Hybrid inertial navigation system with improved integrity

• US 6,982,669 B2
• Filed: 09/24/2002
• Issued: 01/03/2006
• Est. Priority Date: 09/28/2001
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Guillard, Patrice, Coatantiec, Jacques
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US10/488,941
• Publication Number:
  US 20040239560A1
• Time in Patent Office: 1,197 Days
• Field of Search: 342/357.01, 342/357.06, 342/357.14, 701/207, 701/213, 701/216, 701/220
• US Class Current: 342/357.62
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial

Abstract

The invention relates to an internal platform hybridized with a GPS receiver. The hybridization is achieved through a Kalman filter through which a new hybrid position D-HYB is estimated on the basis of a noted deviation between pseudo-distance measure by the receiver between the receiver and the various satellites and corresponding distances computed by the inertial platform between the platform and the same satellites. In this filtering, the distance increment from one measurement instant to the next instant, between the pseudo-distance previously measured by the receiver on a satellite axis of a deviation and the new pseudo-distance measured by the receiver on a satellite axis of a deviation and the new pseudo-distance measured by the receiver on this axis, is the phase variation ΔΦ=Φ(t)−ΦI (t−1) of a digital oscillator between the two measurement instants, this variation being referred to distance along the satellite axis. The oscillator is that which makes it possible to slave the local carrier frequency in the receiver to the carrier frequency received from the satellite. Application to the measurement of position.

Claims

1. A navigation system, comprising:

an inertial navigation platform hybridized with at least one satellite based positioning receiver, the inertial platform providing position information resulting at least in part from accelerometric and gyrometric measurements, and the receiver providing pseudo-distances representing the distance between the receiver and satellites, the receiver comprising, for each channel of the receiver, a digitally phase controlled oscillator slaved to the phase of a carrier of a satellite signal corresponding to this channel;

wherein the navigation system provides hybrid position values resulting from a combination of numerical position data originating from the platform and numerical data originating from the receiver;

a means of estimating a new hybrid position on the basis of an observed deviation between pseudo-distances measured by the receiver between the receiver and each one of said satellites and corresponding distances computed by the inertial platform between the platform and said each one of said satellites, this means comprising a digital filter, of Kalman filter type, allowing the prediction of a deviation and the matching of the filter as a function of the comparison between the observed deviations and predicted deviations;

wherein in the digital filter, the distance increment from one measurement instant to the next instant, between a pseudo-distance previously measured by the receiver on a satellite axis and a new pseudo-distance measured by the receiver on said satellite axis, is the phase variation of the digital oscillator between the two measurement instants, this variation being referred to distance along said satellite axis.

2. The navigation system as claimed in claim 1, wherein the estimating means also provides a protection radius associated with the hybrid position found, this protection radius being calculated on the basis of variance data produced in the Kalman filter thus incremented.

3. A method of estimating position using a navigation system having an inertial navigation platform hybridized with at least one satellite based positioning receiver, the inertial platform providing position information resulting at least in part from accelerometric and gyrometric measurements, comprising the steps of providing pseudo-distances representing the distance between the receiver and satellites;

the receiver comprising, for each channel of the receiver, a digitally phase controlled oscillator slaved to the phase of a carrier of a satellite signal corresponding to this channel;

providing hybrid position values resulting from a combination of numerical position data originating from the platform and numerical data originating from the receiver;

estimating a new hybrid position on the basis of an observed deviation between a pseudo-distances measured by the receiver between the receiver and each one of said satellites and a corresponding distances computed by the inertial platform between the platform and said each one of said satellites, predicting a deviation and the matching of the filter as a function of the comparison between the observed deviations and predicted deviations;

calculating a distance increment which is a phase variation of said digital oscillator between one measurement instant and a next measurement instant, this variation being referred to distance along a satellite axis, and adding this increment to a pseudo-distance measured by the receiver on a satellite axis at said one measurement instant to obtain a new pseudo-distance on said satellite axis, and using said new pseudo-distance to compute said observed deviation at said next measurement instant.

4. The method as claimed in claim 3, providing a protection radius associated with the hybrid position found, this protection radius being calculated on the basis of variance data produced in the Kalman filter thus incremented.