METHOD FOR ACQUISITION OF GPS SIGNALS AND GPS RECEIVER WITH SAMPLE TIME ERROR AND FREQUENCY OFFSET COMPENSATION

• US 20080158050A1
• Filed: 12/27/2006
• Published: 07/03/2008
• Est. Priority Date: 12/27/2006
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Levy, Sharon
• Granted Patent: US 7,773,034 B2
• Time in Patent Office: Days
• US Class Current: 342/357.02
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: H03J 1/0008 using a central processing unit, e.g. a microprocessor digital tuning in general H03J5/0245

Abstract

Embodiments of a method for acquisition of GPS signals and a GPS receiver with sample time error and frequency offset compensation are generally described herein. Other embodiments may be described and claimed. In some embodiments, GPS signals are resampled at a plurality of sample rates for each of a plurality of predetermined frequency offsets to compensate for sample time error and frequency offset of a crystal oscillator. The resampled GPS signals may be cross correlated for each of the predetermined frequency offsets. In some embodiments, the sample time error and the frequency offset of the crystal oscillator may substantially exceed a time and frequency drift of reference clocks on GPS satellites.

Claims

1. A method for acquisition of global positioning system (GPS) signals comprising resampling GPS signals at a plurality of sample rates for each of a plurality of predetermined frequency offsets to compensate for sample time error and frequency offset of a crystal oscillator.

2. The method of claim 1 wherein the method further comprises cross-correlating the resampled GPS signals for each of the predetermined frequency offsets,

wherein the sample time error and the frequency offset of the crystal oscillator exceeds a time and frequency drift of reference clocks on GPS satellites, and

wherein the predetermined frequency offsets comprise possible frequency offsets between a reference frequency generated from the crystal oscillator and a reference frequency of the reference clocks of the GPS satellites.

3. The method of claim 2 wherein the resampling is performed in parallel on samples for each of the plurality of sample rates, and

wherein the samples comprise complex I and Q samples generated from the GPS signals.

4. The method of claim 2 further comprising frequency shifting the resampled signals with each of the predetermined frequency offsets after the resampling to generate frequency-shifted samples, and

wherein the cross correlating comprises performing cross correlations with the frequency-shifted samples and known GPS symbols for each resampling operation to generate a correlation output.

5. The method of claim 2 further comprising applying a frequency shift to known GPS symbols by applying each of the predetermined frequency offsets to generate frequency-shifted reference sequences,

wherein the cross correlating comprises performing cross correlations with resampled signals and the frequency-shifted reference sequences for each resampling operation.

6. The method of claim 2 wherein the cross correlating comprises performing cross correlations with resampled outputs from the resampling and one of a plurality of frequency-shifted reference sequences for each resampling operation,

wherein the plurality of frequency-shifted reference sequences are stored in a table, and

wherein the plurality of sample rates and the plurality of frequency-shifted reference sequences are determined from possible frequency offsets between a frequency output of a crystal oscillator of a GPS receiver and a frequency output of the reference clocks of the GPS satellites.

7. The method of claim 2 further comprising performing coherent combining for a period longer than a period of a GPS symbol to detect time and frequency offset of a GPS satellite, and

wherein the cross correlating comprises performing cross correlations using a plurality of reference sequences to increase a correlation length.

8. A GPS receiver comprising:

resampling circuitry to resample received GPS signals at a plurality of sample rates; and

a cross correlator to cross correlate the resampled signals for each of a plurality of predetermined frequency offsets,

wherein resampling operations performed by the resampling circuitry at the plurality of sample rates, and cross correlation operations performed by the cross correlator for the predetermined frequency offsets, compensate for sample time error and frequency offset of a crystal oscillator within the GPS receiver.

9. The GPS receiver of claim 8 wherein the sample time error and the frequency offset of the crystal oscillator exceed time and frequency drift of reference clocks on GPS satellites,

wherein the predetermined frequency offsets comprise possible frequency offsets between a reference frequency generated from the crystal oscillator and a reference frequency of reference clocks of the GPS satellites.

10. The GPS receiver of claim 9 wherein the resampling is performed in parallel on samples for each of the plurality of sample rates, and

wherein the samples comprise complex I and Q samples generated from the received signals.

11. The GPS receiver of claim 8 wherein the resampling circuitry comprises:

a resampler to resample the received GPS signals at the plurality of sample rates;

a complex multiplier to frequency shift the resampled signals from the resampler with each of the predetermined frequency offsets to generate frequency-shifted samples; and

wherein the cross correlator performs cross correlations with the frequency-shifted samples and known GPS symbols for each resampling operation performed by the resampler, to generate a correlation output.

12. The GPS receiver of claim 11 further comprising a resample controller to generate each of the predetermined frequency offsets for application by the complex multiplier,

wherein the resample controller individually provides the predetermined frequency offsets to the complex multiplier for each resampling operation performed by the resampler.

13. The GPS receiver of claim 11 further comprising a resample controller to provide each of the predetermined frequency offsets from a table,

wherein the resample controller individually provides the predetermined frequency offsets to the complex multiplier for each resampling operation performed by the resampler.

14. The GPS receiver of claim 8 wherein the resampling circuitry comprises:

a resampler to resample the received GPS signals at the plurality of sample rates;

a complex multiplier to apply a frequency shift to known GPS symbols by applying each of the predetermined frequency offsets to generate frequency-shifted reference sequences;

wherein the cross correlator performs a cross correlation with resampled signals from the resampler and the frequency-shifted reference sequences for each resampling operation performed by the resampler.

15. The GPS receiver of claim 14 further comprising a resample controller to generate each of the predetermined frequency offsets for application by the complex multiplier,

wherein the resample controller individually provides the predetermined frequency offsets to the complex multiplier for each resampling operation performed by the resampler.

16. The GPS receiver of claim 14 further comprising a resample controller to provide each of the predetermined frequency offsets from a table,

wherein the resample controller individually provides the predetermined frequency offsets to the complex multiplier for each resampling operation performed by the resampler.

17. The GPS receiver of claim 8 wherein the cross correlator performs a cross correlation with resampled outputs from the resampling circuitry and one of a plurality of frequency-shifted reference sequences for each resampling operation;

and

a table to store the plurality of frequency-shifted reference sequences,

wherein the plurality of sample rates and the plurality of frequency-shifted reference sequences are determined from possible frequency offsets and between a frequency output of the crystal oscillator and a frequency output of reference clocks of GPS satellites.

18. The GPS receiver of claim 8 wherein the crystal oscillator is a frequency controlled crystal oscillator used by a synthesizer for generating a LO frequency and a sample clock for the GPS receiver.

19. A spread spectrum receiver comprising:

resampling circuitry to resample received GPS signals at a plurality of sample rates; and

a cross correlator to cross correlate the resampled signals for each of a plurality of predetermined frequency offsets,

wherein resampling operations performed by the resampling circuitry at the plurality of sample rates, and cross correlation operations performed by the cross correlator for the predetermined frequency offsets compensate for sample time error and frequency offset of a crystal oscillator within the receiver,

wherein the cross correlator performs a cross correlation with resampled outputs from the resampling circuitry and one of a plurality of frequency-shifted reference sequences for each resampling operation, and

wherein the plurality of sample rates and the plurality of frequency-shifted reference sequences are determined from possible frequency offsets and between a frequency output of the crystal oscillator and a frequency output of system reference clocks.

20. The receiver of claim 19 wherein the resampling circuitry comprises:

a resampler to resample the received GPS signals at the plurality of sample rates;

a complex multiplier to frequency shift the resampled received GPS signals from the resampler with each of the predetermined frequency offsets to generate frequency-shifted samples; and

wherein the cross correlator performs cross correlations with the frequency-shifted samples and known GPS symbols for each resampling operation performed by the resampler to generate a correlation output.

21. The receiver of claim 19 wherein the resampling circuitry comprises:

a resampler to resample the received GPS signals at the plurality of sample rates;

a complex multiplier to apply a frequency shift to known GPS symbols by applying each of the predetermined frequency offsets to generate frequency-shifted reference sequences;

wherein the cross correlator performs a cross correlation with resampled GPS signals from the resampler and the frequency-shifted reference sequences for each resampling operation performed by the resampler.

22. The receiver of claim 19 wherein the cross correlator performs a cross correlation with resampled outputs from the resampling circuitry and one of a plurality of frequency-shifted reference sequences for each resampling operation performed by the resampler,

wherein the receiver further comprises a table to store the plurality of frequency-shifted reference sequences, and

wherein the plurality of sample rates and the plurality of frequency-shifted reference sequences are determined from possible frequency offsets and between a frequency output of the crystal oscillator and a frequency output of reference clocks of GPS satellites.