HYBRID INS/GNSS SYSTEM WITH INTEGRITY MONITORING AND METHOD FOR INTEGRITY MONITORING

• US 20100026567A1
• Filed: 09/25/2007
• Published: 02/04/2010
• Est. Priority Date: 10/06/2006
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Martin, Nicolas, Coatantiec, Jacques
• Granted Patent: US 7,711,482 B2
• Time in Patent Office: Days
• US Class Current: 342/357.620
• 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 pertains to the monitoring of the integrity of position and speed information arising from a hybridization between an inertial reference system and a satellite-based positioning receiver. The invention relates more precisely to a navigation apparatus known in the art by the name INS/GNSS system (for “Inertial Navigation System” and “Global Navigation Satellite System”) hybridized in closed loop.

Claims

1. A INS/GNSS hybrid system with integrity monitoring, comprising:

a barometric module BARO delivering measurements of barometric altitude MBA;

an inertial measurement unit UMI delivering angle increments Δ

θ and

speed increments Δ

V;

a virtual platform PFV receiving the angle increments Δ

θ

, the speed increments Δ

V and producing inertial positioning and speed data PPVI constituting respectively a hybrid position and a hybrid speed;

a satellite-based positioning receiver GNSS operating on the basis of a constellation of N tracked visible satellites, and producing raw measurements, MB_i of the signals transmitted by these satellites, i denoting a satellite index and lying between 1 and N;

a Kalman hybridization filter MKF receiving the inertial positioning and speed data PPVI, the measurements of barometric altitude MBA, and the raw measurements MB_i of the signals transmitted by the N satellites, said filter delivering;

a hybrid correction HYC comprising an estimation of a state vector VE corresponding to the errors of the hybrid system and obtained by observing the deviations between the inertial positioning and speed data PPVI and the raw measurements MB_i, and

a variance/covariance matrix MHYP of the error made in the estimation of the state vector VE;

a bank of N secondary filters KSF_i each receiving the inertial positioning and speed PPVI, the measurements of barometric altitude MBA, and the raw measurements MB_i of the signals transmitted by the tracked satellites except the satellite of index i, said secondary filters KSF_i delivering hybrid parameters SHYP_i comprising

an estimation of a state vector EVE_i corresponding to the errors of the hybrid system, calculated by observing deviations between the inertial positioning and speed data PPVI and the raw measurements of the signals transmitted by the tracked satellites except the satellite i SPP_i, and

a secondary variance/covariance matrix P_i of the error made in the estimation of the state vector EVE_i;

a calculation module CAL receiving the hybrid parameters SHYP_i and the variance/covariance matrix, MHYP, said calculation module CAL determining a horizontal protection radius R_T associated with the hybrid position, and, when components of the estimation of the state vector EVE_i relating to the position are greater than a detection threshold TH_i, triggering an alarm upon a failure of a secondary filter KSF_i, and optionally identifying a failed satellite from among the N tracked visible satellites,

wherein the secondary filters KSF_i and the virtual platform PFV furthermore receive the hybrid correction HYC.

2. The system as claimed in claim 1, wherein, when the calculation module CAL identifies the satellite of index i as having failed, the secondary filter KSF_i is substituted for the Kalman filter MKF.

3. A method for determining a horizontal protection radius RP_T for monitoring integrity of hybrid positions delivered by a virtual platform PFV of a hybrid system as claimed in claim 1, said method implemented by the calculation module CAL of the hybrid comprising the steps of:

determining an auxiliary horizontal protection radius RP_H1, under an hypothesis termed H₁, that one of the raw measurements, MB_i is erroneous,

determining an auxiliary horizontal protection radius RP_H0, under an hypothesis termed H₀, that none of the raw measurements, MB_i is erroneous;

fixing the value of the horizontal protection radius RP_T as a maximum of the horizontal auxiliary protection radii RP_H0 and RPH_H1,

wherein the determination of the auxiliary horizontal protection radii RP_H0 and RP_H1 is based on determining a radius of a circle enveloping a confidence ellipse in a horizontal plane, and in that the confidence ellipse is determined on the basis of a variance/covariance matrix and of a sought-after probability value.

4. The method as claimed in claim 3, wherein the determination of the auxiliary horizontal protection radius RP_H1 is based on a desired false alarm probability value τ

₁ and on a desired missed detection probability value τ

₂.

5. The method as claimed in claim 3, wherein the determination of the auxiliary horizontal protection radius RP_H0 is based on a desired missed detection probability value τ

₂ and on a value of probability of occurrence of an undetected satellite defect τ

₃.

6. The method as claimed in claim 4, wherein a variance/covariance matrix PEi, of dimension 2×

2, is extracted from an auxiliary matrix PS_i=Pi−

MHYP with axes corresponding to the horizontal positions, and wherein the determination of the auxiliary horizontal protection radius RP_H1 under the hypothesis H₁, comprises the steps of;

Determining P01=1−

τ

₁/N;

Determining a test threshold value TH_i based on the value P01 and on the matrix PEi;

Determining P02=1−

τ

₂;

Determining a value of auxiliary protection radius d_i as equal to the radius of the circle enveloping an ellipse determined on the basis of the matrix PEi and of the probability P02;

Determining the radius value RP_H0 as a maximum value of (TH_i+d_i), for all the values of i between 1 and N.

7. The method as claimed in claim 5, wherein a variance/covariance matrix P of dimension 2×

2 being extracted from the variance/covariance matrix MHYP with axes corresponding to the horizontal positions, and wherein the determination of the auxiliary horizontal protection radius RP_H0 under the hypothesis H₀, comprises the steps of;

determining P03=1τ

τ

₂·

τ

₃;

determining the radius value RP_H0 as equal to the radius of the circle enveloping an ellipse determined on the basis of the matrix P and of the probability P03.