METHOD AND SYSTEM FOR DETERMINING PROTECTION LIMITS WITH INTEGRATED EXTRAPOLATION OVER A GIVEN TIME HORIZON

• US 20120215376A1
• Filed: 09/06/2010
• Published: 08/23/2012
• Est. Priority Date: 09/07/2009
• Status: Active Grant

• Current Assignee: Safran Electronics & Defense
• Original Assignee: Sagem Defense Securite (Safran SA)
• Inventors: Szelewa, Stanislas
• Granted Patent: US 8,843,243 B2
• Time in Patent Office: Days
• US Class Current: 701/1
• 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

Abstract

The invention relates to a method for determining protection limits at a future moment associated with navigation states of a hearer, including the steps of: estimating the navigation states of the bearer at the present moment, developing a statistic model of the estimation errors of navigation states of the bearer at the present moment in the form of a covariance matrix, extrapolating, for a future moment, the statistical model of the estimation errors, calculating protection limits at the future moment from the extrapolated statistical model, wherein the extrapolation of the statistical model of the estimation errors implements the application of a constant and positive transition matrix to a standard deviation vector constructed from the square root of the elements of the diagonal of the covariance matrix, in order to propagate, up to the future moment, the standard deviations of the navigation states developed at the present moment. The invention also relates to a navigation system configured to implement the method.

Claims

1. Method for determining protection limits at a future moment associated with navigation states of a carrier, including steps consisting of:

estimating navigation states of the carrier at the present moment,

producing a statistical model of estimation errors of navigation states of the carrier at the present moment in the form of a covariance matrix,

extrapolating the statistical model of estimation errors to a future moment,

calculating a protection limit at a future moment using the extrapolated statistical model,

characterised in that extrapolation of the statistical estimation error model applies a constant positive transition matrix to a standard deviation vector constructed from the square roots of the elements of the diagonal of the covariance matrix to propagate standard deviations of navigation states produced at the present moment, to a future moment.

2. Method according to claim 1, in which the coefficients of the transition matrix are determined based on assumptions of dynamics of the carrier considered over a time horizon.

3. Method according to claim 2, in which the assumptions of dynamics of the carrier include at least the ground speed, the vertical speed, rotation rate, horizontal and vertical load factors.

4. Method according to one of claims 1 to 3, comprising production of a transition matrix to compensate for the validity delay of the protection limits for estimates of navigation states.

5. Method according to claim 4, in which the coefficients of the transition matrix are determined as a function of the maximum dynamics of the carrier over a time horizon corresponding to one calculation cycle of estimates of navigation states.

6. Method according to one of claims 1 to 3, comprising the production of a transition matrix to compensate for the validity delay of the protection limits related to asynchronism between different navigation systems onboard the carrier.

7. Method according to claim 6, in which the coefficients of the transition matrix are determined as a function of the maximum dynamics of the carrier over a time horizon corresponding to the maximum emission period of the protection limits.

8. Method according to one of claim 6 or 7, in which the extrapolation is made to compensate for the validity delay related to asynchronism between the different navigation systems based on standard deviations previously propagated to the future moment according to one of claim 4 or 5, to compensate for the validity delay of the protection limit for estimates of navigation states.

9. Method according to one of claims 1 to 3, comprising production of a transition matrix to calculate predictive protection limits after a specific carrier mission.

10. Method according to claim 9, in which the coefficients of the transition matrix are determined as a function of the specific dynamics of the carrier during the mission, over a time horizon corresponding to the duration of the mission.

11. Carrier navigation system comprising:

an estimation module (FE) providing navigation state estimates of the carrier at the present moment and a statistical model for estimation errors of the carrier navigation states at the present moment in the form of a covariance matrix,

a module to calculate protection limits (F1) providing protection limits starting from estimates of navigation states and the statistical estimation errors model,

characterised in that it comprises an extrapolation module of the statistical model of estimation errors (3-6) configured to apply a constant positive transition matrix to a vector of standard deviations constructed from the square roots of the elements of the diagonal of the covariance matrix to propagate standard deviations of navigation states produced at the present moment to a future moment, such that the protection limits calculation module calculates the protection limits at the future moment starting from the extrapolated statistical model