GROUND-BASED BEAMFORMING FOR SATELLITE COMMUNICATIONS SYSTEMS

• US 20100302971A1
• Filed: 08/13/2010
• Published: 12/02/2010
• 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: DUBELLAY, Gilles, MENENDEZ, Rolando, WALKER, John L., BURR, Douglas
• Granted Patent: US 8,270,899 B2
• Time in Patent Office: Days
• US Class Current: 370/252
• 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 a plurality of user terminals (16), each communicatively coupled with the satellite by a user link (17) where a ground based beam forming system (400) receives, via feeder link (13), return path signals (452) traveling from the user terminals (16) via the satellite (11) to the at least one gateway (12) and forward path signals (457) traveling from the at least one gateway (12) via the satellite (11) to the user terminals (16), and measures and corrects amplitude and phase errors of the return path signals (452) and the forward path signals (457).

Claims

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

a satellite, said satellite comprising a satellite communications payload, said satellite communications payload comprising a satellite return path and a satellite forward path;

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;

receives, via the feeder link, (i) a plurality of return path signals traveling from the user terminals via the satellite to the at least one gateway, and (ii) a plurality of forward path signals traveling from the at least one gateway via the satellite to the user terminals;

measures a first set of amplitude and phase errors of the plurality of return path signals;

corrects said first set of amplitude and phase errors by generating, on the ground, a first set of corrective beam forming coefficients and applying said first set of corrective beam forming coefficients to the return path signals;

measures a second set of amplitude and phase errors of the plurality of forward path signals; and

corrects said second set of amplitude and phase errors by generating, on the ground, a second set of corrective beam forming coefficients and applying said second set of corrective beam forming coefficients to the forward path signals.

2. The satellite communications network of claim 1 wherein each of said (i) applying the first set of corrective beam forming coefficients to the return path signals and (ii) applying the second set of corrective beam forming coefficients to the forward path signals is performed on the ground.

3. The satellite communications network of claim 1 wherein at least one of the forward path signals and the return path signals 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;

the satellite communications payload comprises a satellite tracking master reference oscillator and a calibration network; and

the GBBF system further comprises a master reference oscillator and a gateway tracking master reference oscillator.

9. The satellite communications network of claim 8 wherein the GBBF system 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 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 a 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 a 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 a 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 a 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:

receiving via a feeder link, (i) a plurality of return path signals traveling from user terminals via the communications satellite payload to at least one gateway, and (ii) a plurality of forward path signals traveling from the at least one gateway via the communications satellite payload to the user terminals;

measuring a first set of amplitude and phase errors of the plurality of return path signals;

correcting said first set of amplitude and phase errors by generating, on the ground, a first set of corrective beam forming coefficients and applying said first set of corrective beam forming coefficients to the return path signals;

measuring a second set of amplitude and phase errors of the plurality of forward path signals; and

correcting said second set of amplitude and phase errors by generating, on the ground, a second set of corrective beam forming coefficients and applying said second set of corrective beam forming coefficients to the forward path signals.

19. The method of claim 18 wherein each of said (i) applying the first set of corrective beam forming coefficients to the return path signals and (ii) applying the second set of corrective beam forming coefficients to the forward path signals is performed on the ground.

20. A satellite, said satellite comprising:

a satellite communications payload communicatively coupled to a gateway via a feeder link, and to a plurality of user terminals via a user link, said satellite communications payload comprising a satellite return path and a satellite forward path,

said satellite configured to operate within a satellite communications network having a ground-based beamforming (GBBF) system wherein the GBBF system;

receives, via the feeder link, (i) a plurality of return path signals traveling from the user terminals via the satellite to the at least one gateway, and (ii) a plurality of forward path signals traveling from the at least one gateway via the satellite to the user terminals;

measures a first set of amplitude and phase errors of the plurality of return path signals;

corrects said first set of amplitude and phase errors by generating, on the ground, a first set of corrective beam forming coefficients and applying said first set of corrective beam forming coefficients to the return path signals;

measures a second set of amplitude and phase errors of the plurality of forward path signals; and

corrects said second set of amplitude and phase errors by generating, on the ground, a second set of corrective beam forming coefficients and applying said second set of corrective beam forming coefficients to the forward path signals.

21. The satellite of claim 20 wherein each of said (i) applying the first set of corrective beam forming coefficients to the return path signals and (ii) applying the second set of corrective beam forming coefficients to the forward path signals is performed on the ground.

22. A gateway, said gateway communicatively coupled to a satellite via a feeder link, and configured to operate within a satellite communications network comprising the satellite, the gateway, and a plurality of user terminals, said satellite communications network having a ground-based beamforming (GBBF) system wherein the GBBF system:

receives, via the feeder link, (i) a plurality of return path signals traveling from the user terminals via the satellite to the at least one gateway, and (ii) a plurality of forward path signals traveling from the at least one gateway via the satellite to the user terminals;

measures a first set of amplitude and phase errors of the plurality of return path signals;

corrects said first set of amplitude and phase errors by generating, on the ground, a first set of corrective beam forming coefficients and applying said first set of corrective beam forming coefficients to the return path signals;

measures a second set of amplitude and phase errors of the plurality of forward path signals; and

corrects said second set of amplitude and phase errors by generating, on the ground, a second set of corrective beam forming coefficients and applying said second set of corrective beam forming coefficients to the forward path signals.

23. The gateway of claim 22 wherein each of said (i) applying the first set of corrective beam forming coefficients to the return path signals and (ii) applying the second set of corrective beam forming coefficients to the forward path signals is performed on the ground.