Inertial GPS navigation system with modified kalman filter

• US 7,193,559 B2
• Filed: 01/15/2004
• Issued: 03/20/2007
• 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
• Primary Examiner(s): Issing; Gregory C.
• Application Number:
  US10/758,363
• Publication Number:
  US 20040150557A1
• Time in Patent Office: 1,160 Days
• Field of Search: 342/357.14, 701/216
• US Class Current: 342/357.32
• 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 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 and maintain 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.

2. The receiver of claim 1 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.

3. 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 of carrier phase that is double differenced over both time and GPS satellites that over time measure position change;

B. making acceleration and attitude related inertial measurements;

C. using the observable and inertial measurements to update and maintain 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; and

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

4. The method of claim 3 further including

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

and

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

5. The method of claim 4 wherein the non-GPS observable is wheel revolutions.