System and method for fast code phase and carrier frequency acquisition in GPS receiver

• US 7,505,508 B2
• Filed: 09/03/2007
• Issued: 03/17/2009
• Est. Priority Date: 08/09/2000
• Status: Expired due to Term

• Current Assignee: SkyBitz, Inc. (Ametek Incorporated)
• Original Assignee: SkyBitz, Inc. (Ametek Incorporated)
• Inventors: Sullivan, Mark C.
• Primary Examiner(s): BURD, KEVIN MICHAEL
• Application Number:
  US11/849,333
• Publication Number:
  US 20070297542A1
• Time in Patent Office: 561 Days
• Field of Search: 375/147, 375/316, 375/340, 375/343, 375/341
• US Class Current: 375/147
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/258 relating to the satellite constellation, e.g. almanac, ephemeris data, lists of satellites in view
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A GPS receiver acquires carrier frequency and Gold code phase using short segments of a received GPS signal. In one embodiment, a 1-ms segment of the GPS signal is transformed to the frequency domain. This is multiplied by a frequency representation of the Gold code. The resulting product is converted to the time domain, and a peak is detected. The location of the peak corresponds to the code phase. If no peak is located, the carrier frequency is changed. Full- and half-bin steps in carrier frequency are considered. Processing gain is achieved by using longer segments of the input signal, for example 4 or 16 ms and integrating 1-ms segments. Considerations are provided for compensating for the effects of a transition, should it occur in the short segment of the GPS signal being processed. Integrations can be performed using non-coherent and coherent techniques. Adjustments are made for non-integral millisecond segment lengths.

Claims

1. A system for detecting code phase and carrier frequency in a GPS signal, comprising:

a. means for performing a coarse acquisition of a carrier frequency and code phase of the GPS signal using non-coherent processing, wherein said non-coherent processing includes;

i. converting a one millisecond segment of a GPS signal to the frequency domain;

ii. multiplying said converted one millisecond segment by a frequency representation of a Gold code corresponding to a GPS satellite to generate a product;

iii. converting said product to the time domain to obtain a correlation signal between said one millisecond segment and said Gold code; and

iv. determining a location of a peak in said correlation signal; and

b. means for performing a fine acquisition of said carrier frequency and code phase of the GPS signal using coherent processing.

2. The system of claim 1, wherein said means for performing a fine acquisition comprises uses a curve fitting routine to refine the location of the peak.

3. The system of claim 1, wherein said means for performing a fine acquisition uses a table lookup method.

4. The system of claim 1, wherein said means for performing a fine acquisition analyzes complex values at locations of said determined peaks.

5. The system of claim 4, wherein said means for performing a fine acquisition analyzes complex values of said determined peak and a few points on either side of said determined peak.

6. The system of claim 1, further comprising:

means for pre-computing the frequency representation of said Gold code; and

means for storing the pre-computed frequency representation of said Gold code in memory.

7. The system of claim 1, wherein said means for performing a coarse acquisition does not use coherent processing.

8. A method for detecting code phase and carrier frequency in a GPS signal, comprising:

a. performing a coarse acquisition of a carrier frequency and code phase of a GPS signal using non-coherent processing, wherein said non-coherent processing includes;

i. converting a one millisecond segment of the GPS signal to the frequency domain;

ii. multiplying said converted one millisecond segment by a frequency representation of a Gold code corresponding to a GPS satellite to generate a product that enables determination of a location of a peak in a correlation signal; and

b. performing a fine acquisition of said carrier frequency and code phase of the GPS signal using coherent processing.

9. The method of claim 8, wherein said performing a fine acquisition uses a curve fitting routine to refine the location of the peak.

10. The method of claim 8, wherein said performing a fine acquisition uses a table lookup method.

11. The method of claim 8, wherein said performing a fine acquisition analyzes complex values at locations of said determined peaks.

12. The method of claim 11, wherein said performing a fine acquisition analyzes complex values of said determined peak and a few points on either side of said determined peak.

13. The system of claim 8, further comprising:

pre-computing the frequency representation of said Gold code; and

storing the pre-computed frequency representation of said Gold code in memory.

14. The method of claim 8, wherein said performing a coarse acquisition comprises performing a coarse acquisition without using coherent processing.

15. A system for detecting code phase and carrier frequency in a GPS signal, comprising:

a. means for performing a coarse acquisition of a carrier frequency and code phase of a GPS signal using non-coherent processing, wherein said non-coherent processing includes;

i. means for converting a one millisecond segment of the GPS signal to the frequency domain;

ii. means for multiplying said converted one millisecond segment by a frequency representation of a Gold code corresponding to a GPS satellite to generate a product that enables determination of a location of a peak in a correlation signal; and

b. means for performing a fine acquisition of said carrier frequency and code phase of the GPS signal using coherent processing.

16. The system of claim 15, wherein said means for performing a fine acquisition comprises uses a curve fitting routine to refine the location of the peak.

17. The system of claim 15, wherein said means for performing a fine acquisition uses a table lookup method.

18. The system of claim 15, wherein said means for performing a fine acquisition analyzes complex values at locations of said determined peak.

19. The system of claim 18, wherein said means for performing a fine acquisition analyzes complex values of said determined peak and a few points on either side of said determined peak.

20. The system of claim 15, wherein said means for performing a coarse acquisition does not use coherent processing.