Patent Description:
The following relates generally to communications, including scanning operations for co-located satellite antennas.

Communications devices may communicate with one another using wired connections, wireless (e.g., radio frequency (RF)) connections, or both. Wireless communications between devices may be performed using wireless spectrum that has been designated for a service provider, wireless technology, or both. In some examples, the amount of information that can be communicated via a wireless communications network is based on an amount of wireless spectrum designated to the service provider, and an amount of frequency reuse within the region in which service is provided. Wireless communications (e.g., cellular communications, satellite communications, etc.) may use beamforming and multiple-input multiple-output (MIMO) techniques for communications between devices to increase frequency reuse, however, providing a high level of frequency reuse in some types of communication systems such as satellite communications presents challenges. An example of prior art is disclosed in the article: "<NPL>).

The described techniques relate to improved methods, systems, devices, and apparatuses that support scanning operations for co-located satellite antennas. A system includes a set of co-located satellite antennas, where an inter-element spacing of satellite antennas of the set of co-located satellite antennas is different across the set of co-located satellite antennas. Additionally, the system includes a central processor configured to apply a first set of beamforming coefficients to a transmit beam signal to generate a set of component transmit signals for transmission by a set of co-located satellite antennas, where the set of co-located satellite antennas are configured to transmit the set of component transmit signals to form a beam at a first time, where a first line segment at a boundary of the beam is tangential to a first sphere having a surface that encompasses a planet, where a location on the first line segment tangential to the surface of the first sphere is above a surface of the planet by a threshold altitude, and where the set of co-located satellite antennas are configured to receive a plurality of component receive signals comprising reflected energy of the beam. Additionally, the central processor is configured to a second set of beamforming coefficients to the plurality of component receive signals to obtain a receive beam signal associated with the beam and to process the plurality of receive beam signals based at least in part on the transmit beam signal to obtain a signature associated with an object within a limb of the planet defined by the first sphere and a second sphere that is concentric with and larger than the first sphere.

In some examples, co-located satellite antennas in a set of satellite antennas may form a beam in order to obtain a signature of (e.g., in order to scan) an object. If the object is located on the surface of the Earth, the reflected energy from the beam on the object may be subjected to background clutter (e.g., interference from other objects) and may have a terrestrial power flux-density transmission limit. The background clutter and the power-flux density transmission limit may decrease the likelihood that the co-located satellite antennas successfully scan the object.

In some examples, an object (e.g., a vehicle, such as a hypersonic vehicle) may be present in an atmospheric limb of the Earth, where an atmospheric limb may be defined as an atmospheric region defined by an arc of the Earth up to a particular atmospheric altitude (e.g., <NUM>), the set of co-located satellite antennas may generate a beam with a boundary that is tangential to the first sphere. By generating the beam that is tangential to the first sphere, the set of satellite antennas may scan the object without background clutter introduced from the surface of the Earth. Additionally or alternatively, as no portion or a reduced portion of the beam interacts with the surface of the Earth, the set of co-located satellite antennas may not be subject to the power-flux density transmission limit. Accordingly, the likelihood that the co-located satellite antennas may successfully scan the object may increase when generating the beam with the boundary that is tangential to the first sphere as compared to generating a beam that scans the surface of the Earth.

Aspects of the disclosure are initially described in the context of wireless communications systems. Additional aspects of the disclosure are described in the context of a scanning scenario, a scanning sequence, and a limb scanning geometry. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to scanning operations for co-located satellite antennas.

<FIG> shows an example of a satellite communications system <NUM> that supports beam management using sparse antenna arrays in accordance with examples described herein. Satellite communications system <NUM> may include a ground system <NUM>, terminals <NUM>, and satellite system <NUM>. The ground system <NUM> may include a network of access nodes <NUM> that are configured to communicate with the satellite system <NUM>. The access nodes <NUM> may be coupled with access node transceivers <NUM> that are configured to process signals received from and to be transmitted through corresponding access node(s) <NUM>. The access node transceivers <NUM> may also be configured to interface with a network <NUM> (e.g., the Internet) - e.g., via a network device <NUM> (e.g., a network operations center, satellite and gateway terminal command centers, or other central processing centers or devices) that may provide an interface for communicating with the network <NUM>.

Terminals <NUM> may include various devices configured to communicate signals with the satellite system <NUM>, which may include fixed terminals (e.g., ground based stationary terminals) or mobile terminals such as terminals on boats, aircraft, ground based vehicles, and the like. A terminal <NUM> may communicate data and information with an access node <NUM> via the satellite system <NUM>. The data and information may be communicated with a destination device such as a network device <NUM>, or some other device or distributed server associated with a network <NUM>.

The satellite system <NUM> may include a single satellite, or a network of satellites that are deployed in space orbits (e.g., low earth orbits, medium earth orbits, geostationary orbits, etc.). One or more satellites included in satellite system <NUM> may be equipped with multiple antennas <NUM> (e.g., one or more antenna arrays). In some cases, the multiple antennas <NUM> may be spread over a large region in space, and the antennas <NUM> may be sparsely located within the region. For example, the distance between the antennas <NUM> may be greater than a distance associated with a wavelength of signals supported for communication by the large, sparse antenna array - e.g., the distance between the antennas <NUM> may be greater than a distance associated with the wavelength. In some examples, the distance between the antennas <NUM> may be greater than ten times the wavelength. In some examples, in addition to being large and sparse, the antenna array <NUM> may be non-harmonic (e.g., the spacing between antennas <NUM> may be random or semi-random). For example, a first distance (d1) between a first antenna <NUM> and a second antenna <NUM> may be different than a second distance (d2) between the second antenna <NUM> and a third antenna <NUM>, and so on throughout antenna array <NUM>. In some examples, the distances between the antennas <NUM> of the antenna array <NUM> may be uncontrolled or partially controlled (e.g., unconstrained in one or more dimensions, or allowed to drift in one or more dimensions relative to other antennas <NUM>).

In some examples, each of the multiple antennas <NUM> may include an antenna subarray <NUM> (e.g., one or more antenna panels that include an array of evenly distributed antenna elements). In some examples, one or more satellites may each be equipped with an antenna array including antennas that are unevenly distributed across a large region. In other examples, the antenna array may include antennas that are evenly distributed across the large region. In some examples, the antennas may be connected to a central entity via wired or wireless links. Deploying the antennas over the large region may increase an aperture size of the antenna array of the satellite relative to an antenna array that includes evenly distributed antennas (e.g., due to limitations associated with manufacturing and deploying a large antenna array with evenly distributed antennas). In some examples, a set of satellites, each including an antenna <NUM>, are unevenly distributed across the large region, where each satellite may communicate with a central entity (e.g., a central server or ground station). In such cases, the antennas <NUM> of the set of satellites may be used to form an antenna array <NUM>. In some examples, a set of satellites, each including an antenna <NUM>, are unevenly distributed across the large region, where each satellite may communicate with a central entity (e.g., a central server or ground station).

The satellite system <NUM> may use the one or more satellites to support multiple-input multiple-output (MIMO) techniques to increase a utilization of frequency resources used for communications - e.g., by enabling wireless spectrum to be reused, in time and frequency, in different geographic regions of a geographic area. Similarly, the satellite system <NUM> may use the one or more satellites to support beamforming techniques to increase a utilization of frequency resources used for communications.

MIMO techniques may be used to exploit multipath signal propagation and increase spectral efficiency by transmitting or receiving multiple signals via different spatial layers. The multiple signals may, for example, be transmitted by a transmitting device (e.g., a satellite system) via a set of antennas in accordance with a set of weighting coefficients. Likewise, the multiple signals may be received by a receiving device (e.g., a satellite system) via a set of antennas in accordance with a set of weighting coefficients. Each of the multiple signals may be associated with a separate spatial stream and may carry bits associated with the same data stream (e.g., the same codeword) or different data streams (e.g., different codewords). MIMO techniques include single-user MIMO (SU-MIMO), where multiple spatial layers are used to communicate with one device, and multiple-user MIMO (MU-MIMO), where multiple spatial layers are used to communicate with multiple devices.

To determine weighting coefficients to apply to the set of antennas such that the N spatial layers are formed, an (M x N) MIMO matrix may be formed, where M may represent the quantity of antennas of the set of antennas. In some examples, M may be equal to N. The MIMO matrix may be determined based on a channel matrix and used to isolate the different spatial layers of the channel. In some examples, the weighting coefficients are selected to emphasize signals transmitted using the different spatial layers while reducing interference of signals transmitted in the other spatial layers. Accordingly, processing signals received at each antenna with the set of antennas (e.g., a signal received at the set of antennas) using the MIMO matrix may result in multiple signals being output, where each of the multiple signals may correspond to one of the spatial layers. The elements of the MIMO matrix used to form the spatial layers of the channel may be determined based on channel sounding probes received at a satellite system <NUM> - e.g., from one or more devices. In some examples, the weighting coefficients used for MIMO communications may be referred to as beam coefficients, and the multiple signals or spatial layers may be referred to as beam signals.

Beamforming techniques may be used to shape or steer a communication beam along a spatial path between a satellite system <NUM> and a geographic area. A communication beam may be formed by determining weighting coefficients for antenna elements of antenna array that result in the signals transmitted from or received at the antenna elements being combined such that signals propagating in a particular orientation with respect to an antenna array experience constructive interference while others experience destructive interference. Thus, beamforming may be used to transmit signals having energy that is focused in a direction of a communication beam and to receive signals that arrive in a direction of the communication with increased signal power (relative to the absence of beamforming). The weighting coefficients may be used to apply amplitude offsets, phase offsets, or both to signals carried via the antennas. In some examples, the weighting coefficients applied to the antennas may be used to form multiple beams associated with multiple directions, where the multiple beams may be used to communicate multiple signals having the same frequency at the same time. The weighting coefficients used for beamforming may be referred to as beam coefficients, and the multiple signals may be referred to as beam signals.

In some examples, beamforming techniques may be used by a satellite system <NUM> to form spot beams that are tiled (e.g., tessellated) across a geographic area. In some examples, the wireless spectrum used by a satellite system <NUM> may be reused across sets of the spot beams for communications between terminals <NUM> and the satellite system. In some examples, the wireless spectrum can be reused in spot beams that do not overlap, where a contiguous geographic region can be covered by overlapping spot beams that each use orthogonal resources (e.g., orthogonal time, frequency, or polarization resources).

To support an increased quantity of users within a geographic area, an antenna array (which may be referred to as a large, sparse antenna array) having antennas with inter-element spacing that is different across the antenna array may be used to increase a resolution of beamforming techniques. That is, the large, sparse antenna array may be used (e.g., in combination with respective beam coefficients) to form communication beams with small coverage areas (e.g., less than <NUM> kilometers in diameter). A large, sparse antenna array, such as antenna array <NUM>, may include multiple antennas <NUM> (e.g., hundreds or thousands of antennas) that are unevenly distributed across an area - e.g., in space. In some examples, each antenna <NUM> is, or is installed on, an individual satellite. In other examples, the antennas <NUM> are installed on a single satellite, where each antenna <NUM> is tethered to a central location - e.g., via a physical connection.

To form the small communication beams, geometric relationships between a geographic region and the antennas <NUM> of the large, sparse antenna array <NUM> may be used. In some examples, the geometric relationships between a geographic region and the antennas <NUM> of the large, sparse antenna array <NUM> may also be used to simplify the processing used for massive-MIMO techniques - e.g., based on the limited directions of signal incidence, location information known for the terminals, or any combination thereof.

In some examples, to support communicating using communication beams <NUM> with small coverage areas, a large, sparse antenna array <NUM> may be used (e.g., in combination with respective beam coefficients) to form discovery beams <NUM> within a geographic area <NUM>, where each discovery beam <NUM> may be formed by a corresponding set of antennas <NUM> of the antenna array <NUM> and may cover a discovery area <NUM> within the geographic area <NUM>. For example, each antenna subarray <NUM> may form a discovery beam <NUM>, and the discovery beams may be tiled across the geographic area <NUM>. Preambles <NUM> transmitted from terminals <NUM> within a discovery area <NUM> of a discovery beam <NUM> may be detected using the large, sparse antenna array <NUM> (e.g., each antenna subarray <NUM> may detect preambles <NUM> transmitted from within a corresponding discovery area <NUM>). Based on detecting a preamble <NUM> using a discovery beam <NUM>, a presence of a terminal <NUM> in a discovery area <NUM> of the discovery beam <NUM> may be determined.

In some examples, based on detecting the presence of the terminal <NUM> within a discovery area <NUM>, one or more antennas <NUM> (e.g., an antenna subarray <NUM> or a group of antennas <NUM>) may be selected to perform communications with the terminal <NUM>. In some cases, the set of antennas <NUM> and a corresponding set of beamforming coefficients are used to form a wide communication beam that has a wide coverage area including a position of the terminal <NUM>. In some examples, a size of the wide coverage area may be similar to a size of a discovery area <NUM>.

In some examples, based on detecting the presence of the terminal <NUM>, a second set of antennas <NUM> (e.g., antennas from more than one antenna subarray <NUM>, a substantial portion of antennas <NUM>, a majority of antennas <NUM>, or all of the antennas <NUM>) of the antenna array <NUM> and corresponding beam coefficients may be selected to form a communication beam <NUM> (e.g., a small or narrow beam) having a beam coverage area <NUM> within the discovery area <NUM> that includes a position of the terminal <NUM>. The second set of antennas may include a larger quantity of antennas than the one or more antennas used to form the wide communication beam. Subsequently, signals detected at the antenna array <NUM> may be processed according to the beam coefficients used to form the narrow communication beam <NUM>, resulting in a beam signal for the narrow communication beam <NUM>. In some examples, the beam signal may include one or more signals transmitted from one or more terminals positioned within the beam coverage area <NUM>.

In some examples, antenna array <NUM> includes multiple antenna subarrays <NUM>, where each antenna subarray <NUM> may be used to form a discovery beam <NUM> associated with a corresponding discovery area <NUM>. Preambles from a set of terminals <NUM> may be detected using a subset of the discovery beams <NUM>. Based on detecting the terminals using the subset of the discovery beams <NUM>, communication beams <NUM> may be formed (e.g., using geometric interpretation or MIMO-based techniques) within the corresponding discovery areas <NUM>, where beam coverage areas <NUM> of the communication beams <NUM> may encompass the detected terminals <NUM>. Communications may be performed between the antenna array <NUM> and detected terminals <NUM> using the communication beams <NUM>, where at least a subset of the communication beams <NUM> may reuse common time, frequency, and polarization resources.

In some examples, techniques for supporting communications using wide and narrow communication beams may be used. For example, techniques for determining when to use a wide communication beam, narrow communication beams <NUM>, or a combination thereof, may be used. For instance, narrow communication beams <NUM> within a wide coverage area of a wide communication beam may be activated based on a utilization of the wide communication beam reaching a threshold (e.g., greater than <NUM>% of the capacity of the wide communication beam). In some examples, techniques for adjusting a beam coverage area <NUM> of a narrow communication beam <NUM> to increase a quality of signals received from a terminal <NUM> that is used as a reference for the narrow communication beam <NUM> may be used. Also, techniques for maintaining the beam coverage area <NUM> of the narrow communication beam <NUM> focused on a position of the reference terminal <NUM> (which may be referred to as "beam tracking") may be used. Additionally, techniques for adjusting a size of beam coverage areas <NUM> of narrow communication beams <NUM> (or for forming additional narrow communication beam <NUM>) to accommodate other terminals may be used.

In some examples, a satellite system <NUM> may form a beam in order to obtain a signature of (e.g., in order to scan) an object. If the object is located on the surface of the Earth, the reflected energy from the object may be subjected to background clutter (e.g., interference from other objects) and may have a terrestrial power flux-density transmission limit. The background clutter and the power-flux density transmission limit may decrease the likelihood that the satellite system <NUM> can successfully scan the object.

In some examples, an object (e.g., a vehicle, such as a hypersonic vehicle) may be present in an atmospheric limb of the Earth, where an atmospheric limb may be defined as a region between a first sphere encompassing the Earth and a second sphere that is larger than the first sphere and concentric with the first sphere. When scanning the object in the atmospheric limb, the satellite system <NUM> may generate a beam with a boundary that is tangential to the first sphere. By generating the beam that is tangential to the first sphere, the satellite system <NUM> may scan the object without background clutter introduced from the surface of the Earth. Additionally or alternatively, as no portion or a reduced portion of the beam interacts with the surface of the Earth, the satellite system <NUM> may not be subject to the power-flux density transmission limit. Accordingly, the likelihood that the satellite system <NUM> may successfully scan the object may increase when generating the beam with the boundary that is tangential to the first sphere as compared to generating a beam that scans the surface of the Earth.

<FIG> illustrates an example of a communications network <NUM> that supports scanning operations for co-located satellite antennas in accordance with aspects of the present disclosure.

Communications network <NUM> depicts a system for scanning an object located at a limb of a planet (e.g., Earth). Communications network <NUM> may include antenna array <NUM>, bus <NUM>, beam manager <NUM>, signature processing component <NUM>, scanning component <NUM>, processor <NUM>, and memory <NUM>. At least a portion (e.g., some or all) of communications network <NUM> may be located within a space segment of communications network <NUM> (e.g., in a satellite system). In some examples, a portion of communications network <NUM> that is not included in the space segment may be located within a ground segment of communications network <NUM> (e.g., in a ground system). For example, antenna array <NUM>, beam manager <NUM>, signature processing component <NUM>, scanning component <NUM>, processor <NUM>, and memory <NUM> may be included in a space segment of communications network <NUM>. In another example, antenna array <NUM> may be included in a space segment of communications network <NUM>, while beam manager <NUM>, signature processing component <NUM>, scanning component <NUM>, processor <NUM>, and memory <NUM> may be included in a ground segment of communications network <NUM>.

Antenna array <NUM> may be an example of the antenna array of <FIG> and may include antennas <NUM>. The antennas <NUM> may be examples of the antennas <NUM> described with reference to <FIG>. In some examples, one or more of the antennas <NUM> may include an antenna subarray, similar to the antenna subarray <NUM> described with reference to <FIG>. The spacing between the antennas <NUM> may be different across antenna array <NUM>. In some examples, a distance (e.g., an average distance) between the antennas <NUM> is greater than a distance associated with a wavelength of signals communicated using antenna array <NUM>. In some examples, a distance (e.g., an average distance) between the antennas <NUM> is greater than a distance associated with ten times the wavelength of the signals communicated using antenna array <NUM>. In some examples, each antenna <NUM> may be an omnidirectional antenna. In some examples, each antenna <NUM> of antenna array <NUM> may be coupled with a respective satellite. In some such examples, the respective satellite coupled with at least one satellite antenna of the set of satellite antennas is different than the respective satellite coupled with another satellite antenna of the set of satellite antennas.

Bus <NUM> may represent an interface over which signals may be exchanged between antenna array <NUM> and a central location that may be used to distribute the signal to the signal processing components of communications network <NUM> (e.g., beam manager <NUM>, signature processing component <NUM>). Bus <NUM> may include a collection of wires that connect to each of the antennas. Additionally, or alternatively, bus <NUM> may be a wireless interface that is used to wirelessly communicate signaling between antenna array <NUM> and the signal processing components - e.g., in accordance with a communication protocol.

Beam manager <NUM> may be configured to form beams, including discovery beams, communication beams, geometric interpretation-based beams, MIMO-based beams, and the like. In some examples, beam manager <NUM> may be configured to form one or more discovery beams (e.g., the discovery beams that cover the discovery areas <NUM> of <FIG>) within a geographic area (e.g., geographic area <NUM> of <FIG>) that is covered by the antenna array <NUM>. To form the discovery beams, native antenna patterns of sets of the antennas <NUM> may be used, or may be combined with beamforming techniques, MIMO techniques, or a combination thereof.

Beam manager <NUM> may also be configured to form one or more communication beams (e.g., the communication beams that form the beam coverage areas <NUM> of <FIG>). To form the communication beams, geometric interpretation-based beamforming techniques, MIMO techniques, or geometrically-informed MIMO techniques may be used. Beam manager <NUM> may include beamforming coefficient component <NUM>, beam signal transmitter <NUM> and beam signal receiver <NUM>.

Beamforming coefficient component <NUM> may be configured to apply beamforming coefficients to beam signals to generate component signals and/or to component signals to generate beam signals. For instance, the beamforming coefficient component <NUM> may apply a first set of beamforming coefficients to a transmit beam signal to generate a set of component transmit signals for transmission by antenna array <NUM>. Additionally, beamforming coefficient component <NUM> may be configured to apply a second set of beamforming coefficients to a set of component receive signals to obtain a receive beam signal associated with a beam. In some examples, beamforming coefficient component <NUM> may be configured to receive, via the antenna array <NUM> and from a system distinct from the antenna array <NUM> and/or the communications network <NUM>, an indication of a beam direction, a velocity of an object, an acceleration of an object or any combination thereof. In some such examples, the beamforming coefficient component <NUM> may be configured to apply the first set of beamforming coefficients based on receiving the indication of the beam direction, the velocity of the object, the acceleration of the object, or any combination thereof.

In some examples, beamforming coefficient component <NUM> may apply one set of beamforming coefficients to multiple transmit beam signals. For instance, beamforming coefficient component <NUM> may apply the first set of beamforming coefficients to a second transmit beam signal to generate a second set of component transmit signals for transmission by the antenna array <NUM>. In other examples, beamforming coefficient component <NUM> may apply different sets of beamforming coefficients to different transmit beam signals or different sets of component signals. For instance, beamforming coefficient component <NUM> may be configured to apply a third set of beamforming coefficients to a second transmit beam signal to generate a second set of component transmit signals for transmission by the antenna array <NUM>. Additionally or alternatively, beamforming coefficient component <NUM> may be configured to apply, at a time different from when beamforming coefficient component <NUM> applies the second set of beamforming coefficients, a fourth set of beamforming coefficients to the second set of component receive signals to obtain a second set of receive beam signals associated with a translated beam.

In some examples, beamforming coefficient component <NUM> may update beamforming coefficients used to generate beam signals or sets of component signals based on previous beamforming coefficients and the signature obtained from a detected object. For instance, beamforming coefficient component <NUM> may generate the third set of beamforming coefficients based on the first set of beamforming coefficients and a signature obtained by signature processing component <NUM>. In some examples, beamforming coefficient component <NUM> may update beamforming coefficients such that communications network <NUM> may track or scan an object.

Beam signal transmitter <NUM> may be configured to transmit, via the antenna array <NUM>, component signals to form a beam. For instance, beam signal transmitter <NUM> may transmit, via the antenna array <NUM> at a first time, the set of component transmit signals to form the beam. In some examples, a first line segment at a boundary of the beam may be tangential to a first sphere having a surface that encompasses a planet (e.g., Earth), where a location on the first line segment tangential to the surface of the first sphere is above a surface of the planet by a threshold altitude.

In some examples, beam signal transmitter <NUM> may be configured to transmit additional component signals to form a translated beam relative to another beam that beam signal transmitter <NUM> transmitted. For instance, beam signal transmitter <NUM> may transmit, via the antenna array <NUM>, the second set of component transmit signals to form the translated beam. In some such examples, a second line segment at a boundary of the translated beam may be tangential to the first sphere and a location on the second line segment tangential to the surface of the first sphere may be above the surface of the planet by the threshold altitude.

In some examples, beam signal receiver <NUM> may be configured to receive, via the antenna array <NUM>, component signals and beamforming coefficient component <NUM> may form a beam (e.g., a receive beam) from the component signals. For instance, beam signal receiver <NUM> may be configured to receive, via the antenna array <NUM>, a set of component receive signals including reflected energy of the beam. Additionally or alternatively, beam signal receiver <NUM> may be configured to receive additional component signals that form a translated beam relative to another beam that beam signal receiver <NUM> has received. For instance, beam signal receiver <NUM> may be configured to receive, via the antenna array <NUM>, a second set of component receive signals including reflected energy of the translated beam.

Signature processing component <NUM> may be configured to process the receive beam signal based on the transmit beam signal to obtain a signature associated with an object within a limb of the planet defined by the first sphere and a second sphere that is concentric with and larger than the first sphere. In some examples, the signature may include a distance to the object, a displacement of the object over one or more of the set of times, an energy reflectivity of the object, a direction of movement of the object over one or more of the set of times, a speed of the object, a velocity of the object, an acceleration of the object, or any combination thereof. In some examples, signature processing component <NUM> may process the second set of receive beam signals based on the second transmit beam signal to obtain a second signature associated with the object within the limb of the planet.

Scanning component <NUM> may be configured to scan a beam in one or more directions over a set of time including the first time. For instance, scanning component <NUM> may indicate, to beam manager <NUM>, to update beamforming coefficients to adjust a direction of a beam (e.g., a transmit beam, a receive beam) generated by beam manager <NUM>. In some examples, scanning component <NUM> may use the signature to scan and/or track an object. For instance, if the signature includes information about a velocity of the object and a distance or location of the object, the scanning component <NUM> may track the object. Additionally or alternatively, scanning component <NUM> may determine whether the object is centered within the beam based on a strength of the signal. If the object is centered, scanning component <NUM> may indicate, to beam manager <NUM>, to adjust beamforming coefficients to dither the beam in order to detect movement. Additionally or alternatively, the scanning component <NUM> may control beamforming coefficient component <NUM> to form separate concurrent receive beams to perform tracking. In some examples, scanning component <NUM> may indicate, to beam manager <NUM>, to generate multiple receive beams at a same time in order to determine where an object is located in a transmit beam (e.g., how off-center the object is). In some examples, each of the multiple receive beams may be generated from the same set of component signals. Alternatively, different ones of the multiple receive beams may be generated from different subsets (e.g., overlapping subsets, disjoint subsets) of the set of component signals received by beam signal receiver <NUM>. The multiple receive beams may be processed by scanning component (e.g., generating sum and/or difference signals between different receive beams) to track the object. Tracking an object using multiple concurrent receive beams may be referred to as synthetic monopulse tracking.

In some examples (e.g., if antenna array <NUM> is moving), antenna array <NUM> may act as a synthetic aperture radar (SAR). In some such examples, the difference in movement of the transmitter and receiver (e.g., the difference in movement between antenna array <NUM> at a first time versus antenna array <NUM> at a later time) may be used to increase an effective aperture size and/or improve spatial resolution of the antenna array <NUM>. Using the antenna array <NUM> as a SAR may be performed if a velocity or speed of the object is determined to be below a threshold amount. In some examples, both SAR systems and non-SAR systems (e.g., an antenna array <NUM> collects each sample at a same time) may use a same scanning mechanism to collect data.

Processor <NUM> may include an intelligent hardware device (e.g., a general-purpose processor, a digital signal processor (DSP), a central processing unit (CPU), a microcontroller, an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof). The processor <NUM> may be configured to execute computer-readable instructions stored in a memory (e.g., memory <NUM>) to cause the communications network <NUM> to perform various functions (e.g., functions or tasks supporting beam management using sparse antenna arrays). For example, the communications network <NUM> or a component of the communications network <NUM> may include a processor <NUM> and memory <NUM> coupled to the processor <NUM> that are configured to perform various functions described herein.

The memory <NUM> may store code that is computer-readable and computer-executable. The code may include instructions that, when executed by the processor <NUM>, cause the communications network <NUM> to perform various functions described herein. The code <NUM> may be stored in a non-transitory computer-readable medium such as system memory or another type of memory. In some cases, the memory <NUM> may contain, among other things, a basic I/O system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices.

In some examples, beam manager <NUM>, beamforming coefficient component <NUM>, beam signal transmitter <NUM>, beam signal receiver <NUM>, signature processing component <NUM>, or various combinations or components thereof, may be implemented in hardware (e.g., in communications management circuitry). The hardware may include a processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, a discrete gate or transistor logic, discrete hardware components, or any combination thereof configured as or otherwise supporting a means for performing the functions described in the present disclosure. In some examples, a processor and memory coupled with the processor may be configured to perform one or more of the functions described herein (e.g., by executing, by the processor, instructions stored in the memory).

Additionally, or alternatively, beam manager <NUM>, beamforming coefficient component <NUM>, beam signal transmitter <NUM>, beam signal receiver <NUM>, signature processing component <NUM>, scanning component <NUM>, or various combinations or components thereof, may be implemented in code <NUM> (e.g., as communications management software or firmware), executed by processor <NUM>. If implemented in code <NUM> executed by processor <NUM>, the functions of beam manager <NUM>, beamforming coefficient component <NUM>, beam signal transmitter <NUM>, beam signal receiver <NUM>, signature processing component <NUM>, scanning component <NUM>, or various combinations or components thereof may be performed by a general-purpose processor, a DSP, a central processing unit (CPU), an ASIC, an FPGA, or any combination of these or other programmable logic devices (e.g., configured as or otherwise supporting a means for performing the functions described in the present disclosure).

<FIG> illustrates an example of a scanning scenario <NUM> that supports scanning operations for co-located satellite antennas in accordance with aspects of the present disclosure.

In some examples, a set of co-located satellite antennas <NUM> (e.g., a satellite system <NUM> or a set of satellite systems <NUM> as described with reference to <FIG>) may be deployed in space orbits (e.g., low earth orbits, medium earth orbits, geostationary orbits) relative to planet <NUM> (e.g., Earth). The set of co-located satellite antennas <NUM> may include satellite antennas <NUM>-a, <NUM>-b, and <NUM>-c. In some examples, an object <NUM> may be located within a limb <NUM> of the planet <NUM>. For instance, the limb <NUM> may be defined by a first sphere <NUM>-a and a second sphere <NUM>-b that is concentric with and larger than the first sphere <NUM>-a. In some examples, each satellite antenna of the set of co-located satellite antennas <NUM> (e.g., satellite antennas <NUM>-a, <NUM>-b, and <NUM>-c) may include an omnidirectional antenna. Additionally or alternatively, each satellite antenna of the set of antenna antennas may be coupled with a respective satellite, where the respective satellite coupled with at least one satellite antenna of the set of satellite antennas is different than the respective satellite coupled with another satellite antennas of the set of satellite antennas.

In some examples, a central processor (e.g., a processor of one of satellite antennas <NUM>-a, <NUM>-b, or <NUM>-c, a processor of another satellite antenna configured to communicate with the set of co-located satellite antennas <NUM>, or a processor of a ground terminal located on planet <NUM> that is configured to communicate with the set of co-located satellite antennas <NUM>) may apply a first set of beamforming coefficients to a transmit beam signal to generate a set of component transmit signals (e.g., component transmit signals <NUM>-a, <NUM>-b, and <NUM>-c) for transmission by the set of co-located satellite antennas <NUM>. The set of co-located satellite antennas <NUM> may transmit the set of component transmit signals to form a beam <NUM>. For instance, satellite antenna <NUM>-a may transmit a first component transmit signal <NUM>-a, satellite antenna <NUM>-b may transmit a second component transmit signal <NUM>-b, and satellite antenna <NUM>-c may transmit a third component transmit signal <NUM>-c. In some examples, a first line segment <NUM> at a boundary of the beam <NUM> may be tangential to the first sphere <NUM>-a encompassing the planet <NUM>. A location on the first line segment <NUM> tangential to the surface of the first sphere <NUM>-a may be above a surface of the planet <NUM> by a threshold altitude <NUM>. In some examples, the boundary of the beam <NUM> may be defined by a contour of a particular decibels (dB) point on a beam profile of the beam <NUM>. For instance, the boundary of the beam <NUM> may be a <NUM> dB contour of the beam <NUM> or a <NUM> dB contour of beam <NUM>. In some examples, the boundary may be configured such that that an amount of energy of the beam <NUM> that is directed towards the planet <NUM> is below a threshold amount and/or such that reflected energy is subjected to below a threshold amount of interference from the surface of the planet <NUM>. In some examples, the set of co-located satellite antennas <NUM> may be configured to receive, from a system distinct from the set of co-located satellite antennas, an indication of a beam direction, a velocity of the object <NUM>, an acceleration of the object <NUM>, or any combination thereof. In some such examples, applying the first set of beamforming coefficients may be based at least in part on receiving the indication of the beam direction, the velocity of the object <NUM>, the acceleration of the object <NUM>, or any combination thereof.

In some examples, the set of co-located satellite antennas <NUM> may receive a set of component receive signals (e.g., component receive signals <NUM>-a, <NUM>-b, and <NUM>-c) that include reflected energy of beam <NUM>. For instance, object <NUM> may reflect at least a portion of the energy of beam <NUM>. In one example, object <NUM> may reflect at least a portion of the energy of beam <NUM> as first component receive signal <NUM>-a, at least a portion of the energy of beam <NUM> as second component receive signal <NUM>-b, and at least a portion of the energy of beam <NUM> as third component receive signal <NUM>-c. The central processor may apply a second set of beamforming coefficients to the set of component receive signals to obtain a receive beam signal associated with the beam and may process the receive beam signal based on the transmit beam signal to obtain a signature associated with object <NUM>.

In some examples, the central processor may apply the first set of beamforming coefficients to a second transmit beam signal to generate a second set of component transmit signals for transmission by the set of co-located satellite antennas <NUM>. In some such examples, the central processor may apply a space-time block code. For instance, the central processor may apply a set of beamforming coefficients and may transmit a different modulated signal using space-time block coding methods at a same frequency (e.g., as opposed to transmitting an identical modulated signal at the same frequency for each antenna element). By transmitting the different modulated signal using the space-time block coding methods, the central processor may form a first net transmit beam signal and a second net transmit beam signal, where processing the set of receive beam signals to obtain the signature is based on applying the space-time block code used in the first net transmit beam signal and the second net transmit beam signal. Space-time block coding may involve transmitting multiple related but different signals across multiple satellite antennas. In some examples, the relation of each modulated signal to each other modulated signal may be determined by the space-time block code.

In some examples, the techniques described herein may be associated with one or more advantages. For instance, scanning the limb <NUM> with a beam with a boundary tangential to first sphere <NUM>-a may be associated with decreased background clutter as compared to scanning the surface of planet <NUM>. Additionally, scanning the limb <NUM> with such a beam may have less stringent or non-existent constraints for terrestrial power-flux density. Accordingly, the likelihood of successfully scanning the object <NUM> may be increased as compared to an object on the surface of the planet <NUM>. Additionally, scanning the object <NUM> in the limb <NUM> may be associated with reduced interference on transmissions that occur on the surface of the planet <NUM>.

<FIG> illustrates an example of a scanning sequence <NUM> that supports scanning operations for co-located satellite antennas in accordance with aspects of the present disclosure. In some examples, scanning sequence <NUM> may implement one or more aspects of scanning scenario <NUM>. For instance, set of co-located satellite antennas <NUM>-a may be an example of a set of co-located satellite antennas <NUM> as described with reference to <FIG> and satellite antennas <NUM>-d, <NUM>-e, and <NUM>-f may each be an example of a satellite antenna <NUM>-a, <NUM>-b, or <NUM>-c as described with reference to <FIG>. Additionally or alternatively, object <NUM>-a may be an example of an object <NUM> as described with reference to <FIG> and beams <NUM>-a and <NUM>-b may be an example of a beam <NUM> as described with reference to <FIG>.

At a first time <NUM>-a, a central processor associated with set of co-located satellite antennas <NUM>-a (e.g., a processor within the set of co-located satellite antennas <NUM>-a, a processor associated with a satellite antenna excluded from the set of co-located satellite antennas <NUM>-a, or a processor of a ground station configured to communicate with the set of co-located satellite antennas <NUM>-a) may apply a first set of beamforming coefficients to a transmit beam signal to generate a set of component transmit signals for transmission by set of co-located satellite antennas <NUM>-a. The set of co-located satellite antennas <NUM>-a may transmit a set of component transmit signals to form beam <NUM>-a. A first line segment at a boundary of beam <NUM>-a may be tangential to a first sphere (e.g., sphere <NUM>-a as described in <FIG>) having a surface that encompasses a planet, where a location on the first line segment tangential to the surface of the first sphere. In some examples, the boundary of beam <NUM>-a may be defined by a contour of a particular dB point. For instance, the boundary of beam <NUM>-a may be a <NUM> dB contour of beam <NUM>-a or a <NUM> dB contour of beam <NUM>-a, although other values may also be used. In some examples, the boundary may be configured such that that an amount of energy of beam <NUM>-a that is directed towards the planet is below a threshold amount (e.g., a power flux density limit) and/or such that reflected energy is subjected to below a threshold amount of interference from the surface of the planet. The set of co-located satellite antennas <NUM>-a may receive a set of component receive signals including reflected energy of beam <NUM>-a. The central processor may apply a second set of beamforming coefficients to the set of component receive signals to obtain a receive beam signal associated with the beam and may process the receive beam signal to obtain a signature associated with object <NUM>-a.

At a second time <NUM>-b (e.g., a time after <NUM>-a) the central processor may apply a third set of beamforming coefficients to a second transmit beam signal to generate a second set of component transmit signals for transmission by the set of co-located satellite antennas <NUM>-a. The set of co-located satellite antennas may transmit the second set of component transmit signals to form a translated beam <NUM>-b, where a second line segment at a boundary of translated beam <NUM>-b may be tangential to the surface of a third sphere that encompasses the planet. In some such examples, a location on the second line segment tangential to the surface of the third sphere may be above the surface of the planet by a second threshold altitude. In some examples, the third sphere may be smaller or larger than the first sphere depending on which direction (e.g., which direction horizontally, which direction vertically) the object <NUM>-a moves from time <NUM>-a to time <NUM>-b and/or depending on a direction of beam <NUM>-b relative to beam <NUM>-a. In other examples, the third sphere may have a same size as the first sphere (e.g., if the object <NUM>-a remains stationary). The set of co-located satellite antennas <NUM>-a may receive a second set of component receive signals including reflected energy of translated beam <NUM>-b and may apply a fourth set of beamforming coefficients to the second set of component receive signals to obtain a second set of receive beam signals associated with translated beam <NUM>-b. In some such examples, the central processor may process the second set of receive beam signals based on the second transmit beam signal to obtain a second signature associated with the object <NUM>-a.

By obtaining the signature at first time <NUM>-a and the second signature at second time <NUM>-b, the central processor may scan the beam in one or more directions over a set of times. In some examples, the one or more directions may include a first direction corresponding to a second time and a second direction corresponding to a third time, where the second direction is an opposing direction to the first direction. In some examples, the signature may include a distance to the object, a displacement of the object over one or more of the set of times, an energy reflectivity of the object, a direction of movement of the object over one or more of the set of times, a speed of the object, a velocity of the object, an acceleration of the object, or any combination thereof.

<FIG> illustrates an example of a limb scanning geometry <NUM> that supports scanning operations for co-located satellite antennas in accordance with aspects of the present disclosure. In some examples, limb scanning geometry <NUM> may implement one or more aspects of scanning scenario <NUM>. For instance, satellite antenna <NUM>-g may be an example of a satellite antenna <NUM>-a, <NUM>-b, or <NUM>-c as described with reference to <FIG>. Additionally or alternatively, satellite antenna <NUM>-g may represent a set of satellite antennas (e.g., a set <NUM> as described with reference to <FIG>). Inner sphere <NUM> may be an example of a planet <NUM> or first sphere <NUM>-a as described with reference to <FIG>, and outer sphere <NUM> may be an example of a first sphere <NUM>-a or a second sphere <NUM>-b as described with reference to <FIG>.

Satellite antenna <NUM>-g may have an altitude <NUM> (i.e., a) relative to inner sphere <NUM>. Additionally, inner sphere <NUM> may have a radius R (e.g., approximately <NUM>). In some examples, satellite antenna <NUM>-g may generate a scanning beam with an inner boundary <NUM> and an outer boundary <NUM>. The inner boundary <NUM> of the scanning beam may be set at a grazing angle θFOV relative to nadir. A first intersection of inner boundary <NUM> with outer sphere <NUM> may be referred to as nearest and a second intersection of inner boundary <NUM> with outer sphere <NUM> may be referred to as farthest. Additionally, a third intersection of inner boundary <NUM> with inner sphere <NUM> may be referred to as tangent. An angle between inner boundary <NUM> and outer boundary <NUM> may be referred to as θincrement. An angle between nadir and a first line extending between a center of inner sphere <NUM> and tangent may be referred to as θLAT. An angle between the first line extending between a center of inner sphere <NUM> and tangent and a second line extending between the center of inner sphere <NUM> and nearest may be referred to as θh. In some examples, a width <NUM> between inner sphere <NUM> and outer sphere <NUM> may be referred to as h (e.g., a maximum altitude of a vehicle that may be scanned in an earth limb). In some examples, a distance from satellite antenna <NUM>-g to tangent may be approximately slantFOV.

In some examples, slantFOV may be equal to <MAT> <MAT>. In some examples, hchord may be equal to <MAT>. In some examples, nearest may be equal to <MAT> and farthest may be equal to slantFOV + <MAT>. In some examples, θLAT may be equal to <MAT> and θh may be equal to <MAT>. In some examples, θincrement may be defined as <MAT>. In some examples, θLAT may be defined as a latitude angle relative to a nadir line. In some examples, θLAT may be equal to <MAT> and θh may be defined as a deviation angle from θLAT.

In cartesian coordinates, the coordinates of tangent may be (Rcos(θLAT), Rsin(θLAT)) and TangentLine (e.g., inner boundary <NUM>) may be defined as <MAT>. In some examples of cartesian coordinates, an xintercept of TangentLine may be defined as <MAT> and a yintercept of TangentLine may be defined as <MAT>. In some examples of cartesian coordinates, nearest may have coordinates defined as ((R + h) cos(θLAT - θh), (R + h) sin(θLAT - θh)) and farthest may have coordinates defined as ((R + h) cos(θLAT + θh), (R + h) sin(θLAT + θh)). In some examples of cartesian coordinates, a NadirLine may be defined as (x, <NUM>) where x may have an integer value, and a location of satellite antenna <NUM>-g may be defined as (R + a, <NUM>).

In polar coordinates (e.g., (ρ, θ)), tangent may be defined as (R, θLAT) and TangentLine may be defined as ( <MAT>, θ). Coordinates of satellite antenna <NUM>-g may be defined as (R + a, <NUM>) and coordinates of NadirLine may be defined as (ρ, <NUM>). Coordinates of nearest may be defined as (R + h, θLAT - θh) and coordinates of farthest may be defined as (R + h, θLAT + θh).

<FIG> shows a flowchart illustrating a method <NUM> that supports scanning operations for co-located satellite antennas in accordance with aspects of the present disclosure. The operations of the method <NUM> may be implemented by a communications network or its components as described herein. For example, the operations of the method <NUM> may be performed by a communications network <NUM> as described with reference to <FIG>. In some examples, a communications network may execute a set of instructions to control the functional elements of the communications network to perform the described functions. Additionally or alternatively, the communications network may perform aspects of the described functions using special-purpose hardware.

At <NUM>, the method includes applying a first set of beamforming coefficients to a transmit beam signal to generate a set of component transmit signals for transmission by a set of co-located satellite antennas, where an inter-element spacing of satellite antennas of the set of co-located satellite antennas is different across the set of co-located satellite antennas. The operations of <NUM> may be performed in accordance with examples as disclosed herein.

At <NUM>, the method includes transmitting, by the set of co-located satellite antennas at a first time, the set of component transmit signals to form a beam, where a first line segment at a boundary of the beam is tangential to a first sphere having a surface that encompasses a planet, where a location on the first line segment tangential to the surface of the first sphere is above a surface of the planet by a threshold altitude. The operations of <NUM> may be performed in accordance with examples as disclosed herein.

At <NUM>, the method includes receiving, by the set of co-located satellite antennas, a set of multiple component receive signals including reflected energy of the beam. The operations of <NUM> may be performed in accordance with examples as disclosed herein.

At <NUM>, the method includes applying a second set of beamforming coefficients to the set of multiple component receive signals to obtain a receive beam signal associated with the beam. The operations of <NUM> may be performed in accordance with examples as disclosed herein.

At <NUM>, the method includes processing the receive beam signal based on the transmit beam signal to obtain a signature associated with an object within a limb of the planet defined by the first sphere and a second sphere that is concentric with and larger than the first sphere. The operations of <NUM> may be performed in accordance with examples as disclosed herein.

<FIG> shows a flowchart illustrating a method <NUM> that supports scanning operations for co-located satellite antennas in accordance with aspects of the present disclosure. The operations of the method <NUM> may be implemented by a communications network or its components as described herein. For example, the operations of the method <NUM> may be performed by a communications network as described with reference to <FIG>. In some examples, a communications network may execute a set of instructions to control the functional elements of the communications network to perform the described functions. Additionally or alternatively, the communications network may perform aspects of the described functions using special-purpose hardware.

At <NUM>, the method includes transmitting, by the set of co-located satellite antennas at a first time, the set of component transmit signals to form a beam, where a first line segment at a boundary of the beam is tangential to a first sphere having a surface that encompasses Earth, where a location on the first line segment tangential to the surface of the first sphere is above a surface of the Earth by a threshold altitude. The operations of <NUM> may be performed in accordance with examples as disclosed herein.

At <NUM>, the method includes processing the receive beam signal based on the transmit beam signal to obtain a signature associated with an object within a limb of the Earth defined by the first sphere and a second sphere that is concentric with and larger than the first sphere. The operations of <NUM> may be performed in accordance with examples as disclosed herein.

At <NUM>, the method may include scanning the beam in one or more directions over a set of times including the first time. The operations of <NUM> may be performed in accordance with examples as disclosed herein.

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.

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.

Claim 1:
A method, comprising:
applying a first set of beamforming coefficients to a transmit beam signal to generate a set of component transmit signals (<NUM>-a, <NUM>-b, <NUM>-c) for transmission by a set of co-located satellite antennas (<NUM>), wherein an inter-element spacing of satellite antennas (<NUM>-a, <NUM>-b, <NUM>-c) of the set of co-located satellite antennas (<NUM>) is different across the set of co-located satellite antennas (<NUM>);
transmitting, by the set of co-located satellite antennas (<NUM>) at a first time (<NUM>-a), the set of component transmit signals (<NUM>-a, <NUM>-b, <NUM>-c) to form a beam (<NUM>), wherein a first line segment (<NUM>) at a boundary of the beam (<NUM>) is tangential to a first sphere (<NUM>-a) having a surface that encompasses Earth (<NUM>), wherein a location on the first line segment (<NUM>) tangential to the surface of the first sphere (<NUM>-a) is above a surface of the Earth (<NUM>) by a threshold altitude (<NUM>);
receiving, by the set of co-located satellite antennas (<NUM>), a plurality of component receive signals (<NUM>-a, <NUM>-b, <NUM>-c) comprising reflected energy of the beam (<NUM>);
applying a second set of beamforming coefficients to the plurality of component receive signals (<NUM>-a, <NUM>-b, <NUM>-c) to obtain a receive beam signal associated with the beam (<NUM>); and
processing the receive beam signal based at least in part on the transmit beam signal to obtain a signature associated with an object (<NUM>) within a limb (<NUM>) of the Earth (<NUM>) defined by the first sphere (<NUM>-a) and a second sphere (<NUM>-b) that is concentric with and larger than the first sphere (<NUM>-b).