Reliability metrics for parameter estimates which account for cumulative error

• US 20030087604A1
• Filed: 04/17/2002
• Published: 05/08/2003
• Est. Priority Date: 11/02/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Amerga, Messay, Fernandez-Corbaton, Ivan, Rick, Roland R., Stein, Jeremy
• Granted Patent: US 7,558,534 B2
• Time in Patent Office: Days
• US Class Current: 455/65
• CPC Class Codes: G01S 5/0218 Multipath in signal reception
• CPC Class Codes: G01S 5/0244 Accuracy or reliability of position solution or of measurements contributing thereto
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A method of producing a reliability metric for a parameter estimate derived from a signal using correlation analysis is described. The method begins by obtaining an indication of whether a non line of sight signal condition is present or likely and/or obtaining an indication of whether a multi-path signal condition is present or likely. Responsive to one or both of these indications, the method derives a reliability metric for the parameter estimate. In one embodiment, the parameter estimate is an estimate of time of arrival (TOA) of the signal, and the reliability metric is root mean square error (RMSE) of the time of arrival estimate. This embodiment obtains an indication of whether a non line of sight signal condition is present or likely based on a measure of the strength of the correlation function at the peak thereof. The measure of the strength of the correlation function at the peak thereof may be energy per chip divided by total received power (E_c/I₀) or may simply be the raw energy of the correlation function at the peak. The RMSE metric which is computed in this embodiment varies inversely with the peak strength of the correlation function.

Claims

1. A method comprising:

determining a non-line of sight signal condition is present or likely; and

responsive thereto, deriving a reliability metric for a parameter estimate.

2. The method of claim 1 wherein the parameter estimate is an estimate of time of arrival (TOA) of a signal.

3. The method of claim 2 wherein the reliability metric is root mean square error (RMSE) of the time of arrival estimate.

4. The method of claim 3 wherein the time of arrival estimate is derived from a peak of a correlation function for the signal.

5. The method of claim 4 further comprising obtaining an indication of whether a non-line sight signal condition is present or likely based on a measure of the strength of the correlation function at the peak thereof.

6. The method of claim 5 wherein the measure of the strength of the correlation function at the peak thereof is energy per chip divided by total received power (E_c/I₀).

7. The method of claim 5 wherein the measure of the strength of the correlation function at the peak thereof is the energy of the correlation function at the peak.

8. The method of claim 5 wherein the RMSE of the TOA estimate is derived using a lookup table.

9. The method of claim 8 wherein the lookup table implements a non-linear relationship between the RMSE of the TOA estimate and the strength of the correlation function at the peak thereof.

10. The method of claim 8 wherein the lookup table implements a relationship between the RMSE of the TOA estimate, the strength of the correlation function at the peak thereof, and the integration time used to derive the correlation function.

11. The method of claim 5, wherein a formula implements a relationship between the RMSE of the TOA estimate, the strength of the correlation function at the peak thereof, and the integration time used to derive the correlation function.

12. The methods of any of claims 1, tangibly embodied as a series of instructions stored on a processor readable medium.

24. The method of any of claims 1, tangibly embodied on a server.

13. A system for providing a reliability metric for a parameter estimate derived from a signal using correlation analysis comprising:

first logic for providing an indication of whether a non-line of sight signal condition is present or likely; and

second logic for deriving a reliability metric for the parameter estimate responsive to the indication provided by the first logic.

14. The system of claim 13 wherein the parameter estimate is an estimate of time of arrival (TOA) of the signal.

15. The system of claim 14 wherein the reliability metric is root mean square error (RMSE) of the time of arrival estimate.

16. The system of claim 15 wherein the time of arrival estimate is derived from a peak of a correlation function for the signal.

17. The system of claim 16 wherein the first logic is configured to provide an indication of whether a non line of sight signal condition is present or likely based on a measure of the strength of the correlation function at the peak thereof.

18. The system of claim 17 wherein the measure of the strength of the correlation function at the peak thereof is energy per chip divided by total received power (E_c/I₀).

19. The system of claim 17 wherein the measure of the strength of the correlation function at the peak thereof is the energy of the correlation function at the peak.

20. The system of claim 17 wherein the second logic is configured to derive the RMSE of the TOA estimate using a lookup table.

21. The system of claim 20 wherein the lookup table implements a non-linear relationship between the RMSE of the TOA estimate and the strength of the correlation function at the peak thereof.

22. The system of claim 20 wherein the lookup table implements a relationship between the RMSE of the TOA estimate, the strength of the correlation function at the peak thereof, and the integration time used to derive the correlation function.

23. The system of claim 17 wherein a formula implements a relationship between the RMSE of the TOA estimate, the strength of the correlation function at the peak thereof, and the integration time used to derive the correlation function.