Method and apparatus for combining measurements and determining clock offsets between different global navigation satellite systems

1. A method of processing satellite signals from a first satellite navigation system and a second satellite navigation system, comprising:

measuring at least one first pseudorange between a satellite signal receiver and at least one satellite of said first satellite navigation system;

measuring at least one second pseudorange between said satellite signal receiver and at least one satellite of said second satellite navigation system;

obtaining a first difference between a first time reference frame of said first satellite navigation system and a time reference;

obtaining a second difference between a second time reference frame of said second satellite navigation system and the time reference; and

combining said at least one first pseudorange and said at least one second pseudorange using said first and second differences.

2. The method of claim 1 , further comprising:

computing at least one of position of said satellite signal receiver and time-of-day using said combined at least one first pseudorange and said at least one second pseudorange.

3. The method of claim 1 , wherein said steps of obtaining and combining comprise:

receiving an estimated position of said satellite signal receiver;

receiving an estimated time-of-day; and

relating said at least one first pseudorange, said at least one second pseudorange, said estimated position, and said estimated time-of-day to a plurality of position and time variables, said plurality of position and time variables including at least one time variable associated with said first and second differences.

4. The method of claim 3 , wherein said at least one time variable comprises a delta-common bias variable.

5. The method of claim 3 , wherein said at least one time variable comprises a first common bias variable associated with said first satellite navigation system and a second common bias variable associated with said second satellite navigation system.

6. The method of claim 1 , wherein said step of obtaining comprises:

receiving an indication of said first and second differences from a reference station.

7. The method of claim 6 , further comprising:

generating said indication at said reference station in response to signal measurements from each of said first satellite navigation system and said second satellite navigation system.

8. The method of claim 6 , further comprising:

decoding said indication from a satellite signal broadcast by at least one of said first satellite navigation system and said second satellite navigation system at said reference station.

9. The method of claim 1 , wherein said step of obtaining comprises:

receiving assistance data at said satellite signal receiver from a server; and

extracting an indication of said first and second differences from said assistance data.

10. The method of claim 1 , wherein said first satellite navigation system comprises at least one of a GALILEO satellite system and a GLONASS satellite system, and wherein said second satellite navigation system comprises a Global Positioning System.

11. A position location system, comprising:

satellite signal receiver circuitry for measuring at least one first pseudorange to at least one satellte of a first satellite navigation system and at least one second pseudorange to at least one satellite of a second satellite navigation system; and

a processor for obtaining a first difference between a first time reference frame of said first satellite navigation system and a time reference and a second difference between a second time reference frame of said second satellite navigation system and the time reference, and for combining said at least one first pseudorange and said at least one second pseudorange using said first and second differences.

12. The system of claim 11 , wherein said processor is further configured to compute at least one of position of said satellite signal receiver and time-of-day using said combined at least one first pseudorange and said at least one second pseudorange.

13. The system of claim 11 , wherein said processor is configured to:

receive an estimated position;

receive an estimated time-of-day; and

relate said at least one first pseudorange, said at least one second pseudorange, said estimated position, and said estimated time-of-day to a plurality of position and time variables, said plurality of position and time variables including at least one time variable associated with said first and second differences.

14. The system of claim 12 , wherein said at least one time variable comprises a delta-common bias variable.

15. The system of claim 12 , wherein said at least one time variable comprises a first common bias variable associated with said first satellite navigation system and a second common bias variable associated with said second satellite navigation system.

16. The system of claim 11 , further comprising:

a wireless transceiver;

wherein said processor is configured to receive an indication of said first and second differences from a server using said wireless transceiver.

17. The system of claim 11 , wherein said first satellite navigation system comprises at least one of a GALILEO satellite system and a GLONASS satellite system, and said second satellite navigation system comprises a Global Positioning System.

18. Apparatus for processing satellite signals from a first satellite navigation system and a second satellite navigation system, comprising:

means for measuring at least one first pseudorange between a satellite signal receiver and at least one satellite of said first satellite navigation system;

means for measuring at least one second pseudorange between said satellite signal receiver and at least one satellite of said second satellite navigation system;

means for obtaining a first difference between a first time reference frame of said first satellite navigation system and a time reference and for obtaining a second difference between a second time reference frame of said second satellite navigation system and the time reference; and

means for combining said at least one first pseudorange and said at least one second pseudorange using said first and second differences.

19. The apparatus of claim 18 , further comprising:

means for computing at least one of position of said satellite signal receiver and time-of-day using said combined at least one first pseudorange and said at least one second pseudorange.

20. The apparatus of claim 18 , wherein said means for obtaining and combining comprise:

means for receiving an estimated position of said satellite signal receiver;

means for receiving an estimated time-of-day; and

means for relating said at least one first pseudorange, said at least one second pseudorange, said estimated position, and said estimated time-of-day to a plurality of position and time variables, said plurality of position and time variables including at least one time variable associated with said first and second difference.