non-geostationary satellites following corresponding orbital paths, the control apparatus including communication interface circuitry and processing circuitry. The processing circuitry is configured to learn a view angle limit for a corresponding geographic location based on collecting connectivity metrics over time for a given user terminal (UT) operating in the corresponding location. The connectivity metrics collected for each such location indicate a view angle characteristically associated with degraded connectivity.

[0009] The processing circuitry of the diversity control apparatus is further configured to serve the UT in a non-diversity service mode, wherein there is a single serving satellite in the constellation at a time for the UT, and predicts that the UT will experience degraded connectivity based on the learned viewing constraints. The processing circuitry is configured to decide, responsive to the prediction, to change from serving the UT in the non-diversity service mode to serving the UT in a diversity service mode, wherein there are two or more serving satellites in the constellation at a time for the UT, and serving the UT in the diversity service mode.

[0010] Another embodiment includes a method operated by a UT, the UT configured to be served by an SCN, the SCN including a constellation of non-geostationary satellites following corresponding 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 control signaling from the SCN, the control signaling indicating a change 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 changing from operating in the non-diversity service mode to operating in the diversity service mode. The UT changing is responsive to one of: receiving the control signaling, or satisfying a diversity mode trigger condition indicated by the control signaling.

[0011] Related embodiments include a UT configured to be served by an SCN comprising a constellation of non-geostationary satellites following corresponding orbital paths. The UT includes communication interface circuitry configured to communicate with the SCN via exchanging wireless signaling with one or more satellites in the constellation. The UT further includes processing circuitry operably associated with the communication interface circuitry and configured to: operate in a non-diversity service mode, wherein the SCN serves the UT via a single serving satellite in the constellation at a time; receive control signaling from the SCN indicating a change 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 change from operating in the non-diversity service mode to operating in the diversity service mode in response to one of: receiving the control signaling or satisfying a diversity mode triggering condition indicated by the control signaling.

[0012] Of course, the present invention is not limited to the above features and advantages. In fact, those skilled in the art will recognize additional features and advantages upon reading the following detailed description and viewing the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a block diagram of a satellite communication network (SCN) according to an example embodiment.

[0014] Figure 2 is a logic flow diagram of a method of operation performed by a diversity control device in an SCN according to an exemplary embodiment.

[0015] Figure 3 is a logic flow diagram of another method of operation performed by a diversity control device in accordance with an exemplary embodiment.

[0016] Figure 4 is a block diagram of a diversity control apparatus according to an exemplary embodiment.

[0017] Figure 5 is a block diagram of a machine learning (ML) model for diversity control decisions instantiated in a runtime environment, according to one embodiment.

[0018] Figure 6 is a block diagram of circuitry configured to split a data stream into two or more data sub-streams for diversity transmission according to an example embodiment.

[0019] Figure 7 and Figure 8 is a diagram illustrating example viewing angles (including restricted viewing angles) of a UT at a given location.

[0020] Figure 9 is a diagram of an example satellite service area including a plurality of locations whose viewing angles have been restricted by SCN characterization.

[0021] Figure 10 is a block diagram of an example database structure that may be used to store data indicative of learned viewpoint constraints for a potentially large number of locations.

[0022] Figure 11 is a logic flow diagram of a method of operations performed by a UT according to an example embodiment.

[0023] Figure 12 is a block diagram of a UT according to an example embodiment. DETAILED DESCRIPTION

[0024] One approach for enhancing the availability of satellite communication networks (SCNs) relies on collaborative beamforming from multiple (two or more) satellites. Beamforming can be performed using various techniques, such as selecting a specific satellite from the plurality of satellites for beamforming and / or adaptively combining signals from two or more satellites for beamforming.

[0025] In some embodiments, with respect to serving a user terminal (UT) with diversity, one or more of the following may be performed: (a) polarization combining from a single satellite, including (i) selecting the best of two polarizations in a fading environment or (ii) combining the two polarizations in an adaptively optimal manner; (b) diversity selection, including (i) picking the best satellite, such as based on signal strength, or (ii) adaptively monitoring multiple satellites and dynamically selecting the best satellite among the multiple satellites; and (c) diversity combining, including (i) combining signals to / from multiple satellites in an adaptively optimal manner, and may further include (ii) performing interference cancellation based on the use of channel sounding.

[0026] Diversity combining may also include interleaving the data to be relayed via the plurality of satellites and applying forward error correction (FEC) coding. In the forward downlink example, the UT in question receives a respective signal from each of the plurality of satellites, demodulates the data from each such signal, and then combines and sorts the data according to the FEC coding. The respective signals may use one or more of different CDMA codes, different polarizations, different frequencies, or different time slots.

[0027] One aspect of this disclosure is the selective use of diversity from multiple non-geosynchronous orbit (NGSO) satellites to enhance the availability of SCNs to cell phones operating in the L-band. Of course, the disclosed methods and apparatus are directly applicable to other bands and other types of satellite receivers. While enhanced availability through diversity is a key advantage, using diversity may also enhance link budget and / or throughput. Unless otherwise specified or the context clearly indicates otherwise, the term "satellite" is intended to refer to an NGSO satellite, and any reference to a "constellation" is understood to refer to an NGSO constellation unless otherwise specified or the context clearly indicates otherwise.

[0028] One or more embodiments disclosed herein are based on the assumption that the ground stations providing forward traffic for relaying via satellites in a constellation know with reasonable accuracy the position and velocity of each satellite in the constellation. In a specific example involving the selective use of diversity service or non-diversity service, there are at least two satellites in the constellation of NGSO satellites that are candidates for serving a given (UT) (e.g., a cell phone). The SCN involved 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 for relaying forward traffic (user data) to a given UT via a forward link and / or relaying reverse traffic from the UT via a reverse link. Unless otherwise specified or the context clearly indicates, "satellite" as used herein refers to an NGSO satellite.

[0029] For two or more candidate satellites, the SCN may choose to serve the UT in a non-diversity service mode, which means that the UT is served by a single satellite in the constellation at a time, or in a diversity service mode, which means that the UT is served by multiple (two or more) satellites in the constellation at a time.

[0030] Diversity service modes improve availability because multiple serving satellites mean that even if a UT experiences a fade relative to one of its serving satellites, service can continue, albeit with reduced throughput or other degradation. Generally, availability for a particular serving satellite will be degraded by problems near the UT, such as: (a) shadowing by large objects, such as hills or large buildings, which may persist and affect all or most of the propagation paths between the UT and the serving satellite; (b) obstruction by narrow objects, such as trees or foliage, which may persist but only affect a limited number of propagation paths between the UT and the serving satellite; and (c) scattering, which is typically caused by satellite signals reflecting off objects and causing multipath propagation, and is only a problem when the elevation angle of the serving satellite is low and the ground reflectivity near the UT is high.

[0031] All of these issues can be interpreted as degraded connectivity between a given UT and its serving satellite. In most cases, with a single serving satellite, a given UT's connectivity will be quite good, as the signal has a clear line of sight and minimal scattering as it moves through space. However, some combinations of terminal location and satellite position may result in obstructions, shadows, or reflections. In other words, a given UT may safely operate within its nominal viewing angle range, but may experience degraded connectivity due to the local environment. Degraded connectivity corresponds to degraded availability.

[0032] In one or more embodiments, the availability enhancement is based on the following operational logic in the SCN: (a) if a UT operating in a non-diversity service mode experiences degraded availability or is predicted by the SCN to experience degraded availability, the SCN switches the UT to a new serving satellite, assuming that another satellite currently exists in the constellation as a candidate to serve the UT; (b) if there is currently no other satellite as a candidate to serve the UT or the UT experiences degraded availability or is predicted to experience degraded availability for all candidate satellites, the SCN takes one of the following two actions: (i) suspends traffic scheduling for the UT to avoid sending user traffic to (or receiving user traffic from) the UT at a time corresponding to the degraded availability; or (ii) selects a diversity service mode to serve the UT from multiple satellites in the constellation.

[0033] One approach involves the SCN developing and maintaining a short-term history (database) for the UT to predict locations where there is or is likely to be degraded availability. The database thus represents a short-term spatial database. When there is a problem with one satellite providing service to the UT, the scheduling algorithm changes the serving satellite. When all candidate satellites for the UT have problems, there are two options: one is to delay communication until one of the candidate satellites moves to a better position. Delay is suitable for certain types of communication services, such as low-priority data transfers, such as software downloads or some text transfers. For other types of communication services that are more sensitive to delay, the SCN activates diversity technology. This decision-making process can use machine learning to improve its understanding of when diversity is needed. One of the benefits of selectively using diversity service is that the SCN does not need to unnecessarily occupy two satellites when they are not needed, thereby achieving good availability.

[0034] With respect to diversity services in the reverse link direction, where traffic travels from the UT to one or more satellites in the constellation and then down to the SCN's terrestrial network, the reverse link signals carrying such traffic may be received at multiple base stations, and the SCN then moves the physical (PHY) layer data (either sampled analog-to-digital converted (ADC) data or processed data that has been downsampled at some level) through the terrestrial network and / or external network links for aggregation in a common processing entity. Once the data is aggregated, the SCN may use a variety of techniques to reliably recover the data. These techniques may include any one or a combination of the following: (a) estimating the gain and phase of each channel and then using the estimates to implement an optimal combining technique; (b) attempting to independently receive the reverse data through any one of the multiple serving satellites.

[0035] In the forward direction, from the terrestrial network to the constellation and then to the UT, one diversity technique is optimal single-channel multiple-input single-output (MISO) or multiple-input multiple-output (MIMO). Here, "multiple-input" refers to transmissions from two or more satellites in the constellation. Using MIMO or MISO transmission for diversity in the forward direction means transmitting from two or more satellites at precise times, with predetermined gain and phase adjustments, so that the two or more downlink signals are optimally combined when received at the UT. This operation can be understood as cooperative beamforming between the two or more satellites participating in the MIMO or MISO transmission.

[0036] Consider the case of forward MISO, where two Satellite Access Nodes (SANs) exist in the SCN's terrestrial network, each associated with a corresponding satellite in the constellation, and each such satellite is a serving satellite for a given UT. In one embodiment, the two SANs transmit the same primary signal, but with different frequencies, gains, phases, and delays, so that the downlink signals from the two satellites overlap at a given UT. While MISO is known in some respects, employing MISO for diversity service in a satellite environment requires innovative use of ephemeris and dynamic adjustments to the channel estimates involved based on changes in the relative motion between the multiple serving satellites and a given UT. Channel estimates can be obtained through channel sounding, where sounding signals are transmitted and received via two or more satellites to estimate the physical channel between the UT and the SCN from or through each of the serving satellites. For example, the SCN transmits different orthogonal signals from each ground station to allow the UT to estimate the channel and transmit back estimates. The SCN performs dynamic adjustments to the channel estimates to account for satellite motion.

[0037] Regarding the dynamic adjustment of channel estimates, in one or more embodiments, the SCN dynamically adjusts past channel estimates to predict new estimates. The SCN uses, for example, a linear or maximum likelihood channel estimator to predict the future channel. Furthermore, at future times, the SCN can use current / most recent sounding information to estimate the error in the corresponding predicted estimate. By repeating this process, the SCN can correct not only past estimates, but also future estimates. This can take the form of estimating the rate of change of channel phase and gain or the rate of change of channel delay. Once the estimator circuitry used in the SCN is trained, it enables the SCN to send a diversity signal that is combined optimally or near-optimally to a given UT.

[0038] Another technique is MISO with time offset. This technique involves transmitting the same signal from each of multiple serving satellites to the UT, but with a defined delay between the signals. If the delay is large enough, the UT can use a rake receiver type structure to combine the two signals. This receiver adjusts the frequency, gain, and phase of the two or more received signals so that the two or more received signals are superimposed on each other. One challenge with this structure is how to avoid self-interference caused by the delay. One way to alleviate this problem is to make the delay long enough so that only one of the two or more serving satellites transmits at the exact location of the UT at a time. Of course, the serving satellites can transmit to other locations. Another way to alleviate this problem is to make the delay longer than the symbol rate and use a maximum likelihood decoder algorithm that will effectively ignore the effects of the delayed signal. A third way to alleviate this problem is to use direct sequence spread spectrum technology to make the delayed signal nearly orthogonal to the non-delayed signal.

[0039] Frequency diversity is another example of forward diversity. In this case, each serving satellite transmits to the UT using a different frequency. Multiple downlink signals can be duplicated, for example, each diversity downlink signal carries the same content (same traffic). The UT can recover the content using any of a variety of techniques, including best signal selection and / or multiple signal combining. This approach has the advantage of simplicity, but consumes more signal bandwidth.

[0040] Another forward diversity technique is message diversity. With message diversity, multiple serving satellites transmit the same message to the UT at different times and potentially on different frequencies. On the positive side, message diversity can be implemented at all levels of the communications protocol stack and offers a relatively simple implementation, but it does use more capacity. Alternatively, due to repeated transmissions of the same message, message diversity is less efficient.

[0041] Figure 1 An SCN 10 is shown according to an exemplary embodiment, wherein the SCN 10 includes a constellation 12 of NGSO satellites 14. As an example, the satellites 14 are LEO satellites or medium earth orbit (MEO) satellites. In addition, the SCN 10 includes a terrestrial network 16 including a core network (CN) 18. Of particular interest herein is that the terrestrial network 16 is configured to selectively (dynamically determine) utilize diversity for each UT 20 served by the SCN 10. To simplify illustration and discussion, Figure 1 A single UT 20 is shown, and it should be understood that the SCN 10 is operable to provide service to potentially many UTs 20 , such as a population of UTs 20 distributed over a large geographic area covered by the constellation 12 .

[0042] In the case of dynamic diversity, the SCN 10 decides whether and when to use a non-diversity service mode or a diversity service mode to provide service to a given UT 20. The diversity service mode itself may use a specifically selected one of two or more diversity techniques. That is, for operation in the diversity service mode, a variety of techniques may be available for selection, depending, for example, on whether diversity is used in the forward direction, the reverse direction, or both. Other variables that influence the specific diversity technique used include the configuration and functionality of the SCN 10 and the UTs 20 involved, as well as the type of communication service that may be involved.

[0043] In the illustrated example, the CN 18 includes a diversity control device 22 that is configured to determine whether the SCN 10 provides service to a given UT 20 in a non-diversity service mode or a diversity service mode. The diversity control device 22 is communicatively coupled to or integrated within a communication processing system (CPS) 24, which performs user scheduling of forward and reverse user traffic for respective UTs 20 in the entire population of UTs 20 served by the SCN 10. Specifically, 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 flows between one or more types of remote devices or systems 28 and respective UTs 20 supported by the SCN 10. In this regard, the SCN 10 should be understood as providing one or more types of communication services, such as mobile broadband services or other types of data and / or voice connectivity, to the respective UTs 20.

[0044] The CPS 24 includes fixed circuitry, programmable circuitry, or a combination of the two. In one or more embodiments, the CPS 24 includes one or more computer servers, each of which includes one or more microprocessors or other types of digital processors, a communication interface (such as an Ethernet or other data network interface), and a memory and / or storage device containing computer program instructions that, when executed by the one or more microprocessors or other types of digital processors, configures the processors to cause the CPS 24 to perform user scheduling and interact with (or implement) the diversity control device 22. As described above, user scheduling involves scheduling forward traffic and / or reverse traffic for each UT in the group of UTs 20 served by the SCN 10.

[0045] Of course, due to the relative motion of the satellites 14 and the UTs 20, scheduling user traffic involves mapping corresponding 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 this end, the terrestrial network 16 includes a plurality of satellite access nodes 30 that are geographically distributed.

[0046] Forward traffic destined for individual UTs 20 flows from one or more of the SANs 30 to the constellation 12, and the satellites 14 in the constellation 12 may participate in mesh routing of this traffic for downlink transmission by the particular satellite 14 serving the target UT 20. Broadly speaking, the CPS 24 has network links 32 to each of the SANs 30, such that at any given time, the CPS may send or receive user traffic for any given UT 20 to or from one or more of the SANs 30 for transmission, either directly or in a meshed manner, to the satellite 14 that then serves the given UT 20.

[0047] Accordingly, each SAN 30 includes optical and / or radio frequency (RF) transceivers for transmitting one or more feeder uplink signals 34 to satellites 14 within the coverage area of ​​the SAN and receiving one or more downlink signals 36 from such satellite(s) 14. These feeder link signals typically carry traffic for multiple UTs 20 according to a defined multiplexing scheme.

[0048] Figure 1 14. Further example details in the diagram include illustrations of beams 40, each beam 40 having a directional orientation and size defining a coverage area for a corresponding satellite 14. The illustrated beams 40 may be associated with coverage areas for corresponding satellites 14 in a forward direction and / or a reverse direction, with each beam 40 having a beam footprint 42 that follows a ground track on the Earth's surface corresponding to the orbital path of the corresponding satellite 14. As described above, cooperative beamforming may be used to serve a given UT 20 in a diversity service mode (such as where corresponding beams 40 from two serving satellites 14 are cooperatively controlled in terms of phase, timing, frequency, etc.) to produce a constructive combination of beams at a particular location of the given UT 20.

[0049] Furthermore, the satellite 14 may simultaneously support the formation of multiple beams 40, for example at different frequencies and / or polarizations. Figure 1Serving merely as an illustrative example of a satellite coverage area for transmitting user downlink signals 44 conveying forward user traffic to a respective UT 20 and receiving user uplink signals 46 conveying reverse user traffic from the respective UT 20. In one or more embodiments, the satellites 14 further include inter-satellite links 48 for grid-based user traffic routing between serving satellites and non-serving satellites 14 in the constellation 12 for a given traffic flow.

[0050] In one or more embodiments, the relative beam orientation of each satellite 14 is fixed or controlled in an open-loop manner. In one or more other embodiments, the satellites 14 perform closed-loop control of their beamforming. A specific example of closed-loop beamforming is two or more satellites 14 engaging in collaborative beamforming to serve UT 20 using multiple-input multiple-output (MIMO) or multiple-input single-output (MISO) diversity. MIMO and MISO are exemplary diversity technologies used by SCN 10 when serving UT 20 in diversity service mode.

[0051] In at least one embodiment, the SCN 10 supports two or more diversity techniques, and does not necessarily use the same diversity technique to serve a given UT 20 being served in diversity service mode. 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.

[0052] Figure 2 An exemplary method 200 is shown of operations performed by diversity control device 22. For example, diversity control device 22 comprises a computer server having a memory storing computer program instructions that, when executed by a microprocessor of the computer server, cause the computer server to perform method 200.

[0053] The method 200 includes learning (block 202) view angle limits for corresponding geographic locations based on collecting connectivity metrics over time for a given UT operating in the corresponding location, wherein the connectivity metrics collected for each such location indicate view angles characteristically associated with degraded connectivity. The learning step 202 may be performed one or more times, and it should be understood that the learning may be ongoing or repeatedly performed based on continuous observation of connectivity metrics, such as received signal quality or strength or error rate or dropped calls, or other such metrics indicative of instances of degraded connectivity between a given UT 20 and its corresponding serving satellite 14.

[0054] The method 200 further includes serving the UT 20 in a non-diversity service mode (block 204), wherein there is a single serving satellite 14 at a time in the constellation 12 for the UT 20, and predicting (block 206) based on the learned viewing angle limit that the UT 20 will experience degraded connectivity. The method 200 further includes responding to the prediction (block 208) by deciding to change from serving the UT 20 in the non-diversity service mode to serving the UT 20 in a diversity service mode, wherein there are two or more serving satellites at a time in the constellation for the UT 20, and serving the UT 20 in the diversity service mode.

[0055] In one or more embodiments, the prediction that the UT 20 will experience degraded connectivity is based on learned view constraints, the UE's location, and the serving satellite ephemeris, and based on these data, determining that serving the UT in a non-diversity service mode will involve a restricted view. For example, over one or more observation intervals, the SCN 10 collects connectivity metrics for a given UT 20 operating at a number of different locations, and the collected metrics are used to identify, for each of the one or more locations, a view that is characteristically associated with degraded connectivity.

[0056] In a specific example, the learned view limits are represented in a database that links each of a plurality of corresponding locations with a corresponding view limit learned for the corresponding location. Here, predicting that the UT will experience degraded connectivity includes indexing into the database based on a transformation of the UT's location to determine the view limits applicable to the location of the UT, and determining that the UT 20 will experience one or more restricted view limits based on the serving satellite ephemeris. In other words, as an example of predicting degraded connectivity, the diversity control device 22 determines that the serving satellite 14 of the UT 20 will be at or passing through a location corresponding to a view limit from the location of the UT 20 that is known or expected to have degraded connectivity.

[0057] The location of the UT 20 may not match any of the database locations for which view constraints have been learned. However, one or more embodiments of the method 200 include determining the view constraints applicable to the location of the UT by performing interpolation or extrapolation of the view constraints corresponding to one or more locations in the database that are closest to the location of the UT 20. The determination may take into account the vector relationship (distance and direction) between the closest database location and the UT location to determine the restricted view constraints applicable to the location of the UT. Additionally or alternatively, the database may include information about the location and orientation of assumed obstacles, and such information may be used to estimate the restricted view constraints for locations not represented in the database.

[0058] Alternatively, in one or more embodiments of the method, the learned view limits are represented in a trained machine learning (ML) model that outputs view limits applicable to the input location. Here, predicting that the UT 20 will experience degraded connectivity includes inputting the UT location into the trained ML model and evaluating the serving satellite ephemeris to determine whether the UT 20 will experience a restricted view indicated by the applicable view limits output by the trained ML model.

[0059] As described above, any given viewing angle includes an azimuth (Az) and an elevation (El). In this way, viewing angle restrictions can be expressed as individual viewing angles or a range of viewing angles. In addition, rather than identifying restricted viewing angles on an explicit or fixed basis, restricted viewing angles can be identified implicitly and dynamically. For example, connectivity metrics collected over time for a particular location can reveal characteristic channel qualities for different viewing angles or ranges. Using such data captured in a database, viewing angles that are considered restricted can be dynamically defined by specifying minimum characteristic channel qualities, and such minimum values ​​can be different for different communication services. Similarly, the collected metrics can be used to assign a grade or other level to a given viewing angle or a range of viewing angles at a particular location, so that whether a viewing angle or a range of viewing angles is considered restricted depends on a minimum acceptable grade. Similarly, the acceptable grade can vary, such as to bias diversity decision control towards or away from diversity services based on changes in SCN load and / or based on changes in the type of communication service involved.

[0060] Furthermore, in the context of method 200, serving the UT 20 in the diversity service mode includes serving the UT 20 in one or both of a forward diversity service mode and a reverse diversity service mode. Serving the UT 20 in the reverse diversity service mode includes, for example, attempting to receive an uplink transmission from the UT 20 at each of two or more satellites 14 in the constellation 12, such that the SCN 10 receives corresponding reverse traffic from the UT 20 upon successful reception of the uplink transmission at one or more of the two or more satellites 14.

[0061] Serving the UT 20 in the 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, collaborative beamforming transmissions from two or more satellites 14 in the constellation 12. Collaborative beamforming includes cooperatively setting any one or more of a transmit carrier frequency, a transmit carrier amplitude, a transmit carrier phase, or a transmit carrier timing offset on two or more satellites 14 to produce a constructive combination of respective downlink transmit signals from the two or more satellites 14 at the UT 20.

[0062] In at least one such embodiment of the method 200, the method further includes performing beamforming updates for collaborative beamforming according to a beam update rate that is faster than a channel sounding rate. Here, the channel sounding rate determines the rate at which the SCN 10 obtains updated channel state information (CSI) based on reference signal transmissions over a physical propagation channel linking the respective UTs 20 to the SCN 10, and wherein the SCN 10 supports faster beam update rates by predicting changes in the CSI between CSI updates. More generally, in one or more embodiments using collaborative beamforming, the method includes updating channel estimates used for collaborative beamforming to account for changes in relative position between two or more satellites 14 participating in the collaborative beamforming.

[0063] In one or more embodiments, deciding to change from serving UT 20 in a non-diversity service mode to serving UT 20 in a diversity service mode includes making a decision further based on a delay tolerance associated with the communication service provided to UT 20 via SCN 10. Making a decision based on the delay tolerance associated with the communication service provided to UT 20 via SCN 10 includes, for example, deciding to change to a diversity service mode in response to stored configuration information identifying the communication service as delay sensitive. In the opposite case, that is, in the case where the stored information indicates that the communication service in question is not delay sensitive, diversity control device 22 will decide not to switch from the non-diversity service mode to the diversity service mode despite predicting that UT 20 will experience degraded connectivity.

[0064] Figure 3 A method 300 is shown as being performed by the diversity control device 22, for example as part of or in support of performing the method 200. The method 300 includes the diversity control device 22 collecting connectivity metrics over time for a given UT served by the SCN (block 302). Example metrics are QoS values, SINR, received signal strength, etc.

[0065] The method 300 continues by the diversity control device 22 identifying, for each of the one or more locations, a perspective that is characteristically associated with degraded connectivity for the UT 20 operating at the location (block 304). The identified results are stored in a database (block 306) for use by the diversity control device 22 in making real-time diversity control decisions for a given UT 20.

[0066] Figure 4An example embodiment of a diversity control device 22 is depicted that is configured to perform the operations included in methods 200 and 300, and any one or more of the extensions and variations described herein. The example diversity control device 22 is configured to operate in an SCN 10 and includes communication interface circuitry 60 and processing circuitry 62 operably associated with the communication interface circuitry 60.

[0067] In an exemplary embodiment in which diversity control device 22 is implemented separately from CPS 24, communication interface circuitry 60 includes, for example, an Ethernet interface or other data network interface, which is used by processing circuitry 62 to exchange control signaling with CPS 24. Such signaling indicates a diversity / non-diversity decision made by processing circuitry 62 to initiate or otherwise control the configuration of SCN 10, which selectively serves a given UT 20 using either a diversity service mode or a non-diversity service mode. For example, diversity control device 22 "serving" UT 20 in either a non-diversity service mode or a diversity service mode may be understood as diversity control device 22 outputting control signaling to cause SCN 10 to perform such operations.

[0068] In another exemplary embodiment, diversity control device 22 is integrated with CPS 24. In this case, communication interface circuitry 60 may include a data bus interface or other inter-processor interface within a computer server or other node including CPS 24.

[0069] The processing circuitry 62 includes, for example, one or more microprocessors 70 that are particularly adapted to perform methods 200 and / or 300 based on the execution of computer program instructions stored in a computer-readable medium. Figure 4 A memory or other storage device 64 is shown storing computer program instructions 66 executed by one or more microprocessors 70. The same storage device 64 may further store data 68, such as configuration data that governs diversity / non-diversity decisions made by the diversity control device 22. In at least one embodiment, the data 68 includes a database, such as Figure 1 The database 50 shown in FIG. The database 50 contains information indicating learned view limits for one or more locations. In at least one embodiment, the data 68 includes training data and parameter data for a machine learning (ML) model 80, such as Figure 5 As shown in .

[0070] exist Figure 5In the context of

[0045] , processing circuitry 62 provides a runtime environment 82 in which ML model 80 is instantiated for training and subsequently used as a trained ML model. In at least one embodiment, diversity control device 22 trains ML model 80 using collected training data 84 (e.g., raw connectivity metrics or filtered connectivity metrics collected over one or more collection intervals). Once trained, ML model 80 takes an input location and outputs a view constraint associated with the input location. The input location does not need to match a specific one of the locations represented in the collected training data 84.

[0071] Broadly speaking, whether Figure 4 still Figure 5 As shown in the embodiment shown in FIG, the exemplary SCN 10 includes control circuitry configured to decide whether or when to use a diversity service mode or a non-diversity service mode to serve a single UT 20 or a group of UTs 20 supported by the SCN 10. In at least one embodiment, the CPS 24 includes stream splitting / encoding circuitry 90, such as Figure 6 In the example scenario, the control circuitry decides to change from serving UT 20 in a non-diversity service mode to serving UT 20 in a diversity service mode, and the control circuitry sends corresponding control signaling to CPS 24 and / or other locations in SCN 10 to initiate or otherwise time the transition.

[0072] In an exemplary forward diversity technique for providing service to UT 20 in the diversity service mode, a forward data stream, such as an IP packet stream, is targeted for delivery to UT 20 via SCN 10. For diversity transmission of the forward data stream, circuitry 90 splits the forward data stream into as many data substreams as there are satellites 14 used to provide service to UT 20 in the diversity service mode. Each satellite 14 transmits a respective one of the data substreams, and in one or more embodiments, circuitry 90 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 corruption affecting any given one or more of the data substreams.

[0073] Figure 7 and 8 is a diagram depicting example details to help understand the viewing angle limitations. Figure 71 , a UT 20 is located at a given location 100 on the Earth's surface and is served by a single serving satellite 14. As the serving satellite 14 moves along its orbital path 104, the UT 20 experiences different views 102. The diagram suggests this movement by showing three different positions of the serving satellite relative to the UT 20, a first position at time t1, a second position at time t2, and a third position at time t3. It can be seen that the UT 20 enjoys a clear LoS to the satellite 14 over a range of views, but a nearby obstacle 106 interferes with the view 102 within a corresponding range. The diagram depicts unimpaired views 102 using solid lines and depicts views 102 impaired by obstacles 106 using dashed lines. As shown in FIG. Figure 8 To reiterate, any given viewing angle may be understood to correspond to a line of direction from UT 20 to satellite 14 and may be expressed as a pair of Az and El values.

[0074] Figure 9 A satellite service area 120 is shown as a potentially large geographic area. Certain locations 122 within the satellite service area 120 are characterized by restricted viewing angles. These characterized locations 122 are shown as solid ovals within the satellite service area 120. To determine viewing angle limits applicable to uncharacterized locations 124, the diversity control device 22 may extrapolate or otherwise infer limits from the nearest characterized location (shown as location 122A in the figure), or the diversity control device may use two (or more) nearest neighbors (e.g., Figure 9 122B) to interpolate or otherwise infer limits.

[0075] Figure 10 The exemplary contents of a database 50 are shown, containing information indicating or otherwise representing learned viewpoint constraints for a plurality of locations. Each database entry represents a location, which can be a "point" or "region," rather than just a precise location. The associated data stored for each location may include vector data representing constrained or unconstrained viewpoints, channel quality data organized by viewpoint, and the like. Such data may be represented for different quantized viewpoint ranges within an overall nominal viewpoint range, rather than for discrete, individual viewpoints.

[0076] Figure 11A method 1100 operated by UT 20 is shown. Method 1100 includes UT 20 operating in a non-diversity service mode (block 1102), wherein SCN 10 serves UT 20 via a single serving satellite 14 in constellation 12 of satellites 14 at a time. Method 1100 further includes UT 20 receiving (block 1104) control signaling from SCN 10 indicating a change from non-diversity service mode to diversity service mode, wherein SCN serves UT 20 via two or more serving satellites 14 in constellation 12 at a time. Still further, method 1100 includes UT 20 changing (block 1106) from operating in the non-diversity service mode to operating in the diversity service mode in response to one of: receiving the control signaling or satisfying a diversity mode trigger condition indicated by the control signaling. Method 1100 may further include UT 20 later returning (block 1108) to operation in the non-diversity service mode.

[0077] In one example, the change to diversity operation is responsive to a diversity mode triggering condition. As a specific example, the diversity mode triggering condition is a time indicated in the control signaling, wherein the time is associated with the UT experiencing a view angle determined to be restricted by the SCN 10. In another example, the diversity mode triggering condition is handing the UT over to a particular satellite 14 in the constellation 12 as the new serving satellite 14.

[0078] Operating in the diversity service mode includes, for example, the UT 20 receiving the forward data stream as two or more forward data substreams transmitted from corresponding ones of the two or more serving satellites 14. Receiving the forward data stream transmitted as two or more forward data substreams includes, for example, the UT 20 receiving a MIMO or MISO transmission from the two or more serving satellites 14. Receiving the MIMO or MISO transmission includes, for example, the UT 20 receiving the MIMO or MISO transmission using a single radio front end.

[0079] In at least one embodiment, UT 20 receiving the forward data stream as two or more forward data sub-streams includes UT 20 receiving each forward data sub-stream at a respective frequency or polarization or at a respective transmission time.

[0080] 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, such that successful transmission is based on successful reception at the UT 20 from any one or more of the two or more serving satellites 14.

[0081] In at least one embodiment, for operation of UT 20 in a diversity service mode, method 1100 includes UT 20 dividing the reverse data stream into two or more reverse data sub-streams, each reverse data sub-stream being received by a corresponding serving satellite among the two or more serving satellites 14.

[0082] In at least one embodiment, in response to a recovery trigger condition (such as the next serving satellite handoff) or after a timer expires, UT 20 recovers back to the non-diversity service mode. As another example, recovery is based on receiving further control signaling from SCN 10 at UT 20.

[0083] Figure 12 An example UT 20 is shown including one or more antennas 130 and an associated antenna interface 132 coupling the antennas 130 with communication interface circuitry 134. Communication interface circuitry 134 is configured to communicate with SCN 10 via the exchange of wireless signaling with one or more satellites 14 in constellation 12.

[0084] In the exemplary depiction, the communication interface circuitry includes a transmitter 136 having a transmitter (TX) front end 138. The TX front end 138 includes analog circuitry for upconverting and amplifying signals transmitted from the antenna 130 as uplink signals for reception at one or more satellites 14 in the constellation 12. The communication interface circuitry 134 further includes a receiver 140 having a receiver (RX) front end 142. The RX front end 142 includes analog circuitry configured to filter, amplify, and downconvert downlink signals received at the antenna 130 from one or more satellites 14 in the constellation 12.

[0085] In one or more embodiments, the RX front end 142 has a wide bandwidth and supports simultaneous reception of two or more downlink signals at different downlink carrier frequencies, as long as 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 is used, for example, to support simultaneous reception of MIMO or MISO transmissions for forward diversity services, and more generally can be used to support simultaneous reception of different data substreams or replicated streams simultaneously transmitted from different satellites 14 at different downlink carrier frequencies.

[0086] Baseband processing of transmit and receive signals may be performed by a baseband processor included in communications interface circuitry 134 or included in processing circuitry 144 , which may be operatively associated with communications interface circuitry 134 .

[0087] 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 in constellation 12 at a time. Furthermore, processing circuitry 144 is configured to receive control signaling from the SCN (via communication interface circuitry 134), wherein the control signaling indicates 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 in constellation 12 at a time. Furthermore, 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 signaling or satisfying a diversity mode trigger condition indicated by the control signaling.

[0088] More broadly, processing circuitry 144 in one or more embodiments is configured to perform 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 reverse diversity transmission, wherein the processing circuitry divides a reverse data stream into two or more reverse data sub-streams, which are transmitted to respective ones of two or more serving satellites 14 in constellation 12. Accordingly, processing circuitry 144 in such embodiments includes the following: Figure 6 The stream splitting and encoding circuit system shown in is used to split the reverse data stream into sub-streams and apply FEC encoding to the sub-streams.

[0089] The processing circuit system 144 includes fixed circuit systems, programmable circuit systems, or a mixture of the two. In at least one embodiment, the processing circuit system includes one or more microprocessors, digital signal processors, or other digital processors that are particularly suitable for performing the operations described herein for the UT 20 based on the execution of computer program instructions stored in the memory of the UT 20.

[0090] It is noted that modifications and other embodiments of the disclosed invention will occur to those skilled in the art having the benefit of the teachings presented in the foregoing description and the associated drawings. Therefore, it should be understood that the invention is not limited to the specific embodiments disclosed, and modifications and other embodiments are intended to be included within the scope of this 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. A method performed by a control device operating in a satellite communication network (SCN), the satellite communication network comprising a constellation of non-geostationary satellites following respective orbital paths, the method comprising: learning a viewpoint restriction for a corresponding geographic location based on collecting connectivity metrics over time for a given user terminal (UT) operating in the corresponding location, wherein the connectivity metrics collected for each such location indicate a viewpoint characteristically associated with degraded connectivity; providing service to a user terminal (UT) in a non-diversity service mode, wherein there is a single serving satellite in the constellation for the UT at a time; predicting that the UT will experience degraded connectivity based on the learned view constraints; as well as In response to the forecast: deciding to change from serving the UT in the non-diversity serving mode to serving the UT in a diversity serving mode, wherein there are two or more serving satellites in the constellation for the UT at a time; and The UT is served in the diversity service mode.

2. The method of claim 1 , wherein predicting that the UT will experience degraded connectivity comprises: A determination is made based on the learned view limit, the UE's location, and the serving satellite ephemeris that serving the UT in the non-diversity service mode will involve a restricted view.

3. The method of claim 1 or 2, wherein the learned view limits are represented in a database linking each respective location among a plurality of respective locations with a corresponding view limit learned for the respective location, and wherein predicting that the UT will experience degraded connectivity comprises: The database is indexed based on changes in the location of the UT to determine view angle restrictions applicable to the location of the UT, and based on serving satellite ephemeris, it is determined that the UT will experience one or more restricted view angles.

4. The method of claim 3 , wherein determining the viewing angle limit applicable to the location of the UT comprises: Interpolation or extrapolation is performed on the view angle limits corresponding to one or more locations in the database that are closest to the location of the UT.

5. The method of claim 1 or 2, wherein the learned view limits are represented in a trained machine learning (ML) model that outputs view limits applicable to an input location, and wherein predicting that the UT will experience degraded connectivity comprises: A UT position is input into the trained ML model, and serving satellite ephemeris is evaluated to determine whether the UT will experience a restricted view angle, as indicated by an applicable view angle limit output by the trained ML model.

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

7. The method of any one of claims 1 to 6, wherein serving the UT in the diversity service mode comprises serving the UT in one or both of a forward diversity service mode and a reverse diversity service mode.

8. The method of claim 7, wherein providing service to the UT in the reverse diversity service mode comprises: Attempting to receive an uplink transmission from the UT at each of two or more satellites in the constellation such that the SCN receives corresponding reverse traffic from the UT upon successful receipt of the uplink transmission at one or more of the two or more satellites.

9. The method of claim 7, wherein providing service to the UT in the forward diversity service mode comprises: Forward data is provided to the UT using multiple-input multiple-output (MIMO) or multiple-input single-output (MISO) forward downlink transmission.

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

11. The method according to claim 10, wherein the method further comprises: Performing beamforming updates for the collaborative beamforming according to a beam update rate that is faster than a channel sounding rate, wherein the channel sounding rate determines a rate at which the SCN obtains updated channel state information (CSI) based on reference signal transmissions over a physical propagation channel linking a corresponding UT to the SCN, and wherein the SCN supports the faster beam update rate by predicting changes in the CSI between CSI updates.

12. The method of claim 10, wherein the method further comprises updating a channel estimate value used for the collaborative beamforming to account for a relative position change between the two or more satellites participating in the collaborative beamforming.

13. The method of any one of claims 1 to 12, wherein deciding to change from serving the UT in the non-diversity service mode to serving the UT in the diversity service mode comprises further making a decision based on a delay tolerance associated with a communication service provided to the UT via the SCN.

14. The method of claim 13 , wherein making the determination based on the delay tolerance associated with the communication service provided to the UT via the SCN comprises: A decision is made to change to the diversity service mode in response to the stored configuration information identifying the communication service as delay sensitive.

15. A control apparatus configured to operate in a satellite communications network (SCN) comprising a constellation of non-geosynchronous satellites following respective orbital paths, the control apparatus comprising: Communication interface circuit system; as well as processing circuitry configured to: learning a viewpoint restriction for a corresponding geographic location based on collecting connectivity metrics over time for a given user terminal (UT) operating in the corresponding location, wherein the connectivity metrics collected for each such location indicate a viewpoint characteristically associated with degraded connectivity; providing service to a user terminal (UT) in a non-diversity service mode, wherein there is a single serving satellite in the constellation for the UT at a time; predicting that the UT will experience degraded connectivity based on the learned view constraints; and In response to the forecast: deciding to change from serving the UT in the non-diversity serving mode to serving the UT in a diversity serving mode, wherein there are two or more serving satellites in the constellation for the UT at a time; and The UT is served in the diversity service mode.

16. The control device according to claim 15, wherein: For predicting that the UT will experience degraded connectivity, the processing circuitry is configured to determine that serving the UT in the non-diversity service mode will involve a restricted view based on the learned view limit, the UE's location, and serving satellite ephemeris.

17. The control device according to claim 15 or 16, wherein the learned viewing angle limit is represented in a database, the database linking each corresponding position among a plurality of corresponding positions with the corresponding viewing angle limit learned for the corresponding position, and wherein, In response to predicting that the UT will experience degraded connectivity, the processing circuitry is configured to index the database based on a change in the location of the UT to determine view angle restrictions applicable to the location of the UT, and determine that the UT will experience one or more restricted view angles based on serving satellite ephemeris.

18. The control apparatus of claim 17 , wherein the processing circuitry is configured to determine the view angle limit applicable to the location of the UT by performing interpolation or extrapolation of view angle limits corresponding to one or more locations in the database that are closest to the location of the UT.

19. A control device according to claim 15 or 16, wherein the learned viewing angle limit is represented in a trained machine learning (ML) model, the trained machine learning model outputting a viewing angle limit applicable to an input position, and wherein For predicting that the UT will experience degraded connectivity, the processing circuitry is configured to input a UT location into the trained ML model and evaluate serving satellite ephemeris to determine whether the UT will experience a restricted view angle, as indicated by an applicable view angle limit output by the trained ML model.

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

21. The control apparatus of 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 reverse diversity service mode.

22. The control device according to claim 21, wherein: For serving the UT in the reverse diversity service mode, the processing circuitry is configured to control the SCN to attempt to receive an uplink transmission from the UT at each of two or more satellites in the constellation, such that the SCN receives corresponding reverse traffic from the UT upon successful receipt of the uplink transmission at one or more of the two or more satellites.

23. The control device according to claim 21, wherein: For serving the UT in the forward diversity service mode, the control device is configured to activate multiple-input multiple-output (MIMO) or multiple-input single-output (MISO) forward downlink transmission to provide forward data to the UT.

24. The control apparatus of claim 23, wherein the MIMO or MISO forward downlink transmission comprises collaborative beamforming transmission from two or more satellites in the constellation, wherein the collaborative beamforming comprises collaboratively setting any one or more of transmit carrier frequency, transmit carrier amplitude, transmit carrier phase, or transmit carrier timing offset between the two or more satellites to produce a constructive combination of respective downlink transmit signals from the two or more satellites at the UT.

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

26. The control device according to claim 24, wherein the control device is configured to update a channel estimation value used for the coordinated beamforming to take into account a relative position change between the two or more satellites participating in the coordinated beamforming.

27. The control device according to any one of claims 15 to 26, wherein: With respect to deciding to change from serving the UT in the non-diversity service mode to serving the UT in the diversity service mode, the processing circuitry is configured to make a decision further based on a delay tolerance associated with a communication service provided to the UT via the SCN.

28. The control device according to claim 27, wherein: With respect to making the decision further based on the delay tolerance, the processing circuitry is configured to decide to change to the diversity service mode in response to the stored configuration information identifying the communication service as delay sensitive.

29. A method operated by a user terminal (UT), the user terminal being configured to be served by a satellite communication network (SCN), the satellite communication network comprising a constellation of non-geostationary satellites following respective orbital paths, the method comprising: operating in a non-diversity serving mode, wherein the SCN serves the UT via a single serving satellite in the constellation at a time; receiving control signaling from the SCN, the control signaling indicating a change 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; The operation is changed from the non-diversity service mode to the diversity service mode in response to one of: receiving the control signaling, or satisfying a diversity mode triggering condition indicated by the control signaling.

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

31. The method of claim 29, wherein the diversity mode triggering condition is handing over the UT to a specific satellite in the constellation as a new serving satellite.

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

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 receives multiple-input multiple-output (MIMO) or multiple-input single-output (MISO) transmissions from the two or more serving satellites.

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

35. The method of claim 32, wherein receiving the forward data stream as the 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. The method according to any one of claims 29 to 31, 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. The method according to any one of claims 29 to 36, wherein For operation of the UT in the diversity service mode, the method includes the UT dividing a reverse data stream into two or more reverse data sub-streams, each reverse data sub-stream being received by a corresponding serving satellite among the two or more serving satellites.

38. A user terminal (UT) configured to be served by a satellite communication network (SCN) comprising a constellation of non-geosynchronous satellites following respective orbital paths, the UT comprising: communications interface circuitry configured to communicate with the SCN via the exchange of wireless signaling with one or more satellites in the constellation; as well as processing circuitry operably associated with the communications interface circuitry and configured to: operating in a non-diversity serving mode, wherein the SCN serves the UT via a single serving satellite in the constellation at a time; receiving control signaling from the SCN, the control signaling indicating a change 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; The operation is changed from the non-diversity service mode to the diversity service mode in response to one of: receiving the control signaling, or satisfying a diversity mode triggering condition indicated by the control signaling.

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

40. The UT of claim 38, wherein the diversity mode triggering condition is handing over the UT to a specific satellite in the constellation as a new serving satellite.

41. The UT according to any one of claims 38 to 40, wherein For 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. The UT of claim 41, wherein the processing circuitry is configured to receive the forward data streams from the two or more serving satellites via multiple-input multiple-output (MIMO) or multiple-input single-output (MISO) transmissions.

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 communication interface circuitry.

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

45. The UT according to any one of claims 38 to 40, 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, and wherein the processing circuitry deems receipt of the forward data stream successful based on receipt of the forward data stream from any one or more of the two or more serving satellites.

46. ​​The UT according to any one of claims 38 to 45, wherein For operation of the UT in the diversity service mode, the processing circuitry is configured to divide a reverse data stream into two or more reverse data sub-streams, each reverse data sub-stream being received by a respective serving satellite among the two or more serving satellites.

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