NAVIGATION SIGNAL RECEIVER TRAJECTORY DETERMINATION

• US 20080117100A1
• Filed: 11/20/2006
• Published: 05/22/2008
• Est. Priority Date: 11/20/2006
• Status: Active Grant

• Current Assignee: CSR Technology Holdings Inc. (Qualcomm, Inc.)
• Original Assignee: SiRF Technology Holdings Incorporated (Qualcomm, Inc.)
• Inventors: Zhang, Wentao, Dong, Lei, Wang, David, Wang, Chi-Shin, Mo, Jun
• Granted Patent: US 7,439,907 B2
• Time in Patent Office: Days
• US Class Current: 342/357.02
• CPC Class Codes: G01S 19/40 Correcting position, velocity or attitude

Abstract

The present invention provides methods and systems that enable a mobile navigation receiver to accurately determine its trajectory with non-current ephemeris in stand-alone mode. In an embodiment, the receiver computes the position for the same location using non-current ephemeris and current ephemeris at different time instances. The receiver then determines a position correction by finding the difference between these two computed positions, and applies this correction to the trajectory generated with non-current ephemeris to obtain a more accurate trajectory. In another embodiment, the receiver computes an initial position of the receiver using non-current ephemeris and finds the difference between the computed initial position and an accurate approximation of the initial position. The receiver then shifts the subsequent receiver trajectory computed using non-current ephemeris by the difference to obtain a more accurate trajectory.

Claims

1. A method of obtaining an accurate navigation receiver trajectory at a receiver, comprising:

computing a receiver trajectory based on non-current ephemeris or a predicted satellite orbit, wherein the predicted satellite orbit is generated at the receiver based on prior satellite navigation messages received by the receiver; and

correcting the computed receiver trajectory to obtain a corrected receiver trajectory.

2. The method of claim 1, wherein the corrected trajectory is a function of an initial position and a computed trajectory of the receiver obtained using the non-current ephemeris or the predicted satellite orbit.

3. The method of claim 2, wherein correcting the computed trajectory comprises:

computing an initial position of the receiver using the non-current ephemeris;

computing a difference in position between the computed initial position and an approximate initial position; and

shifting the computed receiver trajectory by the difference.

4. The method of claim 3, wherein the approximate initial position comprises a last saved position when the receiver was turned off.

5. The method of claim 3, wherein the receiver is on a vehicle, further comprising:

when the vehicle is turned off, automatically saving a last position of the receiver and turning off the receiver; and

when the vehicle is started, automatically starting the receiver to acquire satellite signals, wherein the receiver uses the acquired satellite signals to compute the initial position with the non-current ephemeris and uses the last saved position as the approximate initial position.

6. The method of claim 3, further comprising:

detecting motion of the receiver with a motion detector; and

when motion is detected, automatically starting the receiver to acquire satellite signals, wherein the receiver uses the acquired satellite signals to compute the initial position.

7. The method of claim 3, further comprising:

detecting an indoor to outdoor transition of the receiver; and

when the indoor to outdoor transition is detected, automatically starting the receiver to acquire satellite signals, wherein the receiver uses the acquired signals to compute the initial position and uses a last saved position corresponding to an entrance of the indoor as the approximate initial position.

8. The method of claim 7, further comprising:

validating whether the approximate initial position can be the last saved position using an ecompass.

9. The method of claim 3, further comprising:

enabling a user to manually enter a location into the receiver at anytime beginning at the initial position or at any point of the trajectory; and

when the user enters the location, computing a difference in position between the entered location and a computed position; and

subsequently shifting the computed receiver trajectory by the difference.

10. The method of claim 1, wherein pseudoranges and clock error of new satellites entering the constellation are corrected.

11. The method of claim 10, wherein the pseudorange of each satellite is corrected for multipath.

12. The method of claim 1, wherein obtaining the receiver trajectory and download of new ephemeris are performed in parallel and simultaneously.

13. The method of claim 12, wherein the receiver trajectory is validated upon download of new ephemeris.

14. The method of claim 1, wherein current ephemeris is used in computing receiver position fix whenever the current ephemeris is available at the receiver.

15. The method of claim 1, further comprising:

attempting to download current ephemeris to the receiver when needed to maintain current ephemeris at the receiver; and

when current ephemeris is available at the receiver, obtaining the accurate receiver trajectory based on the current ephemeris instead of the non-current ephemeris or the predicted satellite orbit.

16. The method of claim 15, wherein attempting to download current ephemeris comprises:

alternating between a sleep mode and a wake up mode;

during the wake up mode, determining whether a signal power level is sufficient to download the current ephemeris; and

if the signal power level is sufficient, downloading the current ephemeris to the receiver.

17. A navigation signal receiver, comprising:

a radio frequency (RF) front-end for receiving satellite signals;

a baseband section for processing received signals into correlation values;

a processor coupled to the baseband section; and

a computational module coupled to the processor, wherein the computational module computes a receiver trajectory based on non-current ephemeris or a predicted satellite orbit, and corrects the computed receiver trajectory to obtain a corrected receiver trajectory.

18. The receiver of claim 17, wherein the corrected trajectory is a function of an initial position and a computed trajectory of the receiver obtained using the non-current ephemeris or the predicted satellite orbit.

19. The receiver of claim 17, wherein the computational module computes a receiver trajectory using the non-current ephemeris, and then corrects the computed receiver trajectory to generate the accurate receiver trajectory.

20. The receiver of claim 19, wherein the computational module corrects the computed trajectory by:

computing an initial position of the receiver using the non-current ephemeris;

computing a difference in position between the computed initial position and an approximate initial position; and

shifting the computed receiver trajectory by the difference.

21. The receiver of claim 20, wherein the approximate initial position comprises a last saved position when the receiver was turned off.

22. The receiver of claim 20, wherein the receiver is on a vehicle, and wherein when the vehicle is turned off, the computational module automatically saves a last position of the receiver, and when the vehicle is started, the processor automatically starts acquiring satellite signals, and the computational module uses the acquired satellite signals to compute the initial position with the non-current ephemeris and uses the last saved position as the approximate initial position.

23. The receiver of claim 20, further comprising a motion detector for detecting motion of the receiver, and wherein when motion is detected by the motion detector, the processor automatically starts acquiring satellite signals, and the computational module uses the acquired satellite signals to compute the initial position.

24. The receiver of claim 20, wherein the computational detects an indoor to outdoor transition of the receiver, and when the indoor to outdoor transition is detected, the processor automatically starts acquiring satellite signals, and the computational module uses the acquired signals to compute the initial position and uses a last saved position corresponding to an entrance of the indoor as the approximate initial position.

25. The receiver of claim 24, further comprising an ecompass for detecting direction, and wherein the computational module validates whether the approximate initial position can be the last saved position using the ecompass.

26. The receiver of claim 20, further comprising a user interface for enabling a user to manually enter a location into the receiver at anytime beginning at the initial position or at any point of the trajectory, and wherein when the user enters the location via the user interface, the computational module computes a difference in position between the entered location and a computed position, and subsequently shifts the computed receiver trajectory by the difference.

27. The receiver of claim 17, wherein pseudoranges and clock error of new satellites entering the constellation are corrected.

28. The receiver of claim 27, wherein the pseudorange of each satellite is corrected for multipath.

29. The receiver of claim 17, wherein the computational module computes the receiver trajectory and downloads new ephemeris in parallel and simultaneously.

30. The receiver of claim 29, wherein the computational module validates the receiver trajectory upon download of new ephemeris.

31. The receiver of claim 17, wherein computational module uses the current ephemeris to compute a receiver position fix whenever the current ephemeris is available at the receiver.

32. The receiver of claim 17, wherein the computational module attempts to download current ephemeris when needed to maintain current ephemeris at the receiver, and when current ephemeris is available at the receiver, the computational module generates the accurate receiver trajectory based on the current ephemeris instead of the non-current ephemeris or the predicted satellite orbit.

33. The receiver of claim 32, wherein computational module attempts to download current ephemeris by:

alternating the receiver between a sleep mode and a wake up mode;

during the wake up mode, determining whether a signal power level is sufficient to download the current ephemeris; and

if the signal power level is sufficient, downloading the current ephemeris to the receiver.