Aiding beam identification in a satellite system

• US 20030096574A1
• Filed: 10/22/2002
• Published: 05/22/2003
• Est. Priority Date: 10/25/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Anderson, Jon J., Ngai, Francis M., Dai, Jin, Victor, Edward B.
• Granted Patent: US 7,092,725 B2
• Time in Patent Office: Days
• US Class Current: 455/13.2
• CPC Class Codes: H04B 7/1855 using a telephonic control signal, e.g. propagation delay variation, Doppler frequency variation, power variation, beam identification

Abstract

A system and method for determining timing offset errors in a low earth orbit satellite system based upon Doppler and Doppler rate of change is provided. A user terminal determines first and second timing offsets respectively associated with first and second satellite beams from respective first and second satellites. Next, the user terminal determines the Doppler and Doppler rate of change associated with the first and second satellite beams. A timing offset is estimated from the measured Doppler and Doppler rate of change and is then compared with the user terminal'"'"'s own determined timing offset. If the comparison does not produce a value within a predetermined threshold, a beam identification error is declared.

Claims

1. A method to determine timing offset errors in a satellite system, comprising:

(a) determining in a user terminal a first timing offset associated with a first satellite beam from a first satellite;

(b) determining in the user terminal a second timing offset associated with a second satellite beam from a second satellite based upon the first timing offset;

(c) estimating a first range from the user terminal to the first satellite;

(d) estimating a second range from the user terminal to the second satellite; and

(e) determining an error in the second timing offset based upon a difference between the estimated first and second ranges.

2. The method of claim 1, wherein the first and second timing offsets are pilot signal PN phase offsets.

3. The method of claim 2, wherein the PN phase offsets are associated with a code division multiple access based communications system.

4. The method of claim 1, wherein at least one of (c) and (d) includes determining Doppler characteristics associated with the user terminal and the first and second satellites.

5. The method of claim 4, wherein the Doppler characteristics include Doppler frequency and rate of change of the Doppler frequency.

6. The method of claim 5, wherein the first and second ranges are approximated from the expression:

7. The method of claim 1 wherein the steps of estimating first and second ranges comprises respectively determining (i) a Doppler frequency associated with the first and second satellite beams and (ii) a rate of change in the determined Doppler frequency;

and

8. The method of claim 7, wherein the first and second timing offsets are pilot signal PN phase offsets.

9. The method of claim 8, wherein the PN phase offsets are associated with a code division multiple access based communications system.

10. The method of claim 7, wherein the first and second ranges are derived from the following expression:

11. A method to confirm beam identification in a low earth orbit satellite system, the low earth orbit satellite system including at least one user terminal configured to (i) receive a first satellite beam from an origination satellite, the first satellite beam including a first timing offset, and (ii) facilitate a handoff from the first satellite beam to a second satellite beam, the second satellite beam being radiated from a destination satellite, the method comprising:

(a) determining a second timing offset of the second satellite beam based upon the first timing offset;

(b) estimating a first range from the user terminal to the origination satellite;

(c) estimating a second range from the user terminal to the destination satellite; and

(d) determining an error in the second offset based upon a difference between the estimated first and second ranges.

12. The method of claim 11, wherein (d) includes:

(i) measuring Doppler characteristics associated with the first and second satellite beams;

(ii) determining ranges associated with the first and second satellites; and

(iii) determining a timing difference based upon the determined ranges.

13. The method of claim 12, wherein all of the timing offsets and the timing difference are differences in pilot signal PN phase.

14. The method of claim 13, wherein the pilot signal PN phase offsets and the timing difference are associated with a code division multiple access based communications system.

15. A method to perform beam identification in a user terminal configured to communicate using a low earth orbit satellite system, the user terminal including a processor configured to (i) receive a first satellite beam including a first timing offset from a servicing satellite, and (ii) facilitate a handoff from the first satellite beam to a second satellite beam, the second satellite beam being radiated from a destination satellite, the method comprising:

(a) acquiring the second satellite beam in the user terminal;

(b) determining a second timing offset of the second satellite beam based upon the first timing offset;

(c) identifying the second satellite beam based upon the second timing offset;

(d) estimating a first range from the user terminal to the servicing satellite;

(e) estimating a second range from the user terminal to the destination satellite;

(f) determining a timing difference based upon a difference between the estimated first range and the estimated second range;

(g) calculating a difference between the second timing offset and the timing difference; and

(h) confirming identification of the second satellite beam when the difference between the second timing offset and the timing difference is greater than a predetermined value.

16. The method of claim 15, wherein the predetermined value is user selectable.

17. The method of claim 15, wherein step (g) is accomplished by dividing a difference between the first and second ranges by the speed of light.

18. A user terminal comprising:

a receiving module configured to receive and demodulate first and second satellite beam signals associated with respective first and second satellite beams, the first and second satellite beams being received from respective first and second satellites; and

a processor coupled to the receiving module and configured to (i) determine a first timing offset associated with the first satellite beam signal, the first timing offset being representative of a first beam ID of the first satellite beam, (ii) determine a second timing offset associated with the second satellite beam signal, the second timing offset being determined based upon the first timing offset and being representative of a second beam ID of the second satellite beam, and (iii) measure at the user terminal respective Doppler characteristics associated with the first and second satellite beam signals to respectively verify the first and second beam IDs;

wherein the respective Doppler characteristics are used to determine first and second ranges respectively associated with the user terminal and each of the first and second satellites; and

wherein the user terminal is adapted to convert the first and second ranges into a third timing offset and determine the presence of error in the second beam ID based upon a comparison between the second and third timing offsets.

19. The user terminal of claim 18, wherein the first and second satellite beams signals include encoding based upon a code division multiple access scheme.

20. The user terminal of claim 18, wherein the Doppler characteristics include at least a Doppler frequency and rate of change associated therewith.

21. The user terminal of claim 18, wherein all of the timing offsets include pilot signal PN phase offsets.

22. The user terminal of claim 18, wherein the first and second timing offsets must match within a predetermined window of time.

23. The user terminal of claim 22, wherein the predetermined window of time is less than a positional spacing between the first and second satellite beams.

24. The user terminal of claim 22, wherein the predetermined window of time is greater than a known propagation delay between the first and second satellite beams.

25. A method to determine timing offset errors in a communications system, comprising:

(a) determining in a user terminal a first timing offset associated with a first transmitter signal from a first transmitter;

(b) determining in the user terminal a second timing offset associated with a second transmitter signal from a second transmitter based upon the first timing offset;

(c) estimating a first range from the user terminal to the first transmitter;

(d) estimating a second range from the user terminal to the second transmitter; and

(e) determining an error in the second timing offset based upon a difference between the estimated first and second ranges.

26. The method of claim 25, wherein the first and second timing offsets are beacon signal phase offsets.

27. A user terminal comprising:

a receiving module configured to receive and demodulate first and second transmitter signals associated with respective first and second transmitters; and

a processor coupled to the receiving module and configured to (i) determine a first timing offset associated with the first transmitter signal, the first timing offset being representative of a first transmitter ID, (ii) determine a second timing offset associated with the second transmitter ID, and (iii) measure at the user terminal respective Doppler characteristics associated with the first and second transmitter signals to respectively verify the first and second transmitter IDs;

wherein the respective Doppler characteristics are used to determine first and second ranges respectively associated with the user terminal and each of the first and second transmitters; and

wherein the user terminal is configured to convert the first and second ranges into a timing difference and determine the presence of error in the second transmitter ID based upon a comparison between the second timing offset and the timing difference.