Global positioning systems and inertial measuring unit ultratight coupling method

• US 6,516,021 B1
• Filed: 09/14/1999
• Issued: 02/04/2003
• Est. Priority Date: 09/14/1999
• Status: Expired due to Term

• Current Assignee: Aerospace Corporation
• Original Assignee: Aerospace Corporation
• Inventors: Lillo, Walter E., Abbott, Anthony S.
• Primary Examiner(s): Vo, Don N.
• Assistant Examiner(s): Nguyen, Dung X.
• Application Number:
  US09/396,105
• Time in Patent Office: 1,239 Days
• Field of Search: 375/149, 375/150, 375/343, 375/350, 375/367, 842/108, 701/7, 701/214, 701/215, 342/189, 342/108
• US Class Current: 375/150
• CPC Class Codes: G01S 19/26 involving a sensor measurement for aiding acquisition or tracking

Abstract

An ultratight coupling method generates navigation error state information from an integration Kalman filter for updating the navigation solution based upon inertial measurement data and computes pseudorange and pseudorange rate data from the navigation solution and from ephemeris data, to generate the prompt, early and late replica signals that drive the signal correlators having quadrature outputs samples by a federation of Kalman prefilters providing errors residuals to the integration Kalman filter in a closed coupled tracking loop. The coupled tracking loops offer improved tracking of the received signal based upon updated navigation solution.

Claims

1. A method for carrier and code tracking of a received signal in a receiver, the received signal comprising a received carrier signal and a received code signal, the method comprising the steps of,

demodulating the received signal with a carrier replica signal for generating a carrier demodulated received signal,

correlating the carrier demodulated received signal with a code replica signal for providing output samples,

residual prefiltering the output samples for estimating residual errors between the received and code replica signals and for providing residual error data, the residual prefiltering using a prefilter measurement model relating the output samples to residual state variables and a residual process model relating the residual state variables to the residual error data,

integration filtering the residual error data for estimating an integration error vector, the integration filtering for estimating the integration error vector using an integration measurement model relating the residual error data to integration state variables and an integration process model relating the integration state variables to the integration error vector, carrier adjusting the replica carrier signal by the integration error vector for providing an adjusted replica carrier signal for demodulating the received signal, and

code adjusting the replica code signal by the integration error vector for providing an adjusted replica code signal for correlating the received signal with the adjusted replica code signal for reducing the residual error data during residual prefiltering and for reducing the integration error vector during integration filtering.

2. The method of claim 1 wherein the residual prefiltering step is a Kalman residual prefiltering step, and the integration filtering step is a Kalman integration filtering step.

3. The method of claim 1 wherein the replica signal comprises early, prompt, and late replica signals and the output samples comprise I and Q early, prompt, and late replica signals.

4. The method of claim 1 wherein,

the received signal comprises a plurality of received signals having respective carrier and code received signals,

the replica code signal comprises a respective plurality of code signals,

the replica carrier signal comprise a respective plurality of carrier signals, and

the output samples comprises a respectively plurality of output samples,

the residual prefiltering step comprises a respective plurality of residual prefiltering steps each respectively sampling the respective plurality of output samples, and

the residue error data comprises a plurality of residual error data for each of the respective plurality of residual prefiltering step.

5. A method for carrier and code tracking of a received signal in a receiver, the received signal comprising a received carrier signal and a received code signal transmitted from a transmitter at a range from the receiver, the received signal communicating ephemeris data from the transmitter, the receiver receives inertial data from an inertial measurement unit coupled to the receiver, the method comprising the steps of,

receiver demodulating the received signal with a carrier replica signal for generating a carrier demodulated received signal,

correlating the carrier demodulated received signal with a code replica signal for providing output samples,

residual prefiltering the output samples for estimating residual errors between the received and code replica signals and for providing residual error data, the residual prefiltering using a prefilter measurement model relating the output samples to residual state variables and a residual process model relating the residual state variables to the residual error data,

integration filtering the residual error data for estimating a navigation error vector, the integration filtering for estimating the navigation error vector using an integration measurement model relating the residual error data to integration state variables and an integration process model relating the integration state variables to the navigation error vector,

navigation computing navigation position and velocity data from the inertial data and from the navigation error vector,

ephemeris demodulating the received signal into the ephemeris data,

ephemeris computing transmitter position and velocity data from the ephemeris data,

range computing pseudorange data and pseudorange rate data from the navigation position and velocity data and from the transmitter position and velocity data,

carrier adjusting the replica carrier signal by the pseudorange rate data for providing an adjusted replica carrier signal for demodulating the received signal, and

code adjusting the replica code signal by the pseudorange data for providing an adjusted replica code signal for correlating the received signal with the adjusted replica code signal for reducing the residual error data during residual prefiltering and for reducing the estimated navigation error vector during integration filtering.

6. The method of claim 5 wherein,

the residual prefiltering step is a Kalman prefiltering step,

the integration filtering step is a Kalman filtering step,

the replica signal comprises early, prompt, and late replica signals,

the output samples are I and Q early, prompt and late replica signals

the received signal comprises a plurality of received signals having respective carrier and code received signals,

the replica code signal comprises a respective plurality of code signals,

the replica carrier signal comprise a respective plurality of carrier signals,

the output samples comprises a respectively plurality of output samples,

the residual prefiltering step comprises a respective plurality of residual prefiltering steps each respectively sampling the respective plurality of output samples, and

the residual error data comprises a plurality of residual error vectors for the respective plurality of residual prefiltering steps.

7. The method of claim 5 wherein the transmitter is a satellite transmitter.

8. The method of claim 6 wherein,

the correlating step integrates the output samples over a correlation time period for providing the prefiltering step the output sample at a high rate,

the residual prefiltering step provides the residual errors at a low rate,

the integration filtering step provides the navigation error vector at the low rate,

the navigation computing of the navigation position and velocity data is at a navigation update rate,

the ephemeris computing of the ephemeris position and velocity data is at an ephemeris data update rate,

the code and carrier adjusting of the code and carrier replica signals are at a replica update rate.

9. The method of claim 6 wherein navigation computing step comprises the step of receiving changes in velocity and attitude data for the navigation computing of the navigation position and velocity data.

10. The method of claim 6 wherein,

the received signals comprise f1 and f2 received signals,

the demodulating steps comprises an f1 demodulating step and a f2 demodulating step,

the correlator step comprises a f1 correlator step and a f2 correlator step for respective providing f1 and f2 output samples for the respective f1 and f2 received signals, and

the residual prefiltering step for receiving the f1 and f2 output samples and for providing the residual error data to the integration filtering step, the residual measurement model and the residual process model operates on both f1 and f2 output samples to provide the residual error data, the residual and measurement models serving to combine respective residual errors data from the f1 and f2 output samples into the residual error data, residual error data is a residual error vector comprising at least one single error calculated using the residual and measurements model operating on both of the f1 and f2 output samples.

11. The method of claim 6 wherein the residual error data is a vector comprising pseudorange, pseudorange rate, pseudorange acceleration, total electron content, and total electron content rate errors.

12. The method of claim 11 wherein the residual error vector further comprises a covariance matrix of uncertainties of the errors in the pseudorange, pseudorange rate, pseudorange acceleration, total electron content, and total electron content rate.

13. A method for carrier and code tracking of received signals in a receiver, the received signals each comprising a received carrier signal and a received code signal transmitted, each of the received signals are transmitted from a plurality satellite transmitters at respective ranges from the receiver, the received signals communicating respective ephemeris data from each of the satellite transmitters, the receiver receives inertial data from an inertial measurement unit coupled to the receiver, the method comprising the steps of,

carrier demodulating the received signals with carrier replica signals for generating respective carrier demodulated received signals,

correlating each of the carrier demodulated received signals with respective code early, prompt, and late replica signals for providing respective I and Q early, prompt, and late output samples that are integrated over a high rate predetermined time period and repetitively provided at each high rate predetermined time period,

residual prefiltering each of the respective I and Q early, prompt, and late output samples for estimating residual errors between the received and code replica signals and for providing respective residual error data, the residual prefiltering using a prefilter measurement model relating the output samples to residual state variables and a residual process model relating the residual state variables to the residual error data that is generated over a low rate predetermined time period and provided at each low rate time period, respective residual prefiltering providing respective residual error data,

integration filtering the respective residual error data for estimating a navigation error vector every low rate predetermined time period, the integration filtering for estimating the navigation error vector using an integration measurement model relating the residual error data to integration state variables and an integration process model relating the integration state variables to the navigation error vector,

navigation computing at a navigation update rate navigation position and velocity data from the inertial data and from the navigation error vector,

ephemeris demodulating the received signal into the ephemeris data,

ephemeris computing at an ephemeris update rate transmitter position and velocity data from the ephemeris data,

pseudo computing at a replica update rate pseudorange data and pseudorange rate data from the navigation position and velocity data and from the transmitter position and velocity data,

carrier adjusting at the replica update rate the replica carrier signal by the pseudorange rate data for providing an adjusted replica carrier signal for demodulating the received signal, and

code adjusting at the replica update rate by the pseudorange data for providing an adjusted replica code signal for correlating the received signal with the adjusted replica code signal for reducing the residual error data during residual prefiltering and for reducing the estimated navigation error vector during integration filtering.

14. The method of claim 13 wherein the residual prefiltering step is a Kalman prefiltering step, and the integration filtering step is a Kalman filtering step.

15. The method of claim 13 wherein the respective plurality of received signals are modulated at differing frequencies.

16. The method of claim 13 wherein the inertial data are changes in the velocity and attitude of the receiver, and navigation computing step receives the inertial data at an inertial data update rate.

17. The method of claim of claim 16 wherein the high rate is fifty hertz, the low rate is one hertz, the navigation update rate is one hundred hertz, the ephemeris update rate is one hundred hertz, and the inertial data update rate is one hundred hertz.

18. The method of claim 17 wherein the residual error data comprises errors in pseudorange, pseudorange rate, pseudorange acceleration, total electron content, and total electron content rate.

19. The method of claim 18 wherein the residual error data further comprises a covariance matrix of uncertainties of the errors in the pseudorange, pseudorange rate, pseudorange acceleration, total electron content, and total electron content rate.