GROUND-BASED BEAMFORMING FOR SATELLITE COMMUNICATIONS SYSTEMS

• US 20080051080A1
• Filed: 08/25/2006
• Published: 02/28/2008
• Est. Priority Date: 08/25/2006
• Status: Active Grant

• Current Assignee: Maxar Space LLC (Galileo Parent, Inc.)
• Original Assignee: Space Systems/Loral Incorporated (Loral Space and Communications Incorporated)
• Inventors: Burr, Douglas, Dubellay, Gilles, Menendez, Rolando, Walker, John L.
• Granted Patent: US 7,787,819 B2
• Time in Patent Office: Days
• US Class Current: 455/427
• CPC Class Codes: H04B 7/2041 Spot beam multiple access

Abstract

Methods, systems and apparatus for ground-based beamforming of a satellite communications payload (200) within a satellite communications network (100). An embodiment of the invention comprises a satellite (11) communicatively coupled to at least one gateway (12) via a feeder link (13) and further coupled to a plurality of user terminals (16), each communicatively coupled with the satellite by a user link (17). A ground based beam forming system (400) measures and corrects amplitude and phase errors of a plurality of return path signals (452) traveling from the user terminals (16) via the satellite (11) to the at least one gateway (12), and measures and corrects amplitude and phase errors of a plurality of forward path signals (457) traveling from the at least one gateway (12) via the satellite (11) to the user terminals (16).

Claims

1. A satellite communications network having a ground-based beamforming (GBBF) system, said network comprising:

a satellite;

at least one gateway, communicatively coupled with the satellite via a feeder link; and

a plurality of user terminals, each communicatively coupled with the satellite by a user link;

wherein;

the GBBF system measures and corrects amplitude and phase errors of a plurality of return path signals traveling from the user terminals via the satellite to the at least one gateway, and measures and corrects amplitude and phase errors of a plurality of forward path signals traveling from the at least one gateway via the satellite to the user terminals.

2. The satellite communications network of claim 1 wherein the forward path signals carried over the feeder link are frequency division multiplexed.

3. The satellite communications network of claim 1 wherein the return path signals carried over the feeder link are frequency division multiplexed.

4. The satellite communications network of claim 1 wherein the GBBF system forms beams using a plurality of feed elements in a forward downlink from the satellite to the user terminals and in a return uplink from the user terminals to the satellite.

5. The satellite communications network of claim 1 wherein the GBBF system controls power of a forward uplink from the at least one gateway to the satellite.

6. The satellite communications network of claim 1 wherein the GBBF system minimizes errors associated with Doppler frequency shifts.

7. The satellite communications network of claim 1 wherein the GBBF system corrects for satellite pointing errors.

8. The satellite communications network of claim 1 further comprising a plurality of pointing beacon stations adapted to transmit and receive signals to and from the satellite;

wherein;

a satellite communications payload disposed on the satellite comprises a satellite forward path, a satellite return path, a satellite tracking master reference oscillator, a calibration network, a plurality of couplers, a satellite generated payload beacon signal, a satellite generated payload pilot signal, and a plurality of multiport amplifiers coupled to a plurality of hybrid matrixes; and

the GBBF system further comprises a plurality of hybrid matrix outputs corresponding to a plurality of feed elements, a gateway generated pilot signal, a master reference oscillator, and a gateway tracking master reference oscillator.

9. The satellite communications network of claim 8 wherein the GBBF system measures and corrects amplitude and phase errors of the plurality of return path signals by:

generating an encoded return calibration signal having a known amplitude and phase that is received by the satellite communications payload and applied to each of a plurality of feed elements in a feed array;

receiving from the calibration network over the satellite return path and a return downlink between the satellite and the gateway a plurality of tagged signals, each of the plurality of tagged signals comprising a combination of user communications traffic and the encoded return calibration signal;

determining a difference between the known amplitude and phase of the encoded return calibration signal and an amplitude and a phase of each of the plurality of tagged signals, the difference being representative of amplitude and phase errors of the plurality of return path signals; and

generating and applying corrective beamforming coefficients to minimize the amplitude and phase errors of the plurality of return path signals.

10. The satellite communications network of claim 9, wherein the encoded return calibration signal is applied to each of the plurality of feed elements in the feed array through the calibration network.

11. The satellite communications network of claim 9, wherein the encoded return calibration signal is applied to each of the plurality of feed elements in the feed array via a calibration horn.

12. The satellite communications network of claim 9 wherein the encoded return calibration signal is encoded by means of a Walsh function and pseudo random number scrambling.

13. The satellite communications network of claim 9 wherein the encoded return calibration signal is generated on-board the satellite.

14. The satellite communications network of claim 8 wherein the GBBF system measures and corrects amplitude and phase errors of the plurality of forward path signals by:

generating an encoded forward calibration signal having a known amplitude and phase and a plurality of tagged signals, each of the plurality of tagged signals comprising a combination of user communications traffic and the encoded forward calibration signal;

transmitting the plurality of tagged signals over a forward uplink to the communications payload, which passes the plurality of tagged signals through the satellite forward path and through the calibration network, which passes the plurality of tagged signals to a forward downlink, and passes amplitude and phase characteristics of the plurality of tagged signals through the satellite return path together with an inserted payload beacon signal having a known amplitude and phase;

receiving over a return downlink amplitude and phase characteristics of each of the plurality of tagged signals and a received payload beacon signal;

determining a difference between the known amplitude and phase of the encoded forward calibration signal and amplitude and phase characteristics of each of the plurality of tagged signals, which difference is representative of an error associated with a total path consisting of the forward uplink, the satellite forward path, the satellite return path and the return downlink;

determining a difference between the known amplitude and phase of the inserted payload beacon signal and an amplitude and phase of the received payload beacon signal, which difference is representative of an error associated with a complete return path, the complete return path consisting of the satellite return path and the return downlink;

subtracting the difference representative of the error associated with the complete return path from the difference representative of the error associated with the total path to obtain an error representative of a complete forward path, the complete forward path consisting of the forward uplink and the satellite forward path; and

generating and applying corrective beamforming coefficients and hybrid matrix correction factors to minimize amplitude and phase errors of the plurality of forward path signals.

15. The satellite communications network of claim 8 wherein the GBBF system controls power of a forward uplink by:

transmitting the gateway generated pilot signal over the forward uplink to the satellite communications payload, which passes the gateway generated pilot signal through the satellite forward path, passes the gateway generated pilot signal together with the satellite generated payload pilot signal over the satellite return path to a feeder link transmitter, and transmits a transponded gateway generated pilot signal and the satellite generated payload pilot signal to the at least one gateway over a return downlink;

receiving the transponded gateway generated pilot signal and a received payload pilot signal from the return downlink;

determining a propagation effect associated with the forward uplink by comparing a signal level of the received payload pilot signal to a signal level of the transponded gateway generated pilot signal; and

providing a control signal that adjusts a power level of the forward uplink to compensate for the propagation effect.

16. The satellite communications network of claim 8 wherein Doppler frequency shift errors are minimized by:

locking the gateway generated pilot signal to the master reference oscillator;

transmitting the gateway generated pilot signal over a forward uplink to the satellite communications payload;

applying the gateway generated pilot signal to the satellite tracking master reference oscillator;

locking the satellite tracking master reference oscillator to the satellite generated payload pilot signal;

transmitting the satellite generated payload pilot signal over a return downlink to the at least one gateway;

receiving the satellite generated payload pilot signal at the at least one gateway; and

locking the gateway tracking master reference oscillator to the satellite generated payload pilot signal.

17. The satellite communications network of claim 8 wherein satellite pointing errors are corrected by:

receiving pointing beacon signals generated by the plurality of pointing beacon stations operating at known locations over a return uplink;

transmitting the pointing beacon signals over a return downlink; and

calculating and compensating for errors between measured beam pointing direction and desired beam pointing direction.

18. A method for ground-based beamforming (GBBF) of a communications satellite payload, said method comprising:

measuring amplitude and phase errors of a plurality of return path signals traveling from user terminals via the communications satellite payload to at least one gateway;

measuring amplitude and phase errors of a plurality of forward path signals traveling from the at least one gateway via the satellite to the user terminals; and

correcting amplitude and phase errors of the plurality of return path signals and amplitude and phase errors of the plurality of forward path signals.

19. The method of claim 18 further comprising:

controlling a plurality of feed elements to form desired beam shapes in a forward downlink from the satellite to the user terminals and in a return uplink from the user terminals to the satellite.

20. The method of claim 19, wherein, signals carried over the feeder link in at least one of the forward or return paths are frequency division multiplexed.