EFFICIENT EPHEMERIS CODING

• US 20080191936A1
• Filed: 03/30/2007
• Published: 08/14/2008
• Est. Priority Date: 02/12/2007
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Inventors: Zhang, Gengsheng, Wan, Marlene, Phatak, Makarand S.
• Granted Patent: US 7,839,324 B2
• Time in Patent Office: Days
• US Class Current: 342/357.42
• CPC Class Codes: G01S 19/05 providing aiding data
• CPC Class Codes: G01S 19/258 relating to the satellite constellation, e.g. almanac, ephemeris data, lists of satellites in view

Abstract

In one embodiment, a system is provided that is operable to: predict satellite states using historical satellite state data for at least one satellite of a satellite-based positioning system; derive sets of parameters representative of the predicted satellite states; differentially compress the sets parameters into sets of compressed parameters; transmit the sets of compressed parameters to a client device over a first communication channel; uncompress the sets of compressed parameters into sets of recovered parameters; selectively reconstruct at least one reconstructed satellite state in the client device using the sets of recovered parameters; and determine the position of the client device using the at least one reconstructed satellite state along with timing information of satellite data received over a second communication channel.

Claims

1. A method for determining a position of a client device, comprising:

predicting satellite states using historical satellite state data for at least one satellite of a satellite-based positioning system;

deriving sets of parameters representative of the predicted satellite states;

differentially compressing the sets parameters into sets of compressed parameters;

transmitting the sets of compressed parameters to a client device over a first communication channel;

differentially decoding the sets of compressed parameters into sets of recovered parameters;

selectively reconstructing at least one reconstructed satellite state in the client device using one or more sets of the recovered parameters; and

determining the position of the client device using the at least one reconstructed satellite state along with timing information of satellite data received over a second communication channel.

2. The method of claim 1, wherein the historical state data includes at least one of satellite position state vectors, satellite velocity state vectors, satellite clock biases, and satellite clock rate errors.

3. The method of claim 1, wherein the historical state data is received via at least one coupling with a database, wherein the historical state data is delivered to at least one server.

4. The method of claim 1, wherein the parameters are Kepler parameters.

5. The method of claim 4, wherein differentially compressing the Kepler parameters comprises

providing a plurality of sets of Kepler parameters arranged from a first set to a last set;

for each set of Kepler parameters from a second set to the last set, delta encoding each set with regard to a subsequent set.

6. The method of claim 5, wherein the subsequent set is an immediately-subsequent set.

7. The method of claim 2, wherein the prediction of satellite states collectively covers a span of time having a length of at least seven calendar days.

8. The method of claim 5, wherein differentially decoding the sets of compressed Kepler parameters comprises:

for each set of compressed Kepler parameters from a second set to a last set, delta decoding each set with regard to a subsequent set.

9. The method of claim 1, further comprising:

analyzing historical state data to determine a statistical variation of the parameters in the sets of parameters, wherein the differentially encoding of the sets of parameters uses codewords having a bit length chosen according to the statistical variation.

10. The method of claim 1, wherein predicting satellite states using historical satellite state data comprises numerically integrating satellite equations of motion.

11. The method of claim 10, wherein deriving sets of parameters representative of the predicted satellite states comprising deriving sets of Kepler parameters, each set of Kepler parameters being representative of the predicted satellite states for a period of at least four hours.

12. A client device, comprising:

a communication system that receives sets of differentially-compressed parameters representative of predicted satellite states via a first communication channel, wherein the predicted satellite states are generated for future time periods using historical satellite state data for at least one satellite of a satellite-based positioning system;

a state reconstructor that decompresses the differentially-compressed sets of parameters into recovered sets of parameters and selectively reconstructs at least one reconstructed satellite state using the recovered sets of parameters based upon a pre-determined period of validity for each recovered set of parameters; and

at least one signal processor that uses the at least one reconstructed satellite state to acquire a satellite signal.

13. The client device of claim 12, wherein the sets of differentially-compressed parameters are sets of differentially-compressed Kepler parameters.

14. The client device of claim 13, wherein the pre-determined period of validity is at least four hours.

15. The client device of claim 13, wherein the pre-determined period of validity is at least six hours.

16. A server, comprising:

a prediction generator operable to generates predictions of future satellite states for future time periods using historical satellite state data;

a parameter generator operable to derive sets of parameters representative of the future satellite states and to differentially compress the sets of parameters into compressed sets of parameters; and

a communication system operable to transmit the compressed sets of parameters to client devices that use the transferred sets of parameters to selectively reconstruct at least one reconstructed satellite state.

17. The server of claim 16, wherein the parameters are Kepler parameters.

18. The server of claim 16, wherein the parameter generator is further operable to compress the sets of parameters into compressed sets of using codewords having a bit length chosen according to a statistical variation of the parameters.

19. The server of claim 16, wherein the communication system is operable to transmit the compressed sets of parameters using a wireless communication channel.

20. The server of claim 16, wherein the parameters are Chebyshev parameters.