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

• US 9,223,028 B2
• Filed: 06/03/2013
• Issued: 12/29/2015
• 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:
  US13/908,262
• Publication Number:
  US 20130257653A1
• Time in Patent Office: 939 Days
• Field of Search: 375/147, 375/130, 375/140, 375/316, 375/340, 375/341, 375/343
• US Class Current: 1/1
• 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:

multiplying each of a plurality of frequency domain representations of one millisecond segments of a GPS signal 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 produce a plurality of converted signals; and

combining the plurality of converted signals to determine a correlation peak that is reflective of a code phase of the GPS signal, wherein at least one of the plurality of converted 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 the combining comprises determining a magnitude of each of the plurality of converted signals and summing the determined magnitudes.

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

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

5. 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:

multiplying each of a plurality of frequency domain representations of one millisecond segments of a GPS signal 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 produce a plurality of converted signals; and

combining the plurality of converted signals to determine a correlation peak that is reflective of a code phase of the GPS signal, wherein at least one of the plurality of converted 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 non-transitory computer readable medium of claim 5, wherein the combining comprises determining a magnitude of each of the plurality of converted signals and summing the determined magnitudes.

7. The non-transitory computer readable medium of claim 5, wherein the method further comprises comparing points in the combination to a peak threshold.

8. The non-transitory computer readable medium of claim 5, wherein the method further comprises pre-computing the frequency representation of said Gold code.

9. A device for detecting code phase in a GPS signal, comprising:

one or more circuits for use in the device, wherein the one or more circuits are operable to;

multiply each of a plurality of frequency domain representations of one millisecond segments of a GPS signal by a frequency domain representation of a Gold code corresponding to a GPS satellite to generate a plurality of products;

convert each of the plurality of products to the time domain to produce a plurality of converted signals; and

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

10. The device of claim 9, wherein the one or more circuits are operable to determine a magnitude of each convolution of the plurality of converted signals and summing the determined magnitudes.

11. The device of claim 9, wherein the one or more circuits are further operable to compare points in the combination to a peak threshold.

12. The device of claim 9, wherein the frequency domain representation of the Gold code is pre-computed.