Systems and Methods for Synthesizing GPS Measurements to Improve GPS Location Availability

• US 20100328146A1
• Filed: 11/05/2007
• Published: 12/30/2010
• Est. Priority Date: 11/05/2007
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: SIRF Technology Incorporated (Qualcomm, Inc.)
• Inventors: Phatak, Makarand Shankar, Kandangath, Anil Kumar, Chansarkar, Mangesh, Xie, Gang
• Granted Patent: US 8,159,393 B2
• Time in Patent Office: Days
• US Class Current: 342/357.25
• CPC Class Codes: G01S 19/42 Determining position
• CPC Class Codes: G01S 19/46 the supplementary measurement being of a radio-wave signal type
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial

Abstract

There are situations where GPS signals are received from less than four satellites. In order to improve the GPS location availability, disclosed here are systems and methods for synthesizing GPS measurements, which, together with fewer than four available real GPS signals, can be used to calculate a position fix. In particular, GPS range measurements for lost satellites, which are satellites that were previously tracked but are now not tracked, are synthesized to improve GPS signal availability. The synthesized measurements are used along with real measurements to enable accurate position fix even when GPS satellite availability is poor. Different synthesized measurement generation schemes, depending on whether an INS/DR aiding system is available, are further described herein.

Claims

1. A method for synthesizing global positioning system (GPS) measurements, the method comprising:

receiving GPS signals from signal sources by a navigation device;

estimating pseudorange (PR) and delta pseudo range (DPR) based on the received GPS signals; and

calculating a position fix using the estimated PR and DPR in a navigation solution.

2. The method as defined in claim 1, further comprising:

calculating pseudoranges (PRs) and delta pseudo ranges (DPRs) associated with the GPS signals from the signal sources;

determining whether the GPS signals are received from three or less signal sources of the signal sources;

responsive to determining that the navigation device receives the GPS signals from the three or less signal sources of the signal sources,

determining which signal source was lost, and

estimating PR and DPR for the lost signal source based on the calculated PRs and DPRs; and

calculating a position fix using the calculated PRs and DPRs as well as the estimated PR and DPR in the navigation solution.

3. The method as defined in claim 2, further comprising determining whether the difference between the time associated the previous PRs and DPRs and the time associated with estimating the PR and DPR passed a time threshold.

4. The method as defined in claim 3, wherein estimating the PR and DPR for the lost signal source is based on the previous PRs and DPRs associated with the lost signal source.

5. The method as defined in claim 4, wherein the estimated PR and DPR can be used to obtain a 3D Least Squares position fix in an Assisted GPS (AGPS) mode.

6. The method as defined in claim 1, further comprising determining whether the navigation device includes external aiding sensors, the navigation device include a receiver.

7. The method as defined in claim 6, further comprising responsive to the navigation device having the external aiding sensors, calculating the movement of the receiver using the external aiding sensors.

8. The method as defined in claim 7, further comprising updating the position of the receiver based on the calculated receiver movement.

9. The method as defined in claim 8, further comprising:

determining whether the GPS signals are received from three or less signal sources of the signal sources;

calculating line of sight vectors for the three or less signal sources of the signal sources based on the updated receiver'"'"'s position; and

calculating DPR residuals for the three or less signal sources of the signal sources.

10. The method as defined in claim 9, further comprising calculating a receiver frequency drift by averaging the DPR residuals.

11. The method as defined in claim 10, wherein estimating the PR and DPR for a lost signal source is based on the calculated receiver frequency drift and the calculated receiver movement.

12. The method as defined in claim 11, further comprising initializing a Kalman filter in a standalone GPS navigation solution based on the updated receiver'"'"'s clock frequency drift and the estimated PR and DPR.

13. The method as defined in claim 1, further comprising transmitting the estimated PR and DPR to an Mobile Station (MS)-assisted GPS server in an AGPS operation mode.

14. A system for synthesizing global positioning system (GPS) measurements comprising:

a GPS receiver that is configured to receive GPS signals and estimate pseudorange (PR) and delta pseudo range (DPR) based on the received GPS signals; and

a server in an Assisted GPS (AGPS) operation mode that is configured to;

receive the estimated PR and DPR from the GPS receiver, and

calculate a position fix based on the received estimated PR and DPR.

15. The system as defined in claim 14, wherein the GPS receiver is further configured to:

calculate pseudoranges (PRs) and delta pseudo ranges (DPRs) associated with the GPS signals from three or less signal sources of at least four signal sources

determine whether the GPS signals are received from the three or less signal sources of the at least four signal sources; and

responsive to determining the GPS signals are received from the three or less signal sources of the at least four signal sources,

determining which signal source was lost from the at least four signal sources, and

estimate PR and DPR for the lost signal source based on the calculated PRs and DPRs.

16. The system as defined in claim 15, wherein the GPS receiver is further configured to determine whether the difference between the time associated the previous PRs and DPRs and the time associated with estimating the PR and DPR passed a time threshold.

17. The system as defined in claim 16, wherein the GPS receiver is further configured to estimate the PR and DPR for the lost signal source based on the previous PRs and DPRs associated with the at least four signal sources.

18. The system as defined in claim 17, wherein the server is configured to obtain a 3D Least Squared position fix in AGPS mode based on the received estimated PR and DPR.

19. The system as defined in claim 14, wherein the GPS receiver includes an external aiding sensor or system, the external aiding sensor or system including at least one of inertial navigation system (INS) sensors and automobile ABS dead reckoning (DR) system.

20. The system as defined in claim 19, wherein the GPS receiver is further configured to calculate the movement of the receiver using the external aiding sensors.

21. The system as defined in claim 20, wherein the GPS receiver is further configured to update the position of the receiver based on the calculated receiver movement.

22. The system as defined in claim 21, wherein the GPS receiver is further configured to:

determine whether the GPS signals are received from three or less signal sources of the signal sources,

calculate line of sight vectors for the three or less signal sources of the at least four signal sources based on the updated receiver'"'"'s position, and

calculate DPR residuals for the three or less signal sources of the at least four signal sources.

23. The system as defined in claim 22, wherein the GPS receiver is further configured to calculate a receiver frequency drift based on the calculated line of sight vectors.

24. The system as defined in claim 23, wherein the GPS receiver is further configured to estimate the PR and DPR for the lost signal source based on the calculated receiver frequency drift and the calculated receiver movement.

25. A GPS receiver comprising:

an antenna that is configured to receive GPS signals from at least four signal sources; and

a baseband digital signal processing that is configured to;

receive the GPS signals from the antenna,

calculate pseudoranges (PRs) and delta pseudo ranges (DPRs) associated with the GPS signals from three or less signal sources of the at least four signal sources,

determine whether the GPS signals are received from the three or less signal sources of the at least four signal sources,

responsive to determining that the GPS signals are received from the three or less signal sources of the at least four signal sources,

determine which signal source was lost from the at least four signal sources, and

estimate PR and DPR for the lost signal source based on the

calculated PRs and DPRs, and

calculate a position fix using the calculated PRs and DPRs, and the estimated PR and DPR in a navigation solution.