Acceleration compensation in a GPS-inertial navigation system

• US 6,397,146 B1
• Filed: 10/12/2000
• Issued: 05/28/2002
• Est. Priority Date: 11/29/1999
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Litton Systems Incorporated
• Inventors: Bruner, Charles P.
• Primary Examiner(s): Zanelli, Michael J.
• Assistant Examiner(s): Gibson, Eric M
• Application Number:
  US09/689,387
• Time in Patent Office: 593 Days
• Field of Search: 701/213,214,216,220,221 342/357.14
• US Class Current: 701/213
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial

Abstract

The invention is a method and apparatus for compensating for acceleration in a GPS-inertial navigation system. A translated satellite signal is a satellite signal translated in the GPS receiver to an intermediate-frequency band by a sequence of M mixing operations, M being an integer greater than or equal to one. The m'"'"'th mixing operation consists of mixing the satellite signal with an m'"'"'th mixing signal having a frequency f_m where f_m can be approximated by a function F_m of one or more components A₁, A₂, and A₃ of the acceleration and one or more parameters P_m1, P_m2, . . . , P_mN(m) that are independent of acceleration. The method consists of (a) obtaining values for one or more components of acceleration, (b) obtaining values for one or more parameters, (c)determining the value of one or more functions F_m, and (d) utilizing the data obtained in steps (a), (b), and (c) in compensating for the effects of acceleration in a GPS receiver.

Claims

1. A method for compensating for acceleration in a GPS-inertial navigation system, a translated satellite signal being a satellite signal translated in the GPS receiver to an intermediate-frequency band by a sequence of M mixing operations, M being an integer greater than or equal to one, the m'"'"'th mixing operation consisting of mixing the satellite signal with an m'"'"'th mixing signal having a frequency f_m where f_m can be approximated by a function F_m, of one or more components A₁, A₂, and A₃ of the acceleration and one or more parameters P_m1, P_m2, . . . , P_mN(m) that are independent of acceleration, the method comprising the steps:

(a) obtaining values for one or more components of acceleration;

(b) obtaining values for one or more parameters;

(c) determining the value of one or more functions F_m;

(d) utilizing the data obtained in steps (a), (b), and (c) in compensating for the effects of acceleration in a GPS receiver.

2. The method of claim 1 wherein in step (a) the value of a component of acceleration is obtained from an accelerometer that experiences the same acceleration as the GPS receiver.

3. The method of claim 1 wherein in step (b) the values of the one or more parameters are obtained by a calibration process comprising the steps:

(b1) measuring the value of f_m for each of a plurality of values for the components of acceleration, each measurement resulting in an equation f_m=F_m wherein the only undetermined quantities are one or more parameters;

(b2) solving a plurality of equations for the values of the one or more parameters.

4. The method of claim 1 wherein in step (b) the values of the one or more parameters are determined by a Kalman filter process.

5. The method of claim 1 wherein step (d) comprises the steps:

(d1) synthesizing one or more compensating mixing signals having a frequency that varies with acceleration, the variation in frequency with acceleration of the compensating mixing signals approximating the variation in frequency with acceleration of the translated satellite signal;

(d2) mixing the translated satellite signal with the one or more compensating mixing signals thereby obtaining one or more signals having a difference frequency that is the difference between the frequencies of the translated satellite signal and the one or more compensating mixing signals.

6. The method of claim 5 wherein step (d1) comprises the steps:

(d1a) calculating a value of the frequency f_COMP of the one or more compensating mixing signals, f_COMP being the sum of one or more frequency components;

(d1b) generating one or more compensating mixing signals having a frequency equal to f_COMP.

7. The method of claim 6 wherein in step (d1a) the calculation of the values of one or more frequency components utilizes the results of step (c).

8. The method of claim 6 wherein one of the frequency components is a calculated value of the Doppler shift in frequency arising as a result of motion of the vehicle in which the GPS-inertial navigation system is installed.

9. The method of claim 6 wherein one of the frequency components is a calculated value of the difference in frequencies of the satellite reference oscillator and the GPS receiver reference oscillator scaled by the ratio of the satellite-signal frequency and the satellite reference oscillator frequency.

10. The method of claim 5 wherein in step (d1) there are two compensating mixing signals, one compensating mixing signal being a sine wave, the other compensating mixing signal being a cosine wave.

11. The method of claim 5 wherein step (d1) comprises the steps:

(d1a) calculating a value of the frequency f_COMP of the one or more compensating mixing signals, f_COMP being the sum of one or more frequency components;

(d1b) calculating the phase φ

_COMP by dividing f_COMP by a function F_CL of one or more components A₁, A₂, and A₃ of the acceleration and one or more parameters P_CL1, P_CL2, . . . . , P_CLN(CL) that are independent of acceleration, F_CL being an approximation of the frequency f_CL of a clock signal derived from the frequency reference of the GPS receiver;

(d1c) generating the argument for the one or more compensating mixing signals by accumulating the phase φ

_COMP at a rate f_CL;

(d1d) generating one or more compensating mixing signals having the argument obtained in step (d1c).

12. Apparatus for practicing the method of claim 1.

13. Apparatus for compensating for acceleration in a GPS-inertial navigation system, a translated satellite signal being a satellite signal translated in the GPS receiver to an intermediate-frequency band by a sequence of M mixing operations, M being an integer greater than or equal to one, the m'"'"'th mixing operation consisting of mixing the satellite signal with an m'"'"'th mixing signal having a frequency f_m where f_m can be approximated by a function F_m of one or more components A₁, A₂, and A₃ of the acceleration and one or more parameters P_m1, P_m2, . . . , P_mN(m,) that are independent of acceleration, the apparatus comprising:

one or more accelerometers for obtaining values for one or more components of acceleration;

a memory and retrieval means for obtaining values for one or more parameters;

a data processor for determining the values of one or more functions F_m;

a signal processor that utilizes the values of one of more functions F_m in compensating for the effects of acceleration in a GPS receiver.

14. The apparatus of claim 13 wherein the one or more accelerometers experience the same acceleration as the GPS receiver.

15. The apparatus of claim 13 wherein the data processor determines the values of the one or more parameters by (1) measuring the value of f_m for each of a plurality of values for the components of acceleration, each measurement resulting in an equation f_m=F_m wherein the only undetermined quantities are one or more parameters and (2) solving a plurality of equations for the values of the one or more parameters.

16. The apparatus of claim 13 wherein the data processor determines the values of the one or more parameters by a Kalman filter process.

17. The apparatus of claim 13 wherein the signal processor comprises:

a signal synthesizer for synthesizing one or more compensating mixing signals having a frequency that varies with acceleration, the variation in frequency with acceleration of the compensating mixing signals approximating the variation in frequency with acceleration of the translated satellite signal;

one or more mixers for mixing the translated satellite signal with the one or more compensating mixing signals thereby obtaining one or more signals having a difference frequency that is the difference between the frequencies of the translated satellite signal and the one or more compensating mixing signals.

18. The apparatus of claim 17 wherein the data processor calculates a value of the frequency f_COMP of the one or more compensating mixing signals, f_COMP being the sum of one or more frequency components, and the signal processor generates one or more compensating mixing signals having a frequency equal to f_COMP.

19. The apparatus of claim 18 wherein the calculation of the values of one or more frequency components utilizes the values of one or more functions F_m.

20. The apparatus of claim 18 wherein one of the frequency components is a calculated value of the Doppler shift in frequency arising as a result of motion of the vehicle in which the GPS-inertial navigation system is installed.

21. The apparatus of claim 18 wherein one of the frequency components is a calculated value of the difference in frequencies of the satellite reference oscillator and the GPS receiver reference oscillator scaled by the ratio of the satellite-signal frequency and the satellite reference oscillator frequency.

22. The apparatus of claim 17 wherein there are two compensating mixing signals, one compensating mixing signal being a sine wave, the other compensating mixing signal being a cosine wave.

23. The apparatus of claim 17 wherein:

the data processor calculates (1) a value of the frequency f_COMP of the one or more compensating mixing signals, f_COMP being the sum of one or more frequency components and (2) the phase φ

_COMP by dividing f_COMP by a function F_CL of one or more components A₁, A₂, and A₃ of the acceleration and one or more parameters P_CL1, P_CL2, . . . , P_CLN(CL) that are independent of acceleration, F_CL being an approximation of the frequency f_CL of a clock signal derived from the frequency reference of the GPS receiver;

the signal processor generates (1) the argument for the one or more compensating mixing signals by accumulating the phase φ

_COMP at a rate f_CL and (2) one or more compensating mixing signals having the argument.