Method for processing in dual frequency civilian GPS receiver

• US 6,784,830 B1
• Filed: 04/14/2003
• Issued: 08/31/2004
• Est. Priority Date: 04/16/2002
• Status: Expired due to Term

• Current Assignee: Novariant Incorporated (Kubota Corporation)
• Original Assignee: Integrinautics Corporation (Kubota Corporation)
• Inventors: Cobb, H. Stewart, Lawrence, David G., Montgomery, Paul Y.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US10/413,354
• Time in Patent Office: 505 Days
• Field of Search: 342/357.12, 342/357.06
• US Class Current: 342/357.72
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/32 Multimode operation in a single same satellite system, e.g. GPS L1/L2
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain

Abstract

A method and a system for L1/L2 phase and magnitude determination in satellite navigation equipment is disclosed herein. The method generates separate W code estimates for the L1 signal and the L2 signal, the estimates being uncorrelated with the error in the inphase and the quadrature components of the corresponding signals. The W code is estimated using both the L1 signal as well as the L2 signal. The L1 and L2 baseband signals are obtained from the corresponding RF signals. The baseband signals are added and then filtered using a non-causal FIR LPF. This filter has the property that the output at a time instant is uncorrelated with the input at that time instant. In the preferred embodiment, a one-W-code-bit I&D filter is used instead of a FIR LPF. In an alternate embodiment, a single W code estimate is obtained for both the L1 and the L2 signal.

Claims

1. A method of estimating phase and magnitude of an L2 GPS signal, the L2 signal having a P code, and a W code modulated onto it, the W code being an unknown code, the method comprising the steps of:

a. generating an L1 baseband signal using the L1 signal;

b. generating an L2 baseband signal using the L2 signal;

c. accumulating the L1 baseband signal over one P code bit to generate an L1 second baseband signal;

d. accumulating the L2 baseband signal over one P code bit to generate an L2second baseband signal;

e. generating the L2 W code estimate using the L1 second baseband signal and the L2 second baseband signal, the W code estimate at a time instant being uncorrelated with the error in the inphase and the quadrature components of the L2 signal at that time instant;

f. removing the L2 W code estimate from the L2 second baseband signal to generate an L2 first signal; and

g. accumulating the L2 first signal to generate an L2 accumulated signal, the L2accumulated signal being a measure of the phase and the magnitude of the L2 Y code carrier signal.

2. The method according to claim 1 wherein the step of generating an L1 baseband signal comprises the sub-steps of:

a. filtering, down-converting and sampling the L1 signal to generate an L1 first complex signal;

b. generating an estimate of L1 P code and an estimate of L1 carrier signal;

c. removing the estimate of L1 P code and the estimate of L1 carrier signal from the L1 first complex signal to generate an L1 baseband signal.

3. The method according to claim 1 wherein the step of generating the L2 W code estimate comprises the sub-steps of:

a. adding the L1 second baseband signal and the L2 second baseband signal to generate a pre-estimate signal;

b. filtering the pre-estimate signal using a non-causal FIR LPF to generate a first intermediate signal, the first intermediate signal being correlated with the error in the L1 signal and the error in the L2 signal;

c. subtracting the L2 second baseband signal from the first intermediate signal to generate an L2 estimate signal, the L2 estimate signal being uncorrelated with the errors in the L2 signal; and

d. estimating the L2 W code using the L2 estimate signal.

4. A system for estimating phase and magnitude of an L2 GPS signal, the L2 signal having a P code and a W code modulated onto it, the W code being an unknown code, the system comprising:

a. means for generating an L1 baseband signal using the L1 signal;

b. means for generating an L2 baseband signal using the L2 signal;

c. a first accumulator accumulating the L1 baseband signal over one P code bit to generate an L1 second baseband signal;

d. a second accumulator accumulating the L2 baseband signal over one P code bit to generate an L2 second baseband signal;

e. a W code generator, the W code generator generating an L2 W code estimate using the L1 second baseband signal and the L2 second baseband signal, the W code estimate at a time instant being uncorrelated with the error in the inphase and the quadrature components of the L2 signal at that time instant;

f. a multiplier removing the L2 W code estimate from the L2 second baseband signal to generate an L2 first signal; and

g. a third accumulator accumulating the L2 first signal to generate an L2 accumulated signal which is a measure of the phase and the magnitude of the L2 Y code carrier signal.

5. The system according to claim 4 wherein the means for generating an L1 baseband signal comprises:

a. an L1 RF section filtering, down-converting and sampling the L1 signal to generate an L1 first complex signal; and

b. a signal generator generating an estimate of L1 P code and an estimate of L1 carrier signal; and

c. a first multiplier removing the estimate of L1 P code and the estimate of L1 carrier signal from the L1 first complex signal to generate an L1 baseband signal.

6. The system according to claim 4 wherein the W code generator comprises:

a. a first adder adding the L1 second baseband signal and the L2 second baseband signal to generate a pre-estimate signal;

b. a non-causal FIR LPF filtering the pre-estimate signal to generate an intermediate signal, the non-causal FIR LPF being such that when the L2 second baseband signal is subtracted from the output of the non-causal FIR LPF, the resulting signal is uncorrelated with the instantaneous input to the filter;

c. a second adder subtracting the L2 second baseband signal from the first intermediate signal to generate an L2 estimate signal; and

d. a W code estimator estimating the L2 W code using the L2 estimate signal.

7. A method of estimating the W code for an L2 GPS signal, the L2 signal having a P code and a W code modulated onto it, the W code being an unknown code, the method comprising the steps of:

a. generating an L1 baseband signal using the L1 signal;

b. generating an L2 baseband signal using the L2 signal; and

c. generating the W code estimate using the L1 baseband signal and the L2 baseband signal, the W code estimate at a time instant being uncorrelated with the error in the inphase and the quadrature components of the L2 signal at that time instant.

8. The method according to claim 7 wherein the step of generating the W code estimate comprises the sub-steps of:

a. adding the L1 baseband signal and the L2 baseband signal to generate a pre-estimate signal;

b. filtering the pre-estimate signal using a narrow-band non-causal FIR LPF to generate a first intermediate signal, the first intermediate signal being correlated with the error in the L1 signal and the error in the L2 signal;

c. filtering the L2 baseband signal using a wide-band non-causal FIR LPF to generate an L2 second intermediate signal, the L2 second intermediate signal being correlated with the errors in the L2 signal;

d. subtracting the L2 second intermediate signal from the first intermediate signal to generate an L2 estimate signal, the L2 estimate signal being uncorrelated with the errors in the L2 signal; and

e. estimating the W code using the L2 estimate signal.

9. A system for estimating the W code for an L2 GPS signal, the L2 signal having a P code and a W code modulated onto it, the W code being an unknown code, the system comprising:

a. means for generating an L1 baseband signal using the L1 signal;

b. means for generating an L2 baseband signal using the L2 signal; and

c. a W code generator generating the W code estimate using the L1 baseband signal and the L2 baseband signal, the W code estimate at a time instant being uncorrelated with the error in the inphase and the quadrature components of the L2 signal at that time instant.

10. The system according to claim 9 wherein the W code generator comprises:

a. a first adder adding the L1 baseband signal and the L2 baseband signal to generate a pre-estimate signal;

b. a narrow-band non-causal FIR LPF filtering the pre-estimate signal to generate a first intermediate signal;

c. a wide-band non-causal FIR LPF filtering the L2 baseband signal to generate an L2 second intermediate signal, the wide-band non-causal FIR LPF being such that when the output of the wide-band non-causal FIR LPF is subtracted from the output of the narrow-band non-causal FIR LPF, the resulting signal is uncorrelated with the instantaneous input to the filters;

d. a second adder subtracting the L2 second intermediate signal from the first intermediate signal to generate an L2 estimate signal; and

e. a W code estimator estimating the L2 W code using the L2 estimate signal.

11. A method of estimating the W code for L1 GPS signals and L2 GPS signals, the signals having a P code and a W code modulated onto it, the W code being an unknown code, the method comprising the steps of:

a. generating an L1 primary signal using the L1 signal;

b. generating an L2 primary signal using the L2 signal; and

c. generatng the W code estimate using the L1 primary signal and the L2 primary signal, the W code estimate at a time instant being uncorrelated with the errors in the inphase and the quadrature components of the L1 signal and the L2 signal at that time instant.

12. The method according to claim 11 wherein the step of generating the W code estimate comprises the sub-steps of:

a. projecting the L1 primary signal onto a common phasor to generate an L1 projected signal, the common phasor being an estimated inphase direction of the L1 signal;

b. projecting the L2 primary signal onto the common phasor to generate an L2 projected signal, the common phasor being an estimated inphase direction of the L2 signal;

c. adding the L1 projected signal and the L2 projected signal to generate a pre-estimate signal;

d. filtering the pre-estimate signal using a non-causal FIR LPF to generate an estimate signal, the estimate signal being uncorrelated with the error in the inphase and the quadrature components of the L1 signal and the L2 signal; and

e. estimating the W code using the estimate signal.

13. A system for estimating the W code for L1 GPS signals and L2 GPS signals, the signals having a P code and a W code modulated onto it, the W code being an unknown code, the system comprising:

a. means for generating an L1 primary signal using the L1 signal;

b. means for generating an L2 primary signal using the L2 signal;

c. a W code generator generating the W code estimate using the L1 primary signal and the L2 primary signal, the W code estimate at a time instant being uncorrelated with the errors in the inphase and the quadrature components of the L1 signal and the L2 signal at that time instant.

14. The system according to claim 13 wherein the W code generator comprises:

a. means for projecting the L1 primary signal onto a common phasor to generate an L1 projected signal;

b. means for projecting the L2 primary signal onto a common phasor to generate an L2 projected signal;

c. a first adder adding the L1 projected signal and the L2 projected signal to generate a pre-estimate signal;

d. a non-causal FIR LPF filtering the pre-estimate signal to generate an estimate signal, the non-causal FIR LPF being such that the output at a time instant is uncorrelated with the input at that time instant; and

e. a W code estimator estimating the W code using the estimate signal, the W code estimate being the same for both the L1 signal and the L2 signal.

15. A method of estimating phase and magnitude of L1 and L2 signals, the signals having a P code and a W code modulated onto it, the W code being an unknown code, the method comprising the steps of:

a. generating an L1 baseband signal using the L1 signal;

b. generating an L2 baseband signal using the L2 signal;

c. generating an L1 W code estimate and an L2 W code estimate using the L1 baseband signal and the L2 baseband signal, the L1 W code estimate at a time instant being uncorrelated with the error in the inphase and the quadrature components of the L1 signal at that instant, the L2 W code estimate at a time instant being uncorrelated with the error in the inphase and the quadrature components of the L2 signal at that instant;

d. removing the L1 W code estimate from the L1 baseband signal to generate an L1 first signal;

e. removing the L2 W code estimate from the L2 baseband signal to generate an L2 first signal;

f. accumulating the L1 first signal to generate an L1 accumulated signal, the L1 accumulated signal being a measure of the phase and the magnitude of the L1 Y code carrier signal; and

g. accumulating the L2 first signal to generate an L2 accumulated signal, the L2 accumulated signal being a measure of the phase and the magnitude of the L2 Y code carrier signal.

16. The method according to claim 15 wherein the estimate of carrier signal for the L2 signal is generated using the feedback from the L2 accumulated signal.

17. The method according to claim 15 wherein the step of generating the L1 W code estimate and the L2 W code estimate comprises the sub-steps of:

a. adding the L1 baseband signal and the L2 baseband signal to generate a pre-estimate signal;

b. filtering the pre-estimate signal using a narrow-band non causal FIR LPF to generate a first intermediate signal, the first intermediate signal being correlated with the errors in the L1 signal and the L2 signal;

c. filtering the L1 baseband signal using a wide-band non-causal FIR LPF to generate an L1 second intermediate signal, the L1 second intermediate signal being correlated with the error in the L1 signal;

d. filtering the L2 baseband signal using a wide-band non-causal FIR LPF to generate an L2 second intermediate signal, the L2 second intermediate signal being correlated with the error in the L2 signal;

e. subtracting the L1 second intermediate signal from the first intermediate signal to generate an L1 estimate signal, the L1 estimate signal being uncorrelated with the error in the L1 signal;

f. subtracting the L2 second intermediate signal from the first intermediate signal to generate an L2 estimate signal, the L2 estimate signal being uncorrelated with the error in the L2 signal;

g. estimating the L1 W code using the L1 estimate signal; and

h. estimating the L2 W code using the L2 estimate signal.

18. A system for estimating phase and magnitude of L1 and L2 signals, the signals having a P code and a W code modulated onto it, the W code being an unknown code, the system comprising:

a. means for generating an L1 baseband signal using the L1 signal;

b. means for generating an L2 baseband signal using the L2 signal;

c. a W code generator, the W code generator generating an L1 W code estimate and an L2 W code estimate using the L1 baseband signal and the L2 baseband signal, the L1 W code estimate at a time instant being uncorrelated with the error in the inphase and the quadrature components of the L1 signal at that time instant, the L2 W code estimate at a time instant being uncorrelated with the error in the inphase and the quadrature components of the L2 signal at that time. instant;

d. a first multiplier removing the L1 W code estimate from the L1 baseband signal to generate an L1 first signal;

e. a second multiplier removing the L2 W code estimate from the L2 baseband signal to generate an L2 first signal;

f. a first accumulator accumulating the L1 first signal to generate an L1 accumulated signal, the L1 accumulated signal being a measure of the phase and the magnitude of the L1 Y code carrier signal; and

g. a second accumulator accumulating the L2 first signal to generate an L2 accumulated signal, the L2 accumulated signal being a measure of the phase and the magnitude of the L2 Y code carrier signal.

19. The system according to claim 18 wherein the W code generator comprises:

a. a first adder adding the L1 baseband signal and the L2 baseband signal to generate a pre-estimate signal;

b. a narrow-band non-causal FIR LPF filtering the pre-estimate signal to generate a first intermediate signal;

c. a first wide-band non-causal FIR LPF filtering the L1 baseband signal to generate an L1 second intermediate signal, the first wide-band non-causal FIR LPF being such that when the output of the first wide-band non-causal FIR LPF is subtracted from the output of the narrow-band non-causal FIR LPF, the resulting signal is uncorrelated with the instantaneous input to the filters;

d. a second wide-band non-causal FIR LPF filtering the L2 baseband signal to generate an L2 second intermediate signal, the second wide-band non-causal FIR LPF being such that when the output of the second wide-band non-causal FIR LPF is subtracted from the output of the narrow-band non-causal FIR LPF, the resulting signal is uncorrelated with the instantaneous input to the filters;

e. a second adder subtracting the L1 second intermediate signal from the first intermediate signal to generate an L1 estimate signal;

f. a third adder subtracting the L2 second intermediate signal from the first intermediate signal to generate an L2 estimate signal;

g. a first W code estimator estimating the L1 W code estimate using the L1 estimate signal; and

h. a second W code estimator estimating the L2 W code estimate using the L2 estimate signal.

20. The system according to claim 19 wherein the W code estimator is selected from a group consisting of:

hard decision estimator, soft decision estimator, optimal soft decision estimator, a linear approximation to an optimal soft decision estimator and a saturated linear approximation to an optimal soft decision estimator.

21. The system according to claim 19 wherein the bandwidth of the narrow-band non-causal FIR LPF is related to the W code chipping rate and the bandwidth of the wide-band non-causal FIR LPF is related to the P code chipping rate.

22. The system according to claim 19 wherein the FIR LPFs are selected from a group consisting of:

a triangle filter, a boxcar filter.