Patent Publication Number: US-2023140643-A1

Title: Lensing using lower earth orbit repeaters

Description:
CROSS REFERENCE 
     The present Application for Patent is a 371 National Phase Application of International Patent Application No. PCT/US2021/019395 by HANCHARIK, entitled “LENSING USING LOWER EARTH ORBIT REPEATERS” filed Feb. 24, 2021, which claims the benefit of U.S. Provisional Patent Application No. 62/981,000 by HANCHARIK, entitled “LENSING USING LOWER EARTH ORBIT REPEATERS,” filed Feb. 24, 2020, each of which is assigned to the assignee hereof, and each of which is expressly incorporated by reference in its entirety herein. 
    
    
     BACKGROUND 
     The following relates generally to communications and more specifically to signal detection. 
     An antenna array at a satellite in a geostationary orbit may illuminate a geographic area that is associated with a coverage area of the satellite. In some examples, the satellite may be used to support communications between access node terminals and user terminals in the coverage area. The satellite may also be used to detect signals emitted within a coverage area of the satellite. In some examples, the detection resolution of the satellite may be limited—e.g., due to the distance of the satellite from a target geographic area. For example, the satellite may be unable to detect signals that are transmitted or emitted within the geographic area at low power levels or not intentionally directed to the satellite. 
     SUMMARY 
     The described techniques relate to improved methods, systems, devices, and apparatuses that support lensing using lower earth orbit repeaters. A first satellite may be in a first orbit, and a set of second satellites may be in second orbits that are lower than the first orbit. The second satellites may detect signal components of a signal originating from a geographic area that is within a coverage area of the first satellite. The second satellites may relay the respective signal components to the first satellite. A beamformer coupled with the first satellite may form a beam associated with the geographic area. The beamformer may also obtain a beam signal based on the respective signal components, forming the beam, and a return channel. The return channel may at least include a channel between the geographic area and the set of second satellites. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  shows a diagram of a communications system that supports lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. 
         FIG.  1 B  shows components of satellites that support lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. 
         FIG.  2    shows an example of a coverage diagram that supports lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. 
         FIG.  3    shows an exemplary set of operations that support lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. 
         FIG.  4    shows an example of a constellation diagram that supports lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. 
         FIG.  5    shows a block diagram of a signal analyzer that supports lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. 
         FIG.  6    shows a diagram of a communications device that supports lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. 
         FIG.  7    shows a flowchart illustrating a method that supports lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     A satellite communications system may include satellites in geostationary earth orbits (GEOs), which may be referred to as GEO satellites; and satellites in non-GEO earth orbits, which may be referred to as non-GEO satellites. In some examples, the non-GEOs are lower in altitude than the GEOs. Some examples of non-GEO satellites include satellites in medium earth orbits (MEOs), which may be referred to as MEO satellites; and satellites in low earth orbits (LEDs), which may be referred to as LEO satellites. Satellites (e.g., GEO, MEO, or LEO satellites) may be used to detect signals emitted from stationary or mobile sources on land, water, or in the sky. In some examples, a satellite network operator may use the detected signals to determine whether a known or unknown emitter is in a geographic area. 
     A GEO satellite may be used to detect known and unknown signal emitters in a geographic area. In some examples, a resolution of the GEO satellite associated with surveying particular geographic areas may be limited based on a size of an antenna array at the GEO satellite. Thus, for a GEO satellite, a 3 dB boundary of a beam used to survey a geographic area of interest may be excessively large relative to a boundary of the geographic area of interest. 
     According to various aspects described herein, multiple non-GEO satellites may be used to survey a large geographic area with increased resolution—e.g., based on multiple non-GEO satellites having a larger aperture than a single satellite. In some examples, a relay link may be established between a first satellite (e.g., a GEO satellite) in a first orbit (e.g., a GEO) and one or more second satellites (e.g., non-GEO satellites) in one or more second orbits (e.g., one or more non-GEOs). The use of the one or more second satellites as relay satellites to the first satellite can allow the second satellites to be relatively low complexity (e.g., lower cost, smaller size, etc.), as compared to fully functional satellites having high-power transponders and high-gain tracking antenna systems to transmit the signals directly to ground stations. The one or more second satellites may each have one or more antennas illuminated by at least a portion of one or more geographic areas and may each detect signal components of one or more signals emitted in the one or more geographic areas. The one or more second satellites may relay the respective signal components of the one or more signals to the first satellite. In some examples, when ground-based beamforming is used, the first satellite may transmit the signal components, or representations of the signal components, to a ground system in one or more signals. In some examples, the ground system may determine and apply beamforming weights to the one or more signals received from the first satellite to obtain one or more beam signals corresponding to signals detected in the one or more geographic areas. 
     In other examples, when on-board beamforming is used, the first satellite may process the signal components, determining and applying beamforming weights to the signal components to obtain one or more beams signals corresponding to signals detected from the one or more geographic areas. In such cases, the first satellite may transmit representations of the one or more beam signals to the ground system. By using the signal components detected at the one or more second satellites, post-processing may be performed that enables a processing system to focus on the one or more geographic areas with enhanced sensitivity, effectively increasing a detection resolution of the first satellite. 
     In some examples, in addition to the respective signal components received from the one or more second satellites, the first satellite may detect an additional signal component of the one or more signals in the one or more geographic areas—e.g., via a direct path. In such cases, the second satellites may effectively increase an aperture of the first satellite. In some examples, the first satellite may transmit the additional signal component of the one or more signals, or a representation of the detected additional signal component of the one or more signals, to the ground system. The ground system may use the additional signal component to obtain the representations of the one or more signals detected in the one or more geographic areas. In other examples, the first satellite may use the additional signal component to obtain the representations of the one or more signals. By supplementing a direct signal component received at the first satellite with the signal components received at the one or more second satellites, the quality of the signal detected by the first satellite may be improved relative to if only the direct signal component is used to detect the signal (e.g., the signal strength may be increased). 
     Aspects of the disclosure are initially described in the context of a satellite communications system. Specific examples are then described of a coverage diagram, process flow, and constellation diagram. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams and flowcharts that relate to lensing using lower earth orbit repeaters. 
       FIG.  1 A  shows a diagram of a communications system that supports lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. Satellite communications system  100  may include a network of satellites, including first satellite  105  and second satellites  115 . Satellite communications system  100  may also include a ground system  130  that includes one or more gateways  135 . The one or more gateways  135  may include (or be otherwise coupled with) beamformer  155 . In some examples, beamformer  155  may be included in ground station processor  153 . Ground station processor  153  may use beamformer  155  to determine beam coefficients. Ground station processor  153  may also be configured to demodulate (and, in some examples, decode) beam signals generated by beamformer  155 . 
     A satellite (e.g., first satellite  105  or a second satellite  115 ) may be configured to support wireless communications between one or more access node terminals (e.g., in a ground system  130 ) and user terminals located in a coverage area (e.g., coverage area  150 ). A satellite may also be configured to detect signals emitted within coverage area  150 . In some examples, a satellite may include an antenna assembly having one or more antenna feed elements. Each of the antenna feed elements may also include, or be otherwise coupled with, a radio frequency (RF) signal transducer, a low noise amplifier (LNA), or power amplifier (PA), and may be coupled with one or more transponders in the satellite. 
     In some examples, some or all antenna feed elements at a satellite may be arranged as an array of constituent receive and/or transmit antenna feed elements that cooperate to enable various examples of beamforming, such as ground-based beamforming (GBBF), on-board beamforming (OBBF), end-to-end (E2E) beamforming, or other types of beamforming. For OBBF, the satellite may include N 1  transmitters and an N 1 ×K 1  beam weight matrix may be used to generate K 1  user beams. Similarly, for GBBF, the satellite may include L 1  transmitters and receive L 1  signals corresponding to respective transmitters in the satellite (e.g., frequency-division multiplexed) from one or more access node terminals. The one or more access node terminals may apply an L 1 ×K 1  beam weight matrix to generate K 1  user beams. For E2E beamforming, the satellite may include L 1  transponders. The L 1  transponders may be used to receive signals from M access node terminals, where the received signals may be weighted (e.g., weighting each of K 1  beam signals for respective sets of one or more access node terminals) before transmission by the access node terminals to support beamforming for K 1  user beams. It should be noted that the present examples describe the forward link, while similar arrangements may be made for the return link. 
     Satellites may be launched into different orbits—a GEO or a non-GEO orbit. A satellite in a GEO may be referred to as a GEO satellite. Non-GEO orbits may include MEOs, LEOs, equatorial low earth orbit (ELEO), and the like. A satellite in a MEO may be referred to as a MEO satellite, a satellite in a LEO may be referred to as a LEO satellite, and so on. A GEO satellite may orbit the earth at a speed that matches the rotational speed of the earth, and thus, may remain in a single location relative to a point on the earth. A LEO satellite may orbit the earth at a speed (e.g., relative to the ground) that exceeds the rotational speed of the earth, and thus, a location of the satellite relative to a point on the earth may change as the satellite travels through the LEO. LEO satellites may be launched with low inclination (e.g., ELEOs) or high inclination (e.g., polar orbits) to provide different types of coverage and revisit times for given regions of the earth. A MEO satellite may also orbit the earth at a speed that exceeds the rotational speed of the earth but may be at a higher altitude than a LEO satellite. A HEO satellite may orbit the earth in an elliptical pattern where the satellite moves closer to and farther from the earth throughout the HEO. 
     In some examples, GEO satellites may be more expensive and more architecturally complex (e.g., may include more repeaters, antenna elements, transponders, etc.) than non-GEO satellites. Despite the increased complexity of GEO satellites, networks of non-GEO satellites may be capable of providing services and surveilling the earth with more granularity than GEO satellites (e.g., based on being more numerous and closer to the earth). In some examples, GEO satellites and non-GEO satellites operate independently of one another. In some examples, first satellite  105  may be a GEO satellite. Second satellites  115  may include LEO satellites, MEO satellites, or a combination thereof. 
     In some examples, a satellite network may be used to surveil at least a portion of the earth for signals emitted from known and unknown transmitters. For example, a satellite network may use first satellite  105  to detect signals that originate from a geographic area (e.g., the geographic area encompassed by coverage area  150 ). In some examples, first satellite  105  may transmit detected signal energy to a ground system  130  (e.g., to one or more of gateways  135 ) that processes (e.g., determine and apply beamforming coefficients to) the detected signal energy to obtain one or more signals—e.g., when ground-based beamforming is used. In other examples, first satellite  105  may process (e.g., determine and apply beamforming coefficients to) the detected signal energy and transmit the one or more signals to the ground system  130 —e.g., when on-board beamforming is used. 
     A GEO satellite may be used to detect known and unknown signal emitters in a geographic area. In some examples, a resolution of the GEO satellite associated with surveying particular geographic areas may be limited based on a size of an antenna array at the GEO satellite and a distance of the GEO satellite from a point of interest. Thus, for a GEO satellite, a 3 dB boundary of a beam used to survey a geographic area of interest may be excessively large relative to a boundary of the geographic area of interest. 
     According to various aspects described herein, multiple non-GEO satellites may be used to survey a large geographic area with increased resolution—e.g., based on multiple non-GEO satellites having a larger aperture than a single satellite (e.g., a GEO, MEO, or LEO satellite). In some examples, a relay link may be established between a first satellite  105  (e.g., a GEO satellite) in a first orbit (e.g., a GEO) and one or more second satellites  115  (e.g., non-GEO satellites) in one or more second orbits (e.g., one or more non-GEOs). The one or more second satellites  115  may each have one or more antennas illuminating at least a portion of one or more geographic areas  140  and may each detect signal components  125  of one or more signals emitted in the one or more geographic areas. According to various aspects described herein, the one or more antennas of the second satellites  115  are described as being illuminated by (instead of illuminating) the portion of the one or more geographic areas  140 . It is worth noting that these terms may be used interchangeably to describe that the one or more antennas of the second satellites  115  may be used to transmit signals to or detect signals from the one or more geographic areas  140 . 
     The one or more second satellites  115  may relay the respective signal components  125  of the one or more signals to the first satellite  105 . In some examples, when ground-based beamforming is used, the first satellite  105  may transmit the signal components, or representations of the signal components, in one or more signals to ground system  130 . In some examples, the ground system  130  may determine and apply beamforming weights to the one or more signals received from the first satellite  105  to obtain one or more beam signals corresponding to the one or more signals detected in the one or more geographic areas  140 . 
     In other examples, when on-board beamforming is used, the first satellite  105  may process the relayed signal components  110 , determining and applying beamforming weights to the signal components to obtain one or more beam signals corresponding to the one or more signals. In such cases, the first satellite  105  may transmit representations of the one or more beam signal signals to ground system  130 . By using the signal components detected at the one or more second satellites  115 , post-processing may be performed that enables a processing system to focus on the one or more geographic areas  140  with enhanced sensitivity, effectively increasing a detection resolution of the first satellite  105 . 
     In some examples, in addition to the respective signal components relayed from the one or more second satellites  115 , the first satellite  105  may detect an additional signal component (e.g., direct signal component  120 ) of the one or more signals in the one or more geographic area—e.g., via a direct path. In such cases, the second satellites may effectively increase an aperture of the first satellite. In some examples, the first satellite  105  may use the additional signal component to obtain the representations of the one or more signals. In other examples, the first satellite  105  may transmit the additional signal component of the one or more signals, or a representation of the detected additional signal component of the one or more signals, to the ground system  130 . The ground system  130  may use the additional signal component to obtain the representations of the one or more signals detected in the one or more geographic areas  140 . By supplementing a direct signal component  120  received at the first satellite  105  with the signal components received at the one or more second satellites  115 , the quality of the signal detected by the first satellite  105  may be improved relative to if only the direct signal component  120  is used to detect the signal (e.g., the signal strength may be increased). 
     As RF signal energy radiates from an emitter (e.g., a transmitter or thermal energy emitter), each second satellite  115  detects components (e.g., having respective phase shifts or amplitude variations due to different channels between the emitter and the respective second satellite  115 ) of the signal. When used in combination with first satellite  105  to detect signal components in geographic areas  140  corresponding to a location of an emitter (e.g., emitter  145 ), the second satellites  115  may be referred to as relay satellites  115 . The geographic areas  140  may be positioned within coverage area  150  of first satellite  105 . For example, first relay satellite  115 - 1  may receive first detected signal component  125 - 1  based on a signal emitted from emitter  145  within first geographic area  140 - 1 . In some examples, first relay satellite  115 - 1  receives first detected signal component  125 - 1  via a first return channel (which may be referred to as A TL     1   ), second relay satellite  115 - 2  receives a second detected signal component via a second return channel (which may be referred to as A TL     2   ), and so on. In some examples, the return channels between the relay satellites  115  and first geographic area  140 - 1  may be included in a combined return channel matrix (which may be referred to as A1 RTN ). Relay satellites  115  may similarly receive signal components detected from other geographic areas  140  (including Pth geographic area  140 -P). 
     In some examples, return channels between relay satellite  115  and a set of geographic areas  140  may be included in the combined return channel matrix A1 RTN . The matrix A1 RTN  may include a quantity of rows that is based on a quantity of repeaters included in the relay satellites  115  and a quantity of the relay satellites  115 , and a quantity of columns that is based on a quantity of geographic areas  140  monitored by the relay satellites  115 . For example, if S relay satellites  115  include Q repeaters and are used to monitor P geographic areas  140 , the A1 RTN  matrix may have Q S rows and P columns. 
     The relay satellites  115  may relay the detected signal components  125  (or representations of the detected signal components) to first satellite  105 . In some examples, relaying the detected signal components  125  involves frequency-shifting the detected signal component, amplifying the detected signal components, or both, before the detected signal components are relayed to first satellite  105 . 
       FIG.  1 B  shows components of satellites that support lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. As depicted in  FIG.  1 B , a relay satellite  115  may include one or more repeaters  160  that are used to amplify and/or frequency shift a detected signal before relaying the detected signal to first satellite  105 . A repeater  160  may be a non-processing repeater. That is, the repeater  160  may perform operations that interpret or re-format data within the signal waveform. For example, the repeater  160  may not digitize, demodulate, decode, apply beamforming weights, or reformat the detected signals before relaying the detected signals to first satellite  105 . A repeater  160  may include frequency translator  165 , amplifier  170 , or both. Frequency translator  165  may be configured to shift a frequency of a detected signal (e.g., by mixing the detected signal with another frequency). In some examples, the frequency translators  165  in different relay satellites  115  may be configured to apply different frequency shifts to detected signals. Amplifier  170  may be configured to amplify a detected signal before relaying the amplified signal to first satellite  105 . 
     In some examples, first relay satellite  115 - 1  may send first relayed signal component  110 - 1  (which may correspond to an amplified version of first detected signal component  125 - 1 ) to first satellite  105 . In some examples, first relay satellite  115 - 1  transmits first relayed signal component  110 - 1  to first satellite  105  via a first return channel (which may be referred to as A LG     1   ), second relay satellite  115 - 2  transmits a second transmitted signal component via a second return channel (which may be referred to as A LG     2   ), and so on. The return channels between the relay satellites  115  and first satellite  105  may be included in a second combined return channel matrix (which may be referred to as A2 RTN ). The relay satellites  115  may similarly transmit signal components detected from other geographic areas  140  (including Pth geographic area  140 -P) via the second combined return channel A2 RTN . 
     The matrix A2 RTN  may include a quantity of rows that is based on a quantity of uplink/downlink transponder paths at first satellite  105 , and a quantity of columns that is based on a quantity of relay satellites  115  and a quantity of repeaters included in the relay satellites  115 . For example, if first satellite  105  includes L uplink/downlink transponder paths and there are S relay satellites  115  with Q repeaters, the A2 RTN  matrix may have L rows and Q·S columns. 
     Thus, the return channel between the geographic areas  140  and first satellite  105  may be a composite return channel that includes multiple components—a first channel component between the relay satellites  115  and the geographic areas  140  (which may be represented by A1 RTN ) and a second channel component between the relay satellites  115  and first satellite  105  (which may be represented by A2 RTN ). In some examples, the composite return channel between the geographic areas  140  and first satellite  105  may be represented by an A2 RTN A1 RTN  matrix. In some examples, if first satellite  105  includes L uplink/downlink transponder paths and P geographic areas  140  are monitored, the A2 RTN A1 RTN  matrix may have L rows and P columns. 
     In some examples, first satellite  105  may receive direct signal components from one or more of the geographic areas  140 . For example, first satellite  105  may receive direct signal component  120  from emitter  145  via a direct return channel (which may be represented as A TG ) between first satellite  105  and first geographic area  140 - 1 . In some examples, the return channels between the geographic areas  140 , relay satellites  115 , and first satellite  105  may be combined with the direct return channel to form a composite return channel matrix (which may be represented as A RTN ), where A RTN =A TG +Σ S=0   S A TL     S   A LG     S   . The matrix A RTN  may include a quantity of rows that is based on a quantity of uplink/downlink transponder paths included in first satellite  105 , and a quantity of columns that is based on a quantity of geographic areas  140  monitored by the relay satellites  115 . For example, if first satellite  105  includes L uplink/downlink transponder paths and is used to monitor P geographic areas  140 , A RTN  may have L rows and P columns. 
     Similarly, a full return channel between the geographic areas  140  and ground system  130  may be a composite return channel that includes multiple components. In some examples, the full return channel includes the channel component between the geographic areas  140  and first satellite  105  (which may be represented by A2 RTN A1 RTN  or A RTN ); a channel component within first satellite  105  between the uplink and downlink transponders on first satellite  105  (which may be represented by a matrix E RTN ); and a channel component between first satellite  105  and ground system  130  (which may be represented by a matrix C RTN ). 
     As depicted in  FIG.  1 B , first satellite  105  may include one or more transponders  175  that are used to amplify and/or frequency shift a detected signal before transmitting a received signal to first satellite  105 . A transponder  175  may include frequency translator  165 , amplifier  170 , or both. Frequency translator  180  may be configured to shift a frequency of a received signal (e.g., by mixing the detected signal with another frequency). Amplifier  185  may be configured to amplify a received signal before transmitting the amplified signal to ground system  130 . In some examples, the transponder  175  may be coupled with on-board processing components, such as beamformer  190 , a demodulator, a decoder, a reformatting component, or a combination thereof. In some examples, the on-board processing components may be included in an on-board processor  187 . In some examples, when beamformer  190  is included in first satellite  105 , ground system  130  may not use beamformer  155  to process signals received from first satellite  105 . 
     In some examples, the channel component within first satellite  105  is based on paths through transponders in first satellite  105 , where the matrix E RTN  may include a quantity of rows and columns that are based on a quantity of transponders included in first satellite  105 . For example, if first satellite  105  includes L transponders, the E RTN  matrix may include L rows and L columns. 
     Also, the channel component between first satellite  105  and ground system  130  (represented by the C RTN  matrix) may be based on a quantity of ground stations included in ground system  130  and a quantity of repeaters included in first satellite  105 . For example, if ground system includes M ground stations (e.g., gateways) and first satellite  105  includes L uplink/downlink transponder paths, the C RTN  matrix may include M rows and L columns. 
     In some examples, the full return channel between the geographic areas  140  and ground system  130  may be represented by a matrix H RTN , where H RTN =C RTN E RTN A2 RTN A1 RTN  In some examples, if ground system  130  includes M ground stations and P geographic areas  140  are monitored, the H RTN  matrix may have M rows and P columns. 
     In some examples, ground system  130  may estimate the full return channel H RTN  based on signals received from known emitters positioned within coverage area  150 . Ground system  130  may use the signals received from the known emitters to determine return channels associated with the received signals and may interpolate the determined return channels to estimate the return channels between geographic areas  140  and ground system  130 . In some examples, ground system  130  may use the received signals to estimate a portion of the full return channel components. For example, ground system  130  may use the signals to estimate the channel component associated with A1 RTN , where the other channel components may be estimated based on reference signals communicated between devices to support channel estimation. 
     Ground system  130  may use the estimated channel components to determine return covariance (which may be represented by the matrix R RTN ). In some examples, the ground system may use the estimated channel component to determine a return covariance between signals received from different geographic areas  140  at M different ground stations, where R RTN =2σ dl   2 I m +2σ ul   2 C RTN E RTN E RTN   H C RNT   H +H RTN H RTN   H , where σ dl   2  is a noise term associated with a downlink (which may also be referred to as a forward link); σ ul   2  is a noise term associated with an uplink (which may also be referred to as a reverse link); and I m  is an M×M identity matrix. In some examples, the return covariance may also include covariance caused by interfering user traffic (e.g., for J interferers). In such cases, R′ RTN =R RTN +2σ ul-J   2 C RTN E RTN J RTN J RTN   H e RTN   H C RTN   H , where J RTN  may be the channel between the interferers and the ground system. Both of the R RTN  and R′ RTN  matrices may have M rows and M columns. 
     Ground system  130  may use the estimated full return channel and estimated return covariance to determine beam coefficients to apply to signals received over the full return channel. In some examples, the beam coefficients are represented by the matrix B RTN , where B RTN =(R RTN   −1 H RTN ) H . The matrix B RTN  may include a quantity of rows that is based on a quantity of monitored geographic areas  140  and a quantity of columns based on a quantity of ground stations in a ground system  130 . For example, for P geographic areas and M ground stations, the matrix B RTN  may include P rows and M columns. Thus, the beamformed channel between the ground system  130  and the one or more geographic areas  140  may be represented as H RTN-BF , where H RTN-BF =B RTN H RTN =B RTN C RTN E RTN A RTN . 
     In some examples, instead of applying the beam coefficients to signals received at ground system  130 , first satellite  105  may apply similarly determined beam coefficients to signals received from relay satellites  115 . In such examples, first satellite  105  may transmit a composite signal to ground system  130  that includes a representation of signals detected in each monitored geographic area  140 . When the beamforming is performed at first satellite  105 , the C RTN  matrix may be an identity matrix (e.g., an M×L identity matrix, where M may equal  1 ). 
     In some examples, instead of transmitting the signal components detected at relay satellites  115  to first satellite  105 , relay satellites  115  may transmit the detected signal components directly to ground system  130 . In addition to the signal components transmitted to ground system  130 , first satellite  105  may transmit a direct signal component to ground system  130 . In such cases, the signal components of a signal detected at relay satellites  115  may supplement the direct signal component of the signal detected by first satellite  105 . 
     Although generally described with reference to detecting signals originating from geographic areas  140  within coverage area  150 , similar techniques may be used to transmit signals to user terminals with geographic areas  140  on a forward link. In such cases, forward channels between ground system  130  and geographic areas  140  may similarly include multiple channel components, including a channel component between ground system  130  and first satellite  105 , a channel component between first satellite  105  and relay satellites  115 , and a channel component between relay satellites  115  and the geographic areas  140 . In such cases, ground system  130  may similarly estimate the forward channels (and, in some examples, individually estimate one or more of the forward channel components). Also, ground system  130  may determine and apply beam coefficients to signals to be transmitted in the different geographic areas—e.g., applying a first set of beam coefficients to a first signal to cause relay satellites  115  to focus a transmission of the first signal within first geographic area  140 - 1 , a second set of beam coefficients to a second signal to cause relay satellite  115  to focus a transmission of the second signal within a second geographic area, and so on. In such examples, first satellite  105  may transmit different components of a signal to the relay satellites  115 , and the relay satellites  115  may transmit the different signal components, the different signal components coherently combining within a desired geographic area  140 . In some examples, relay satellites  115  may reduce a transmission power of the different signal components to comply with signal strength thresholds on earth (e.g., as set by a regulatory agency). 
       FIG.  2    shows an example of a coverage diagram that supports lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. Coverage diagram  200  depicts a coverage area of a first satellite (e.g., a GEO satellite, a first satellite  105  of  FIG.  1   ) and a GEO satellite that uses one or more second satellites (e.g., LEO satellites, MEO satellites, LEO and MEO satellites, relay satellites  115  of  FIG.  1   ) to focus on a geographic area. 
     In some examples, an antenna array at a first satellite is associated with coverage area  250 . The boundary of coverage area  250  may represent points from which signals received at the antenna array have a signal strength that is at a 3 dB point. In some cases, coverage area  250  may represent the coverage area for a beamformed beam for transmission or reception from coverage area  250  via the first satellite. In some examples, the first satellite may be capable of processing signals received from within coverage area  250 . However, with regard to detecting signals within coverage area  250 , the first satellite may be unable to determine where within coverage area  250  the signal originated. As described herein to increase a detection resolution (and, in some examples, to effectively increase an aperture) of a first satellite, one or more second satellites (that orbit lower than the first satellite) may be used to detect signals originating from geographic regions within coverage area  250 . 
     In some examples, each of the second satellites may have a smaller coverage area  205  relative to the first satellite. Like coverage area  250 , the boundaries of coverage areas  205  may represent a 3 dB point for detecting signals originating from within coverage areas  205 . For first focused coverage area  205 - 1 , for example, the corresponding second satellite may be capable of detecting signals originating from a geographic region corresponding to first focused coverage area  205 - 1 , but not signals originating from within coverage area  250  but outside of first focused coverage area  205 - 1 . In some examples, energy from within overlapping coverage areas  205  of the second satellites may be combined to focus on particular geographic areas  240 . For example, the second satellites may be used to focus on first geographic area  240 - 1 . 
     In some examples, the second satellites may be used to focus (e.g., simultaneously) on multiple geographic areas  240  within coverage area  250  for the detection of signals. For example, in addition to focusing on first geographic area  240 - 1 , the second satellites may be used to focus on other geographic areas (e.g., first geographic area  240 - 1 , Pth geographic area  240 -P). The different geographic areas  240  monitored using the second satellites may be non-overlapping or overlapping. In some examples, the second satellites may similarly be used to focus on one or more geographic areas within coverage area  250  for the transmission of signals to user devices within the one or more geographic areas. 
       FIG.  3    shows an exemplary set of operations that support lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. Process flow  300  may be performed by second satellites  303 , first satellite  305 , and ground system  307 , which may be examples of second satellites  115 , first satellite  105 , and ground system  130  as described in  FIG.  1   . In some examples, process flow  300  illustrates an exemplary sequence of operations performed to support using lower earth orbit repeaters. For example, process flow  300  depicts operations for detecting signals transmitted in geographic areas within a coverage area of a GEO satellite. 
     It is understood that one or more of the operations described in process flow  300  may be performed earlier or later in the process, omitted, replaced, supplemented, or combined with another operation. Also, additional operations described herein that are not included in process flow  300  may be included. 
     At arrow  315 , emitter  301  may emit a signal while positioned within a geographic area. In some examples, emitter  301  emits the signal while wirelessly communicating with another device that is not second satellites  303  or first satellite  305 . In other examples, emitter  301  involuntarily emits the signal (e.g., emitter  301  may be a rocket, and the signal may be associated with a flare produced by the rocket). One or more of second satellites  303  may detect the signal. That is, the signal may radiate from the emitter  301  and each of the second satellites  303  may detect a different signal component associated with the emitted signal. In some examples, in addition to being detected at second satellites  303 , a direct signal component of the emitted signal may be detected at first satellite  305 . 
     At arrows  320 , second satellites  303  may relay the detected signal components (or representations of the received signal components) to first satellite  305 . In some examples, second satellites  303  may apply the detected signal components to one or more repeaters that are used to relay the detected signal components to first satellite  305 . A repeater may be used to amplify, apply a frequency shift to, or apply a phase shift to a detected signal component (or a combination thereof) before transmission to first satellite  305 . In some examples, first satellite  305  may receive the signal components at one or more antenna elements. First satellite  305  may also receive the direct signal component at one or more antenna elements. 
     At arrow  325 , first satellite  305  may transmit a representation of the signal emitted by emitter  301  to ground system  307 . First satellite  305  may transmit the signal components (in some examples, including the direct signal component) to ground system  307 . In some examples, first satellite  305  transmits the signal components to ground system  307  in one or more beams to one or more ground stations. Ground system  307  may receive the signal transmitted from first satellite  305 . In some examples, ground system  307  may receive the signal transmitted from first satellite  305  at one or more ground stations. 
     At block  330 , ground system  307  may estimate a channel (which may be referred to as a return channel and represented by H RTN ) between ground system  307  and emitter  301  based on the received signals. In some examples, ground system  307  may also estimate the channel based on signals received from known transmitters located within or around a geographic area (e.g., a geographic area  140  in  FIG.  1    or a geographic area  240  in  FIG.  2   ) that includes emitter  301 . In some examples, the signals received from the known transmitters may be transmitted concurrently with the signals detected by second satellites  303 . In some examples, the signals received from the known transmitters may be transmitted before the signals are detected by second satellites  303 —in some cases, the signals may be received by a different set of second satellites than second satellites  303 . That is, a channel estimation for relay by a given set of second satellites may be made using information of signals from known transmitters relayed by a different (e.g., non-overlapping, partially overlapping) set of second satellites. 
     In some examples, to estimate the return channel, ground system  307  may estimate a portion of the return channel between emitter  301  and second satellites  303  (which may be represented by A1 RTN ), a portion of the return channel between second satellites  303  and first satellite  305  (which may be represented by A2 RTN ), a portion of the return channel between uplink and downlink transponders within first satellite  305  (which may be represented by E RTN ), and a portion of the return channel between first satellite  305  and ground system  307  (which may be represented by C RTN ). When first satellite also receives a direct signal component, ground system may estimate a portion of the return channel between emitter  301  and first satellite  305  (which may be represented by A RTN ). 
     In some examples, ground system  307  estimates the channel between emitter and second satellites  303  (A1 RTN ) based on interpolating signals transmitted by known transmitters within a vicinity of a set of monitored geographic areas. And estimates the channel (e.g., A2 RTN , E RTN , and C RTN  between second satellites  303  and ground system  307  based on reference signals transmitted from known transmitters in the set of monitored geographic areas. In other examples, the components of the channel are estimated individually. For example, the channel between second satellites  303  and first satellite  305  (A2 RTN ) may be estimated (e.g., by first satellite  305 ) based on reference signals transmitted between second satellites  303  and first satellite  305 . The return channel of the transponders of the first satellite (E RTN ) may also be estimated by first satellite  305 . First satellite  305  may indicate the estimated channels to ground system  307 . And the channel between first satellite  305  and ground system  307  (C RTN ) may be estimated (e.g., by ground system  307 ) based on reference signals transmitted between first satellite  305  and ground system  307 . 
     At block  335 , ground system  307  may estimate covariance associated with the return channel—e.g., based on the estimated return channel/components of the estimated return channel. The covariance may provide information regarding interference between transmissions of signal components detected in different geographic areas to ground system  307  and interference from other communications with ground system  307 . In some examples, the interference between signals components from different geographic areas may be represented by R RTN =2σ dl   2 I m +2σ ul   2 C RTN E RTN E RTN   H C RTN   H +H RTN H RTN   H . Also, the interference between J users may be represented by R RTN-int =2σ ul-J   2 C RTN E RTN J RTN J RTN   H E RTN   H C RTN   H . And the combined covariance may be represented by R′ RTN =R RTN +R RTN-int . 
     At block  340 , ground system  307  may use the estimated return channel and the estimated return covariance to determine beam coefficients to apply to signals received from first satellite  305 . In some examples, the beam coefficients may be represented by the matrix B RTN , where B RTN  where equal (R RTN   −1 H RTN ) H . In some examples, the beam coefficients and the return channel are determined based on a same time period, where the signals received to estimate the channel may also be used to determine the beam coefficients. In some examples, ground system  307  may constantly (e.g., every millisecond) update the estimated return channel and beam coefficients based on received signals. For example, the ground system  307  may process a first set of signals to estimate the return channel and reprocess the first set of signals to determine the beam coefficients based on the estimated return channel. 
     At block  345 , ground system  307  may apply beam coefficients to the signal received from first satellite  305  to obtain one or more beam signals corresponding to one or more geographic areas. In some examples, the one or more beam signals correspond to representations of one or more signals emitted in the geographic areas. The one or more beam signals may include a beam signal that is a representation of the signal emitted by emitter  301  in a geographic area. In some examples, when digital beamforming is used, applying the beam coefficients may include applying beam coefficients to a digital representation of the signal—e.g., by multiplying a beam coefficient matrix with a matrix representing the signal. In other examples, applying the beam coefficients may include combining components of the analog signal received at ground system  307  to obtain an analog beam signal. 
     At block  350 , ground system  307  may process (e.g., filter, analyze, demodulate, decode) the one or more beam signals to determine whether a signal has been detected in a geographic area of interest. In some examples, ground system  307  determines a type of signal (e.g., a communication signal, a signal associated with a rocket, etc.) that has been detected in a geographic area of interest. 
     As suggested above, an order of the operations of process flow  300  may be changed. In some examples, the operations for estimating a return channel and covariance associated with the return channel and determining beam coefficients may be performed by ground system  307  before the representation of the signal emitted by emitter  301  is received from first satellite  305 . 
     In some examples, operations of process flow  300  may be performed by different devices. For example, the operations for estimating a return channel and covariance associated with the return channel; determining beam coefficients; and applying beam coefficients may be performed by first satellite  305  (e.g., if first satellite is configured to perform OBBF). In such cases, first satellite  305  may transmit one or more beam signals corresponding to the signal emitted by emitter  301  to ground system  307 . And ground system  307  may process the received one or more beam signals as described herein. 
     Although described in the context of using second satellites  303  to detect signals via return channels associated with geographic areas within a coverage area of first satellite  305 , similar operations may be performed to estimate forward channels associated with the geographic areas and to use second satellites  303  to relay signals to user devices within the geographic areas. 
       FIG.  4    shows an example of a constellation diagram that supports lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. Constellation diagram  400  depicts a set of second satellites (e.g., LEO satellites, MEO satellites, relay satellites  115  of  FIG.  1   , etc.) that may be used in combination with a first satellite (e.g., a GEO satellite, first satellite  105  of  FIG.  1   , etc.) to increase a detection resolution (and, in some examples, to effectively increase an aperture) of the first satellite for detecting signals within a coverage area. In some examples, the coverage areas of the second satellites  415  may correspond to respective focused coverage areas  205  described in  FIG.  2   . 
     Constellation diagram  400  may include S second satellites  415 , where S may equal nine. Sets of the second satellites  415  may be positioned in different orbital planes  405  (e.g., in K orbital planes). In some examples, the second satellites  415  are distributed amongst three orbital planes  405 , where first orbital plane  405 - 1  may have a negative five (−5) degree inclination, second orbital plane  405 - 2  may have a zero (0) degree inclination, and third orbital plane  405 - 3  may have a five (5) degree inclination. In some examples, the second satellites  415  may be evenly distributed amongst the three orbital planes  405 , such that three of the second satellites  415  are included in each of the orbital planes. In some examples, the second satellites  415  included in a same orbital plane  405  may be separated from one another based on a degree of separation. For example, a degree of separation between the second satellites  415  included in a same orbital plane  405  may be equal to (or around) five (5) degrees. 
       FIG.  5    shows a block diagram of a signal analyzer that supports lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. The signal analyzer  520  may be an example of aspects of a first satellite or ground station as described with reference to  FIG.  1 A . The signal analyzer  520 , or various components thereof, may be an example of means for performing various aspects of lensing using lower earth orbit repeaters as described herein. For example, the signal analyzer  520  may include a channel estimator  525 , a beamformer  530 , a signal manager  535 , a covariance estimator  540 , a demodulator  545 , a decoder  550 , or any combination thereof. Each of these components may communicate, directly or indirectly, with one another (e.g., via one or more buses). 
     The signal analyzer  520  may support communications in accordance with examples as disclosed herein. The beamformer  530  may be configured as or otherwise support a means for obtaining beam coefficients of a beam associated with a geographic area based at least in part on an estimated return channel that comprises a first channel component between the geographic area and a plurality of second satellites and a second channel component between the plurality of second satellites and a first satellite; and forming a beam associated with the geographic area to obtain a beam signal based at least in part on the beam coefficients and a plurality of signal components of a signal originating from the geographic area and relayed by the plurality of second satellite to the first satellite. 
     In some examples, the channel estimator  525  may be configured as or otherwise support a means for estimating a return channel from a geographic area, the return channel comprising a first channel component between a first satellite and a plurality of second satellites and a second channel component between the plurality of second satellites and the geographic area. In some examples, to support estimating the return channel of the geographic area, the channel estimator  525  may be configured as or otherwise support a means for determining a plurality of return channels based at least in part on one or more other signals received from known geographic locations. In some examples, the one or more other signals comprise one or more reference signals transmitted by transmitters in the known geographic locations. In some examples, to support estimating the return channel of the geographic area, the channel estimator  525  may be configured as or otherwise support a means for interpolating characteristics of the plurality of return channels to estimate characteristics of the return channel. 
     In some examples, the signal manager  535  may be configured as or otherwise support a means for obtaining a representation of the plurality of signal components relayed by the plurality of second satellites and a representation of a direct signal component of the signal received at the first satellite from the geographic area, wherein the beam signal is determined based at least in part on the representation of the plurality of signal components and the representation of the direct signal component. 
     In some examples, the covariance estimator  540  may be configured as or otherwise support a means for estimating a return covariance associated with the geographic area based at least in part on the return channel. In some examples, the beamformer  530  may be configured as or otherwise support a means for determining beam coefficients of the beam based at least in part on the return channel and the return covariance. 
     In some examples, to support obtaining the beam signal, the beamformer  530  may be configured as or otherwise support a means for applying beam coefficients of the beam to a representation of the plurality of signal components of the signal to obtain one or more beam signals. 
     In some examples, the channel estimator  525  may be configured as or otherwise support a means for estimating a plurality of return channels from a plurality of geographic areas, the plurality of return channels comprising the return channel and the plurality of geographic areas comprising the geographic area. In some examples, the covariance estimator  540  may be configured as or otherwise support a means for estimating a return covariance based at least in part on the plurality of return channels. In some examples, the beamformer  530  may be configured as or otherwise support a means for determining a plurality of beam coefficients of a plurality of beams based at least in part on the plurality of return channels and the return covariance. 
     In some examples, the beamformer  530  may be configured as or otherwise support a means for applying the plurality of beam coefficients of the plurality of beams to representations of pluralities of signal components associated with a plurality of signals originating from the plurality of geographic areas to obtain one or more beam signals, the one or more beam signals comprising the beam signal. 
     In some examples, the demodulator  545  may be configured as or otherwise support a means for demodulating the beam signal. In some examples, the decoder  550  may be configured as or otherwise support a means for decoding a demodulated beam signal. 
       FIG.  6    shows a diagram of a communications device that supports lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. The communications device  605  may be an example of or include the components of a first satellite  105  (e.g., a geosynchronous satellite that support on-board beamforming) or ground system  130  as described herein. The communications device  605  may include components for processing signals, such as an input/output (I/O) controller  610 , a transceiver  615 , an antenna  625 , a signal analyzer  620 , a memory  630 , code  635 , and a processor  640 . These components may be in electronic communication or otherwise coupled (e.g., operatively, communicatively, functionally, electronically, electrically) via one or more buses (e.g., a bus  645 ). 
     The I/O controller  610  may manage input and output signals for the communications device  605 . The I/O controller  610  may also manage peripherals not integrated into the communications device  605 . In some cases, the I/O controller  610  may represent a physical connection or port to an external peripheral. In some cases, the I/O controller  610  may utilize an operating system such as iOS®, ANDROID®, MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, or another known operating system. Additionally, or alternatively, the I/ 0  controller  610  may represent or interact with a modem, a keyboard, a mouse, a touchscreen, or a similar device. In some cases, the I/O controller  610  may be implemented as part of a processor, such as the processor  640 . In some cases, a user may interact with the communications device  605  via the I/O controller  610  or via hardware components controlled by the I/O controller  610 . 
     In some cases, antenna  625  may be a single antenna. In some other cases, the antenna  625  may include multiple antennas (or antenna elements), which may be capable of concurrently transmitting or receiving multiple wireless transmissions. The transceiver  615  may communicate bi-directionally, via the one or more antennas  625 , wired, or wireless links as described herein. For example, the transceiver  615  may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver  615  may also include a modem to modulate the packets, to provide the modulated packets to one or more antennas  625  for transmission, and to demodulate packets received from the one or more antennas  625 . 
     The memory  630  may include random-access memory (RAM) and read-only memory (ROM). The memory  630  may store code  635 . Code  635  may be computer-readable and computer-executable code and may include instructions that, when executed by the processor  640 , cause the communications device  605  to perform various functions described herein. The code  635  may be stored in a non-transitory computer-readable medium such as system memory or another type of memory. In some cases, the code  635  may not be directly executable by the processor  640  but may cause a computer (e.g., when compiled and executed) to perform functions described herein. In some cases, the memory  630  may contain, among other things, a basic input/output system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices. 
     The processor  640  may include an intelligent hardware device (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof). In some cases, the processor  640  may be configured to operate a memory array using a memory controller. In some other cases, a memory controller may be integrated into the processor  640 . The processor  640  may be configured to execute computer-readable instructions stored in a memory (e.g., the memory  630 ) to cause the communications device  605  to perform various functions (e.g., functions or tasks supporting reporting angular offsets across a frequency range). For example, the communications device  605  or a component of the communications device  605  may include a processor  640  and memory  630  coupled to the processor  640 , the processor  640  and memory  630  configured to perform various functions described herein. Processor  640  may include (or be an example of) ground station processor  153  or on-board processor  187 . 
     The signal analyzer  620  may support signal analysis at a first satellite (e.g., a geosynchronous satellite) or ground station in accordance with examples as disclosed herein. For example, the signal analyzer  620  may be configured as or otherwise support a means for obtaining beam coefficients of a beam associated with a geographic area based at least in part on an estimated return channel that comprises a first channel component between the geographic area and a plurality of second satellites and a second channel component between the plurality of second satellites and a first satellite. The signal analyzer  620  may be configured as or otherwise support a means for forming a beam associated with the geographic area to obtain a beam signal based at least in part on the beam coefficients and a plurality of signal components of a signal originating from the geographic area and relayed by the plurality of second satellite to the first satellite. 
     In some examples, the signal analyzer  620  may be configured to perform various operations (e.g., receiving, monitoring, transmitting) using or otherwise in cooperation with the transceiver  615 , the one or more antennas  625 , or any combination thereof. Although the signal analyzer  620  is illustrated as a separate component, in some examples, one or more functions described with reference to the signal analyzer  620  may be supported by or performed by the processor  640 , the memory  630 , the code  635 , or any combination thereof. For example, the code  635  may include instructions executable by the processor  640  to cause the communications device  605  to perform various aspects of reporting angular offsets across a frequency range as described herein, or the processor  640  and the memory  630  may be otherwise configured to perform or support such operations. 
       FIG.  7    shows a flowchart illustrating a method that supports lensing using lower earth orbit repeaters in accordance with examples as disclosed herein. The operations of the method may be implemented by components of a first satellite (e.g., a geosynchronous satellite that support on-board beamforming) or ground station as described herein. In some examples, a first satellite or ground station may execute a set of instructions to control the functional elements of the first satellite or ground station to perform the described functions. Additionally, or alternatively, the first satellite or ground station may perform aspects of the described functions using special-purpose hardware. 
     At  705 , the method may include obtaining beam coefficients of a beam associated with a geographic area based at least in part on an estimated return channel that comprises a first channel component between the geographic area and a plurality of second satellites and a second channel component between the plurality of second satellites and a first satellite. The operations of  705  may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of  705  may be performed by a channel estimator  525  as described with reference to  FIG.  5   . 
     At  710 , the method may include forming a beam associated with the geographic area to obtain a beam signal based at least in part on the beam coefficients and a plurality of signal components of a signal originating from the geographic area and relayed by the plurality of second satellite to the first satellite. The operations of  710  may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of  710  may be performed by a beamformer  530  as described with reference to  FIG.  5   . 
     In some examples, an apparatus as described herein may perform a method or methods, such as the method  700 . The apparatus may include, features, circuitry, logic, means, or instructions (e.g., a non-transitory computer-readable medium storing instructions executable by a processor) for obtaining beam coefficients of a beam associated with a geographic area based at least in part on an estimated return channel that comprises channel components between the geographic area and a plurality of second satellites; and forming a beam associated with the geographic area to obtain a beam signal based at least in part on the beam coefficients and a plurality of signal components associated with a signal originating from the geographic area. 
     Some examples of the method  700  and the apparatus described herein may further include operations, features, means, or instructions for receiving a representation of the plurality of signal components, wherein the beam signal is obtained based at least in part on applying the beam coefficients of the beam to the representation of the plurality of signal components. 
     Some examples of the method  700  and the apparatus described herein may further include operations, features, means, or instructions for estimating a return channel from a geographic area, the return channel comprising a first channel component between a first satellite and a plurality of second satellites and a second channel component between the plurality of second satellites and the geographic area. 
     In some examples of the method  700  and the apparatus described herein, estimating the return channel of the geographic area may include operations, features, circuitry, logic, means, or instructions for determining a plurality of return channels based at least in part on one or more other signals received from known geographic locations and interpolating characteristics of the plurality of return channels to estimate characteristics of the return channel. 
     In some examples of the method  700  and the apparatus described herein, the one or more other signals comprise one or more reference signals transmitted by transmitters in the known geographic locations. 
     Some examples of the method  700  and the apparatus described herein may further include operations, features, means, or instructions for obtaining a representation of the plurality of signal components relayed by the plurality of second satellites and a representation of a direct signal component of the signal received at the first satellite from the geographic area, wherein the beam signal may be determined based at least in part on the representation of the plurality of signal components and the representation of the direct signal component. 
     Some examples of the method  700  and the apparatus described herein may further include operations, features, means, or instructions for estimating a return covariance associated with the geographic area based at least in part on the return channel and determining beam coefficients of the beam based at least in part on the return channel and the return covariance. 
     In some examples of the method  700  and the apparatus described herein, obtaining the beam signal may include operations, features, circuitry, logic, means, or instructions for applying beam coefficients of the beam to a representation of the plurality of signal components of the signal to obtain one or more beam signals. 
     Some examples of the method  700  and the apparatus described herein may further include operations, features, means, or instructions for estimating a plurality of return channels from a plurality of geographic areas, the plurality of return channels comprising the return channel and the plurality of geographic areas comprising the geographic area, estimating a return covariance based at least in part on the plurality of return channels, and determining a plurality of beam coefficients of a plurality of beams based at least in part on the plurality of return channels and the return covariance. 
     Some examples of the method  700  and the apparatus described herein may further include operations, features, means, or instructions for applying the plurality of beam coefficients of the plurality of beams to representations of pluralities of signal components associated with a plurality of signals originating from the plurality of geographic areas to obtain one or more beam signals, the one or more beam signals comprising the beam signal. 
     A system for communications is described. The system may include a first satellite in a first orbit, a plurality of second satellites in second orbits that are lower than the first orbit, wherein the plurality of second satellites are configured to detect respective signal components of a signal originating from a geographic area and to relay the respective signal components to the first satellite, and a beamformer configured to form a beam associated with the geographic area to obtain a beam signal based at least in part on the respective signal components and an estimated return channel, wherein the estimated return channel comprises channel components between the geographic area and the plurality of second satellites. 
     In some examples of the system, the first satellite comprises a plurality of transponders, wherein to transmit a representation of the signal to a ground system, each transponder of the plurality of transponders may be configured to receive the respective signal components relayed by the plurality of second satellites and to transmit a representation of the respective signal components to the ground system. 
     In some examples of the system, each satellite of the plurality of second satellites comprises at least one repeater, wherein to relay the respective signal components to the first satellite, repeaters of the plurality of second satellites may be configured to amplify the respective detected signal components and transmit respective amplified signal components to the first satellite. In some examples of the system, the at least one repeater may be a non-processing repeater. 
     In some examples of the system, the repeaters of the plurality of second satellites may be configured to transmit the respective amplified signal components at a same frequency as the respective signal components detected at the repeaters. 
     In some examples of the system, the repeaters of the plurality of second satellites may be configured to transmit the respective amplified signal components at a different frequency than the respective signal components detected at the repeaters. 
     In some examples of the system, each of the repeaters of the plurality of second satellites may be configured to transmit a respective amplified signal component at a respective frequency of a plurality of frequencies. 
     In some examples of the system, the respective signal components detected by the plurality of second satellites may be detected via a first channel between the plurality of second satellites and the geographic area, the respective signal components may be relayed to the first satellite via a second channel between the plurality of second satellites and the first satellite, and the first satellite may be configured to transmit a representation of the respective signal components to a ground system via a third channel between the first satellite and the ground system. 
     In some examples of the system, the beamformer may be further configured to estimate a return covariance associated with the estimated return channel, determine beam coefficients of the beam based at least in part on the estimated return channel and the return covariance, and apply the beam coefficients to the respective signal components to obtain the beam signal. 
     In some examples, the system may include a ground system comprising, a plurality of gateways configured to receive a representation of the respective signal components, and the beamformer, wherein the beamformer may be coupled with the plurality of gateways and configured to apply beam coefficients of the beam to the representation of the respective signal components to obtain the beam signal. 
     In some examples of the system, the first satellite comprises the beamformer and may be further configured to transmit the beam signal to a ground system. 
     In some examples of the system, the plurality of second satellites may be configured to detect a plurality of respective signal components of a plurality of signals originating from a plurality of geographic areas, the plurality of signals comprising the signal and the plurality of geographic areas comprising the geographic area and the beamformer may be configured to form a plurality of beams associated with the plurality of geographic areas to obtain a plurality of beam signals based at least in part on the plurality of respective signal components and a plurality of estimated return channels, the plurality of estimated return channels comprising the estimated return channel. 
     In some examples of the system, the beamformer may be further configured to estimate a return covariance associated with the plurality of geographic areas and determine beam coefficients of the beam based at least in part on the estimated return channel and the return covariance and to apply the beam coefficients of the beam to the plurality of respective signal components to obtain the plurality of beam signals. 
     In some examples of the system, the first satellite may be configured to detect a direct signal component of the signal. 
     In some examples of the system, the beamformer may be further configured to obtain the beam signal based at least in part on the direct signal component. 
     In some examples of the system, the beamformer may be further configured to estimate the estimated return channel based at least in part on other signals received from one or more other geographic areas. In some examples of the system, the other signals comprise one or more reference signals transmitted by transmitters in known locations. 
     In some examples of the system, the plurality of second satellites comprises a first set of satellites in a first orbital plane of the second orbits. In some examples of the system, the plurality of second satellites comprises a second set of satellites in a second orbital plane of the second orbits. 
     In some examples, the system includes a processor configured to demodulate the beam signal. In some examples, the system includes a processor that comprises the beamformer. In some examples of the system, the first orbit may be a geostationary orbit. 
     A communications device is described. The communications device may include a processor, memory coupled with the processor and comprising instructions executable by the processor to cause the communications device to, estimate a return channel from a geographic area, the return channel comprising a first channel component between a first satellite and a plurality of second satellites and a second channel component between the plurality of second satellites and the geographic area, and obtain, based at least in part on a plurality of signal components associated with a signal originating from the geographic area, a beam signal, wherein the plurality of signal components are relayed by respective second satellites of the plurality of second satellites. 
     In some examples of the communications device, the instructions for estimating the return channel may be further executable by the processor to determine a plurality of return channels based at least in part on one or more other signals received from known geographic locations and interpolate characteristics of the plurality of return channels to estimate characteristics of the return channel. 
     In some examples of the communications device, the instructions may be further executable by the processor to obtain a representation of the plurality of signal components relayed by the plurality of second satellites and a representation of a direct signal component of the signal received at the first satellite from the geographic area, wherein the beam signal may be determined based at least in part on the representation of the plurality of signal components and the representation of the direct signal component. 
     In some examples of the communications device, the instructions may be further executable by the processor to estimate a return covariance associated with the geographic area based at least in part on the return channel and determine beam coefficients of the beam based at least in part on the return channel and the return covariance. 
     In some examples of the communications device, the instructions for obtaining the beam signal may be further executable by the processor to apply beam coefficients of the beam to a representation of the plurality of signal components of the signal to obtain one or more beam signals. 
     In some examples of the communications device, the instructions may be further executable by the processor to estimate a plurality of return channels from a plurality of geographic areas, the plurality of return channels comprising the return channel and the plurality of geographic areas comprising the geographic area, estimate a return covariance based at least in part on the plurality of return channels, and determine a plurality of beam coefficients of a plurality of beams based at least in part on the plurality of return channels and the return covariance. 
     In some examples of the communications device, the instructions may be further executable by the processor to apply the plurality of beam coefficients of the plurality of beams to representations of pluralities of signal components associated with a plurality of signals originating from the plurality of geographic areas to obtain one or more beam signals, the one or more beam signals comprising the beam signal. 
     It should be noted that these methods describe examples of implementations, and that the operations and the steps may be rearranged or otherwise modified such that other implementations are possible. In some examples, aspects from two or more of the methods may be combined. For example, aspects of each of the methods may include steps or aspects of the other methods, or other steps or techniques described herein. 
     Information and signals described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     The various illustrative blocks and modules described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a DSP, an ASIC, an FPGA, or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a digital signal processor (DSP) and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration). 
     The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described herein can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. 
     Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A non-transitory storage medium may be any available medium that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, non-transitory computer-readable media may include RAM, ROM, electrically erasable programmable read-only memory (EEPROM), flash memory, compact disk read-only memory (CDROM) or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, include CD, laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media. 
     As used herein, including in the claims, “or” as used in a list of items (e.g., a list of items prefaced by a phrase such as “at least one of” or “one or more of”) indicates an inclusive list such that, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C). Also, as used herein, the phrase “based on” shall not be construed as a reference to a closed set of conditions. For example, an exemplary step that is described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase “based on” shall be construed in the same manner as the phrase “based at least in part on.” 
     In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If just the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label, or other subsequent reference label. 
     The description set forth herein, in connection with the appended drawings, describes example configurations and does not represent all the examples that may be implemented or that are within the scope of the claims. The term “exemplary” used herein means “serving as an example, instance, or illustration,” and not “preferred” or “advantageous over other examples.” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described examples. 
     The description herein is provided to enable a person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.