Non-cooperative position, navigation, and timing extraction from VSAT communications signals using multi-beam phased array antenna
A ground antenna determines the current time and its own position from received signals that were transmitted by artificial earth satellites for communication. A high-gain multi-beam electrically-steered antenna is combined with a processing system to measure the angles between two or more satellites and determine the present distance to each satellite by the information broadcast on the TT&C channel. The knowledge of the angles and distances, as well as the trajectory of the satellites, can be combined with their locations as predicted by the satellite ephemeris data to triangulate the location of the receiver. This system is different from conventional GPS antennas because it does not require the cooperation of active communication with the satellites to derive a location estimate. The location is computed by the ground terminal, not by the satellite. This system can be used in cases where other locating services are offline, jammed, or otherwise unavailable to maintain location and time synchronization.
1. A system for generating estimates of location and time, comprising:
an electrically-steered multi-beam antenna, each beam from the multi-beam antenna steered to track and passively identify an individual signal of one or more satellite signals receivable by the multi-beam antenna from a corresponding satellite;
a receiver respectively for each beam of the multi-beam antenna, the receiver configured to receive the signal;
a processing device configured to determine a location of the system, based on the received one or more signals and based on ephemeris data for the corresponding satellites, by determining the current positions of the one or more identified satellites sending the one or more received signals, the one or more signals are non-positioning signals not providing location and time data extractable by ground terminals.
2. The system of claim 1 , the processing device configured to estimate an angular position of the satellite based on a direction of arrival of the individual signal as determined by a steering angle of the identifying beam, the processing device further configured to triangulate the location of the system.
3. The system of claim 1 , the processing device extracting a current time from the one or more signals.
4. The system of claim 3 , further comprising an onboard atomic clock to supplement and stabilize the extracted current time.
5. The system of claim 3 , the processing device determining time-of-flight and distance from the corresponding satellites based on the current time and received non-satellite positioning system signals.
6. The system of claim 5 , wherein the distance from the corresponding satellites is used to determine a position of the respective receivers.
7. The system of claim 1 , wherein doppler shift of signal channels is used to infer relative velocity and trajectory of the corresponding satellites relative to the receiver.
8. The system of claim 1 , wherein angle of arrival, time of flight, and doppler shift measurements are combined to improve location estimate accuracy.
9. The system of claim 1 , wherein multiple measurements of an individual satellite of the one or more satellites over time are used to estimate satellite trajectory to improve estimated location and accuracy.
10. The system of claim 1 , wherein a local IMU sensor correlates the signals received at different times to improve estimated location and accuracy.
11. The system of claim 1 , wherein one or more bidirectional general-purpose communications links with the one or more non-satellite positioning system satellites are established to obtain orbital ephemeris data on all of the other non-satellite positioning system satellites being tracked.
12. The system of claim 1 , wherein a cooperative satellite broadcast is transmitted by one or more of the corresponding satellites to distribute orbital ephemeris data on all of the corresponding satellites.
13. The system of claim 1 , wherein a terrestrial data connection is used to obtain orbital ephemeris data on all of the corresponding satellites.
14. The system of claim 1 , wherein ephemeris data for potential corresponding satellites is preserved in local data storage for access.
15. The system of claim 1 , wherein uncertainty of each independent measurement is used to estimate overall position uncertainty.
16. The system of claim 1 , wherein the multi-beam antenna is a VSAT antenna.
17. The system of claim 16 , wherein the multi-beam antenna is a phased array.
18. The system of claim 16 , wherein the multi-beam antenna is a lens antenna array.
19. The system of claim 1 , wherein the one or more satellites are in LEO.
20. The system of claim 1 , wherein the one or more satellites are in MEO.
21. The system of claim 1 , wherein the one or more satellites are in GEO.