Non-cooperative positioning, navigation, and timing recovery from VSAT communication signals using multibeam phased array antennas.

Abstract

A ground antenna determines the current time and its own location from received signals transmitted by communication artificial Earth satellites. A high-gain, multi-beam, electrically steered antenna, combined with a processing system, measures the angle between two or more satellites and determines the current distance to each satellite through information broadcast on the TT&C channel. Knowledge of the angle and distance, along with the satellites' trajectories, can be combined with their locations predicted by satellite ephemeris data to triangulate the receiver's location. This system differs from traditional GPS antennas because it does not require coordinated active communication with the satellites to derive a location estimate. Location is calculated by the ground terminal, not the satellite. This system can be used when other location services are offline, jammed, or otherwise unavailable to maintain location and time synchronization.

Description

[Technical Field]

[0001] The present invention relates to determining the location and time of a receiver based on signals transmitted from satellites.

[0002] [Related Applications] This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 958,043, filed January 7, 2020, on the contents of which the present application relies, the contents of which are incorporated herein by reference in their entirety. [Background technology]

[0003] The Global Positioning System (GPS) and more generally the Global Navigation Satellite System (GNSS) are commonly used worldwide for civilian and defense purposes. These systems broadcast highly accurate, dedicated GNSS signals using constellations of specially designed satellites, collectively referred to herein as GNSS satellites. These dedicated GNSS signals are structured to enable a receiver to obtain direct time synchronization and determine distance measurements from each satellite in the constellation to the receiver, thereby determining the receiver's location on Earth. Multiple such GNSS satellite systems are in operation or planned for operation, including GPS (USA), Galileo (EU), GLONASS (Russia), BeiDou (China), and others. Most of these systems operate at the same or closely separated frequencies between about 1 GHz and about 2 GHz and are intended to interoperate, allowing a receiver to access multiple networks for greater accuracy and reliability. If one constellation is unavailable, another may still be accessible.

[0004] GNSS systems operate in the same basic way. A receiver interprets signals transmitted from satellites and determines the current time based on the GPS system epoch. The time and signal structure are used to determine the distance from each satellite, which is then used to estimate position. Dedicated GNSS signals transmit using CDMA (Code Division Multiple Access) technology, which allows multiple satellites to transmit on the same frequency without interfering with each other. This approach is effective in very low signal-to-noise ratio (SNR) environments, where very long codes improve SNR through signal correlation and allow signals to be reliably identified. The coded signals from dedicated GNSS satellites are designed to provide precise time calibration and contain information about the health and status of the satellite and others in the constellation, including orbital parameters. A conventional GNSS receiver is shown in Figure 1. In Figure 1, an antenna 102 of the receiver 101 simultaneously receives signals from multiple GNSS satellites 103, 105 in one or more constellations. Signals 107, 109 from satellites in each constellation are received by antenna 102 and separated and interpreted by receiver 101 to produce calculations of the time and location of the receiver.

[0005] Assuming the current time is already known with high accuracy, to determine location, highly accurate estimates of the current time and the time-of-flight of radio signals from three or more satellite locations are required to establish the receiver's position in three dimensions. The minimum number of satellites required to simultaneously determine the current time and unknown location is four. Four measurements (each resulting in an equation) are required to be able to determine the four unknowns: the values ​​of the three position variables x, y, z, and time t. Once the distance and time of transmission start are determined for each transmitting satellite, the satellite's position is then calculated based on its known ephemeris and the current time, and the receiver's position can be calculated by trilateration.

[0006] Like all wireless communication systems, GNSS transmissions are susceptible to jamming or can even be intentionally disabled by operators. By operating in similar bands, jamming signals can affect all networks simultaneously. By sharing a common architecture and frequency band, the benefit of interoperability comes with the disadvantage that multiple networks can potentially become unavailable simultaneously due to the same cause.

[0007] For this reason, alternative positioning, navigation, and timing (PNT) systems are desirable as backups to GNSS systems. Alternatives may include the use of high-precision local clocks and inertial measurement units (IMUs), ground-based positioning systems like LORAN (Long-Range Navigation), or triangulation from terrestrial cell phone towers. With the exception of standalone IMU approaches (which have limited precision and accuracy), these alternatives still require support from larger systems and infrastructure, and as dedicated PNT systems, they are susceptible to jamming or disabling in the same way as their satellite counterparts.

[0008] There are many more visible non-GNSS satellites than are available in dedicated GNSS constellations. As used herein, a non-GNSS satellite refers to any satellite that broadcasts a signal to the ground but is not part of a dedicated, coordinated satellite system to support independent measurements of position and time by ground receivers. Specifically, a non-GNSS satellite is a satellite that does not broadcast a signal designed to be used for positioning (e.g., without limitation in framing structure, coding, error correction coding, data message content, frequency band and bandwidth, and power level) and is therefore typically not usable or immediately usable in any way by a ground terminal for performing positioning and timing calculations. With the emergence of low-Earth orbit (LEO) megaconstellations of communications and Earth observation satellites, the number of visible non-GNSS satellites is rapidly increasing. If the positions and trajectories of non-GNSS satellites are known (although typically not to the same accuracy as dedicated GNSS satellites, since that accuracy is not required for typical non-GNSS purposes), the distance to those non-GNSS satellites can be calculated, and the time can be determined, then a ground terminal can calculate its own position independent of the dedicated GNSS system.

[0009] However, calculating the distance to non-GNSS satellites presents a challenge. GNSS systems are specifically designed to transmit signals that can be received by small, low-gain, low-efficiency receivers, using signals designed to be demodulated and interpreted well below the noise floor, and to transmit data that specifically supports the extraction of time and position information. However, non-GNSS satellites are not designed to function as positioning systems and therefore operate at different (often much higher) frequencies, transmit different information with varying degrees of accuracy where timing information is less prominent, and require a much higher signal-to-noise ratio at the receiver to demodulate the transmitted information.

[0010] To date, proposals for using non-GNSS satellites for geolocation have relied on active methods from the perspective of the ground terminal by communicating with the satellite to calculate round-trip signal propagation times, or to estimate the location on the ground from which the signal originates and then relay that information back to the ground, or to reflect radar pulses clearly off the satellite to measure range and direction. While these methods are sufficient for some applications, they lack the advantages of traditional GNSS approaches. Chief among these advantages is that ground receivers are passive and do not necessarily need to announce their location using broadcasts. Summary of the Invention

[0011] A ground antenna determines the current time and its own location from received signals transmitted by communication artificial Earth satellites. A high-gain, multi-beam, electrically steered antenna, combined with a processing system, measures the angle between two or more satellites and determines the current distance to each satellite through information broadcast on the TT&C channel or other broadcast or communication channel. Knowledge of the angle and distance, along with the satellites' trajectories, can be combined with their locations predicted by satellite ephemeris data to triangulate the receiver's location. This system differs from traditional GPS antennas and receivers because it does not require satellites to broadcast dedicated signals to calculate position and time, and from other non-GNSS methods of determining position and time because it does not require coordinated and active communication with satellites to derive location estimates. Location is calculated by the ground terminal, not the satellite. This system can be used when other location services are offline, jammed, or otherwise unavailable to maintain location and time synchronization. [Brief explanation of the drawings]

[0012] [Figure 1]FIG. 1 illustrates a standard GNSS receiver with a multiple satellite constellation indicative of a conventional satellite PNT system. [Figure 2] FIG. 1 illustrates a multi-beam, high-gain VSAT (Very Small-Aperture Terminal) antenna configured to listen for signals, such as Telemetry, Tracking, & Control (TT&C) signals, from multiple satellites in different orbits and constellations to enable calculation of PNT data by one or more of the angular separation between the satellites, the trajectories of the individual satellites, the signal time of flight to each satellite, and the Doppler shift of the signal from each satellite. [Figure 3] 1 illustrates a multi-beam high-gain VSAT antenna with a receiver for measuring signals and a computational element for determining the location of the receiver. [Figure 4] FIG. 1 illustrates an antenna configured to receive signals such as TT&C signals from each of a LEO (Low Earth Orbit), a MEO (Medium-Earth Orbit), and a GEO (Geostationary Earth Orbit) satellite. [Figure 5] FIG. 1 illustrates a VSAT PNT system configured with one of several possible external communication systems that access satellite ephemeris data: a) a two-way satellite link; b) satellite broadcast; c) a terrestrial wireless or wired communication network; or d) stored ephemeris data. [Figure 6] FIG. 10 is a process diagram of the operation of the antenna to calculate timing and position data. DETAILED DESCRIPTION OF THE INVENTION

[0013] As described above, conventional GNSS and GPS systems utilize specially configured signals in dedicated frequency bands to support and enable highly accurate time and position determination. The present system and method instead enable the determination of location and timing information without support from dedicated signals from non-GNSS satellites in a different frequency band than the GNSS system (such as those readily available from GNSS satellites), and can include information from any transmitting non-GNSS satellite in the receiver's operating frequency band. To calculate position, the present system relies on the simultaneous reception of signals from multiple non-GNSS satellites in different directions relative to the receiver, which requires the receiver to generate multiple antenna beams to receive the signals. The system operates non-cooperatively because it does not require the non-GNSS satellites to transmit special signals or even the receiver to be aware of their presence or that the signals are being used for PNT extraction. For example, a receiver can simultaneously extract timing synchronization signals transmitted by beacons or independent TT&C links in the Ka or Ku SATCOM bands from multiple satellites in the same or different LEO communication or Earth observation constellations and combine the timing information derived from those signals with timing information received from GEO or MEO satellites to generate reliable time and location estimates. Thus, non-GNSS satellites can continue to transmit and receive standard non-GNSS signals without any operational (or noticeable) differences between when their signals are being used to calculate position and when they are not. The advantage of this non-cooperative approach is that there is no way for a third party to predict or know which satellites, signals, channels, or frequencies are being used for positioning by a particular end user. This increases the reliability and availability of positioning data because there is no system that can be jammed, spoofed, or interfered with.

[0014] The principles and mathematics behind calculating a receiver's position given distance estimates from a set of known locations are well understood. The present disclosure enables a new source of necessary input data (distance and location of source satellites) compared to traditional GNSS systems. Unlike GNSS receivers that use omnidirectional antennas to listen to a set of known satellites that broadcast specific data to enable position determination, the present system enables distance and location calculations without support or dedicated signals from satellites in frequency bands that operate at signal levels that require electrically large, directional antennas for reception.

[0015] This disclosure describes a different method of obtaining time, position, and distance to distant satellites compared to traditional GNSS systems. This system relies on existing transmissions from non-GNSS satellites, such as beacon transmissions, which are already present on all satellites operating for Time To Know and Control (TT&C) purposes. Beacons are narrowband signals modulated with stationkeeping parameters and other satellite health parameters. Beacons are used by satellite operators to manage spacecraft and by satellite users to locate and lock onto satellites for communication purposes.

[0016] The primary limitation of using non-GNSS satellites for passive geolocation is supporting the frequency bands of interest. Only a limited number of non-GNSS satellites operate in the L-band and other low-frequency channels, due to the availability of much more bandwidth at higher frequencies. However, higher-frequency communication links are generally designed for high-gain directional antennas to improve the spectral efficiency of such communications. Path loss and instantaneous bandwidth increase at higher frequencies, which necessitates either higher power transmission from the satellite or larger (and heavier) directional antennas on both the satellite and the ground, or both. Directional antennas imply the use of electrically large apertures, with sizes significantly larger than the wavelength at the operating frequency, producing gains in the 10-70 dBi, or more commonly 15-50 dBi, range, rather than omnidirectional antennas (such as conventional GNSS patch antennas), which typically have a gain of 0 dBi to 7 dBi. Directional ground antennas, such as parabolic reflectors, can typically only point in one direction at a time and can only listen to one satellite at a time; if signals from more than two satellites are needed simultaneously, many antennas are required.

[0017] The present disclosure overcomes this limitation by using either a multi-beam, electrically steered phased array antenna or a multi-beam, electrically steered lens array antenna. According to this embodiment, a single antenna aperture can generate multiple high-gain receive beams in different directions, while (for example) allowing a single terminal with a single antenna aperture to simultaneously passively listen to multiple Ka-band satellites in different parts of the sky. Only electrically steered antennas, such as phased array antennas, digital beamforming array antennas, liquid crystal antennas, or lens array antennas, are capable of generating multiple independent beams in different, variable directions, which is required for the operation of this system. Additionally, because the beam angles are so narrow, the direction and trajectory of non-GNSS satellites can be directly measured, something that conventional GPS receivers using omnidirectional antennas cannot do. Timing information can be extracted by locking on to and passively listening to each satellite's respective beacon signal, which carries TT&C data. Locking on to a beacon is done in the same way as locking on to a communications satellite transponder, using the antenna's beam-pointing capabilities to track the satellite's location when the satellite or antenna is moving.

[0018] Passive operation is important in some applications where strict transmission control is implemented. One of the advantages of conventional GNSS ground systems compared to active location systems such as radar or transponders is that their use is difficult to detect because they do not transmit signals but only receive signals from GNSS satellites. This system has the same advantage as cooperative positioning methods using non-GNSS satellites, which rely on measuring round-trip communication times (and therefore require transmissions from the receiver).

[0019] The positions and trajectories of non-GNSS satellites are not as precisely determined as those of dedicated GNSS satellites, and the timing or position information onboard each satellite that is broadcast as part of the communication or TT&C signals is not as precise or synchronized between non-GNSS satellites as that of dedicated GNSS satellites. This limits the accuracy that can be obtained. However, alternative methods of geolocation are of great value when the GNSS constellation is jammed or disabled, especially when many different satellites are available. The change from tens of GNSS satellites to hundreds or even thousands of non-GNSS satellites that can be used to determine even coarse location information results in a significant improvement in overall system reliability and resilience, as the increase in the number of satellites, as well as the increase in the frequency bands and spectrum that must be jammed, increases the difficulty of jamming or blocking signals.

[0020] 2 and 3, there is shown a satellite communications system 201 having an antenna 202, a receiver 305, a signal processor 307, and a digital processor 309. The multi-beam, electrically steered antenna 202 can be used to simultaneously receive signals from (and potentially transmit signals to) multiple non-GNSS satellites 203, 205 in different orbits. A receiver 305 is provided for each beam 211, 213, 303 to receive and interpret signals from the satellites. These signals are typically satellite beacons that contain time and location identifying data.

[0021] The signal processor 307 and digital processor 309 control the antenna 202 and calculate the location of the receiver based on the content of the received signal. The signal processor 307 and / or digital processor 309 may each include a processing device such as a processor or controller, computer, ASIC, etc. The signal processor 307 conditions the signal and converts the waveform into a data stream of information. This data stream can then be provided to the digital processor 309. The digital processor 309 may be a controller. The processor 309 combines the signals from all of the receivers 305 to determine location by trilateration and also monitors the signals to control the pointing direction(s) of the antenna 202. The antenna can be selected to operate in any frequency band where non-GNSS satellites transmit, including UHF, L, C, X, Ku, Ka, V, and W bands, although the greatest value lies at higher frequencies (X-band and above, including the common VSAT Ku and Ka bands) where high antenna gain and narrow beamwidths are readily achievable. High-gain antennas are capable of receiving and interpreting low-power signals with reduced error rates. In one exemplary, non-limiting embodiment, an antenna and system is described that operates at frequencies lower than the Ka VSAT frequencies, and selecting a VSAT band allows for the use of any existing communications satellites, as well as reception of future communications satellites (such as LEO networks). However, the system can be used with any satellite communications band or Earth observation band in which satellites broadcast their TT&C information 207, 209.

[0022] The multi-beam antenna is commanded by the controller 309 to search for and locate satellites in view based on an estimate of the current time and a list of satellite ephemeris predicted to be in view, or by a blind search of the sky to locate three or more satellites.

[0023] Once the positions of three or more non-GNSS satellites have been determined by the controller 309 and the antenna 202 has been commanded to steer a beam 303 to each satellite 203, 205, the receiver 305 receives the beacon transmissions from each satellite and extracts the TT&C signals 207, 209. The information carried by the received signals is generated in the receiver 305, further processed and combined in the signal processing system 307, and then passed to the digital processor 309 for analysis and final calculation of position and time. The received data contains timing information and possibly Keplerian components of satellite location, in addition to purely internal signals regarding satellite health that are useful only to the operator. The time at which a signal was transmitted from a satellite is included in the transmission, and the satellite's location at the time the signal was transmitted can be inferred based on the satellite identification, the time of transmission, and ephemeris data obtained from either the transmission itself or an independent almanac.

[0024] The current time at the terminal is determined by the processor 309 by jointly considering information broadcast from all connected non-GNSS satellites and calculating the difference in propagation time between three or more satellites. Then, using the time-of-flight and the known satellite positions at the current known time, the processor 309 calculates the receiver's location. The current time, time difference, and position are calculated according to any suitable technique, such as methods used in GNSS. Once even a coarse time is known or estimated, further refinement of the estimated satellite location can be generated based on satellite ephemeris data. The accuracy of the location and time measurements is affected by the accuracy and synchronization between different non-GNSS satellites and the inevitable variations in signal timing as the signal propagates through the atmosphere. For example, a LEO constellation may have a health signal transmitted from each satellite that periodically transmits a timestamp and a set of satellite-specific data. The timestamp transmission then forms the basis for timing and position calculations.

[0025] Improved time accuracy, which in turn leads to improved position accuracy, can be obtained by including a miniaturized atomic clock or other high-precision timing reference signal in the receiver 305 to improve the holdover (time accuracy over time) of the current time estimate generated from the received satellite signals. The atomic clock supplements and stabilizes clock signals derived from non-GNSS satellite signals, allowing signals to be received from different satellites at different times and subsequently combined into highly accurate position and time estimates.

[0026] In one embodiment, shown in FIG. 5, the system 201 has an almanac or database 501 of ephemeris data for various satellites that can be used to determine its location, or a method for obtaining such an almanac for all satellites in view or a subset of satellites with tracked locations. GNSS systems include mechanisms for standardly distributing timely and accurate almanacs for the entire system in the navigation signals themselves, but non-GNSS communication satellites and systems do not distribute this data or do so in a standard manner. The ephemeris data forming the almanac of a non-GNSS system can be broadcast over a transmission signal or TT&C link in the form of Keplerian elements or other formats, but generally not to the same level of accuracy as that provided by a GNSS almanac. The positioning system 201 must know the locations of the GNSS and / or non-GNSS satellites from whose signals it is receiving information in order to determine its own location.

[0027] Because orbits are subject to perturbations, satellite ephemeris data changes periodically, necessitating a method for periodically obtaining an updated almanac. During a "cold" start, with no knowledge of time or position, some information is needed to estimate initial time and position. The limited number and stable location of geostationary satellites means that their orbital data can be stored in the system's 201 memory 501 to allow for initial position and time determination, even if the data accuracy is limited. A cooperative, active, two-way satellite link 505 established with one or more non-GNSS communication satellites allows for requests for updated almanacs from the Internet to obtain ephemeris data for other non-GNSS satellites that may not be present in the internal database. A cooperative method that maintains the passive nature of the receiver can be used as part of a larger system in which one or more satellite transponders are configured to constantly broadcast ephemeris data (forming an almanac) for a large number of non-GNSS satellites, allowing the positioning system 201 to obtain an accurate almanac without the need for active two-way communication.

[0028] Alternatively, depending on the application and availability, the almanac information can be obtained similarly using terrestrial communication systems such as mobile networks 503 or wired connections. If this system is used in a wider system, the almanac information can also be broadcast by one or more satellites 507, retaining the advantage of not requiring active broadcasting from the receiver to determine location, although this requires support from the satellites even if the signals and systems are not specifically designed to support positioning.

[0029] The process of determining the position and time of the system 201 has several parts. Once the position and time are determined, the system can utilize any suitable algorithms and calculations similar to those used in standard GNSS systems. Referring to Figure 6, the operation of the system is shown. Upon operation beginning (603), an independent non-GNSS satellite is located, locked onto, and listened to (step 607) using each one of a number of beams 605. Due to the difference in frequency bands between GNSS and non-GNSS satellites, it is unlikely that both sets of signals can be used to improve the resulting position measurement.

[0030] 4, once a plurality of at least three beams have located and locked onto a satellite (step 609), each of these beams then tracks (611) a respective satellite over time until it receives (613) signals 413, 423, 433 from a plurality of non-GNSS satellites. The current position of the satellite is calculated by the signal processor 307 based on the time and the almanac data in the almanac database 501. Once all signals are available (step 615), the current time 619 is calculated (617). The signals collected from each of the beams 621 received by 607 and 611 are then used to calculate (625) the distance to each satellite. Once all of the distances are known (step 627), the position of the system 201 can be calculated by trilateration based on the distance 437 between the system 201 and each of the satellites 203, 205 and the known satellite locations (step 629). If the position measurements (step 629) are not sufficient (step 631), the process continues (609) with each beam tracking (611) satellites and receiving (613) their signals. If the position measurements (step 629) are sufficient (step 631), the position is known (step 633). A user of the system can then use the position, for example, to replace information from an unavailable GNSS system.

[0031] An alternative method is to use time information and the satellites' current locations, and optionally measure 623 the angles 439 between the satellites visible by the ground terminal. The angles 439 are derived from the beam locations known by the terminal as it tracks the target satellite. Because a multi-beam antenna tracks each satellite with an independent beam, the angle of each beam 415, 425, 435 identifies the direction to each satellite 411, 421, 431. By measuring three or more angles, the receiver's position can be determined by triangulation.

[0032] Satellites that are not in geostationary orbit move relative to the Earth. This relative motion can be tracked from the Earth by monitoring the position, distance, and received angles over time for one or more non-geostationary orbit (NGSO) satellites 411, 421. In this manner, the satellite's perceived trajectory can be measured by the system 201 and compared to the expected trajectory from the ephemeris data. This additional information can be used to improve the accuracy of the position estimate. This method can be used while the system 201 is stationary or has local motion that is offset in the calculation using an inertial motion unit (IMU). This inertial motion unit includes accelerometer and gyroscope sensors and performs dead reckoning to track the unit's location without access to an external reference. Using an IMU to locally track the relative motion and position of the system 201 allows processing methods such as Kalman filtering to be used to integrate signals received at different times into an overall position estimate, ultimately resulting in both time and position with greater accuracy than would be possible without the use of an IMU.

[0033] Doppler information from the frequency of narrowband signals received over paths including beacon and TT&C links can also provide a more accurate estimate of trajectory. For example, the rate of change of the frequency of beacon and TT&C signals can be used to estimate the midpoint and time of closest satellite approach, which can refine the time estimate and help align current position measurements with reported ephemeris data. Including velocity or trajectory from Doppler shift and time-of-flight and direction-of-arrival information in the position calculation improves the estimate because Doppler shift is less subject to noise and errors than the timing signal itself, and because large apparent motion between position measurements can be checked with velocity information to ensure accuracy. This trajectory over time can be compared with almanac data and used to improve the accuracy of local position calculations because more information (velocity and trajectory vectors) is then available in combination with the satellite's known or constrained orbital dynamics.

[0034] Ultimately, the position of the system 201 is calculated with increasing accuracy by combining calculations based on distance from the satellites, calculations based on angles from the receiver to the satellites, and calculations based on the measured trajectories of the satellites, all combined with the current time and satellite orbital parameters such as those contained in the ephemeris data or almanac.

[0035] Whatever method or combination of methods is used to calculate position, the uncertainty and error estimates for each measurement can be combined to estimate the accuracy or error of the resulting position estimate itself.

[0036] The satellite orbits used in this method are not important as long as the orbital parameters can be obtained. All equatorial satellites can be used for position estimation away from the equator, even though they lie on a single plane (because from the equator they appear as a line). This allows the use of GEO or MEO equatorial satellites. Satellites with inclined orbits in MEO and LEO offer some advantages in that there is always a satellite passing overhead, but they also move at high speeds and are more difficult to lock onto in the first place. The system works for any single orbit or combination of orbits, but provides the most reliable information and accurate estimates when a combination of orbits and inclinations and satellite locations is used.

[0037] In summary, the present disclosure is for a method and system that calculates the current time and distances from multiple satellites as inputs to a computing device (such as a processing device, e.g., a controller or processor). The computing device uses that information to determine the location of the receiver. What distinguishes this system from the GPS system and existing GNSS systems, as well as other positioning systems, is that a multi-beam directional antenna (such as an antenna suitable for VSAT operation) is used to receive signals from satellites (such as Ku-band and Ka-band data communications satellites or TV broadcast satellites) that are too weak (and in a different frequency band) to be received by omnidirectional GNSS antennas or other low-gain antennas. By using a multi-beam directional antenna, the system can extract positioning data from signals and satellites that are not normally usable or readily available (e.g., by the GPS or GNSS systems).

[0038] The only way an antenna can have multiple independently steerable directional beams that can independently track satellites is with an electrically steerable antenna. In contrast, a mechanically steered antenna can point in one direction at a time, requiring multiple antennas to perform the same operations as a single multi-beam antenna. Potential timing references present in existing satellite signals include communication and broadcast signals, synchronization signals between satellites and controllers, or framing structures in satellite health broadcasts and TT&C links. By receiving these signals (which cannot be received by existing GNSS and positioning systems), a receiver can extract timing information and calculate the satellite's distance and location, and then derive the receiver's position from the results.

[0039] Unlike positioning systems that use communications satellites, the present system does not rely on any particular signal obtained from a satellite, but operates using whatever signals are normally transmitted. That is, non-GNSS satellites are uncooperative. In particular, the satellites used for positioning may not be aware that their signals are being used for positioning purposes. The present system does not use satellite-aided positioning, where round-trip signal times when actively communicating with a satellite are used to derive timing information, or where a satellite (or satellite constellation) is used to locate a transmitter on the ground and transmit this position back to a receiver.

[0040] Any frequency band can be used, and the most flexible system is when the antenna and system can operate on and listen to a variety of frequency bands. On the other hand, electrically steered antennas that operate on multiple frequencies are difficult and expensive to build. Therefore, most practical systems operate on a single band, the most common communication system bands being Ka and Ku for VSAT operation.

[0041] Numerous applications of the present system and method will readily occur to those skilled in the art, and therefore it is not desired to limit the invention to the disclosed examples or to the exact construction and operation shown or described. On the contrary, all suitable modifications and equivalents may be used which fall within the scope of the invention. In order to maintain the disclosure of the present application as originally filed, the contents of claims 1 to 24 as originally filed are added below. (Claim 1) 1. A system for generating location and time estimates from passively received non-GNSS communication signals that are not designed, intended, or readily available for extraction of location and time by a ground terminal, comprising: a. an electrically steered multi-beam antenna, wherein each beam from the multi-beam antenna is steered to track and receive signals from an individual satellite; b. a receiver for each beam of the multi-beam antenna; c. a processing device configured to determine the location of the system based on each beam of the multi-beam antenna and the signals received by the receiver, and ephemeris data of the satellites; A system comprising: (Claim 2) 2. The system of claim 1, wherein the processing device is configured to estimate an angular position of the satellite based on a direction of arrival of the signal determined by a steering angle of the beam, and the processing device is further configured to triangulate the location of the system. (Claim 3) The system of claim 1 , wherein the processing device extracts a current time from the signal. (Claim 4) The system of claim 3 , further comprising an on-board atomic clock that complements and stabilizes the current time extracted from different links. (Claim 5) 5. The system of claim 3 or 4, wherein the processing device determines a time of flight and a distance from each satellite based on the current time and the received non-GNSS signals. (Claim 6) The system of claim 5 , wherein the distance from each satellite is used to determine the location of the receiver. (Claim 7) The system of claim 1 , wherein Doppler shifts in signal channels are used to estimate the relative velocity and trajectory of each satellite with respect to the receiver. (Claim 8) 8. A system according to any one of claims 1 to 7, wherein measurements of angle of arrival, time of flight and Doppler shift are combined to improve position estimation accuracy. (Claim 9) 9. The system of claim 1, wherein multiple measurements of the same satellite over time are used to establish an estimate of the satellite's trajectory to improve estimated location and accuracy. (Claim 10) 10. The system of any one of claims 1 to 9, wherein a local IMU sensor is used to correlate signals received at different times to improve estimated location and accuracy. (Claim 11) 10. The system of claim 1, wherein one or more two-way general-purpose communication links are established with non-GNSS satellites to obtain orbital ephemeris data for all of the other non-GNSS satellites being tracked. (Claim 12) The system of claim 1 , wherein a cooperative satellite broadcast is transmitted by one or more of the target satellites to distribute orbital ephemeris data for all of the target satellites. (Claim 13) The system of claim 1 , wherein a terrestrial data connection is used to obtain orbital ephemeris data for all of the target satellites. (Claim 14) 10. The system of claim 1, wherein ephemeris data for potential target satellites is stored for access in a local data storage device. (Claim 15) 16. The system of claim 1, wherein the uncertainty of each independent measurement is used to estimate the overall position uncertainty. (Claim 16) The system of claim 1 , wherein the antenna is a VSAT antenna. (Claim 17) 17. The system of claim 16, wherein the antenna is a phased array. (Claim 18) 17. The system of claim 16, wherein the antenna is a lens antenna array. (Claim 19) The system of claim 1 , wherein the satellite is in a LEO. (Claim 20) The system of claim 1 , wherein the satellite is in a medium earth orbit (MEO). (Claim 21) The system of claim 1 , wherein the satellite is in GEO. (Claim 22) The system of claim 1 , wherein the satellites are in multiple orbits. (Claim 23) The system of claim 1 , wherein the TT&C link is transmitted in the Ka band. (Claim 24) The system of claim 1 , wherein the TT&C link is transmitted in the Ku band.

Claims

1. A system that generates estimates of the system's location and time from non-GNSS communication signals received without broadcast to non-GNSS satellites, comprising: a. an electrically steered multi-beam antenna, wherein each beam from the multi-beam antenna is steered to track and receive signals from an individual satellite; b. a receiver for each beam of the multi-beam antenna; c. a processing device configured to determine a location of the system based on each beam of the multi-beam antenna and the signals received by the receiver and ephemeris data of the satellites; It is equipped with A system in which the Doppler shift of a signal channel is used to estimate the relative velocity and trajectory of each satellite with respect to the receiver.

2. 2. The system of claim 1, wherein the processing device is configured to estimate an angular position of each satellite based on a direction of arrival of the signal identified by a steering angle of the beam, and the processing device is further configured to determine a location of a ground terminal based on the angular position.

3. The system of claim 1 , wherein the processing device determines a current time in the system from a timestamp of the signal received from the satellite, ephemeris data, and a calculated difference in time of flight of the received signal.

4. The system of claim 3 , further comprising an on-board atomic clock that complements and stabilizes the current time extracted from several links of different said beams.

5. The system of claim 3 or 4, wherein the processing device determines a time of flight and distance from each satellite based on the current time and the ephemeris data of the received non-GNSS signals.

6. The system of claim 5 , wherein the distance from each satellite is used to determine the location of the receiver.

7. A system described in any one of claims 1 to 6, wherein measurements of the angle from the receiver to the satellite, the time of flight from each satellite, and the Doppler shift of the signal from each satellite are combined to improve position estimation accuracy.

8. 8. The system of claim 1, wherein the antenna tracks the satellite, the position of the satellite is measured at a plurality of different times, the measured position is used by the processing unit to determine an orbit of the satellite, and the processing unit uses the determined orbit to determine the location of a ground terminal.

9. A system described in any one of claims 1 to 8, wherein the system is equipped with a local IMU sensor, the processing unit uses signals from the local IMU sensor to track the relative movement and position of the system, and the processing unit uses the relative movement and position of the system to determine the location of the system.

10. The system of claim 1 , wherein one or more two-way general-purpose communication links are established with non-GNSS satellites to obtain orbital ephemeris data for all of the other non-GNSS satellites being tracked.

11. The system described in claim 1, wherein a satellite broadcast is transmitted by one or more of the satellites to deliver orbital ephemeris data for all of the satellites.

12. The system of claim 1 , wherein a terrestrial data connection is used to obtain orbital ephemeris data for all of the satellites.

13. The system of claim 1, wherein the ephemeris data for potential satellites is stored for access in a local data storage device.

14. The system of claim 1 , wherein the antenna is a VSAT antenna.

15. The system of claim 14 , wherein the antenna is a phased array.

16. The system of claim 14 , wherein the antenna is a lens antenna array.

17. The system of claim 1 , wherein the satellite is in a low energy orbit (LEO).

18. The system of claim 1 , wherein the satellite is in a medium earth orbit (MEO).

19. The system of claim 1 , wherein the satellite is in GEO.

20. The system of claim 1 , wherein the satellites are in multiple orbits.

21. The system of claim 1, wherein the system receives telemetry, tracking and control signals in the Ka band.

22. The system of claim 1, wherein the system receives telemetry, tracking, and control signals in the Ku band.

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