Methods and apparatuses for optical link selection in a satellite communications system

Abstract

The disclosed methods and apparatuses provide various advantages in satellite communications systems employing optical feeder links.

Description

METHODS AND APPARATUSES FOR OPTICAL LINK SELECTION IN A SATELLITE COMMUNICATIONS SYSTEMTECHNICAL FIELD

[0001] The present disclosure relates to satellite communications systems, and more particularly to methods and apparatuses for optical link selection between satellites and multiple remote optical endpoints.BACKGROUND

[0002] Satellite communications systems increasingly rely on optical feeder links to provide high-bandwidth connectivity between satellites and ground-based infrastructure, or between respective satellites. Optical links offer advantages over traditional radio frequency communications, including higher data rates, reduced interference, and more efficient spectrum utilization. In optical feeder link architectures, laser communication terminals (LCTs) positioned on satellites establish optical connections with optical ground stations distributed across geographic regions, or with other satellites having onboard LCTs. An LCT may be understood as an optical endpoint anchoring one end of an optical communications link, such as an optical feeder link between a satellite and an optical ground station.

[0003] Various atmospheric and environmental conditions affect the performance of optical feeder links. For example, in the context of optical ground stations, weather phenomena such as cloud coverage, atmospheric turbulence, and precipitation can degrade or interrupt optical transmissions between satellites and ground stations. Additionally, solar positioning relative to ground station equipment may impact link quality during certain periods of operation. Ground station hardware failures and maintenance activities can also render individual stations temporarily unavailable for communications.

[0004] To maintain reliable communications service, satellite communications systems typically deploy networks of geographically distributed optical ground stations that provide site diversity. When atmospheric conditions or other factors affect the active optical link at one ground station, the system can transition communications to an alternative ground station with more favorable conditions. This handover process helps achieve higher overall network availability by leveraging the statistical independence of weather patterns and operational conditions across different geographic locations.

[0005] Traditional approaches to managing optical link handovers often rely on ground- based monitoring systems that measure local atmospheric conditions, weather parameters, and equipment status at each ground station. This information is typically transmitted to centralized control centers where decisions are made regarding when to initiate handovers and whichalternative ground stations to select. Such approaches may involve complex coordination between multiple ground stations, control centers, and satellite systems, potentially introducing complexity or delay in the handover process and requiring extensive ground-based monitoring infrastructure.SUMMARY

[0006] The disclosed methods and apparatuses provide various advantages in satellite communications systems employing optical feeder links. By enabling satellite-based observation and selection of optical ground stations or other remote optical endpoints such as lower-altitude satellites, the disclosed approaches reduce reliance on ground-based monitoring infrastructure and centralized control systems. The use of a wide field-of-view optical telescope for simultaneous observation of multiple remote endpoints allows for rapid assessment of link conditions and efficient handover decisions. In at least some implementations, the disclosed techniques reduce handover latency, improve overall network availability, enhance security, and simplify coordination requirements for optical link handovers.

[0007] In an example embodiment, an optical endpoint is configured for use in a satellite communications system. The optical endpoint includes a first optical telescope having a field of view (FoV) sized for simultaneous observation of a plurality of remote optical endpoints that are spatially separated and individually selectable as a targeted endpoint. Further included are a second optical telescope having a FoV smaller than the first optical telescope and configured for optical link communications with the targeted endpoint, and a control system. The control system is configured to maintain selection preferences with respect to the plurality of remote optical endpoints, based on respective optical measurements made via the simultaneous observation, and control which remote optical endpoint is selected as the targeted endpoint in dependence on the selection preferences.

[0008] A related embodiment comprises a method of operating an optical endpoint in a satellite communications system. The method includes obtaining respective optical measurements for a plurality of remote optical endpoints that are spatially separated and individually selectable as a targeted endpoint for optical communications via a second optical telescope of the optical endpoint. The respective optical measurements are obtained by simultaneously observing the plurality of remote optical endpoints via a first optical telescope of the optical endpoint. The first optical telescope has a FoV that is larger than a FoV of the second optical telescope and sized for simultaneous observation of the plurality of remote optical endpoints. The method further includes maintaining selection preferences for the plurality of remote optical endpoints, based on the respective optical measurements, and controlling whichremote optical endpoint is selected as the targeted endpoint, in dependence on the selection preferences.

[0009] Another embodiment comprises a satellite communications system that includes a ground segment and a space segment. The space segment includes a satellite operating in a defined orbit and the ground segment includes a plurality of optical ground stations that are geographically distributed, with each optical ground station operative to support an optical communications link with the satellite. Correspondingly, the satellite includes a first optical telescope and a second optical telescope. The first optical telescope has a FoV sized for simultaneous observation of the plurality of optical ground stations, whereas the second optical telescope has a FoV smaller than the FoV of the first optical telescope and is configured to support the optical communications link with any one of the optical ground stations that is selected as a targeted endpoint for the satellite. A control system of the satellite is configured to maintain selection preferences for the plurality of optical ground stations, based on observing the plurality of optical ground stations via the first optical telescope, and further configured to control which optical ground station is selected as the targeted endpoint, in dependence on the selection preferences.

[0010] Of course, the present invention is not limited to the above 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 DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a diagram of an optical endpoint configured for monitoring a plurality of remote optical endpoints, according to an example embodiment.

[0012] Figures 2A-2C are diagrams of example scenarios involving implementation of the optical endpoint of Figure 1 as a satellite in combination with various types of remote optical endpoints, according to respective example embodiments.

[0013] Figure 3 is a diagram of an observed image frame illustrating a constellation or spatial arrangement of detected remote optical endpoints, according to an example embodiment.

[0014] Figures 4A and 4B are diagrams illustrating comparative usage of reference image frame for validating remote optical endpoints detected in an observed image frame, according to an example embodiment.

[0015] Figure 5 is a logic flow diagram of a method of validating detected remote optical endpoints, according to an example embodiment.

[0016] Figure 6 is a block diagram of an example configuration of selection preferences corresponding to remote optical endpoints, according to an example embodiment.

[0017] Figure 7 is a block diagram illustrating a multiplicity of factors used for determination of selection preferences, according to an example embodiment.

[0018] Figures 8 and 9 are block diagrams of example satellite communications systems (SCSs), according to an example embodiment.

[0019] Figure 10 is a block diagram of a control system of an optical endpoint configured for monitoring and link-selection with respect to a plurality of remote optical endpoints, according to an example embodiment.

[0020] Figure 11 is a logic flow diagram of a method of monitoring a plurality of remote optical endpoints and selecting respective ones as a targeted endpoint, according to an example embodiment.DETAILED DESCRIPTION

[0021] Figure 1 illustrates an optical endpoint 10, according to an example embodiment. Here, the term “optical endpoint” refers to a system or assembly configured for use at one end of an optical communications link, such as an optical feeder link between an optical ground station of a satellite communications system (SCS) and a satellite in the SCS. Correspondingly, the illustrated optical endpoint 10 is configured for use in an SCS and it includes a first optical telescope 12, a second optical telescope 14, a control system 16, and a beam steering assembly (BSA) 18. In one or more embodiments, the optical endpoint 10 further includes or is operatively associated with a telemetry and control transceiver 20, shown as “telemetry / control transceiver 20” in the diagram.

[0022] The first optical telescope 12 has a field of view (FoV) sized for simultaneous observation of a plurality of remote optical endpoints which are not shown but are spatially separated and individually selectable as a targeted endpoint. The second optical telescope 14 has a FoV smaller than the first optical telescope 12 and it is configured for optical link communications with the targeted endpoint.

[0023] The control system 16 is configured to maintain selection preferences with respect to the plurality of remote optical endpoints, based on respective optical measurements made via the simultaneous observation. Further, the control system 16 is configured to control which remote optical endpoint is selected as the targeted endpoint in dependence on the selection preferences. For example, the control system 16 is configured to select the targeted endpoint based on rankingthe plurality of remote optical endpoints in terms of the selection preferences and choosing a highest ranked one as the targeted endpoint.

[0024] In an example embodiment, the control system 16 is configured to maintain the corresponding selection preference for each remote optical endpoint based on a combined consideration of a current optical measurement and historical information. The historical information comprises at least one of: historical availability, historical serving performance, and historical variance of previous optical measurements made for the remote optical endpoint.

[0025] As for the respective measurements, they are respective brightness measurements for example. In at least one embodiment, the “current optical measurement” corresponding to each remote optical endpoint comprises a most recent measurement made for the remote optical endpoint, and each such measurement may itself be an average of individual measurements such as may be taken over a defined interval.

[0026] The first optical telescope 12 includes an optical filter in one or more embodiments, where the optical filter is configured to pass a certain optical wavelength while blocking other optical wavelengths. Correspondingly, each remote optical endpoint outputs a beacon beam at the certain optical wavelength, and the respective optical measurements made by the optical endpoint 10 made for the plurality of remote optical endpoints correspond to beacon-beam reception at the optical endpoint 10 via the first optical telescope 12. For example, the first optical telescope 12 includes or is associated with a shortwave infrared (SWIR) camera that is used for obtaining the respective optical measurements. As an example, the SWIR camera is sensitive to light within a range of 0.9 micrometers to 1.7 micrometers.

[0027] Broadly, the respective optical measurements made by the optical endpoint 10 for the plurality of remote optical endpoints are based on the optical endpoint 10 receiving respective optical beacon beams from the plurality of remote optical endpoints via the first optical telescope. In at least one embodiment, the plurality of remote optical endpoints transmits the respective optical beacon beams according to a defined timing, and wherein the control system 16 of the optical endpoint 10 is configured to obtain the respective optical measurements according to the defined timing.

[0028] As noted, the FoV of the first optical telescope 12 is sized for simultaneous observation of the plurality of remote optical endpoints. In comparison, the FoV of the second optical telescope is sized for observation of one remote optical endpoint at a time. Merely by way of example, the FoV of the second optical telescope 14 is thirty to fifty times smaller than the FoV of the first optical telescope 12.

[0029] The control system 16 in one or more embodiments is configured to change which remote optical endpoint is selected as the targeted endpoint by changing from a currentlyselected one to a newly selected one, responsive to detecting deteriorating optical link quality with respect to the currently selected one. The control system is configured to detect the deteriorating optical link quality with respect to a defined minimum quality threshold, for example.

[0030] In an example embodiment, the optical endpoint 10 comprises a satellite and the plurality of remote optical endpoints comprises any one of or any mix of a plurality of geographically distributed optical ground stations; a plurality of satellites orbiting below the satellite; or a plurality of high-altitude platforms or aircraft. Figure 2A illustrates the optical endpoint 10 implemented as a satellite 30 and illustrates a plurality optical ground stations (OGSs) 32 as an example of the aforementioned plurality of remote optical endpoints. In an operational example, the satellite 30 selects one of the OGSs 32 as a targeted endpoint for establishing an optical communications link 34. Each such OGS 32 provides a respective optical beacon 36 used by the satellite 30 for maintaining selection preferences with respect to the plurality of OGSs 32. That is, the satellite 30 makes the aforementioned respective optical measurements via simultaneous observation of the plurality of optical beacons 36.

[0031] Figure 2B illustrates another example case where the plurality of remote optical endpoints comprises a plurality of other satellites 40 orbiting below the satellite 30. Figure 2C illustrates yet another example case where the plurality of remote optical endpoints comprises a plurality of high altitude platforms (HAPs) or aircraft 42. Of course, the plurality of remote optical endpoints need not be a homogenous set; for example, the plurality of remote optical endpoints comprises a mesh or mix of any two or more of OGSs 32, lower-orbit satellites 40, or HAPs / aircraft 42. In one or more embodiments, the satellite 30 is configured for operation as a geostationary satellite, where the geo orbital height provides for the wide FoV associated with the first optical telescope 12. Correspondingly, the plurality of remote optical endpoints may comprise medium Earth orbit (MEO) or low Earth orbit (LEO) satellites.

[0032] As a more detailed example, the optical endpoint 10 comprises a satellite 30 configured for geostationary operation and the plurality of remote optical endpoints comprises a plurality of geographically distributed OGSs 32. The control system 16 is configured to maintain the selection preferences based on a multiplicity of factors, the multiplicity of factors comprising the respective optical measurements and one or more of positioning of the sun relative to the satellite from the perspective of each OGS 32; atmospheric conditions associated with each OGS 32; operational statuses of the respective OGSs 32; traffic loading of the respective OGSs 32; variance of past optical measurements made for each OGS 32; and historical performance with respect to past selections of individual ones of the OGSs 32 as the targeted endpoint. Historical performance comprises experienced optical link quality, for example, which may be measureddirectly in terms of received optical power or may be measured indirectly, such as based on traffic throughput.

[0033] In at least one embodiment, the control system 16 is configured for automatic reselection of the targeted endpoint from among the plurality of remote optical endpoints, based on the selection preferences, where each automatic reselection constitutes an automatic optical communications link handover. In such embodiments, the control system 16 is configured to communicate optical communications link handover information towards a ground network of an SCS, for each automatic optical communications link handover. For example, the control system 16 uses the aforementioned telemetry / control transceiver 20 to communicate the optical communications link handover information to the ground network.

[0034] Figure 3 illustrates an example observed image frame 50, such as may be obtained using the first optical telescope 12. Observed image frames 50 may be referred to as observed image maps.

[0035] The extents of the observed image frame 50 correspond to the FoV of the first optical telescope and it illustrates a plurality of detected remote optical endpoints 52 within the observed image frame 50. In embodiments where the first optical telescope 12 includes a SWIR camera or other imager, each detected remoted optical endpoint 52 is represented as an illumination point (a spot) within an otherwise dark field or background. Each spot represents reception of an optical beacon 36 from a corresponding one among the plurality of remote optical endpoints, and the spot size correlates with beacon brightness.

[0036] In at least one embodiment, the control system 16 is configured to prevent selection of remote optical endpoints that are unaffiliated with the SCS by limiting the plurality of remote optical endpoints it considers for selection to validated remote optical endpoints. “Limiting” in this context means that the control system 16 considers only validated remote optical endpoints with respect to selection as a targeted endpoint. Considering only validated remote optical endpoints increases security of the SCS by eliminating or reducing the risk posed by unauthorized or fraudulent communications stations.

[0037] The control system 16 in at least one such embodiment is configured to perform a validation process in which the control system uses a reference image frame 54, as shown in Figure 4A. The reference image frame 54 may be referred to as a reference image map and it contains a reference constellation of remote optical endpoints 56.

[0038] In other words, the remote optical endpoints 56 represented in the reference image frame 54 represent authorized locations at which the optical endpoint 10 should expect to see a valid remote optical endpoint. Figure 4B illustrates a corresponding observed image map 50 — i.e., an actually acquired image map that contains an “observed constellation.” The controlsystem 16 is configured to compare the observed constellation to the reference constellation to determine whether any detected remote optical endpoint 52 does not correlate with the reference constellation. Figure 4B illustrates one uncorrelated remote optical endpoint 52 identified from the correlation, which is deemed by the control system 16 as being “unaffiliated” and not valid for consideration.

[0039] With such examples in mind, the control system 16 in one or more embodiments is configured to perform a validation process, shown as a method 500 in Figure 5.

[0040] The method 500 includes acquiring (block 504) an image map depicting an observed constellation of putative (detected) remote optical endpoints. Each putative remote optical endpoint is a remote source of optical illumination at a beacon-beam wavelength used by a SCS and visible within the FoV of the first optical telescope 12.

[0041] The method 500 further includes identifying (block 506) unaffiliated remote optical endpoints by correlating the observed constellation of putative remote optical endpoints with a reference image map depicting a reference constellation of valid remote optical endpoints. The control system 16 in at least one such embodiment is configured to perform the correlating as a spatial correlation that compares locations of putative remote optical endpoints in the observed constellation with locations of valid remote optical endpoints in the reference constellation.

[0042] The method 500 may further include, as a preparatory step, the control system 16 obtaining / storing (block 502) a reference image map depicting the reference constellation. For example, optical endpoint 10 comprises a satellite 30 and the ground network of the SCS transmits information defining the reference image map, for reception by the control system 16 via the telemetry / control transceiver 20.

[0043] In at least one embodiment, the optical endpoint 10 is a satellite, such as the satellite 30 shown in Figures 2A, 2B, and 2C. With respect to operation of the satellite in orbit, the control system 16 is configured to provide optical-measurement feedback for siting optical ground stations, the optical-measurement feedback based on the first optical telescope 12 observing a pilot optical beam transmitted from a prospective ground station site. In the same or one or more other embodiments, the control system 16 is configured to receive information from a ground network of the SCS, indicating one or more prospective ground station sites within the FoV of the first optical telescope 12 for which the satellite is to provide the optical-measurement feedback.

[0044] Figures 6 and 7 illustrate example details for the control system 16 to form and use selection preferences based on optical measurements made with respect to a plurality of remote optical endpoints that are individually selectable as a targeted endpoint for optical communications. According to Figure 6, the control system 16 maintains selection preferences60 for a plurality of remote optical endpoints, which are denoted as “Candidates” in the diagram. The selection preference for Candidate 1 derives from brightness measurements made for Candidate 1. Similarly, the selection preference for Candidate 2 derives from brightness measurements made for Candidate 2, and so on through the Nth Candidate from among N remote optical endpoints. Thus, the selection preferences 60 may be ranked or compared for deciding which remote optical endpoint is preferred for selection as the targeted endpoint.

[0045] Figure 7 illustrates that the brightness measurements may be one among a multiplicity of parameters or factors considered for determining the selection preference for each candidate. In one or more embodiments, the selection preference for each candidate is based on a multiplicity of factors including: brightness, brightness variation, relative position of the sun, availability over a last or current assessment interval, last link duration, and availability statistics or predictions. Here, “last link duration” refers to the length of time that the candidate remained selected the last time it was selected / used as the targeted endpoint.

[0046] Figure 8 illustrates an example SCS 70 comprising a ground network 72 that includes N OGSs 32, along with a control center 74. The control center 74 comprises, for example, one or more network computer servers configured for SCS control. The satellite 30 comprises a geo satellite for example, and it shall be understood as representing an example implementation of the optical endpoint 10, with the plurality of OGSs 32 representing an example plurality of remote optical endpoints that are individually selectable as a targeted endpoint for optical communications between the satellite 30 and the ground network 72.

[0047] According to the illustration, the satellite 30 provides the control center 74 with handover information, such as the selection preferences based on the satellite 30 observing optical beacons from the respective OGSs 32, and the control center 74 uses the handover information to make handover decisions. For example, the control center 74 decides when the satellite 30 should be handed over from one OGS 32 to another OGS 32. With reference back to Figure 1, the satellite 30 will be understood as implementing the illustrated optical endpoint 10, which may be referred to as a laser communications terminal or LCT, including illustrated first and second optical telescopes 12 and 14, the control system 16, the BSA 18, and the telemetry / control transceiver 20.

[0048] Thus, in one or more example embodiments, the satellite 30 has a radiofrequency (RF) link with the control center 74 via the telemetry / control transceiver 20. The satellite 30 uses the RF link to send the handover information and receive handover commands. When commanded to change from one OGS 32 to another OGS 32, the control system 16 controls the BSA 18 to steer the second optical telescope 14 into optical alignment with the newly selected OGS 32.

[0049] Figure 9 illustrates a variation relative to the arrangement depicted in Figure 8. According to the variation, the satellite 30 is configured to make autonomous handover decisions. For example, the satellite 30 maintains selection preferences for the plurality of OGSs 32 in the ground network 72 of the SCS 70 and decides when to handover its optical communications link from a currently selected one of the OGSs 32 to a newly selected one of the OGSs 32. Of course, even with autonomous handover control by the satellite 30, the control center 74 may influence or tune decision-making by the satellite 30, such as by providing control parameter values that influence the decision-making. For example, the control center 74 may adjust preference thresholds or other values to make the handover decision-making more aggressive or less aggressive, or to exclude certain OGSs 32 from consideration.

[0050] With example reference to Figures 8 and 9, an example SCS 70 includes a space segment having a satellite 30 that operates in a defined orbit. The SCS 70 further includes a ground segment having a plurality of OGSs 32 that are geographically distributed, where each OGS 32 is operative to support an optical communications link with the satellite 30.

[0051] Operating as an optical endpoint in the sense detailed for the optical endpoint 10 introduced in Figure 1, the satellite 30 includes a first optical telescope 12 having a FoV sized for simultaneous observation of the plurality of OGSs 32 and includes a second optical telescope 14. The second optical telescope 14 has a FoV smaller than the FoV of the first optical telescope 12 and is configured to support the optical communications link with any one of the OGSs 32 that is selected as a targeted endpoint for the satellite 30.

[0052] Still further, the satellite 30 includes a control system 16 that is configured to maintain selection preferences for the plurality of OGSs 32. The control system 16 maintains these selection preferences based on observing the plurality of OGSs 32 via the first optical telescope 12 and is further configured to control which OGS 32 is selected as the targeted endpoint, in dependence on the selection preferences.

[0053] Regarding communications with the targeted endpoint, the satellite 30 further includes a communications transceiver and the control system 16 is configured to communicate optical communications link handover information to the ground segment, responsive to changing which OGS 32 is selected as the targeted endpoint. For example, the control system 16 uses its telemetry / control transceiver 20 to send the handover information to the ground network 72 as radio frequency signaling. Such handover information comprises or is based on the respective optical measurements made for the plurality of OGSs 32 that are selectable as a targeted endpoint. Observing comprises, for example, the control system 16 obtaining brightness measurements for the plurality of OGSs 32 and basing its selection preferences on the brightness measurements.

[0054] Figure 10 illustrates example implementation details for the control system 16, such as may be implemented in the satellite 30. The example control system 16 comprises fixed circuitry or programmatically configured circuitry or a mix of both. In at least one embodiment, the control system 16 comprises one or more microcontrollers 80 that are specially adapted to carry out the control -system operations described herein, based on executing computer program instructions (CPI) 82 held in storage 84, which may further contain provisioned or working data 86. In one example, the data 86 includes the selection preferences maintained for remote optical endpoint selection. Examples of the storage 84 include one or more types of computer readable media, such as volatile and non-volatile memory.

[0055] Input / output circuitry 88, also referred to as interface circuitry, interfaces the microcontroller(s) 80 with a BSA control arrangement 90, which is configured for control of the BSA 18 and corresponding steering of the second optical telescope 14. Components of the BSA control arrangement 90 include multi-axis steering motors 92 and multi-axis position encoders 94, such as may be integrated with azimuthal and elevational axes of the BSA 18. In one or more embodiments, the first optical telescope 12 is also steered.

[0056] The input / output circuitry 88 in the example arrangement also includes an interface to a camera 96 that is included in or associated with the first optical telescope 12. For example, the camera 96 is a SWIR camera positioned to receive light incoming through a set of optics 98 comprised in the optical telescope. Correspondingly, the microcontroller s) 80 obtain the observed image frames 50 described earlier or obtain raw sensor data from which such image frames are derived.

[0057] Although not part of the control system 16, Figure 10 further illustrates an optoelectronic interface 100 for interfacing with the second optical telescope 14, along with an associated communications transceiver 102. In an example case where the optical endpoint 10 comprises a satellite 30, the satellite 30 communicates with an OGS 32 or other satellite 40 (or HAP / aircraft 42) via an optical communications link that includes one or more optical transmit beams and one or more optical receive beams, carrying communications and control signals. Such signals may be converted between the optical and electrical domains via the optoelectronic interface 100.

[0058] For example, the communications transceiver 102 outputs one or more transmit signals in the electrical domain, e.g., intermediate frequency or radio frequency transmit signals, which are converted into optical signals for transmission via the second optical telescope 14. In the opposite direction, the communications transceiver 102 receives one or more incoming receive signals in the electrical domain, as recovered or detected from one or more optical beams incoming to the second optical telescope 14. Further, it should be understood that the secondoptical telescope 14 may be realized as two separate optical telescopes, such as one for reception and one for transmission.

[0059] Figure 11 illustrates and example method 1100 of operating an optical endpoint in an SCS. For example, the optical endpoint 10 introduced in Figure 1 is implemented as the satellite 30 included in the SCS 70 shown in Figure 8 or 9.

[0060] The method 1100 includes the optical endpoint obtaining (block 1102) respective optical measurements for a plurality of remote optical endpoints that are spatially separated and individually selectable as a targeted endpoint for optical communications via a second optical telescope of the optical endpoint. Here, the optical endpoint obtains the respective optical measurements by simultaneously observing the plurality of remote optical endpoints via a first optical telescope of the optical endpoint, the first optical telescope having a FoV that is larger than a FoV of the second optical telescope and sized for simultaneous observation of the plurality of remote optical endpoints.

[0061] Further operations in the method 1100 include the optical endpoint maintaining (block 1104) selection preferences for the plurality of remote optical endpoints, based on the respective optical measurements, and controlling (block 1106) which remote optical endpoint is selected as the targeted endpoint, in dependence on the selection preferences. Controlling which remote optical endpoint is selected as the targeted endpoint comprises, for example, ranking the plurality of remote optical endpoints in terms of the selection preferences and choosing a highest ranked one as the targeted endpoint.

[0062] As another example, controlling which remote optical endpoint is selected as the targeted endpoint comprises changing from a currently selected remote optical endpoint to a newly selected optical endpoint in response to detecting deteriorating optical link quality with respect to the currently selected remote optical endpoint, and choosing the newly selected optical endpoint in dependence on ranking the corresponding selection preferences.

[0063] In the context of Figure 8, controlling which remote optical endpoint is selected comprises the satellite 30 determining the selection preferences and sending handover information to the ground network 72. Such information indicates the selection preferences (or indicates a particular preferred one among the remote optical endpoints) and thus drives the endpoint selection decisions made by the control center 74 in the ground network 72. In the context of Figure 9, controlling the selection refers to the satellite 30 making selection decisions autonomously and communicating such decisions to the ground network 72. In either control case, the ground network 72 is configured to control user traffic routing and other operational aspects, to account for optical link handovers.

[0064] One example of maintaining the selection preferences on which such control is based comprises, for each remote optical endpoint among the plurality of remote optical endpoints that are selectable as the targeted endpoint, the corresponding selection preference is maintained as a combined consideration of a current optical measurement and historical information. The historical information includes at least one of: historical availability, historical serving performance, and historical variance of previous optical measurements made for the remote optical endpoint. The respective optical measurements are, for example, respective brightness measurements.

[0065] The method 1100 in one or more embodiments further includes carrying out the optical communications with the targeted endpoint via the second optical telescope. The method may further include carrying out a tracking procedure for maintaining fine optical alignment between the second optical telescope and the targeted endpoint, for ongoing optical communications.

[0066] As noted, in one or more embodiments, the plurality of remote optical endpoints is configured to transmit respective beacon beams according to a defined timing, and the method 1100 in one or more embodiments includes performing the optical measurements according to the defined timing. As an example, the control system 16 performs optical measurements on a scheduled basis, according to the times and durations of beacon transmission.

[0067] The method 1100 in one or more embodiments further comprises performing automatic optical communications link handovers in association with changing which one among the plurality of remote optical endpoints is selected as the targeted endpoint.Additionally, or alternatively, the method 1100 may include transmitting optical communications link handover information towards a control node in a ground network of the satellite communications system.

[0068] The optical endpoint carrying out the method 1100 comprises a satellite configured for geostationary operation, for example, and the plurality of remote optical endpoints comprises a plurality of geographically distributed OGSs. In this example context, method 1100 may include maintaining the selection preferences based on a multiplicity of factors. Such factors include the respective optical measurements and one or more of: positioning of the sun relative to the satellite from the perspective of each optical ground station; atmospheric conditions associated with each optical ground station; operational statuses of the respective optical ground stations; traffic loading of the respective optical ground stations; variance of past optical measurements made for each optical ground station; and historical performance with respect to past selections of individual ones of the optical ground stations as the targeted endpoint.

[0069] With the above example embodiments in mind, the disclosed methods and apparatuses provide for seamless and autonomous optical link handover approach. In an example case, a satellite operates in a geostationary orbit and communicates via an optical link with a targeted endpoint, which is a selected one among a plurality of remote optical endpoints. Examples include any one or more (or mix) of OGSs, lower-orbit space vehicles, HAPs, or aircraft.

[0070] Link handovers may be necessitated by technological outages as well as atmospheric and meteorological conditions at a given location. Additionally, handovers between geo and lower orbit satellites may be necessary due to the obstruction of the line of sight by the Earth. This seamless and autonomous switching is facilitated by continuous monitoring and tracking of network nodes (OGSs and / or satellites) from the geo orbit, utilizing the techniques described herein. The optical-endpoint components or elements that provide for such monitoring and tracking may be referred to in the aggregate as a Multi-Target Tracking and Monitoring System (MTT MS). The MTT MS comprises a large-field optical telescope with a narrow optical bandwidth, a camera, an image processing unit, and software for data processing and storage. See, for example, the first optical telescope 12 and control system 16 introduced in Figure 1 and see the further example details in Figure 10.

[0071] The MTT MS delivers advantageous functionality that, in one or more embodiments, includes ground network monitoring by a geo satellite. For example, a geo satellite uses its large- FOV telescope to simultaneously monitor a network of OGSs. There may be many (e.g., tens of OGSs that are candidates for selection by the geo satellite as a targeted endpoint for optical communications) and the geo satellite may use its optical measurements of the respective OGS beacons to generate statistics on the availability of each OGS over time. Such operation is possible with the large FoV of the monitoring telescope onboard the geo satellite, where the size of that FoV is balanced with respect to the required open pointing resolution.

[0072] The tracking and monitoring may be applied to constellations of OGSs, constellations of lower-orbit (MEO or LEO) satellites, collections of HAPs or aircraft, or hybrid mixes of one or more such entities. In at least one example, the geo satellite monitors a mix of OGSs and lower-orbit satellites as selectable targets for optical link communications.

[0073] Monitoring in one or more embodiments comprises the collection or generation of availability statistics and predictions. For example, the geo satellite computes statistics for each remote optical endpoint being monitored with its large-FoV telescope, based on continuous monitoring of the plurality of remote optical endpoints. As noted, the large FoV allows for simultaneous observation of the plurality remote optical endpoints on a continuous basis. Here, “continuous” may be understood as meaning “ongoing” and not necessarily withoutinterruptions, such as where the remote optical endpoints transmit optical beacons for observation at scheduled times or on a known periodicity.

[0074] In any case, the continuous monitoring provides a basis for deriving various statistics regarding the desirability of each remote optical endpoint for selection as a targeted endpoint. For example, the control system 16 operates with a prediction model derived from the availability statistics, which are derived from the monitored availability and thus obviate the need for ground-based atmospheric measurements. As a further advantage, such statistics provide invaluable insight to the SCS operator regarding ground station optimization and future network expansion.

[0075] In one or more embodiments, the control system 16 performs live node categorization, which means that the control system 16 maintains a live categorization of each remote optical endpoint included in the monitoring. Example categorization relies on performance metrics, observed beacon brightness and observed stability, along with short term and long term availability, etc.

[0076] In one or more embodiments, the control system 16 provides for autonomous link handover from a fading node or nodes to a brighter node or nodes, where “node” as used here is interchangeable with “remote optical endpoint.” Performing autonomous link handover eliminates the need for ground personal involvement in the link management. Such operations provide full autonomy of the optical link connectivity, including any required ground station switching, without relying on information from ground station atmospheric / weather monitoring systems or personnel.

[0077] In one or more embodiments, operations include safety measures, which comprise protective or security -related operations to identify valid nodes, which protects against false sources trying to interfere with the SCS. The solution can be secure against jamming and can identify incorrect or malicious nodes by correlating acquired image maps with a predefined references maps. For example, a reference map indicates the locations of valid remote optical endpoints with an image frame corresponding to the large-FoV used for remote-endpoint monitoring, with the control system 16 excluding from selection consideration any detected remote optical endpoint not correlated with a valid location. Thus, a malicious endpoint would need to be physically located within very close vicinity to a valid endpoint to escape such security measures. Even then, the SCS may use particular timing or scheduling for beacon-signal transmission or other orchestrations to guard against a malicious endpoint being mistaken as one valid for selection consideration.

[0078] In one or more embodiments, the control system 16 supports site assessments by identifying the ground locations with good availability. For example, the SCS operator deploys asimplified pilot site at a contemplated ground location and uses monitoring-based statistics generated by the control system 16 as a basis for deciding whether the site is attractive for deployment of a full OGS.

[0079] In broad example terms, an optical endpoint 10, such as may be implemented as a geo satellite 30, comprises a large-field optical telescope with a narrow optical bandwidth, a SWIR camera, and processing circuitry configured via software for image processing and storage. Processing operations include, for example, node validation algorithms, node availability statistics and prediction algorithms, and optical-communications-link handover algorithms. In cases where the geo satellite 30 supports more than one optical communications link simultaneously, such operations may be applied individually to each respective link.

[0080] The large-field optical telescope is co-aligned with the optical-link telescope, and it may share the same BSA. With reference back to Figure 1, the first and second optical telescopes 12 and 14 may share the BSA 18. The sensor utilized in the large-field optical telescope comprises, for example, a SWIR Indium Gallium Arsenide (InGaAs) focal plane array with narrow-band optical filtering that provides high background rejection. That is, the filtering leaves optical detection sensitive to the optical beacons transmitted by the remote optical endpoints being monitored and insensitive to background light sources. Such filtering thus allows for reliable acquisition and monitoring of the remote optical endpoints even in the presence of strong Earth background under different solar illumination, operating day and night. In an example implementation, the optical beacons are in the 1550 nm band.

[0081] In an example case where the remote optical endpoints selectable by a geo satellite as a targeted endpoint include multiple OGSs, the currently selected OGS may be referred to as the “active” OGS. The remaining OGSs may be referred to as “idle” OGSs, meaning they are idle at least with respect to the subject satellite. All such OGSs may illuminate the satellite at the same time, signaling their respective readiness to communicate. In some embodiments, the main telescope of each idle OGS will remain closed to protect the main mirror.

[0082] With respect to deciding which OGS to select as the active OGS, the control system 16 onboard the satellite 30 may aggregate multiple availability factors into several performance metrics used for selection decision-making. In one or more embodiments, the SCS network operator sets the thresholds to be used by the control system 16 with respect to making handover decisions. The control system 16 uses such thresholds to decide which OGS to select as the active OGS and / or to decide when to reselect to a new active OGS. Such switching can be entirely automated, removing the need for ground operator intervention and significantly decreasing the investment required for ground monitoring infrastructure and personnel. As noted, the control system 16 onboard the satellite 30 may choose the active OGS or it may provide theground network with the selection preferences (e.g., the availability and prediction metrics), for use by the ground network in choosing the active OGS.

[0083] Further, given that the availability factors for each OGS typically exhibit slow variability, optical measurements may be performed according to defined duty cycles. In an example approach, a plurality of OGSs operate their optical beacons on an alternating on / off basis, rather than continuously illuminating the satellite. This strategy reduces the power consumption of the OGSs, albeit at the expense of affecting the temporal resolution of the availability statistics generated by the control system 16 onboard the satellite. For geo links, a fifty-percent duty cycle may be sufficient for maintaining high quality selection preferences.

[0084] Notably, 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. Therefore, it is to be understood that the invention(s) is / are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

CLAIMSWhat is claimed is:

1. An optical endpoint configured for use in a satellite communications system, the optical endpoint comprising: a first optical telescope having a field of view (FoV) sized for simultaneous observation of a plurality of remote optical endpoints that are spatially separated and individually selectable as a targeted endpoint; a second optical telescope having a FoV smaller than the first optical telescope and configured for optical link communications with the targeted endpoint; and a control system configured to maintain selection preferences with respect to the plurality of remote optical endpoints, based on respective optical measurements made via the simultaneous observation, and control which remote optical endpoint is selected as the targeted endpoint in dependence on the selection preferences.

2. The optical endpoint according to claim 1, wherein the control system is configured to select the targeted endpoint based on ranking the plurality of remote optical endpoints in terms of the selection preferences and choosing a highest ranked one as the targeted endpoint.

3. The optical endpoint according to claim 1, wherein the control system is configured to maintain the corresponding selection preference for each remote optical endpoint based on a combined consideration of a current optical measurement and historical information, the historical information comprising at least one of: historical availability, historical serving performance, and historical variance of previous optical measurements made for the remote optical endpoint.

4. The optical endpoint according to any one of claims 1-3, wherein the respective optical measurements are respective brightness measurements.

5. The optical endpoint according to any one of claims 1-4, wherein the first optical telescope includes an optical filter configured to pass a certain optical wavelength while blocking other optical wavelengths, wherein each remote optical endpoint outputs a beacon beam at the certain optical wavelength, and wherein the respective optical measurements correspond to beacon-beam reception at the optical endpoint via the first optical telescope.

6. The optical endpoint according to any one of claims 1-5, wherein the first optical telescope includes or is associated with a shortwave infrared (SWIR) camera that is used for obtaining the respective optical measurements.

7. The optical endpoint according to claim 6, wherein the SWIR camera is sensitive to light within a range of 0.9 micrometers to 1.7 micrometers.

8. The optical endpoint according to any one of claims 1-7, wherein the respective optical measurements are based on receiving respective optical beacon beams from the plurality of remote optical endpoints via the first optical telescope.

9. The optical endpoint according to claim 8, wherein the plurality of remote optical endpoints transmits the respective optical beacon beams according to a defined timing, and wherein the control system is configured to obtain the respective optical measurements according to the defined timing.

10. The optical endpoint according to any one of claims 1-9, wherein, in comparison to the FoV of the first optical telescope being sized for simultaneous observation of the plurality of remote optical endpoints, the FoV of the second optical telescope is sized for observation of one remote optical endpoint at a time.

11. The optical endpoint according to any one of claims 1-10, wherein the control system is configured to change which remote optical endpoint is selected as the targeted endpoint by changing from a currently selected one to a newly selected one, responsive to detecting deteriorating optical link quality with respect to the currently selected one.

12. The optical endpoint according to claim 11, wherein the control system is configured to detect the deteriorating optical link quality with respect to a defined minimum quality threshold.

13. The optical endpoint according to any one of claims 1-12, wherein the optical endpoint comprises a satellite and the plurality of remote optical endpoints comprises any one of or any mix of: a plurality of geographically distributed optical ground stations; a plurality of satellites orbiting below the satellite; or a plurality of high-altitude platforms or aircraft.

14. The optical endpoint according to claim 13, wherein the satellite is configured for operation as a geostationary satellite.

15. The optical endpoint according to claim 14, wherein the plurality of other satellites comprises medium Earth orbit (MEO) or low Earth orbit (LEO) satellites.

16. The optical endpoint according to any one of claims 1-15, wherein the optical endpoint comprises a satellite configured for geostationary operation and wherein the plurality of remote optical endpoints comprises a plurality of geographically-distributed optical ground stations, and wherein the control system is configured to maintain the selection preferences based on a multiplicity of factors, the multiplicity of factors comprising the respective optical measurements and one or more of positioning of the sun relative to the satellite from the perspective of each optical ground station; atmospheric conditions associated with each optical ground station; operational statuses of the respective optical ground stations; traffic loading of the respective optical ground stations; variance of past optical measurements made for each optical ground station; and historical performance with respect to past selections of individual ones of the optical ground stations as the targeted endpoint.

17. The optical endpoint according to any one of claims 1-16, wherein the control system is configured for automatic reselection of the targeted endpoint from among the plurality of remote optical endpoints, based on the selection preferences, wherein each automatic reselection constitutes an automatic optical communications link handover, and wherein the control system is configured to communicate optical communications link handover information towards a ground network of the satellite communications system, for each automatic optical communications link handover.

18. The optical endpoint according to any one of claims 1-17, wherein the control system is configured to prevent selection of remote optical endpoints that are unaffiliated with the satellite communications system by limiting the plurality of remote optical endpoints to validated remote optical endpoints, and wherein the control system is configured to perform a validation process comprising:acquiring an image map depicting an observed constellation of putative remote optical endpoints, each putative remote optical endpoint being a remote source of optical illumination at a beacon-beam wavelength used by the satellite communications system and visible within the FoV of the first optical telescope; and identifying unaffiliated remoted optical endpoints by correlating the observed constellation of putative remote optical endpoints with a reference image map depicting a reference constellation of valid remote optical endpoints.

19. The optical endpoint according to claim 18, wherein the control system is configured to perform the correlating as a spatial correlation that compares locations of putative remote optical endpoints in the observed constellation with locations of valid remote optical endpoints in the reference constellation.

20. The optical endpoint according to any one of claims 1-19, wherein the optical endpoint is a satellite and, with respect to operation of the satellite in orbit, the control system is configured to provide optical-measurement feedback for siting optical ground stations, the optical- measurement feedback based on the first optical telescope observing a pilot optical beam transmitted from a prospective ground station site.

21. The optical endpoint according to claim 20, wherein the control system is configured to receive information from a ground network of the satellite communications system, indicating one or more prospective ground station sites within the FoV of the first optical telescope for which the satellite is to provide the optical-measurement feedback.

22. A method of operating an optical endpoint in a satellite communications system, the method comprising: obtaining respective optical measurements for a plurality of remote optical endpoints that are spatially separated and individually selectable as a targeted endpoint for optical communications via a second optical telescope of the optical endpoint, the respective optical measurements obtained by simultaneously observing the plurality of remote optical endpoints via a first optical telescope of the optical endpoint, the first optical telescope having a field of view (FoV) that is larger than a FoV of the second optical telescope and sized for simultaneous observation of the plurality of remote optical endpoints;maintaining selection preferences for the plurality of remote optical endpoints, based on the respective optical measurements; and controlling which remote optical endpoint is selected as the targeted endpoint, in dependence on the selection preferences.

23. The method according to claim 22, wherein controlling which remote optical endpoint is selected as the targeted endpoint comprises ranking the plurality of remote optical endpoints in terms of the selection preferences and choosing a highest ranked one as the targeted endpoint.

24. The method according to claim 22 or 23, wherein controlling which remote optical endpoint is selected as the targeted endpoint comprises changing from a currently selected remote optical endpoint to a newly selected optical endpoint in response to detecting deteriorating optical link quality with respect to the currently selected remote optical endpoint, and choosing the newly selected optical endpoint in dependence on ranking the corresponding selection preferences.

25. The method according to any one of claims 22-24, wherein maintaining the selection preferences comprises, for each remote optical endpoint, maintaining the corresponding selection preference as a combined consideration of a current optical measurement and historical information comprising at least one of: historical availability, historical serving performance, and historical variance of previous optical measurements made for the remote optical endpoint.

26. The method according to any one of claims 22-25, further comprising performing the respective optical measurements as respective brightness measurements.

27. The method according to claim 26, further comprising carrying out the optical communications with the targeted endpoint via the second optical telescope.

28. The method according to claim 27, further comprising carrying out a tracking procedure for maintaining fine optical alignment between the second optical telescope and the targeted endpoint, for ongoing optical communications.

29. The method according to any one of claims 22-28, wherein the plurality of remote optical endpoints is configured to transmit respective beacon beams according to a defined timing, andwherein the method includes performing the optical measurements according to the defined timing.

30. The method according to any one of claims 22-29, wherein the method further comprises performing automatic optical communications link handovers in association with changing which one among the plurality of remote optical endpoints is selected as the targeted endpoint.

31. The method according to claim 30, wherein the method further comprises transmitting optical communications link handover information towards a control node in a ground network of the satellite communications system.

32. The method according to any one of claims 22-30, wherein the remote optical endpoint is a geostationary satellite and wherein the plurality of remote optical endpoints comprises medium Earth orbit (MEO) satellites or low Earth orbit (LEO) satellites.

33. The method according to any one of claims 22-32, where the remote optical endpoint is a satellite and wherein the plurality of remote optical endpoints comprises a plurality of geographically distributed optical ground stations.

34. The method according to any one of claims 22-33, wherein the optical endpoint comprises a satellite configured for geostationary operation and wherein the plurality of remote optical endpoints comprises a plurality of geographically distributed optical ground stations, and wherein the method comprises maintaining the selection preferences based on a multiplicity of factors, the multiplicity of factors comprising the respective optical measurements and one or more of: positioning of the sun relative to the satellite from the perspective of each optical ground station; atmospheric conditions associated with each optical ground station; operational statuses of the respective optical ground stations; traffic loading of the respective optical ground stations; variance of past optical measurements made for each optical ground station; and historical performance with respect to past selections of individual ones of the optical ground stations as the targeted endpoint.

35. The method according to any one of claims 22-34, wherein the method further comprises preventing selection of remote optical endpoints that are unaffiliated with the satellite communications system by limiting the plurality of remote optical endpoints to validated remote optical endpoints, based on performing a validation process comprising: acquiring an image map depicting an observed constellation of putative remote optical endpoints, each putative remote optical endpoint being a remote source of optical illumination at a beacon-beam wavelength used by the satellite communications system and visible within the FoV of the first optical telescope; and identifying unaffiliated remote optical endpoints by correlating the observed constellation of putative remote optical endpoints with a reference image map depicting a reference constellation of valid remote optical endpoints.

36. The method according to claim 35, wherein the step of correlation comprises performing a spatial correlation that compares locations of putative remote optical endpoints in the observed constellation with locations of valid remote optical endpoints in the reference constellation.

37. The method according to any one of claims 22-36, wherein the optical endpoint is a satellite and, with respect to operation of the satellite in orbit, the method further comprises providing optical-measurement feedback for siting optical ground stations, the optical- measurement feedback based on the first optical telescope observing a pilot optical beam transmitted from a prospective ground station site.

38. The method according to claim 37, wherein the method further comprises receiving information from a ground network of the satellite communications system, indicating one or more prospective ground station sites within the FoV of the first optical telescope for which the satellite is to provide the optical-measurement feedback.

39. A satellite communications system comprising: a space segment comprising a satellite operating in a defined orbit; and a ground segment comprising a plurality of optical ground stations that are geographically distributed, each optical ground station operative to support an optical communications link with the satellite; wherein the satellite comprises: a first optical telescope having a field of view (FoV) sized for simultaneous observation of the plurality of optical ground stations;a second optical telescope having a FoV smaller than the FoV of the first optical telescope and configured to support the optical communications link with any one of the optical ground stations that is selected as a targeted endpoint for the satellite; and a control system that is configured to maintain selection preferences for the plurality of optical ground stations, based on observing the plurality of optical ground stations via the first optical telescope, and further configured to control which optical ground station is selected as the targeted endpoint, in dependence on the selection preferences.

40. The satellite communications system according to claim 39, wherein the satellite further includes a communications transceiver and wherein the control system is configured to communicate optical communications link handover information to the ground segment, responsive to changing which optical ground station is selected as the targeted endpoint.

41. The satellite communications system according to claim 39 or 40, wherein, for observing the plurality of optical ground stations, the control system is configured to obtain brightness measurements for the plurality of optical ground stations and is further configured to base the selection preferences on the brightness measurements.

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