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

• US 8,457,177 B2
• Filed: 02/27/2009
• Issued: 06/04/2013
• 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 M
• Application Number:
  US12/395,243
• Publication Number:
  US 20090161736A1
• Time in Patent Office: 1,558 Days
• Field of Search: 375/316, 375/340, 375/341, 375/343, 375/147
• 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 method for detecting code phase in a GPS signal, comprising:

collecting a multiple millisecond portion of a GPS signal in a GPS receiver;

partitioning the multiple millisecond portion of the GPS signal into a plurality of one millisecond segments;

converting each of the one millisecond segments to the frequency domain;

multiplying each of the converted one millisecond segments by a frequency domain representation of a Gold code corresponding to a GPS satellite to generate a plurality of products;

converting each of the plurality of products to the time domain to obtain convolution signals between each one millisecond segment and the Gold code; and

combining said convolution signals to determine a correlation peak that is reflective of a code phase of the GPS signal, wherein at least one of said convolution signals has been multiplied by a complex exponential to compensate for a frequency difference between an input signal and an estimated carrier frequency.

2. The method of claim 1, wherein said combining comprises determining a magnitude of each convolution signal and summing said determined magnitudes.

3. The method of claim 1, further comprising comparing points in said combination to a peak threshold.

4. The method of claim 1, further comprising pre-computing said frequency representation of said Gold code.

5. A method for detecting code phase in a GPS signal, comprising:

partitioning a multiple millisecond portion of a GPS signal into a plurality of one millisecond segments;

generating a plurality of products, each product representing a multiplication of a frequency domain representation of a one millisecond segment of the GPS signal with a frequency domain representation of a Gold code corresponding to a GPS satellite that produced the GPS signal;

converting each of the plurality of products to the time domain to obtain convolution signals between each one millisecond segment of the GPS signal and the Gold code; and

combining said convolution signals to determine a correlation peak that is reflective of a code phase of the GPS signal, wherein at least one of said convolution signals has been multiplied by a complex exponential to compensate for a frequency difference between an input signal and an estimated carrier frequency.

6. The method of claim 5, wherein said combining comprises determining a magnitude of each convolution signal and summing said determined magnitudes.

7. The method of claim 5, further comprising comparing points in said combination to a peak threshold.

8. The method of claim 5, further comprising pre-computing said frequency representation of said Gold code.

9. The method of claim 5, further comprising generating a frequency domain representation using a Fast Fourier Transform.

10. The method of claim 5, further comprising generating a time domain representation using an inverse Fast Fourier Transform.

11. A non-transitory computer-readable medium that stores a program for controlling a computer device to perform a method for detecting code phase in a GPS signal, the method comprising:

partitioning a multiple millisecond portion of a GPS signal into a plurality of one millisecond segments;

generating a plurality of products, each product representing a multiplication of a frequency domain representation of a one millisecond segment of the GPS signal with a frequency domain representation of a Gold code corresponding to a GPS satellite that produced the GPS signal;

converting each of the plurality of products to the time domain to obtain convolution signals between each one millisecond segment of the GPS signal and the Gold code; and

combining said convolution signals to determine a correlation peak that is reflective of a code phase of the GPS signal, wherein at least one of said convolution signals has been multiplied by a complex exponential to compensate for a frequency difference between an input signal and an estimated carrier frequency.

12. The non-transitory computer readable medium of claim 11, wherein said combining comprises determining a magnitude of each convolution signal and summing said determined magnitudes.

13. The non-transitory computer readable medium of claim 11, wherein the method further comprises comparing points in said combination to a peak threshold.

14. The non-transitory computer readable medium of claim 11, wherein the method further comprises pre-computing said frequency representation of said Gold code.

15. The non-transitory computer readable medium of claim 11, wherein the method further comprises generating a frequency domain representation using a Fast Fourier Transform.

16. The non-transitory computer readable medium of claim 11, wherein the method further comprises generating a time domain representation using an inverse Fast Fourier Transform.