Patent Publication Number: US-11652540-B2

Title: Load balancing for a satellite network

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 16/850,887, which was filed on Apr. 16, 2020; which is a continuation of U.S. patent application Ser. No. 16/293,941, which was filed on Mar. 6, 2019, now U.S. Pat. No. 10,631,206, issued on Apr. 21, 2020; which is a continuation of U.S. patent application Ser. No. 15/616,012, which was filed on Jun. 7, 2017, now U.S. Pat. No. 10,244,407, issued on Mar. 26, 2019; which claims the benefit of U.S. Provisional Patent Application No. 62/347,076 filed on Jun. 7, 2016, the disclosures of each of which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The disclosure relates generally to satellite networks, and more specifically to load balancing for satellite networks. 
     SUMMARY 
     According to one implementation of the disclosure, load balancing within a constellation of communications satellites is performed. Anticipated positions of satellites are determined. Each satellite is configured to provide multiple beams that define a coverage footprint for the satellite. Based on the anticipated positions of the satellites, it is determined that a first coverage footprint for a first satellite provides primary coverage of a high traffic region and portions of the first coverage footprint for the first satellite also will be covered by coverage footprints for other satellites, Based on these determinations, a beam assignments are defined in which a first subset of beams of the first satellite configured to provide coverage of a first portion of the first coverage footprint are inactive and a second subset of beams of the second satellite are active. The second subset of beams of the second satellite provide coverage within the first portion of the first coverage footprint. 
     According to another implementation of the disclosure, congestion within a constellation of low-Earth orbit communications satellites is mitigated. Each satellite has a phased array antenna configured to provide multiple beams that collectively define a coverage footprint for the satellite with individual ones of the beams configured to provide coverage of a respective portion of the coverage footprint. It is determined that a first coverage footprint for a first satellite within the constellation of satellites provides primary coverage of a high traffic region. As a consequence of having determined that the first coverage footprint for the first satellite covers a high traffic region, a first subset of beams of the first satellite configured to provide coverage of a first portion of the first coverage footprint is inactivated. While the first subset of beams of the first satellite are inactive, a second satellite within the constellation of satellites for which a second coverage footprint overlaps with the first coverage footprint is operated with a second subset of beams configured to provide coverage within the first portion of the first coverage footprint as active. 
     Other features of the present disclosure will be apparent in view of the following detailed description of the disclosure and the accompanying drawings. Implementations described herein, including the above-described implementations, may include a method or process, a system, or computer-readable program code embodied on computer-readable media. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure, reference now is made to the following description taken in connection with the accompanying drawings. 
         FIG.  1    is a high-level block diagram of a satellite system in accordance with a non-limiting implementation of the present disclosure. 
         FIGS.  2 A and  2 B  are flow charts of methods for out-of-band interference mitigation and load balancing, respectively, in satellite communication networks in accordance with non-limiting implementations of the present disclosure. 
         FIG.  3    is an example of beam laydown patterns for several satellites in a satellite network in accordance with a non-limiting implementation of the present disclosure. 
         FIG.  4    is an example time-lapse illustration of a satellite system in accordance with a non-limiting implementation of the present disclosure. 
         FIGS.  5 A and  5 B  are examples of beam laydown patterns for several satellites in a satellite system in accordance with a non-limiting implementation of the present disclosure. 
         FIG.  6    is a high-level block diagram of a satellite system in accordance with a non-limiting implementation of the present disclosure. 
         FIGS.  7 A and  7 B  are examples of beam laydown patterns for several satellites in a satellite system in accordance with a non-limiting implementation of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     A constellation of low-Earth orbit (“LEO”) (e.g., at an altitude between the Earth&#39;s surface and approximately 2,000 km or 1,200 miles) communications satellites may provide mobile and/or fixed communications services (e.g., voice and data communications services) across much of the Earth. In fact, in some implementations, a constellation of LEO communications satellites may be configured to provide communications services across the entire globe (or substantially the entire globe). For example, the Iridium® LEO satellite constellation provides global communications services. 
     In some implementations, constellations of LEO communications satellites include satellites arranged into orbital planes. For example, in one particular implementation, a constellation of LEO communications satellites includes 66 satellites arranged in 6 near-polar orbital planes of 11 satellites each such that the satellites&#39; orbits converge over the poles and are farthest apart near the equator. In some implementations, individual satellites within constellations of LEO communications satellites may be configured to establish wireless communications cross-links (e.g., radio frequency (“RF”), optical, etc. communications cross-links) with neighboring satellites, effectively forming a mesh network in space. In other implementations, individual satellites within a constellation may not be cross-linked. 
       FIG.  6    illustrates one example of a LEO constellation of cross-linked communications satellites  600 . In this particular implementation, the constellation of satellites  600  is arranged in 6 near-polar orbital planes  602 ( a )- 602 ( f ) of 11 satellites each. As illustrated in  FIG.  6   , individual satellites maintain communications crosslinks with neighboring satellites in the fore, aft, east, and west directions. As further illustrated in  FIG.  6   , the orbital planes  602 ( a )- 602 ( f ) converge near the Polar Regions and are farthest apart near the equator. The constellation of satellites  600  is configured so that the coverage footprints of the individual satellites collectively cover the entire Earth. Near the equator, where the orbital planes  602 ( a )- 602 ( f ) are spaced relatively far apart, there may be relatively little overlap of the coverage footprints provided by individual satellites. However, as you move north and south from the equator and the orbital planes  602 ( a )- 602 ( f ) begin to converge, there may be progressively more overlap of the coverage footprints provided by individual satellites. 
     Consider the illustrations in  FIGS.  5 A and  5 B  showing examples of beam coverage provided by one example of a LEO satellite constellation in a scenario where an individual satellite is not providing any coverage.  FIG.  5 A  illustrates the resulting coverage hole  502  near 0° latitude where individual satellites are spaced relatively far apart while  FIG.  5 B  illustrates the resulting coverage hole  504  near 500 latitude where individual satellites are spaced more closely together. As can be understood by comparing the coverage holes  502  and  504  illustrated in  FIGS.  5 A and  5 B , respectively, as satellites move north and/or south away from the equator, their coverage footprints increasingly overlap. Consequently, in the scenario where an individual satellite within the constellation is not providing any coverage, the resulting size of the coverage hole decreases as that satellite moves away from the equator. 
     In some cases, individual satellites within a LEO constellation of communications satellites may be limited as to the number of simultaneous active communication sessions they can service. For example, an individual satellite may be limited by the number of channels and/or carriers the satellite can accommodate, satellite-to-satellite cross-link bandwidth limitations, satellite processing capacity, and/or network bandwidth among other potential limitations. In fact, in certain situations, even if an individual satellite is not fully loaded in terms of the number of communications sessions it is serving with subscriber equipment at a given point, other limitations, including satellite-processing capacity, among others, may limit the number of communications sessions the satellite can service. 
     In certain implementations, an individual subscriber terminal may attempt to initiate a communications session or otherwise secure a communication channel by transmitting a signal or service acquisition request to a satellite, such as, for example, the satellite that is within range of the subscriber terminal from which the subscriber terminal receives the strongest signal. In response, the satellite may assign the communications session to one or more channels based on a variety of factors, including, for example, availability and service level agreements. In some cases, if the satellite has no channels available for allocation or does not have sufficient resources to service the communication session, the satellite may deny or otherwise block the acquisition request. In certain scenarios, the denial of an acquisition request may result the in issuance of a flow control event. Flow control events may be network management messages generated in response to a satellite network event, such as, for example, when a subscriber signal acquisition request is blocked due to lack of satellite resources. Flow control threshold events can be triggered in similar situations when certain resource availability thresholds within a satellite (or, for example, bandwidth limitations within an area of a satellite network) are exceeded. 
     In some cases, even though a LEO constellation of communications satellites may provide coverage of the entire globe or of very large regions of the globe, a small number of regions nevertheless may be responsible for a majority or a substantial amount of the overall network traffic. In such cases, network flow control events may be more likely to be triggered by satellites covering these particular heavy traffic regions than satellites covering neighboring regions where resource demand is lower. In one particular example, Central and Western Europe may represent a region where demand for satellite communications resources is quite high due to a large number of active subscribers, and the coverage footprint of a single satellite may be configured to substantially cover the entire region during a given period of time. Meanwhile, neighboring regions, such as, for example, including portions of the Atlantic Ocean and Eastern Europe and Russia to the west and east, respectively, may represent regions where resource demand is lower. 
     For example, referring to  FIG.  7 A , the coverage footprint  700  of a first satellite at a particular point of time may provide primary coverage for much of the high traffic region of Central and Western Europe, while the coverage footprint  704  of a second, neighboring satellite provides primary coverage for a region of the Atlantic Ocean and the coverage footprint  706  of a third, neighboring satellite provides primary coverage for a region including much of Eastern Europe and a portion of Russia. If the first satellite is used to service all of the demand in the high traffic region of central a Western Europe for which its coverage footprint  702  provides primary coverage, in some situations, the first satellite may become overloaded. Therefore, as described in greater detail below, in some implementations, neighboring satellites with coverage footprints that overlap coverage footprint  702 , such as for example, coverage footprint  704  of the second satellite and coverage footprint  706  of the third satellite, may be used to service some of the load from the high traffic region of Central and Western Europe. 
     In some implementations, individual communications satellites have phased array antennas that provide multiple beams that collectively define the coverage footprints of their respective satellites. In one particular implementation, each individual communications satellite may have a phased array antenna configured to provide 48 beams, which collectively define the coverage footprint for the satellite. For example, referring to  FIG.  7 A , coverage footprint  702  is composed of 18 interior, circular beams and 30 finger-shaped beams extending outward from the interior. Furthermore, each beam may provide a number of different frequency sub-bands and/or one or more different multiplexing schemes may be employed to enable the beam to service multiple different communications channels concurrently. For example, in one particular implementation, each beam may provide 24 frequency sub-bands, each of which may be capable of servicing 10 communications sessions concurrently, such that each individual beam is capable of servicing  240  concurrent communications sessions. In some implementations, the beam pattern for an individual satellite may be fixed. Alternatively, in other implementations, individual satellites may be configured to provide steerable or otherwise configurable beams and/or beam patterns. 
     Under certain circumstances, the phased array antennas and/or other subsystems of the communications satellites may generate out-of-band interference. For example, communications satellites may generate a significant amount of noise and/or other spurious transmissions in adjacent, neighboring, and/or nearby frequency bands. As one particular example, some L-band communications satellites systems have been cited as causing out-of-band interference with observations being attempted by radio astronomers. In some implementations, each beam provided by the antenna of an individual satellite is powered by at least one high-power beam driver, for example, including one or more amplifiers. Such beam drivers and/or amplifiers may generate out-of-band transmissions that potentially may cause interference that may be problematic for applications in other frequency bands. Moreover, intermodulation products generated by phased array antennas driving multiple beams also pose the potential to create out-of-band interference. Such intermodulation products may stem from front-end amplifiers entering non-linear operation regions, for example, resulting in composite intermodulation products at the 3rd, 5th, 7th, and 9th harmonics of carrier signal frequencies. As the number of simultaneously active carriers is increased, the out-of-band interference effects, for example, attributable to the intermodulation products may increase dramatically. 
     The teachings of the present disclosure describe systems and methods for balancing loads in satellite networks and systems and methods for mitigating out-of-band interference in satellite networks. As described in greater detail below, in some specific implementations, decreasing the number of active satellite beams on certain satellite vehicles (e.g., satellites located over particular regions) may reduce or otherwise mitigate out-of-band interference, which may be particularly useful when the satellite vehicles are located over regions susceptible to out-of-band interference, such as, for example, radio astronomy observation centers. Additionally or alternatively, and as also described in greater detail below, neighboring satellites may be used to balance loads such that loads are moved away from satellites having coverage footprints that provide primary coverage of high traffic regions. In some cases, sharing loads with neighboring satellites in this manner may decrease load acquisition blocking and other service request denials, improve load servicing, decrease beam driver noise from active beams, and decrease composite intermodulation product interference from simultaneous carrier transmission on and across active beams. 
     Intuition suggests that, in order to provide adequate coverage of a high traffic area, as many beams as possible should be activated to service the high traffic area. However, as described herein, in certain implementations, loads are shifted from one satellite that provides primary coverage to a high traffic region to a neighboring satellite by deactivating one or more beams of the satellite that provides primary coverage to the high traffic region. Among other things, loads can refer to, for example, subscriber terminal devices such as satellite phones, satellite hotspot devices, machine-to-machine or “Internet of Things” sensors and corresponding communications devices, other data consumers such as network subscribers, or any other device capable of initiating communication sessions with a satellite network. 
     In certain implementations, each satellite within a LEO constellation of satellites includes a controller that manages the activation and deactivation of beams provided by the satellite&#39;s antenna system. For example, in some implementations, the controller may be configured to manage the activation and deactivation of beams by switching on and off one or more corresponding beam drivers and/or amplifiers that power individual beams. The controller can activate or de-activate particular beams responsive to instructions, such as instructions received from a terrestrial Earth station or instructions in a beam laydown table loaded into a memory of the satellite that is accessible by the controller. In some implementations, the activation of beams of each satellite is dependent upon one or more of the physical location of the satellite along its orbit (e.g., the latitude of the satellite) and/or a time. For example, a beam laydown table for a particular satellite may specify activation instructions for each beam provided by the satellite for each of multiple predefined increments of time, for instance, in four-second time intervals. Additionally or alternatively, in some implementations, beam activation can be controlled dynamically during any period of time, including on a continuous ongoing basis, such as, for example, in response to real-time updates from a terrestrial Earth station or by logic on board an individual satellite. 
     In particular implementations, a load balancing system may be operated in conjunction with an out-of-band interference mitigation system. For example, the techniques described in the present disclosure, in addition to mitigating out-of-band interference, also may alleviate overloading (e.g., of individual satellite capacity and/or network or communication cross-link bandwidth). In some implementations, the load balancing system can process real-time feedback from satellites regarding resource loads. In some such implementations, this information can be used to formulate a strategy for both out-of-band interference mitigation and load balancing. 
     In certain implementations, a particular region is targeted for out-of-band interference mitigation. For example, certain applications susceptible to out-of-band interference (e.g., radio astronomy) may be most prevalent in regions between ±350-550 latitude. In this example, each region between ±350 and 550 latitude (i.e., the region between +350 and +550 latitude and the region between −35° and −55° latitude) is considered within the target region. In particular implementations, out-of-band interference, resulting, for example, from beam driver noise and/or composite intermodulation interference effects may be mitigated by deactivating one or more beams from one or more satellites that provide coverage within or nearby the target region. 
     In certain implementations, a satellite that provides coverage of the target region (e.g., a satellite that provides primary coverage of the target region) receives instructions to de-activate particular beams, for example, upon determination that the satellite is responsible for covering the target region. In such implementations, terminals located in the target region that otherwise may be serviced by the de-activated beams may instead establish communications sessions via one or more beams provided by an alternative neighboring satellite that provides an overlapping coverage footprint. In particular implementations, a communications session or signal “hand-off” procedure is implemented prior to de-activating any beams. In such implementations, the hand-off procedure may involve transitioning an active communications session from one satellite to another and/or from one beam to another. In this case, the hand-off procedure transfers management and servicing of the communications session to a neighboring satellite and/or an alternative beam. The neighboring satellite and/or beam may have sufficient, or even a surplus of additional resources, available to service the transferred session. 
     In certain implementations, beams provided by the antenna systems of satellites may be steerable such that the beam patterns of the satellites can be changed to produce virtually any arbitrary laydown pattern. In alternative implementations, beam patterns may be fixed. Consider an example beam laydown pattern as shown in  FIG.  3   . In certain implementations, beams are merely activated or de-activated (i.e., turned on and/or off), and beam shape is not modified. In certain alternative implementations, beam shapes may be modified to extend beam coverage from neighboring low load satellites to high load regions to assist in transferring loads from high load satellites. For example, as illustrated in  FIG.  3   , satellite  310   a  provides beams  55   a - h  having configurable patterns, satellite  310   b  provides beams  61   a - j  having configurable patterns, and satellite  310   c  provides beams  100   a - 100   f  having configurable patterns. 
     Consider also the time lapsed illustration of satellite beam coverage for an example satellite  420  in low earth orbit as shown in  FIG.  4   . Dotted line  410  represents the satellite&#39;s  410  near-polar orbit, while dotted line  412  represents the equator. When the satellite  420  is near the equator (i.e., off the coast of South America as illustrated in  FIG.  4   ) (represented by reference numeral  420   c ), all or nearly all of the satellite&#39;s beams are turned on. In fact, the large extent of the satellite&#39;s  420   c  coverage footprint  422   c  is easily seen in the illustration. By contrast, consider the same satellite&#39;s  420  coverage footprint  422   b  along its orbit above the East coast of North America (represented by reference numeral  420   b ), which, for the purposes of this example, may be considered a high load region (e.g., due to the large number of active subscriber terminals expected in the region). As illustrated in  FIG.  4   , the coverage footprint  422   b  of the satellite  420   b  at this stage is much smaller in extent, as one or more of the beams of the satellite  420   b  have been deactivated, and coverage of the area is shared with one or more beams from one or more other neighboring satellites that can “steal” loads that otherwise might be serviced by the satellite  420   b . The load balancing illustrated in this particular example is accomplished by switching off active beams from the satellite  420  when positioned over regions associated with high traffic or other loading. Beams from other satellites then are used to help service portions of the high load region. 
     With reference to  FIG.  1   , a system  100  for load balancing and/or out-of-band interference mitigation is illustrated in the context of a satellite communications network in a non-limiting implementation of the present disclosure. System  100  includes satellite network  110  (e.g., a LEO constellation of communications satellites), which also includes individual satellites  120  and  130 . Each satellite includes a controller  124  configured to, among other functions, control phased array antenna  122  to control characteristics of the one or more beams provided by phased array antenna  122 . Satellite network  110  transmits and receives messages to/from Earth station  160  through terminal  162 , which, among other features, functions as an interface for routing communications between satellite network  110  and external network  170 . Earth station  160  includes server  150  that includes memory  152 , processor(s)  156   a , hard disk  156   b , interface  156   c , and input/output device  156   d . Processor(s)  156   a  loads instructions into memory  152  and executes instructions that have been loaded into memory  152 , such as, for example, beam planning process  154 . 
     As illustrated in  FIG.  1   , satellite  130  and neighboring satellite  120  provide overlapping coverage regions. Satellite  130  provides coverage by driving individual beams (e.g., beam  134 ) that collectively define the coverage footprint of satellite  130 , for example, as illustrated in  FIG.  1   , between dotted lines  132   a  and  132   b . Meanwhile, satellite  120  provides coverage by driving individual beams (e.g., beam  144 ) that collectively define the coverage footprint of satellite  120 , for example, as illustrated in  FIG.  1   , between lines  122   a  and  122   b . Beam  144  from satellite  120  and beam  134  from satellite  130  provide respective beam coverage areas  126  and  136  respectively. Beam coverage areas  126  and  136  overlap to produce overlapping coverage region  140 . 
     In certain implementations, a subscriber terminal located in overlapping coverage region  140  may request a communications session from satellite  130 . For example, a user of the terminal may initiate a telephony voice call or a data request using a satellite phone. The subscriber terminal may be configured to detect coverage provided by multiple satellites and, when coverage from multiple satellites is detected, to employ one or more methods to determine from which satellite to request a communications session. For example, in certain implementations, the terminal may determine the relative strength of each of beams  144  and  134 . As illustrated in  FIG.  1   , since satellite  130  is located more directly over the terminal and is closer to overlapping region  140 , beam  134  may be generally stronger than beam  144 . Accordingly, the terminal may be configured to initiate the communications session via satellite  130 . If so, satellite  130  will allocate bandwidth and other resources for use in the communications session with the terminal. For example, satellite  130  may allocate a frequency sub-band, carrier, and/or specified time slot within beam  134  for the communications session and initiate the communications session with the terminal. However, in the event that satellite  130  is overloaded (e.g., due to satellite processing capacity limitations and/or network or wireless communications cross-link bandwidth limitations) or satellite  130  otherwise is unable to allocate enough resources to service the communications session (e.g., due to other contemporaneous resource demands, such as by other terminals within service area  132 ), the terminal may repeat its request to initiate a communication session with satellite  130 , which may be denied repeatedly due to resource constraints. 
     As illustrated in  FIG.  1   , a special interest region  182  is shown with dotted lines. Special interest region  182  may be a region that has been identified as being susceptible to out-of-band interference and/or a high traffic region. For example, other applications that potentially may be impacted negatively by out-of-band interference may be located within special interest region  182 , such as, for example, radio astronomy observatory  190 . Additionally or alternatively, historical and/or real time utilization data may be used to determine that special interest region  182  is a high traffic region. In some implementations, a region like special interest region  182  may be defined based on a latitude range. However, any of a variety of different characteristics could be used to define a region like special interest region  182 . For example, a special interest region may be defined as a square or a circle having a specified area. As described herein, beam planning process  154  may make beam assignment determinations for an individual satellite based on whether the satellite provides coverage (e.g., primary coverage) of or within a special interest region like special interest region  182 . 
     In certain implementations, beam planning process  154  determines position information for each satellite in network  110 , for example, based on predetermined orbits for the satellites and/or based on real-time position and trajectory information. Additionally or alternatively, beam planning process  154  determines when each satellite in network  110  is positioned to provide coverage (e.g., primary coverage) of a high traffic region and/or a region susceptible to out-of-band interference. For example, beam planning process  154  may utilize satellite location information to determine when beams provided by an individual satellite may cause out-of-band interference that may negatively impact other applications, such as, for example, radio astronomy observatory  190 . In such implementations, beam planning process  154  also determines beam laydown assignments (e.g., in some cases in the form of beam laydown tables or beam operating instructions) for individual satellites, for example, based on anticipated satellite position and/or whether beam planning process  154  determines the satellites are positioned to provide coverage of a high traffic region and/or a region susceptible to out-of-band interference. In some implementations, beam planning process  154  may make the above described determinations based on historical satellite network  110  data. Additionally or alternatively, beam planning process  154  may make such determinations based on real-time observations and/or predictions. 
     In some implementations, beam planning process  154  may determine beam assignments (e.g., active or inactive) for an individual satellite based on satellite resource utilization levels. For example, thresholds regarding resource utilization levels may direct that utilization of the satellite remain below a predetermined threshold. If the threshold is exceeded, or a threat to exceed the threshold is detected, beam planning process  154  may modify beam assignments, for example, to offload certain loads from the satellite to neighboring satellites. For example, if a first satellite is expected to be servicing a high load region during a particular period of time and is not capable of keeping its resource utilization below, for example, 80% of its maximum capacity, the first satellite may be flagged for load redistribution to neighboring satellites. If so, beam coverage areas of the first satellite may be reviewed to identify beam coverage areas expected to service regions associated with high loads. Those coverage areas then may be crosschecked against beam coverage areas from neighboring satellites to determine if one or more neighboring satellite beams overlap with and can service the regions associated with the high loads. 
     In particular implementations, an instruction to turn off or de-activate a beam of an individual satellite (e.g., beam  134  on satellite  130 ) is generated and stored in a beam assignment table. For example, beam planning process  154  may predict the position of satellite  130  with respect to region  182  during a particular period of time and generate an instruction to turn off beam  134  while satellite  130  is providing coverage of region  182 . Similarly, beam planning process  154  may generate instructions to turn on or activate one or more beams on one or more neighboring satellites that, for example, provide overlapping coverage with beam  134 , such as, for example, beam  144  of satellite  120 . In certain implementations, two or more beams from two or more neighboring satellites may be used to cover the overlapping region. For example, when beam  134  is deactivated, satellite  130  may not provide any coverage within region  136 . Consequently, additional beams from satellite  120 , such as, for example, beam  144 , and/or other network satellites may be used to service region  136  while beam  134  remains deactivated. 
     In certain implementations, beam planning process  154  generates beam assignments for individual satellites for each of multiple different intervals of time for an extended period of time into the future. For example, in some implementations, beam planning process  154  generates a beam assignment for each satellite for each 4-second interval for an extended period of time into the future (e.g., 36 hours). 
     Additionally or alternatively, in particular implementations, beam planning process  154  may generate a real-time or near real-time beam assignment that is transmitted to satellites  110  on a real-time or near real-time basis. For example, in such implementations, beam planning process  154  may use real-time satellite resource utilization information and/or anticipated service demand (e.g., load information) to prepare the real-time or near real-time beam assignments. 
     In particular implementations, beam planning process  154  transmits beam assignments (e.g., in the form of beam laydown tables, beam assignment tables, instructions, or the like) to each satellite  110  and/or receives information from (or relevant to) individual satellites  110  (e.g., like satellite resource utilization information, service demand information, and loading information) via Earth station  160  and ground terminal  162 . In such implementations, after an individual satellite, such as, for example, satellite  120  or satellite  130  receives a beam assignment from beam planning process  154 , the individual satellite may store the beam assignment in memory  126 , such as, for example, the beam laydown table  128  stored in memory  126 . Controller  124  then may access the beam assignment from memory  126  and control antenna array  122  in accordance with the beam assignment. 
     With reference to  FIG.  2 A , a method  200  for out-of-band interference mitigation for a satellite communications network is shown in accordance with a non-limiting implementation of the present disclosure. In some implementations, the method  200  illustrated in  FIG.  2 A  may be performed by the processor(s)  156   a  of  FIG.  1    executing beam planning process  154  stored in memory  152 . 
     As illustrated in  FIG.  2 A , at step  210 , anticipated positions of individual satellites within a satellite communications network (e.g., a LEO constellation of communications satellites) are determined. In some implementations, the anticipated positions of the individual satellites may be determined based on planned orbits for the satellites. Additionally or alternatively, in some implementations, the anticipated positions of the individual satellites may be determined based on satellite ephemeris data and/or real-time or near real-time data received from one or more of the individual satellites. 
     At step  215 , a determination is made, based on the anticipated positions of the satellites, that, during a defined period of time, portions of a coverage footprint for a first satellite also will be covered by one or more coverage footprints of other satellites of the satellite communications network. For example, as illustrated in  FIG.  7 A , a determination may be made that portions of the coverage footprint  702  of a first satellite also will be covered by the coverage footprints of other satellites (e.g., coverage footprints  704  and  706  of a second and third satellite, respectively) during a defined time period. In certain implementations, the coverage footprint of an individual satellite may be considered to be the footprint that would be covered (or the footprint within which a minimum service level and/or signal strength is available) if all of the beams provided by the satellite were active concurrently. In other implementations, the coverage footprint of an individual satellite may be defined according to one or more additional or alternative characteristics of the satellite&#39;s coverage. For example, with reference to  FIG.  7 A , the coverage footprint  702  of the first satellite may be considered to be the footprint covered when all 48 beams of the first satellite are active as illustrated for coverage footprint  702  in  FIG.  7 A . Alternatively, the coverage footprint  702  may be considered to be the circle that best fits the coverage footprint shape  702  when all 48 beams of the first satellite are active. In certain implementations, the individual beams of a satellite may be remain in fixed positions relative to the satellite. In such implementations, the coverage footprint for the satellite and/or the footprints covered by individual beams provided by the satellite may be determined based on the fixed positioning of the individual beams relative to the position of the satellite and the anticipated position of the satellite. In alternative implementations, individual beams may be configurable and/or steerable such that the coverage footprint of a satellite or individual beams provided by the satellite may be modified dynamically. 
     Based on having determined that portions of the coverage footprint for the first satellite also will be covered by coverage footprints for the other satellites during the defined time period, at step  220 , a beam assignment for the first satellite is defined for the defined time period in which a subset of the beams of the first satellite are inactive, and, at step  225 , a beam assignment for a second satellite is defined for the defined time period in which a subset of the beams of the second satellite are active. For example, referring to  FIG.  7 B , based on having determined that portions of the coverage footprint  702  of the first satellite also will be covered by the coverage footprints of other satellites, including, for example, the coverage footprints  704  and  706  of a second and third satellite, respectively, a beam assignment for the first satellite may be defined in which the 30 finger-shaped beams extending out from the center of coverage footprint  702  are deactivated while the 18 inner beams remain activated. Meanwhile, all 48 beams of the second satellite may be activated. In this manner, individual ones of some of the finger-shaped beams extending out from the center of coverage footprint  704  may provide coverage for a portion of the coverage footprint  702  that is not covered by the first satellite following the deactivation of the 30 finger-shaped beams extending out from the center of coverage footprint  702 . Similarly, as also illustrated in  FIG.  7 B , all 48 beams of the third satellite also may be activated. In this manner, individual ones of some of the finger-shaped beams extending out from the center of coverage footprint  706  may provide coverage for a portion of the coverage footprint  702  that is not covered by the first satellite following the deactivation of the 30 finger-shaped beams extending out from the center of coverage footprint  702 . Consequently, a subscriber terminal located within coverage footprint  702  that otherwise may be serviced by the first satellite if the 30 finger-shaped beams extending from the center of coverage footprint were not deactivated may be serviced instead by the second or third satellite. Deactivating some of the beams of the first satellite in this manner may result in reducing the out-of-band interference caused by the first satellite within coverage footprint  702 . 
     It will be understood that  FIGS.  7 A and  7 B  are discussed in connection with the method  200  of  FIG.  2 A  for illustration purposes only and are not intended to limit the scope of the present disclosure. For example,  FIGS.  7 A and  7 B  do not illustrate coverage being provided for all of coverage footprint  702  that is not covered by the first satellite following the deactivation of the 30 finger-shaped beams extending out from the center of coverage footprint  702 . Nevertheless, in some particular implementations, beam assignments for one or more additional satellites may be defined such that beams from one or more other such satellites provide coverage for the remaining portion of the coverage footprint  702  that is not covered by the first satellite following the deactivation of the 30 finger-shaped beams extending out from the center of coverage footprint  702 . Furthermore,  FIG.  7 B  illustrates all 48 beams of the second satellite and all 48 beams of the third satellite as being activated. However, in some particular implementations, the beam assignments defined for the second and third satellites may call for one or more beams of the second satellite being deactivated and one or more beams of the third satellite being deactivated such that one or more portions of coverage footprint  704  are not covered by the second satellite and/or one or more portions of coverage footprint  706  are not covered by the third satellite. In this manner, out-of-band interference generated by the second and/or third satellite also may be reduced. Moreover, while  FIG.  7 B  illustrates the beam assignment for the first satellite calling for a relatively simple pattern where all 30 of the finger-shaped beams extending from the center of coverage footprint  702  being deactivated and all 18 of the inner beams of coverage footprint  702  remaining active, a beam assignment could call for any possible variation or permutation of individual beams being deactivated and activated. 
     In certain implementations, particularly for LEO constellations of communications satellites in near-polar orbits, beam assignments for an individual satellite in which one or more of the beams of the satellite are deactivated may be sought following a determination that the satellite is anticipated to reach a position in its orbit that exceeds a predefined latitude (e.g., ±300 or 350 latitude). In such implementations, the system may attempt to define beam assignments during a defined period of time for all satellites in the system that exceed the predefined latitude in a manner that seeks to provide full (or nearly full) coverage for the regions above the defined latitude while minimizing the total number of active beams system wide. In some systems, when a particular region is covered by two or more beams subject to deactivation, the heuristics involved in defining the beam assignments for the individual satellites may call for selecting the beam to cover the particular region that is provided by the satellite at the highest latitude. Additionally or alternatively, in certain implementations, beam assignments for an individual satellite in which one or more of the beams of the satellite are deactivated may be sought following a determination that the satellite is anticipated to reach a position in its orbit from which the satellite is expected to provide primary coverage for a region determined to be sensitive to out-of-band interference. 
     Additionally or alternatively, in certain implementations, the beam assignment for the first satellite may be determined based on a predicted or actual amount of out-of-band interference generated by the first satellite according to the number of beams of the first satellite activated during the defined time period. For example, in such implementations, if the predicted or actual out-of-band interference exceeds a predefined threshold value, the beam assignment for the first satellite may include instructions to shut off or de-activate particular beams of the first satellite. 
     In certain implementations, the beam assignments defined for the first and second satellites at steps  220  and  225  may be recorded or otherwise stored in the form of beam laydown tables for the first and second satellites. 
     At step  230 , the beam assignments for the first and second satellites are transmitted to the first and second satellites, respectively. In some implementations, the beam assignments may be instructions that each respective satellite acts on. Furthermore, in certain implementations, beam assignments may be controlled by the transmission of the instructions from a central control unit, such as, for example, a terrestrial management system located at or in communication with an Earth station. In such implementations, a beam controller on each satellite controls the beams provided by the satellite responsive to instructions received from the Earth station. In alternative implementations, process  200  may be performed by one or more processors or other electronic logic units on board one or more of the satellites of the satellite network. In such implementations, beam assignments may be communicated to other satellites via wireless communications cross-links. Such implementations may be useful for real-time or near real-time distribution of beam assignment instructions, for example, to cut down on latency. In particular implementations, a series of beam assignments for some future time span is transmitted. In such implementations, the beam assignments may be stored in memory at each satellite and used until a new or updated set of assignments or instructions is received at some future time. In certain implementations, the beam assignments are pre-loaded before satellite launch and are updated periodically when new beam assignments are defined. 
     With reference to  FIG.  2 B , a method  250  for load balancing for a satellite communications network is shown in accordance with a non-limiting implementation of the present disclosure. In some implementations, the method  250  illustrated in  FIG.  2 B  may be performed by the processor(s)  156   a  of  FIG.  1    executing beam planning process  154  stored in memory  152 . 
     As illustrated in  FIG.  2 B , at step  255 , anticipated positions of individual satellites within a satellite communications network (e.g., a LEO constellation of communications satellites) are determined. In some implementations, the anticipated positions of the individual satellites may be determined based on planned orbits for the satellites. Additionally or alternatively, in some implementations, the anticipated positions of the individual satellites may be determined based on satellite ephemeris data and/or real-time or near real-time data received from one or more of the individual satellites. 
     At step  260 , a determination is made, based on the anticipated positions of the satellites, that, during a defined period of time, a coverage footprint for a first satellite provides primary coverage of a high traffic region during a defined time period. With reference to  FIG.  7 A , for example, a determination may be made that the coverage footprint  702  for a first satellite provides primary coverage for a high traffic region in Western and Central Europe. 
     The determination that a satellite provides primary coverage for any particular region during a defined period of time, including, for example, a high traffic region, may be based on any of a number of different criteria. For example, in some implementations, it may be determined that a satellite provides primary coverage for a particular region during a defined period of time if, during the defined period of time, the satellite is the closest satellite among the satellites of the satellite network to the particular region. Additionally or alternatively, in some implementations, it may be determined that a satellite provides primary coverage for a particular region during a defined period of time if, during the defined period of time, the coverage footprint of the satellite covers the greatest percentage of the area of the particular region out of all of the satellites of the satellite network. Furthermore, in some implementations, it may be determined that a satellite provides primary coverage for a particular region if, on average, the beams provided by the satellite that provide coverage for the particular region during the defined time period are the highest strength and/or have the highest gain of all of the beams provided by satellites of the satellite network that provide coverage for the particular region during the defined time period. In some implementations, one or more high traffic regions may be predefined, for example, based on historical communications traffic volume through the satellite network originating from and/or terminating in the particular region. In such implementations, the predefined high traffic regions may remain defined as high traffic regions until the system is otherwise updated. Additionally or alternatively, in some implementations, one or more high traffic regions may be defined in real-time or near real-time, for example, based on current, or a recent sliding window of, communications traffic volume through the satellite network originating from and/or terminating in the particular region. 
     In some implementations, when the coverage footprint for an individual satellite is determined to provide primary coverage of a high traffic region, a process to reduce the number of beams provided by the satellite while the coverage footprint for the satellite provides primary coverage of the high traffic region may be triggered automatically. 
     At step  265 , a determination is made, based on the anticipated positions of the satellites, that, during the defined period of time, portions of the coverage footprint for the first satellite (and/or the high traffic region) also will be covered by one or more coverage footprints of other satellites of the satellite communications network. For example, as illustrated in  FIG.  7 A , a determination may be made that portions of the coverage footprint  702  of the first satellite also will be covered by the coverage footprints of other satellites (e.g., coverage footprints  704  and  706  of a second and third satellite, respectively) during the defined time period. 
     Based on having determined that the coverage footprint for the first satellite provides primary coverage of the high traffic region during the defined time period and that portions of the coverage footprint for the first satellite also will be covered by coverage footprints for the other satellites during the defined time period, at step  270 , a beam assignment for the first satellite is defined for the defined time period in which a subset of the beams of the first satellite are inactive, and, at step  275 , a beam assignment for a second satellite is defined for the defined time period in which a subset of the beams of the second satellite are active. For example, referring to  FIG.  7 B , based on having determined that the coverage footprint  702  of the first satellite provides primary coverage of the high traffic region (e.g., Western and Central Europe) and that portions of the coverage footprint  702  of the first satellite also will be covered by the coverage footprints of other satellites, including, for example, the coverage footprints  704  and  706  of a second and third satellite, respectively, a beam assignment for the first satellite may be defined in which the 30 finger-shaped beams extending out from the center of coverage footprint  702  are deactivated while the 18 inner beams remain activated. Meanwhile, all 48 beams of the second satellite may be activated. In this manner, individual ones of some of the finger-shaped beams extending out from the center of coverage footprint  704  may provide coverage for a portion of the coverage footprint  702  that is not covered by the first satellite following the deactivation of the 30 finger-shaped beams extending out from the center of coverage footprint  702 . Similarly, as also illustrated in  FIG.  7 B , all 48 beams of the third satellite also may be activated. In this manner, individual ones of some of the finger-shaped beams extending out from the center of coverage footprint  706  may provide coverage for a portion of the coverage footprint  702  that is not covered by the first satellite following the deactivation of the 30 finger-shaped beams extending out from the center of coverage footprint  702 . Consequently, a subscriber terminal located within coverage footprint  702  that otherwise may be serviced by the first satellite if the 30 finger-shaped beams extending from the center of coverage footprint were not deactivated may be serviced instead by the second satellite or the third satellite. Deactivating some of the beams of the first satellite in this manner may result in reducing the load on the first satellite and/or balancing the load on the satellite network attributable to the high traffic region across multiple satellites during the defined time period instead of servicing it entirely (or primarily) with the first satellite. 
     It will be understood that  FIGS.  7 A and  7 B  are discussed in connection with  FIG.  2 B  for illustration purposes only and are not intended to limit the scope of the present disclosure. For example,  FIGS.  7 A and  7 B  do not illustrate coverage being provided for all of coverage footprint  702  that is not covered by the first satellite following the deactivation of the 30 finger-shaped beams extending out from the center of coverage footprint  702 . Nevertheless, in some particular implementations, beam assignments for one or more additional satellites may be defined such that beams from one or more other such satellites provide coverage for the remaining portion of the coverage footprint  702  that is not covered by the first satellite following the deactivation of the 30 finger-shaped beams extending out from the center of coverage footprint  702 . Furthermore,  FIG.  7 B  illustrates all 48 beams of the second satellite and all 48 beams of the third satellite as being activated. However, in some particular implementations, the beam assignments defined for the second and third satellites may call for one or more beams of the second satellite being deactivated and one or more beams of the third satellite being deactivated such that one or more portions of coverage footprint  704  are not covered by the second satellite and/or one or more portions of coverage footprint  706  are not covered by the third satellite. In this manner, loads within one or more regions under (or partially covered by) these coverage footprints similarly may be balanced across multiple satellites. Moreover, while  FIG.  7 B  illustrates the beam assignment for the first satellite calling for a relatively simple pattern where all 30 of the finger-shaped beams extending from the center of coverage footprint  702  are deactivated and all 18 of the inner beams of coverage footprint  702  remain active, a beam assignment could call for any possible variation or permutation of individual beams being deactivated and activated. 
     In certain implementations, the beam assignments defined for the first and second satellites at steps  270  and  275  may be recorded or otherwise stored in the form of beam laydown tables for the first and second satellites. 
     At step  280 , the beam assignments for the first and second satellites are transmitted to the first and second satellites, respectively. In some implementations, the beam assignments may be instructions that each respective satellite acts on. Furthermore, in certain implementations, beam assignments may be controlled by the transmission of the instructions from a central control unit, such as, for example, a terrestrial management system located at or in communication with an Earth station. In such implementations, a beam controller on each satellite controls the beams provided by the satellite responsive to instructions received from the Earth station. In alternative implementations, process  250  may be performed by one or more processors or other electronic logic units on board one or more of the satellites of the satellite network. In such implementations, beam assignments may be communicated to other satellites via wireless communications cross-links. Such implementations may be useful for real-time or near real-time distribution of beam assignment instructions, for example, to cut down on latency. In particular implementations, a series of beam assignments for some future time span is transmitted. In such implementations, the beam assignments may be stored in memory at each satellite and used until a new or updated set of assignments or instructions is received at some future time. In certain implementations, the beam assignments are pre-loaded before satellite launch and are updated periodically when new beam assignments are defined. 
     Aspects of the present disclosure may be implemented entirely in hardware, entirely in software (including firmware, resident software, micro-code, etc.) or in combinations of software and hardware that may all generally be referred to herein as a “circuit,” “module,” “component,” or “system.” Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer-readable media having computer-readable program code embodied thereon. 
     Any combination of one or more computer-readable media may be utilized. The computer-readable media may be a computer-readable signal medium or a computer-readable storage medium. A computer-readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of such a computer-readable storage medium include the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an appropriate optical fiber with a repeater, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer-readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. 
     A computer-readable signal medium may include a propagated data signal with computer-readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer-readable signal medium may be any computer-readable medium that is not a computer-readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. Program code embodied on a computer-readable signal medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF signals, etc., or any suitable combination of the foregoing. 
     Computer program code for carrying out operations for aspects of the present disclosure may be written in any combination of one or more programming languages, including object oriented programming languages, dynamic programming languages, and/or procedural programming languages. 
     The flowchart and block diagrams in the figures illustrate examples of the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various aspects of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order illustrated in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
     While the out-of-band interference mitigation techniques and the load balancing techniques disclosed herein are described frequently in the context of LEO constellations of communications satellites in near-polar orbits, the out-of-band interference mitigation techniques and the load balancing techniques disclosed herein may be employed in any of a number of a variety of other satellite network configurations, including, for example, in orbits other than near-polar orbits and/or low-Earth orbit including medium-Earth orbit (“MEO”) and geostationary orbit (“GEO”). 
     The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of any means or step plus function elements in the claims below are intended to include any disclosed structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The aspects of the disclosure herein were chosen and described in order to explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure with various modifications as are suited to the particular use contemplated.