System and Method for GPS Signal Acquisition

• US 20080297411A1
• Filed: 12/13/2007
• Published: 12/04/2008
• Est. Priority Date: 06/02/2007
• Status: Active Grant

• Current Assignee: Inchul Kang
• Original Assignee: Inchul Kang
• Inventors: KANG, Inchul
• Granted Patent: US 7,782,252 B2
• Time in Patent Office: Days
• US Class Current: 342/357.64
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence

Abstract

A method for acquiring a GPS signal includes receiving a GPS signal portion over a coarse acquisition (C/A) frame period. The received GPS signal portion is stored and correlated to each of a plurality of versions of a reference coarse acquisition code to obtain a respective plurality of autocorrelation values. A peak value is selected among the autocorrelation values, the peak value corresponding to a version of the reference coarse acquisition code which is most aligned with the received GPS signal.

Claims

1. A method for acquiring a GPS signal having a predefined coarse acquisition frame period, the method comprising:

receiving a GPS signal portion over the coarse acquisition (C/A) frame period;

storing the received GPS signal portion;

correlating the received GPS signal portion to each of a plurality of versions of a reference coarse acquisition (C/A) code to obtain a respective plurality of autocorrelation values; and

selecting a peak value among the autocorrelation values.

2. The method of claim 1, wherein storing comprises storing the received GPS signal portion within each of at least first and second sample and hold circuits, the first and second sample and hold circuits triggered to sample the received GPS signal portion at different respective times.

3. The method of claim 1, wherein correlating the received GPS signal portion comprises:

(i) correlating the received GPS signal portion to a reference coarse acquisition code to obtain a first autocorrelation value;

(ii) circularly-shifting the reference coarse acquisition code to obtain a shifted reference coarse acquisition code; and

(iii) correlating the received GPS signal portion to the circularly-shifted reference coarse acquisition code to obtain a second autocorrelation value.

4. The method of claim 1, wherein selecting a peak value comprises:

comparing the magnitude of the first and second autocorrelation values; and

selecting the larger of the first or second autocorrelation values.

5. The method of claim 3, further comprising repeating (ii) and (iii) until the reference C/A code has shifted through one complete revolution, whereby the received GPS signal portion is correlated to each of the reference and shifted versions of the C/A code.

6. The method of claim 5, wherein the collective period over which the received GPS signal is correlated to each of the reference and shifted versions of the C/A code is less than or equal to the C/A frame period.

7. The method of claim 2, further comprising level adjusting the received GPS signal stored in at least one of the first or second sample and hold circuits.

8. The method of claim 7, whereby the magnitude of the received GPS signal portion stored in the first sample and hold circuit is adjusted as a function of the time the received GPS signal portion is stored therein.

9. The method of claim 8, wherein level adjusting comprises amplifying the magnitude of the received GPS signal portion stored in the first sample and hold circuit by an amount K:

K=e^t/RC

where t is the duration the received GPS signal portion is held in the first sample and hold circuit, R is the equivalent leakage resistance of the first sample and hold circuit, and C is the equivalent leakage capacitance of the first sample and hold circuit.

10. The method of claim 7, wherein the magnitude of the received GPS signal portion stored in the second sample and hold circuit is adjusted as a function of the received GPS signal portion'"'"'s storage time within the first sample and hold circuit.

11. The method of claim 10, wherein level adjusting comprises attenuating the magnitude of the received GPS signal portion stored in the second sample and hold circuit by an amount K:

K=e^t/RC

where t is the duration the received GPS signal portion is held in the first sample and hold circuit, R is the equivalent leakage resistance of the first sample and hold circuit, and C is the equivalent leakage capacitance of the first sample and hold circuit.

12. A method for acquiring a GPS signal having a predefined coarse acquisition frame period, the method comprising:

receiving a GPS signal portion over the coarse acquisition (C/A) frame period;

storing the received GPS signal portion within a plurality of sample and hold circuits, the plurality of the sample and hold circuits triggered to sample the received GPS signal portion at different respective times;

correlating the received GPS signal portion to each of a plurality of versions of a reference coarse acquisition (C/A) code to obtain a respective plurality of autocorrelation values; and

selecting a peak value among the autocorrelation values.

13. A method for acquiring a GPS signal having a predefined coarse acquisition frame period, the method comprising:

receiving a GPS signal portion over the coarse acquisition (C/A) frame period;

storing the received GPS signal portion;

circularly-correlating the received GPS signal portion to each of a plurality of versions of a reference coarse acquisition (C/A) code to obtain a respective plurality of autocorrelation values,

wherein the circular correlation continues until the reference C/A code has shifted through one complete revolution, and

wherein the complete revolution of the circular correlation occurs over a time period which is less than the C/A frame period; and

selecting a peak value among the autocorrelation values.

14. A system for acquiring a GPS signal having a predefined coarse acquisition frame period, the system comprising:

receiver circuitry configured to receive a GPS signal portion over the coarse acquisition (C/A) frame period;

circuitry configured to store the received GPS signal portion;

a correlator configured to correlate the received GPS signal portion to each of a plurality of versions of a reference coarse acquisition (C/A) code to obtain a respective plurality of autocorrelation values; and

a comparator configured to select a peak value among the autocorrelation values.

15. The system of claim 14, wherein the circuitry configured to store comprises at least first and second sample and hold circuits, the first and second sample and hold circuits triggered to sample the received GPS signal portion at different respective times.

16. The system of claim 14, wherein the correlator comprises:

(i) means for correlating the received GPS signal portion to a reference coarse acquisition code (2201) to obtain a first autocorrelation value;

(ii) means for circularly-shifting the reference coarse acquisition code to obtain a shifted reference coarse acquisition code; and

(iii) means for correlating the received GPS signal portion to the circularly-shifted reference coarse acquisition code to obtain a second autocorrelation value.

17. The system of claim 16, wherein the correlator further comprises means for repeating (ii) and (iii) until the reference C/A code has shifted through one complete revolution, whereby the received GPS signal portion is correlated to each of the reference and shifted versions of the C/A code.

18. The system of claim 15, further comprising a level controller configured to adjust the magnitude of a sample signal stored in at least one of the first or second sample and hold circuits.

19. The system of claim 18, whereby the magnitude of the received GPS signal portion stored in the first sample and hold circuit is adjusted as a function of the time the received GPS signal portion is stored therein.

20. The system of claim 19, wherein level adjusting comprises amplifying the magnitude of the received GPS signal portion stored in the first sample and hold circuit by an amount K:

K=e^t/RC

where t is the duration the received GPS signal portion is held in the first sample and hold circuit, R is the equivalent leakage resistance of the first sample and hold circuit, and C is the equivalent leakage capacitance of the first sample and hold circuit.

21. The system of claim 18, wherein the magnitude of the received GPS signal portion stored in the second sample and hold circuit is adjusted as a function of the received GPS signal portion'"'"'s storage time within the first sample and hold circuit.

22. The system of claim 21, wherein level adjusting comprises attenuating the magnitude of the received GPS signal portion stored in the second sample and hold circuit by an amount K:

K=e^t/RC

where t is the duration the received GPS signal portion is held in the first sample and hold circuit, R is the equivalent leakage resistance of the first sample and hold circuit, and C is the equivalent leakage capacitance of the first sample and hold circuit.