Discriminator function for GPS code alignment

• US 20070121708A1
• Filed: 11/28/2005
• Published: 05/31/2007
• Est. Priority Date: 11/28/2005
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Simpson, Robert
• Granted Patent: US 7,742,518 B2
• Time in Patent Office: Days
• US Class Current: 375/149
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence

Abstract

Embodiments of the present invention pertain generally to methods and systems of processing a global positioning satellite (GPS) signal. More particularly, embodiments of the present invention provide an improved discriminator function that utilizes the early, prompt, and late correlator values. For example, the improved discriminator function may be normalized based on all three of the early, prompt, and late correlator values. The improved discriminator function behaves linearly across a prescribed region whose width depends on the separation between correlators.

Claims

1. A method of aligning a local code with a code in a received signal, said method comprising:

generating a prompt replica of the local code;

generating a late replica of the local code and an early replica of the local code based on shifting the prompt replica by half of a chip at most;

correlating the early, prompt, and late replicas of the local code with the received signal;

determining an early correlator power, a prompt correlator power, and a late correlator power based on the correlations of the replicas of the local code with the received signal;

calculating a discrimination output based on comparing the early correlator power and the late correlator power and normalizing the comparison based on the early correlator power, the late correlator power, and the prompt correlator power; and

adjusting a rate of the local code based on the discrimination output.

2. The method of claim 1, wherein generating the prompt replica of the local code comprises generating the prompt replica of a pseudo-random noise code.

3. The method of claim 1, wherein generating the prompt replica of the local code comprises generating the prompt replica of a coarse/acquisition code used by a global positioning satellite.

4. The method of claim 1, wherein calculating the discrimination output based on the early correlator power, the prompt correlator power, and the late correlator power comprises:

determining if the early correlator power is greater than the late correlator power; and

calculating the discrimination output based on a quotient, when the early correlator power is greater than the late correlator power, wherein a numerator of the quotient is based on a difference between the early correlator power and the late correlator power and a denominator of the quotient is based on a first factor times a difference between the early correlator power and the prompt correlator power and a second factor times a difference between the late correlator power and the prompt correlator power.

5. The method of claim 4, wherein calculating the discrimination output based on the early correlator power, the prompt correlator power, and the late correlator power at correlator spacings of ½

chip comprises;

calculating the discrimination output based on the quotient, when the early correlator power is greater than the late correlator power, wherein the numerator of the quotient is equal to the difference between the early correlator power and the late correlator power and the denominator of the quotient is equal to 4/3 times the difference between the early correlator power and the prompt correlator power minus four times the difference between the late correlator power and the prompt correlator power.

6. The method of claim 4, wherein calculating the discrimination output based on the early correlator power, the prompt correlator power, and the late correlator power at correlator spacings of 1/20 chip comprises:

calculating the discrimination output based on the quotient, when the early correlator power is greater than the late correlator power, wherein the numerator of the quotient is equal to two times the difference between the early correlator power and the late correlator power and the denominator of the quotient is equal to 40/39 times the difference between the early correlator power and the prompt correlator power minus 40 times the difference between the late correlator power and the prompt correlator power.

7. The method of claim 1, wherein calculating the discrimination output based on the early correlator power, the prompt correlator power, and the late correlator power comprises:

determining if the early correlator power is less than the late correlator power; and

calculating the discrimination output based on a quotient, when the early correlator power is less than the late correlator power, wherein a numerator of the quotient is based on a difference between the early correlator power and the late correlator power and a denominator of the quotient is based on a first factor times a difference between the late correlator power and the prompt correlator power and a second factor times a difference between the early correlator power and the prompt correlator power.

8. The method of claim 7, wherein calculating the discrimination output based on the early correlator power, the prompt correlator power, and the late correlator power at correlator spacings of ½

chip comprises;

calculating the discrimination output based on the quotient, when the early correlator power is less than the late correlator power, wherein the numerator of the quotient is equal to the difference between the early correlator power and the late correlator power and the denominator of the quotient is equal to 4/3 times the difference between the late correlator power and the prompt correlator power minus four times the difference between the early correlator power and the prompt correlator power.

9. The method of claim 7, wherein calculating the discrimination output based on the early correlator power, the prompt correlator power, and the late correlator power at correlator spacings of 1/20 chip comprises:

calculating the discrimination output based on the quotient, when the early correlator power is less than the late correlator power, wherein the numerator of the quotient is equal to two times the difference between the early correlator power and the late correlator power and the denominator of the quotient is equal to 40/39 times the difference between the late correlator power and the prompt correlator power minus 40 times the difference between the early correlator power and the prompt correlator power.

10. An apparatus for aligning a local code with a code in a received signal, said apparatus comprising:

means for generating a prompt replica of the local code;

means for generating a late replica of the local code and an early replica of the local code based on shifting the prompt replica by half of a chip at most;

means for correlating the early, prompt, and late replicas of the local code with the received signal;

means for determining an early correlator power, a prompt correlator power, and a late correlator power based on the correlations of the replicas of the local code with the received signal;

means for calculating a discrimination output based on comparing the early correlator power and the late correlator power and normalizing the comparison based on the early correlator power, the late correlator power, and the prompt correlator power; and

means for adjusting a rate of the local code based on the discrimination output.

11. The apparatus of claim 10, wherein the means for generating the prompt replica of the local code comprises means for generating the prompt replica of a pseudo-random noise code.

12. The apparatus of claim 10, wherein the means for generating the prompt replica of the local code comprises means for generating the prompt replica of a clear/acquisition code used by a global positioning satellite.

13. The apparatus of claim 10, wherein the means for calculating the discrimination output based on the early correlator power, the prompt correlator power, and the late correlator power comprises:

means for determining if the early correlator power is greater than the late correlator power; and

means for calculating the discrimination output based on a quotient, when the early correlator power is greater than the late correlator power, wherein a numerator of the quotient is based on a difference between the early correlator power and the late correlator power and a denominator of the quotient is based on a first factor times a difference between the early correlator power and the prompt correlator power and a second factor times a difference between the late correlator power and the prompt correlator power.

14. The apparatus of claim 13, wherein the means for calculating the discrimination output based on the early correlator power, the prompt correlator power, and the late correlator power when the correlator spacing is ½

chip comprises;

means for calculating the discrimination output based on the quotient, when the early correlator power is greater than the late correlator power, wherein the numerator of the quotient is equal to the difference between the early correlator power and the late correlator power and the denominator of the quotient is equal to 4/3 times the difference between the early correlator power and the prompt correlator power minus four times the difference between the late correlator power and the prompt correlator power.

15. The apparatus of claim 10, wherein the means for calculating the discrimination output based on the early correlator power, the prompt correlator power, and the late correlator power comprises:

means for determining if the early correlator power is less than the late correlator power; and

means for calculating the discrimination output based on a quotient, when the early correlator power is less than the late correlator power, wherein a numerator of the quotient is based on a difference between the early correlator power and the late correlator power and a denominator of the quotient is based on a first factor times a difference between the late correlator power and the prompt correlator power and a second factor times a difference between the early correlator power and the prompt correlator power.

16. The apparatus of claim 15, wherein the means for calculating the discrimination output based on the early correlator power, the prompt correlator power, and the late correlator power for correlator spacings of ½

chip comprises;

means for calculating the discrimination output based on the quotient, when the early correlator power is less than the late correlator power, wherein the numerator of the quotient is equal to two the difference between the early correlator power and the late correlator power and the denominator of the quotient is equal to 4/3 times the difference between the late correlator power and the prompt correlator power minus four times the difference between the early correlator power and the prompt correlator power.

18. The delay lock loop of claim 15, wherein the code generator is configured to generate the early, prompt, and late code replicas based on an even spacing of at most ½

of a chip.

19. The delay lock loop of claim 15, wherein the code generator is configured to generate the early, prompt, and late code replicas based on an unequal spacing.

17. A delay lock loop configured to track a pseudo random noise code in a received signal, said delay lock loop comprising:

a code generator that generates a prompt replica of the local code, a late replica of the local code and an early replica of the local code based on shifting the prompt replica by half of a chip at most;

a demodulator configured to correlate the early, prompt, and late replicas of the local code with the received signal;

a processor configured to calculate an early correlator power, a prompt correlator power, and a late correlator power based on the correlations of the replicas of the local code with the received signal;

a code discriminator configured to calculate a discrimination output based on comparing the early correlator power and the late correlator power and normalizing the comparison based on the early correlator power, the late correlator power, and the prompt correlator power; and

a feedback module configured to provide a signal that indicates an adjustment to a rate of the local code generated by the code generator based on the discrimination output.

20. The delay lock loop of claim 17, wherein the code generator is configured to generate the early code replica based on a spacing from the prompt code replica that is greater than a spacing from the prompt code replica to the late code replica.