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

1. A method for determining a position of a mobile receiver, comprising:

measuring a first pseudorange from the mobile receiver to a first satellite of a first satellite navigation system;

measuring a second pseudorange from the mobile receiver to a second satellite of a second satellite navigation system;

determining a difference between a first time reference of the first satellite navigation system and a second time reference of the second satellite navigation system; and

combining the first pseudorange and the second pseudorange using the difference to generate combined first and second pseudoranges.

2. The method of claim 1 , further comprising:

computing the position of the mobile receiver using the combined first and second pseudoranges.

3. The method of claim 2 , further comprising:

sending the measured first and second pseudoranges from the mobile receiver to a server; and

computing the position of the mobile receiver at the server.

4. The method of claim 1 , further comprising: receiving the difference between the first time reference and the second time reference from a server.

5. The method of claim 1 , further comprising: receiving the difference between the first time reference and the second time reference from the first satellite navigation system.

6. The method of claim 1 , further comprising:

computing a time of day using the combined first and second pseudoranges.

7. The method of claim 1 , wherein combining the first pseudorange and the second pseudorange comprises converting the first pseudorange from the first time reference to the second time reference.

8. The method of claim 1 , further comprising:

forming a first pseudorange residual as a difference between an expected first pseudorange and the measured first pseudorange; and

forming a second pseudorange residual as a difference between an expected second pseudorange and the measured second pseudorange.

9. The method of claim 8 , further comprising:

computing a position update of the position of the mobile receiver using the first and second pseudorange residuals.

10. The method of claim 8 , further comprising:

computing an update to a time of day measurement using the first and second pseudorange residuals.

11. The method of claim 1 , wherein the first satellite navigation, system and the second satellite navigation system include any two of GPS, GALILEO, and GLONASS.

12. A mobile receiver, comprising:

satellite receiver circuitry configured to receive first and second satellite signals from first and second satellites respectively, the first and second satellites corresponding to first and second respective satellite navigation systems; and

a processor configured to:

measure a first pseudorange from the mobile receiver to the first satellite of the first satellite navigation system based on the first satellite signal;

measure a second pseudorange from the mobile receiver to the second satellite of the second satellite navigation system based on the second satellite signal;

determine a difference between a first time reference of the first satellite navigation system and a second time reference of the second satellite navigation system; and

combine the first pseudorange and the second pseudorange using the difference to generate combined first and second pseudoranges.

13. The mobile receiver of claim 12 , wherein the processor is further configured to compute a position of the mobile receiver using the combined first and second pseudoranges.

14. The mobile receiver of claim 12 , further comprising:

a wireless transceiver configured to receive the difference between the first time reference and the second time reference from a server.

15. The mobile receiver of claim 12 , wherein the satellite receiver circuitry is further configured to receive the difference between the first time reference and the second time reference from the first satellite navigation system.

16. The mobile receiver of claim 12 , wherein the processor is further configured to:

form a first pseudorange residual as a difference between an expected first pseudorange and the measured first pseudorange;

form a second pseudorange residual as a difference between an expected second pseudorange and the measured second pseudorange; and

compute a position update of a position of the mobile receiver using the first and second pseudorange residuals.

17. A system, comprising:

a mobile receiver configured to measure first and second pseudoranges from the mobile receiver to first and second satellites respectively, the first and second satellites corresponding to first and second respective satellite navigation systems; and

a server configured to receive the first and second pseudoranges from the mobile receiver, to obtain a difference between a first time reference of the first satellite navigation system and a second time reference of the second satellite navigation system, and to compute a position of the mobile receiver based on the first and second pseudoranges and the difference between the first time reference of the first satellite navigation system and the second time reference of the second satellite navigation system.

18. The system of claim 17 , further comprising:

a reference station configured to determine the difference between the first time reference of the first satellite navigation system and the second time reference of the second satellite navigation system and to send the difference to the server.

19. The system of claim 17 , wherein the server is further configured to combine the first pseudorange and the second pseudorange using the difference to generate combined first and second pseudoranges.

20. The system of claim 17 , wherein the server is further configured to convert the first pseudorange from the first time reference to the second time reference.