Inertial GPS navigation system with modified kalman filter

• US 20040150557A1
• Filed: 01/15/2004
• Published: 08/05/2004
• Est. Priority Date: 01/21/2003
• Status: Active Grant

• Current Assignee: Novatel Incorporated (Hexagon AB)
• Original Assignee: Novatel Incorporated (Hexagon AB)
• Inventors: Hamilton, Jason, Bobye, Michael, Ford, Thomas John
• Granted Patent: US 7,193,559 B2
• Time in Patent Office: Days
• US Class Current: 342/357.14
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• CPC Class Codes: G01C 21/188 for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems
• CPC Class Codes: G01S 19/26 involving a sensor measurement for aiding acquisition or tracking
• CPC Class Codes: G01S 19/49 whereby the further system is an inertial position system, e.g. loosely-coupled

Abstract

An inertial (“INS”)/GPS receiver includes an INS sub-system which incorporates, into a modified Kalman filter, GPS observables and/or other observables that span previous and current times. The INS filter utilizes the observables to update position information relating to both the current and the previous times, and to propagate the current position, velocity and attitude related information. The GPS observable may be delta phase measurements, and the other observables may be, for example, wheel pick-offs (or counts of wheel revolutions) that are used to calculate along track differences, and so forth. The inclusion of the measurements in the filter together with the current and the previous position related information essentially eliminates the effect of system dynamics from the system model. A position difference can thus be formed that is directly observable by the phase difference or along track difference measured between the previous and current time epochs. Further, the delta phase measurements can be incorporated in the INS filter without having to maintain GPS carrier ambiguity states. The INS sub-system and the GPS sub-system share GPS and INS position and covariance information. The receiver time tags the INS and any other non-GPS measurement data with GPS time, and then uses the INS and GPS filters to produce INS and GPS position information that is synchronized in time. The GPS/INS receiver utilizes GPS position and associated covariance information and the GPS and/or other observables in the updating of the INS filter. The INS filter, in turn, provides updated system error information that is used to propagate inertial current position, velocity and attitude information. Further, the receiver utilizes the inertial position, velocity and covariance information in the GPS filters to speed up GPS satellite signal re-acquisition and associated ambiguity resolution operations

Claims

1. An inertial/global positioning system (GPS) receiver including:

A. a GPS sub-system for providing correlation measurements and GPS observables associated with signals received from a plurality of GPS satellites;

B. an inertial sub-system for providing inertial measurements from a plurality of accelerometers and gyroscopes;

C. a clock that maintains GPS time;

D. a processor for time-tagging the inertial measurements with the GPS time and calculating GPS position based on the correlation measurements and inertial position, velocity and attitude that are determined relative to the GPS position and are based on the inertial measurements and the GPS observables, the processor using

GPS position, associated covariance information and GPS observables to control the adverse effects in the inertial calculations of inaccuracies in the inertial sub-system measurements,

inertial position, velocity and associated covariance information to assist in signal re-acquisition operations of the GPS sub-system; and

inertial position and associated covariance information to assist in carrier cycle ambiguity resolution operations that are part of the signal re-acquisition operations.

2. The inertial/global positioning system receiver of claim 1 wherein the processor further calculates GPS position relative to a base receiver with a known position.

3. The inertial/global positioning system receiver of claim 2 wherein the processor

processes the GPS correlation measurements using one or more GPS filters, and

processes the inertial measurements and GPS observables using an inertial Kalman filter that updates previous and current position related information and propagates current position, velocity and attitude related information.

4. The inertial/global positioning system receiver of claim 3 wherein the GPS observable is delta phase measurements.

5. The inertial/global positioning system receiver of claims 4 wherein the processor further

determines when the receiver is stationary after initial movement, and

when the receiver is stationary saves system components and performs a zero velocity update of the inertial Kalman filter using predetermined velocity values instead of velocity observational values.

6. The inertial/global positioning system receiver of claim 4 wherein

the inertial subsystem includes a distance measuring unit that provides distance measuring observables, and

the processor further uses the distance measuring observables in the inertial Kalman filter to update the previous and current position related information.

7. An INS/GPS receiver including:

A. an antenna for receiving signals from a plurality of GPS satellites;

B. a GPS sub-system for

acquiring and tracking the signals from the respective GPS satellites in view;

determining GPS position and related covariance information, and producing associated delta phase measurements that are double differenced across both time and the GPS satellites,

C. an inertial measurement unit for making measurements associated with the acceleration and relative orientation of the receiver;

D. an INS Kalman filter that uses the inertial measurements and the delta phase measurements to update current and previous position related information and propagate current position, velocity and attitude related information; and

E. a mechanization task that determines inertial position, velocity and attitude based on the inertial measurements and the updated information produced by the INS Kalman filter.

8. The receiver of claim 7 further including

a distance measurement unit that provides a measurement that is associated with the distance traveled over a measurement interval;

and

the INS Kalman filter further calculates an along track difference based on the measurement made by the distance measurement unit and a trajectory that is based on the inertial measurements over the same interval, the INS Kalman filter using the along track difference to update previous and current position related information and propagate current position, velocity and attitude.

9. A method of determining GPS position including:

A. receiving signals from a plurality of GPS satellites;

B. acquiring and tracking carriers and codes in the satellite signals and determining delta phase measurements;

C. determining GPS pseudoranges, Doppler offsets, and GPS position and covariance related information;

D. taking inertial measurements relating to acceleration and orientation;

E. updating inertial current and previous position related information using the inertial measurements, the GPS position and covariance related information, and the delta phase measurements;

F. propagating the updated current position information and velocity information; and

G. using the propagated position and velocity information to determine the current GPS position.

10. The method of claim 9 further including

taking other observable measurements that correspond to distance traveled over a measurement interval;

and

in the step of updating the inertial current and previous position related information, further using the other observable measurements in the updating of the current and previous inertial position related information.

11. A method of determining inertial position using an INS Kalman filter, the method including the steps of:

A. receiving from a GPS sub-system GPS position covariance information and GPS observables that over time measure position change;

B. making acceleration and attitude related inertial measurements;

C. using the observable and inertial measurements to update position information relating to a current position and a previous position and using the inertial measurements and the updated information to propagate current position, velocity and attitude related information;

D. using the propagated current position related information to determine an inertial position.

12. The method of claim 11 wherein, the GPS observable is carrier phase that is double differenced over both time and GPS satellites.

13. The method of claim 11 further including

making measurements and determining other observables that over time measure position change;

and

including the other observables in the updating of previous and current position information.

14. The method of claim 13 wherein the other observable is wheel revolutions.