Cross-correlation mitigation method and apparatus for use in a global positioning system receiver

• US 7,623,070 B2
• Filed: 04/19/2007
• Issued: 11/24/2009
• Est. Priority Date: 07/10/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Roh, Mark Charles
• Primary Examiner(s): Issing; Gregory C
• Application Number:
  US11/737,266
• Publication Number:
  US 20080129585A1
• Time in Patent Office: 950 Days
• Field of Search: 342/357.02, 342/357.1, 342/357.15
• US Class Current: 342/357.59
• CPC Class Codes: G01S 19/09 providing processing capability normally carried out by the receiver
• CPC Class Codes: G01S 19/14 specially adapted for specific applications
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: G01S 19/25 involving aiding data received from a cooperating element, e.g. assisted GPS
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence

Abstract

A method and apparatus mitigating the effects of cross-correlation signals on received satellite signals in a Global Positioning System (GPS) receiver is described. MS-Assisted and MS-Based cross-correlation detection and mitigation methods and apparatus are described. A GPS search mode architecture is used to detect SV signals and identify potential cross-correlations. The GPS search modes have different coherent integration lengths and different degrees of sensitivity. After detection, measurements are logged into a database for further processing. Several cross-correlation tests are described. For example, a “Mainlobe” cross-correlation test is described that identifies the most significant cross-correlations that occur when the Doppler difference between the interfering SV signal and the target SV signal is nonzero and a multiple of 1 kHz. Appropriate C/No and Doppler thresholds, or masks, are selected and used to identify the mainlobe cross-correlations. A wide Doppler mask is used to account for the effects on cross-correlations caused by BPSK data bit modulation. Appropriate MS-Assisted and MS-Based cross-correlation masks are described. Other cross-correlation tests include “variable C/No”, “strong”, “wide Doppler” and “pre-emptive” cross-correlation detection tests.

Claims

1. A communication apparatus comprising:

one or more antennae configured to receive signals indicative of communication information and signals indicative of location information;

a communication process module configured to process the communication information;

a location process module configured to process the location information, the location process module configured to;

perform a higher mode search using a higher mode search length and a higher mode signal detection threshold to detect one or more received signals indicative of location information;

perform a lower mode search after performance of the higher mode search, for a second length of time, using a lower mode search length and a lower mode signal detection threshold to detect one or more received signals indicative of the location information, wherein the second length of time is greater than the first length of time, the lower mode search being performed to detect one or more received signals not detected with a signal strength above a threshold level during the performance of the higher mode search; and

determine cross correlation between at least one signal detected using the higher mode search and at least one signal detected using the lower mode search.

2. The communication apparatus of claim 1, wherein the one or more received signals indicative of location information include a first satellite signal and a second satellite signal.

3. The communication apparatus of claim 1, wherein the communication apparatus comprises a cellular telephone, and wherein the communication process module is adapted to process received cellular telephone signals.

4. The communication apparatus of claim 1, wherein the higher mode signal detection threshold is greater than the lower mode signal detection threshold.

5. The communication apparatus of claim 1, wherein the one or more received signals include a first received satellite signal and a second received satellite signal, wherein the higher mode search is adapted to detect the first received satellite signal and the lower mode search is adapted to detect the second received satellite signal, and wherein the location process module is adapted to determine cross-correlation between the first received satellite signal and the second received satellite signal, and wherein the location process module is further adapted to process at least one of the first received satellite signal and the second received satellite signal to remove determined cross-correlation.

6. The communication apparatus of claim 1, wherein the location process module is further adapted to perfonn a medium mode search using a medium mode search length and a medium mode signal detection threshold.

7. The communication apparatus of claim 1, wherein the location process module is implemented using hardware, software, or both.

8. The communication apparatus of claim 1, wherein the communication apparatus is adapted to determine cross correlation based, at least in part on:

comparing carrier-to-noise ratio measurements for signals of location information; and

identifying a weaker measurement as a cross correlation if a difference between the carrier-to-noise ratio measurements exceeds a predetennined carrier-to-noise threshold, and if a difference between Doppler measurements falls within a predetennined Doppler difference threshold.

9. An apparatus comprising:

means for receiving signals indicative of communication information and signals indicative of location information;

means for processing the communication information;

means for performing a higher mode search, for a first length of time, using a higher mode search length and a higher mode signal detection threshold to detect one or more received signals indicative of location information;

means for performing a lower mode search after performance of the higher mode search, for a second length of time, using a lower mode search length and a lower mode signal detection threshold to detect one or more received signals indicative of location information, wherein the second length of time is greater than the first length of time, the lower mode search being performed to detect one or more received signals not detected with a signal strength above a threshold level during the performance of the higher mode search; and

means for determining cross correlation between at least one signal detected using the higher mode search and at least one signal detected using the lower mode search.

10. The apparatus of claim 9, wherein the one or more received signals indicative of location information include a first satellite signal and a second satellite signal.

11. The communication apparatus of claim 9, wherein the communication apparatus comprises a cellular telephone, and wherein the means for processing the communication information is adapted to process received cellular telephone signals.

12. The apparatus of claim 9, wherein the higher mode signal detection threshold is greater than the lower mode signal detection threshold.

13. The apparatus of claim 9, wherein the one or more received signals include a first received satellite signal and a second received satellite signal, wherein the higher mode search is adapted to detect the first received satellite signal and the lower mode search is adapted to detect the second received satellite signal, and

further comprising means for processing location information adapted to dctcrrninc cross-correlation between the first received satellite signal and the second received satellite signal, and for processing process at least one of the first received satellite signal and the second received satellite signal to remove determined cross-correlation.

14. The apparatus of claim 9, further comprising means for performing a medium mode search using a medium mode search length and a medium mode signal detection threshold.

15. The apparatus of claim 9, wherein at least one of the means for performing a higher mode search or the means for performing a lower mode search is implemented using hardware, software, or both.

16. The apparatus of claim 9, wherein the means for determining cross correlation is adapted to determine cross correlation based, at least in part on:

comparing carrier-to-noise ratio measurements for signals of location information; and

identifying a weaker measurement as a cross correlation if a difference between the carrier-to-noise ratio measurements exceeds a predetermined carrier-to-noise threshold, and if a difference between Doppler measurements falls within a predetermined Doppler difference threshold.

17. A method, comprising:

receiving signals indicative of communication information and signals indicative of location information;

performing a higher mode search, for a first length of time, using a higher mode search length and a higher mode signal detection threshold to detect one or more received signals indicative of the location information;

performing a lower mode search after performance of the higher mode search, for a second length of time, using a lower mode search length and a lower mode signal detection threshold to detect one or more received signals indicative of the location information, wherein the second length of time is greater than the first length of time, the lower mode search being performed to detect one or more received signals not detected with a signal strength above a threshold level during the performance of the higher mode search; and

determining cross correlation between at least one signal detected using the higher mode search and at least one signal detected using the lower mode search.

18. The method of claim 17, wherein the one or more received signals indicative of location information include a first satellite signal and a second satellite signal.

19. The method of claim 17, further comprising processing received cellular telephone signals.

20. The method of claim 17, wherein the higher mode signal detection threshold is greater than the lower mode signal detcction threshold.

21. The method of claim 17, wherein the one or more received signals include a first received satellite signal and a second received satellite signal, wherein the higher mode search is adapted to detect the first received satellite signal and the lower mode search is adapted to detect the second received satellite signal, the method further comprising:

determining cross-correlation between the first received satellite signal and the second received satellite signal, and processing at least one of the first received satellite signal and the second received satellite signal to remove determined cross-correlation.

22. The method of claim 17, further comprising performing a medium mode search using a medium mode search length and a medium mode signal detection threshold.

23. The method of claim 17, further comprising utilizing hardware, software, or both, to process the location information.

24. The method of claim 17, further comprising:

comparing carrier-to-noise ratio measurements for signals of location information; and

identifying a weaker measurement as a cross correlation if a difference between the carrier-to-noise ratio measurements exceeds a predetermined carrier-to-noise threshold, and if a difference between Doppler measurements falls within a predetermined Doppler difference threshold.

25. An article comprising:

a storage medium comprising machine-readable instructions stored thereon which, if executed by a processor, are adapted to enable the processor to;

perform a higher mode search of signals indicative of communication information and signals indicative of location information, for a first length of time, using a higher mode search length and a higher mode signal detection threshold to detect one or more received signals indicative of location information;

perform a lower mode search after performance of the higher mode search, for a second length of time, using a lower mode search length and a lower mode signal detection threshold to detect one or more received signals indicative of location information, wherein the second length of time is greater than the first length of time, the lower mode search being performed to detect one or more received signals not detected with a signal strength above a threshold level during the performance of the higher mode search; and

determine cross correlation between at least one signal detected using the higher mode search and at least one signal detected using the lower mode search.

26. The article of claim 25, wherein the one or more received signals indicative of location information include a first satellite signal and a second satellite signal.

27. The article of claim 25, wherein the machine-readable instructions, if executed by the processor, are further adapted to enable the processor to process received cellular telephone signals.

28. The article of claim 25, wherein the machine-readable instructions, if executed by the processor, are further adapted to enable the processor to utilize a higher mode signal detection threshold that is greater than the lower mode signal detection threshold.

29. The article of claim 25, wherein the one or more received signals include a first received satellite signal and a second received satellite signal, wherein the higher mode search is adapted to detect the first received satellite signal and the lower mode search is adapted to detect the second received satellite signal, the machine-readable instructions, if executed by the processor, being further adapted to enable the computing platform processor to:

determine cross-correlation between the first received satellite signal and the second received satellite signal, and process at least one of the first received satellite signal and the second received satellite signal to remove determined cross-correlation.

30. The article of claim 25, wherein the machine-readable instructions, if executed by the processor, are further adapted to direct the processor to perform a medium mode search using a medium mode search length and a medium mode signal detection threshold.

31. The article of claim 25, wherein the machine-readable instructions, if executed by the processor, are further adapted to direct the processor to utilize hardware, software, or both, to process the location information.

32. The article of claim 25, wherein the machine-readable instructions, if executed by the processor, are further adapted to direct the processor to:

compare carrier-to-noise ratio measurements for signals of location information; and

identify a weaker measurement as a cross correlation if a difference between the carrier-to-noise ratio measurements exceeds a predetermined carrier-to-noise threshold, and if a difference between Doppler measurements falls within a predetermined Doppler difference threshold.