Hybrid inertial navigation system with improved integrity

• US 20040239560A1
• Filed: 03/09/2004
• Published: 12/02/2004
• Est. Priority Date: 09/28/2001
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Coatantiec, Jacques, Guillard, Patrice
• Granted Patent: US 6,982,669 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: 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 inertial system hybridised with a GPS receiver. Said hybridisation is carried out by Kalman filtering, by means of which is a new hybrid position D HYB is estimated from a deviation observed (Yo) between (i) pseudo-distances measure by the receiver between the receiver and the different satellites and (ii) the corresponding distances calculated by the inertial system between the system and the same satellites. In the aforementioned filtering, the distance increment from one measuring time to the next, between (i) the pseudo-distance previously measured by the receiver on a satellite axis in order to observe a deviation and (ii) the new pseudo-distance measured by the receiver on said axis, is the phase variation ΔΦ=Φ_i(t)−Φ_i(t-1) of a digital oscillator between the two measuring times, said variation being brought along the length of the satellite axis in terms of distance. The oscillator can be used to slave the local carrier frequency in the receiver to the carrier frequency received from the satellite. The invention can be used for position measuring, with an increased degree of security.

Claims

1. A navigation system, comprising:

an inertial navigation platform hybridized with at least one satellite based positioning receiver (GPS), the inertial platform providing position information resulting at least in part from accelerometric and gyrornetric measurements, and the receiver providing pseudo-distances (PD_i) 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 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 a noted deviation between pseudo-distances measured 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, 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 noted deviations and predicted deviations;

wherein in the digital filter, the distance increment from one measurement instant to the next instant, between the pseudo-distance previously measured by the receiver on a satellite axis noting a deviation and the new pseudo-distance measured by the receiver on this axis, is the phase variation of the digital oscillator between the two measurement instants, this variation being referred to distance along the 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 (C_INERT) hybridized with at least one satellite based positioning receiver (GPS), 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 (NCO2) 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 a noted deviation between pseudo-distances measured 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, predicting a deviation and the matching of the filter as a function of the comparison between the noted deviations and predicted deviations;

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

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