System and method for selecting a local C/A code for GPS signal processing

• US 8,049,665 B1
• Filed: 01/22/2009
• Issued: 11/01/2011
• Est. Priority Date: 06/02/2007
• Status: Expired due to Fees

• Current Assignee: Inchul Kang
• Original Assignee: Inchul Kang
• Inventors: Kang, Inchul
• Primary Examiner(s): Tarcza; Thomas
• Assistant Examiner(s): Nguyen; Nga X
• Application Number:
  US12/358,104
• Time in Patent Office: 1,013 Days
• Field of Search: 3423572-35778
• US Class Current: 342/357.77
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence

Abstract

A method for selecting a local C/A code for GPS signal processing includes performing an autocorrelation of a received GPS C/A code with a plurality of versions of a local coarse acquisition (C/A) code. In such an autocorrelation, each local C/A code version is autocorrelated with the received GPS C/A code over a plurality of autocorrelation periods, and an autocorrelation result is generated for each autocorrelation period. A maximum autocorrelation result and a minimum autocorrelation result are determined from among the autocorrelation results of each C/A code version. Next, one of the local C/A code versions is selected based upon that version'"'"'s maximum autocorrelation result and the minimum autocorrelation result.

Claims

1. A method for selecting a local coarse acquisition (C/A) code for GPS signal processing, the method comprising:

performing autocorrelation of a received GPS coarse acquisition (C/A) code with a plurality of versions of a local coarse acquisition (C/A) code,

wherein each local C/A code version is autocorrelated with the received GPS C/A code over a plurality of autocorrelation periods;

wherein an autocorrelation result is generated for each autocorrelation period, and

wherein, from among the autocorrelation results of each local C/A code version, a maximum autocorrelation result and a minimum autocorrelation result is determined for each local C/A code version; and

selecting one of the plurality of local C/A code versions based upon the maximum autocorrelation result and the minimum autocorrelation result thereof, comprising;

computing an autocorrelation difference value for each local C/A code version, whereby a plurality of autocorrelation difference values are computed, each autocorrelation difference value of a particular local C/A code version comprising a difference between the maximum and minimum autocorrelation values of the particular local C/A code version;

determining the largest autocorrelation difference value among the plurality of autocorrelation difference values; and

selecting the local C/A code version having the largest autocorrelation difference value.

2. The method of claim 1, wherein computing an autocorrelation difference value for a local C/A code version comprises:

determining a maximum autocorrelation result as the most positive autocorrelation result obtained over a plurality of different autocorrelation periods N;

determining a minimum autocorrelation result as the most negative autocorrelation result obtained over a plurality of different autocorrelation periods N;

subtracting the minimum autocorrelation result from the maximum autocorrelation result to compute a delta value; and

adding the delta value to a running autocorrelation difference value to obtain an updated running autocorrelation difference value, wherein the updated running autocorrelation difference value comprises the autocorrelation difference value of the local C/A code version.

3. The method of claim 1, wherein computing an autocorrelation difference value for a local C/A code version comprises:

determining a maximum autocorrelation result comprising accumulating a plurality of positive autocorrelation results from the autocorrelation periods;

determining a minimum autocorrelation result comprising accumulating a plurality of negative autocorrelation results from the autocorrelation periods; and

subtracting the minimum autocorrelation result from the maximum autocorrelation result to compute the autocorrelation difference value.

4. The method of claim 1, wherein selecting a local C/A code version comprises:

computing an autocorrelation variance value σ

² for each local C/A code version, whereby a plurality of autocorrelation variance values σ

² are computed;

determining a largest autocorrelation variance value σ

²_max from among a plurality of autocorrelation variance values σ

²; and

selecting the local C/A code version having the largest autocorrelation variance value σ

²_max.

5. The method of claim 4, wherein computing an autocorrelation variance value σ

² comprises computing an autocorrelation variance value σ

² according to the equation;

6. The method of claim 1, wherein the predefined number of 1 mS duration autocorrelation periods is a function of a Doppler shift of a carrier frequency of the received GPS C/A code.

7. A system operable to select a coarse acquisition code for GPS signal processing, the system comprising:

a correlator operable to perform autocorrelation of a received GPS coarse acquisition (C/A) code with a plurality of versions of a local coarse acquisition (C/A) code,

wherein each local C/A code version is autocorrelated with the received GPS C/A code over a plurality of autocorrelation periods;

wherein an autocorrelation result is generated for each autocorrelation period, and

wherein, from among the autocorrelation results of each local C/A code version, a maximum autocorrelation result and a minimum autocorrelation result is determined for each local C/A code version; and

selection means operable to select one of the plurality of local C/A code versions based upon the maximum autocorrelation result and the minimum autocorrelation result thereof, comprising;

means for computing an autocorrelation difference value for each local C/A code version, whereby a plurality of autocorrelation difference values are computed, each autocorrelation difference value of a particular local C/A code version comprising a difference between the maximum and minimum autocorrelation values of the particular local C/A code version;

means for determining the largest autocorrelation difference value among the plurality of autocorrelation difference values; and

means for selecting the local C/A code version having the largest autocorrelation difference value.

8. The system of claim 7, wherein the means for computing an autocorrelation difference value for a local C/A code version comprises:

means for determining a maximum autocorrelation result as the most positive autocorrelation result obtained over a plurality of different autocorrelation periods N;

means for determining a minimum autocorrelation result as the most negative autocorrelation result obtained over a plurality of different autocorrelation periods N means for subtracting the minimum autocorrelation result from the maximum autocorrelation result to compute a delta value; and

means for adding the delta value to a running autocorrelation difference value to obtain an updated running autocorrelation difference value, wherein the updated running autocorrelation difference value comprises the autocorrelation difference value of the local C/A code version.

9. The system of claim 7, wherein computing an autocorrelation difference value for a local C/A code version comprises:

means for determining a maximum autocorrelation result comprising accumulating a plurality of positive autocorrelation results from the autocorrelation periods;

means for determining a minimum autocorrelation result comprising accumulating a plurality of negative autocorrelation results from the autocorrelation periods; and

means for subtracting the minimum autocorrelation result from the maximum autocorrelation result to compute the autocorrelation difference value.

10. The system of claim 7, wherein the selection means for selecting a local C/A code version comprises:

means for computing an autocorrelation variance value σ

² for each local C/A code version, whereby a plurality of autocorrelation variance values σ

² are computed;

means for determining a largest autocorrelation variance value σ

²_max from among a plurality of autocorrelation variance values σ

²; and

means for selecting the local C/A code version having the largest autocorrelation variance value σ

²_max.

11. The system of claim 10, wherein the means for computing an autocorrelation variance value σ

² comprises means for computing an autocorrelation variance value σ

according to the equation;

12. The system of claim 7, wherein the predefined number of 1 mS duration autocorrelation periods is a function of a Doppler shift of a carrier frequency of the received GPS C/A code.

13. A GPS system comprising:

a coarse selection system, the system comprising;

a correlator operable to perform autocorrelation of a received GPS signal with a plurality of versions of a coarse acquisition (C/A) code,

wherein each local C/A code version is autocorrelated with the received GPS signal over a plurality of autocorrelation periods;

wherein an autocorrelation result is generated for each autocorrelation period, and

wherein, from among the autocorrelation results of each local C/A code version, a maximum autocorrelation result and a minimum autocorrelation result is determined for each local C/A code version; and

selection means operable to select one of the plurality of local C/A code versions based upon the maximum autocorrelation result and the minimum autocorrelation result thereof,

means for computing an autocorrelation difference value for each local C/A code version, whereby a plurality of autocorrelation difference values are computed, each autocorrelation difference value of a particular local C/A code version comprising a difference between the maximum and minimum autocorrelation values of the particular local C/A code version;

means for determining the largest autocorrelation difference value among the plurality of autocorrelation difference values; and

means for selecting the local C/A code version having the largest autocorrelation difference value.

14. The system of claim 13, wherein the means for computing an autocorrelation difference value for a local C/A code version comprises:

means for determining a maximum autocorrelation result as the most positive autocorrelation result obtained over a plurality of different autocorrelation periods N;

means for determining a minimum autocorrelation result as the most negative autocorrelation result obtained over a plurality of different autocorrelation periods N means for subtracting the minimum autocorrelation result from the maximum autocorrelation result to compute a delta value; and

means for adding the delta value to a running autocorrelation difference value to obtain an updated running autocorrelation difference value, wherein the updated running autocorrelation difference value comprises the autocorrelation difference value of the local C/A code version.

15. The system of claim 13, wherein the means for computing an autocorrelation difference value for a local C/A code version comprises:

means for determining a maximum autocorrelation result comprising accumulating a plurality of positive autocorrelation results from the autocorrelation periods;

means for determining a minimum autocorrelation result comprising accumulating a plurality of negative autocorrelation results from the autocorrelation periods; and

means for subtracting the minimum autocorrelation result from the maximum autocorrelation result to compute the autocorrelation difference value.

16. The system of claim 13, wherein the selection means for selecting a local C/A code version comprises:

means for computing an autocorrelation variance value σ

² for each local C/A code version, whereby a plurality of autocorrelation variance values σ

² are computed;

means for determining a largest autocorrelation variance value σ

²_max from among a plurality of autocorrelation variance values σ

²; and

means for selecting the local C/A code version having the largest autocorrelation variance value σ

²_max.

17. The system of claim 16, wherein the means for computing an autocorrelation variance value σ

² comprises means for computing an autocorrelation variance value σ

² according to the equation;

18. A computer program product, resident of a computer readable medium, operable to provide instructions for selecting a coarse acquisition code for GPS signal processing, the computer program product comprising:

instruction code to perform autocorrelation of a received GPS signal with a plurality of versions of a coarse acquisition (C/A) code,

wherein each local C/A code version is autocorrelated with the received GPS signal over a plurality of autocorrelation periods;

wherein an autocorrelation result is generated for each autocorrelation period, and

wherein, from among the autocorrelation results of each local C/A code version, a maximum autocorrelation result and a minimum autocorrelation result is determined for each local C/A code version; and

instruction code to select one of the plurality of local C/A code versions based upon the maximum autocorrelation result and the minimum autocorrelation result thereof, comprising;

instruction code to compute an autocorrelation difference value for each local C/A code version, whereby a plurality of autocorrelation difference values are computed, each autocorrelation difference value of a particular local C/A code version comprising a difference between the maximum and minimum autocorrelation values of the particular local C/A code version;

instruction code to determine the largest autocorrelation difference value among the plurality of autocorrelation difference values; and

instruction code to select the local C/A code version having the largest autocorrelation difference value.

19. The computer program product of claim 18, wherein the instruction code to compute an autocorrelation difference value for a local C/A code version comprises:

instruction code to determine a maximum autocorrelation result as the most positive autocorrelation result obtained over a plurality of different autocorrelation periods N;

instruction code to determine a minimum autocorrelation result as the most negative autocorrelation result obtained over a plurality of different autocorrelation periods N

instruction code to subtract the minimum autocorrelation result from the maximum autocorrelation result to compute a delta value; and

instruction code to add the delta value to a running autocorrelation difference value to obtain an updated running autocorrelation difference value, wherein the updated running autocorrelation difference value comprises the autocorrelation difference value of the local C/A code version.

20. The computer program product of claim 18, wherein the instruction code to compute an autocorrelation difference value for a local C/A code version comprises:

instruction code to determine a maximum autocorrelation result comprising accumulating a plurality of positive autocorrelation results from the autocorrelation periods;

instruction code to determine a minimum autocorrelation result comprising accumulating a plurality of negative autocorrelation results from the autocorrelation periods; and

instruction code to subtract the minimum autocorrelation result from the maximum autocorrelation result to compute the autocorrelation difference value.

21. The computer program product of claim 18, wherein the instruction code to select comprises:

instruction code to compute an autocorrelation variance value σ

² for each local C/A code version, whereby a plurality of autocorrelation variance values σ

² are computed;

instruction code to determine a largest autocorrelation variance value σ

²_max from among a plurality of autocorrelation variance values σ

²; and

instruction code to select the local C/A code version having the largest autocorrelation variance value σ

²_max.

22. The computer program product of claim 21, wherein the instruction code to compute an autocorrelation variance value σ

² comprises instruction code to compute an autocorrelation variance value σ

²;