Systems and methods for synthesizing GPS measurements to improve GPS location availability

• US 8,159,393 B2
• Filed: 11/05/2007
• Issued: 04/17/2012
• Est. Priority Date: 11/05/2007
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Inventors: Xie, Gang, Phatak, Makarand Shankar, Chansarkar, Mangesh, Kandangath, Anil Kumar
• Primary Examiner(s): Tarcza, Thomas
• Assistant Examiner(s): GALT, CASSI J
• Application Number:
  US11/934,832
• Publication Number:
  US 20100328146A1
• Time in Patent Office: 1,625 Days
• Field of Search: 342/357.3, 342/357.78, 342/357.23, 342/357.35
• US Class Current: 342/357.78
• 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 at least four signal sources by a navigation device;

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

identifying a lost signal source when the GPS signals are received from less than four of the at least four signal sources;

estimating PRs and DPRs for the lost signal source based on previously calculated PRs and DPRs of the lost signal source; and

calculating a position fix using the calculated PRs and DPRs, and the estimated PRs and DPRs in a navigation solution.

2. The method as defined in claim 1, further comprising determining whether the difference between a time associated with the previously calculated PRs and DPRs and a time associated with the estimated PRs and DPRs passed a time threshold.

3. The method as defined in claim 2, wherein the estimated PRs and DPRs can be used to obtain a 3D Least Squares position fix in an Assisted GPS (AGPS) mode.

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

5. The method as defined in claim 4, further comprising responsive to determining that the navigation device includes the external aiding sensors, calculating the movement of the receiver using the external aiding sensors.

6. The method as defined in claim 5, further comprising updating the position of the receiver based on the calculated receiver movement.

7. The method as defined in claim 6, further comprising:

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

8. The method as defined in claim 7, further comprising calculating a receiver frequency drift by averaging the DPR residuals.

9. The method as defined in claim 8, wherein estimating the PRs and DPRs for the lost signal source is based on the calculated receiver frequency drift and the calculated receiver movement.

10. The method as defined in claim 9, further comprising initializing a Kalman filter in a standalone GPS navigation solution based on the updated receiver'"'"'s clock frequency drift and the estimated PRs and DPRs.

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

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

a GPS receiver that is configured to;

receive GPS signals from at least four satellites,

calculate pseudoranges (PRs) and delta pseudo ranges (DPRs) associated with the GPS signals from the at least four satellites,

identify a lost satellite when the GPS signals are received from less than four of the at least four satellites, and

estimate PRs and DPRs for the lost satellite based on previously calculated PRs and DPRs of the lost satellite,

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

receive the calculated PRs and DPRs, and the estimated PRs and DPRs from the GPS receiver,

calculate a position fix of the GPS receiver based on the received calculated PRs and DPRs, and the received estimated PRs and DPRs, and

transmit the position fix to the GPS receiver.

13. The system as defined in claim 12, wherein the GPS receiver is further configured to determine whether the difference between a time associated with the previously calculated PRs and DPRs and a time associated with the estimated PRs and DPRs has passed a time threshold.

14. The system as defined in claim 12, wherein the server is configured to obtain a 3D Least Squared position fix in AGPS mode based on the received estimated PRs and DPRs.

15. The system as defined in claim 12, 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.

16. The system as defined in claim 15, wherein the GPS receiver is further configured to calculate the movement of the receiver using the external aiding sensors.

17. The system as defined in claim 16, wherein the GPS receiver is further configured to update the position of the receiver based on the calculated receiver movement.

18. The system as defined in claim 17, wherein the GPS receiver is further configured to:

determine whether the at least four 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.

19. The system as defined in claim 18, wherein the GPS receiver is further configured to calculate a receiver frequency drift based on the calculated line of sight vectors.

20. The system as defined in claim 19, wherein the GPS receiver is further configured to estimate the PRs and DPRs for the lost signal source based on the calculated receiver frequency drift and the calculated receiver movement.

21. A GPS receiver comprising:

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

a baseband digital signal processor 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 the at least four signal sources,

identify a lost signal source when the GPS signals are received from less than four of the at least four signal sources;

estimate PRs and DPRs for the lost signal source based on previously calculated PRs and DPRs of the lost signal source; and

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