Method and apparatus for mitigating the effects of cross correlation in a GPS receiver

• US 8,072,376 B2
• Filed: 12/19/2008
• Issued: 12/06/2011
• Est. Priority Date: 06/27/2008
• Status: Expired due to Fees

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: SIRF Technology Incorporated (Qualcomm, Inc.)
• Inventors: Lennen, Gary
• Primary Examiner(s): Phan, Dao
• Application Number:
  US12/340,498
• Publication Number:
  US 20090322604A1
• Time in Patent Office: 1,082 Days
• Field of Search: 342/357.26, 342/357.42, 342/357.63, 342/357.71, 342/357.46, 701/207, 701/213
• US Class Current: 342/357.63
• 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 19/246 involving long acquisition integration times, extended snapshots of signals or methods specifically directed towards weak signal acquisition

Abstract

A positioning system receiver that mitigates cross correlation of received signals from positioning system satellite vehicles by generating the strong satellite vehicle signal and subtracting it from the received signal before correlation while eliminating the need for cross correlation signature without changing the C/A code.

Claims

1. A method for acquiring or tracking weak satellite vehicle (SV) signals in the presence of strong SV signals by mitigating the cross correlation of a received signal from the strong SV signals and a clear/acquisition (C/A) code of a received signal from a weak SV, comprising:

estimating at least two strong SV signals;

combining the at least two estimated strong SV signals;

subtracting the combined estimated strong SV signals from the actual received signal from a weak SV; and

performing correlation of the subtracted signal with the C/A code of the weak SV.

2. The method of claim 1, where each of the at least two strong SV signals is reconstructed using a code phase obtained from tracking each of the at least two strong SV signals.

3. The method of claim 2, where the code phase of each of the at least two strong SV signals is maintained with carrier-to-code aiding to track any change in the carrier frequency caused by Doppler or oscillator error.

4. The method of claim 1, where each of the at least two strong SV signals is reconstructed using demodulated data bits obtained from tracking each of the at least two strong SV signals.

5. The method of claim 1, where each of the at least two strong SV signals is reconstructed using a carrier phase and carrier frequency obtained from tracking each of the at least two strong SV signals.

6. The method of claim 1, where each of the at least two strong SV signals is reconstructed using an estimated amplitude of the at least two strong SV signals.

7. The method of claim 6, where estimating the amplitude of each of the at least two strong SV satellite signals comprises:

reconstructing each of the at least two strong SV signals;

subtracting each of the reconstructed at least two strong SV signals from the actual received signal;

performing correlation of the subtracted signal with the C/A of each of the at least two strong SV signals; and

updating the estimated amplitude to minimize such correlation.

8. The method of claim 7, where each of the at least two strong SV signals is reconstructed using code phase, carrier phase, carrier frequency, and demodulated data bits obtained from tracking each of the at least two strong SV signals.

9. The method of claim 1, where a carrier-to-noise (C/No) test is used to determine whether strong SV cross correlation mitigation is necessary.

10. The method of claim 1, where each of the at least two strong SV signals is first acquired and tracked to derive a code phase, carrier phase, carrier frequency, and demodulated data bits.

11. The method of claim 7, where a cross correlation error output from an amplitude control loop can be monitored to measure the quality of mitigation achieved.

12. A GPS position signal receiver, comprising:

an input sample memory in receipt of digital samples of positioning signals from at least two satellite vehicles (SVs);

a carrier numerical controlled oscillator that generates a carrier offset signal;

a complex mixer that combines digital samples from the input sample memory and the carrier offset signal from the carrier numerical controlled oscillator and results in a baseband signal;

a strong satellite reconstruction module that generates an estimated strong SV signal; and

a signal combiner that subtracts the estimated strong SV signal from the base band signal prior to filtering the baseband signal with a matched filter having a weak SV pseudo random number (PRN) as an input.

13. The GPS receiver of claim 12, where the strong satellite reconstruction module further includes a complex mixer that multiplies a complex carrier with a strong SV PRN and then applies a strong SV amplitude signal that results in the estimated strong SV signal.

14. The GPS receiver of claim 13, where the complex carrier is generated by a sin/cos LUT module that is in receipt of a frequency offset from a second carrier numerical controlled oscillator.

15. The GPS receiver of claim 12, where the strong satellite reconstruction module further includes the strong satellite reconstruction module being in receipt of phase, carrier frequency, and data information associated with the strong SV signal.

16. The GPS receiver of claim 12, further including an amplitude control loop that estimates the amplitude of the strong SV signal and cross correlates the output of the signal combiner.

17. The GPS receiver of claim 16, where the amplitude control loop tracks amplitude variations of the strong SV signal in a dynamic signal environment.

18. A computer-readable medium containing controller-executable instructions that when executed result in a method for acquiring or tracking weak SV signals in the presence of strong SV signals by mitigating cross correlation of a received signal from the strong SV signals and the C/A code of a received signal from a weak SV, the controller-executable instructions comprising instructions for:

estimating each of the at least two strong SV signals;

combining the at least two strong SV signals;

subtracting the combined estimated strong SV signals from the actual received signal from a weak SV; and

performing correlation of the subtracted signal with the C/A code of the weak SV.

19. The computer-readable medium containing controller-executable instructions of claim 18, where each of the at least two strong SV signals is reconstructed using a code phase obtained from tracking each of the at least two strong SV signals.

20. The computer-readable medium containing controller-executable instructions of claim 19, where the code phase of each of the at least two strong SV signals is maintained with carrier-to-code aiding to track any change in a carrier frequency caused by Doppler or oscillator error.

21. The computer-readable medium containing controller-executable instructions of claim 18, where each of the at least two strong SV signals is reconstructed using demodulated data bits obtained from tracking each of the at least two strong SV signals.

22. The computer-readable medium containing controller-executable instructions of claim 18, where each of the at least two strong SV signals is reconstructed using a carrier phase and carrier frequency obtained from tracking each of the at least two strong SV signals.

23. The computer-readable medium containing controller-executable instructions of claim 18, where each of the at least two strong SV signals is reconstructed using an estimated amplitude of each of the at least two strong SV signals.

24. The computer-readable media containing controller-executable instructions of claim 23, where estimating the amplitude of each of the at least two strong SV signals comprises:

reconstructing each of the at least two strong SV signals;

subtracting each of the reconstructed at least two strong SV signals from the actual received signal from a weak SV;

performing correlation of the subtracted signal with the C/A of each of the at least two strong SV signals; and

updating the estimated amplitude to minimize such correlation.

25. The computer-readable medium containing controller-executable instructions of claim 24, where each of the at least two strong SV signals is reconstructed using code phase, carrier phase, carrier frequency, demodulated data bits obtained from tracking each of the at least two strong SV signals.

26. The computer-readable medium containing controller-executable instructions of claim 24, where the cross correlation error output from the amplitude control loop is monitored to measure quality of mitigation achieved.

27. The computer-readable media containing controller-executable instructions of claim 18, where a software C/No test is used to determine whether strong SV cross correlation mitigation is necessary.

28. The computer-readable medium containing controller-executable instructions of claim 18, where each of the at least two strong SV signals is first acquired and tracked to derive code phase, carrier phase, carrier frequency, and demodulated data bits.