Method of determining navigation parameters for a carrier and hybridization device

• US 8,942,923 B2
• Filed: 07/09/2010
• Issued: 01/27/2015
• Est. Priority Date: 07/10/2009
• Status: Active Grant

• Current Assignee: Safran Electronics & Defense
• Original Assignee: Sagem Defense Securite (Safran SA)
• Inventors: Riedinger, Didier, Chafouk, Houcine
• Primary Examiner(s): Olszewski, John R
• Assistant Examiner(s): Do, Truc M
• Application Number:
  US13/383,202
• Publication Number:
  US 20120123679A1
• Time in Patent Office: 1,663 Days
• Field of Search: 701/472, 701/469, 701/470, 701/501, 701/532, 701/119, 701/3, 701/4, 701/408, 701/14, 701/16, 342/62, 342/63, 342/64, 342/357.53, 342/357.56, 342/357.59, 342/357.65
• US Class Current: 701/480
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• CPC Class Codes: G01S 19/40 Correcting position, velocity or attitude
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial

Abstract

Method of determining navigation parameters for a carrier by a hybridization device comprising a Kalman filter (3) formulating a hybrid navigation solution on the basis of inertial measurements calculated by a virtual platform (2) and of raw measurements of signals emitted by a constellation of satellites delivered by a satellite positioning system (GNSS), characterized in that it comprises, the steps of: —determination, for each satellite, of at least one likelihood ratio (Ir, Ir′) between a hypothesis regarding a fault of a given nature of the satellite and a hypothesis regarding an absence of fault of the satellite, —declaration, of a fault of a given nature on a satellite as a function of the likelihood ratio (Ir, Ir′) associated with this fault and of a threshold value, —estimation of the impact of the declared fault on the hybrid navigation solution, and □correction of the hybrid navigation solution as a function of the estimation of the impact of the declared fault.

Claims

1. A process for determination of navigation parameters of a carrier by a hybridisation device comprising a Kalman filter (3) working out a hybrid navigation solution from inertial measurements calculated by a virtual platform (2) and raw measurements of signals emitted by constellations of satellites delivered by a satellite-positioning system (GNSS), comprising the steps of:

determination for each satellite of at least one (Ir, Ir′

) probability ratio between a hypothetical breakdown of a given type of the satellite and a hypothetical absence of breakdown of the satellite,

declaration of a breakdown of given type on a satellite as a function of the (Ir, Ir′

) probability ratio associated with this breakdown and a threshold value,

estimation of an impact of the declared breakdown on the hybrid navigation solution, and

correction of the hybrid navigation solution as a function of the estimation of the impact of the declared breakdown.

2. The process as claimed in claim 1, in which for each satellite at least one (Ir, Ir′

) probability ratio is determined at each incrementation of the Kalman filter on a sliding storage window, a breakdown of given type being declared when the sum of the (Ir, Ir′

) probability ratios associated with this breakdown is greater than the associated threshold value.

3. The process as claimed in claim 2, also comprising, when a breakdown is declared, a step of exclusion of raw measurements of signals emitted by the satellite declared in breakdown.

4. The process as claimed in claims 1, 2, or 3, in which the (Ir, Ir′

) probability ratio is determined as a function of an innovation vector and of innovation covariances provided by the Kalman filter and from estimation of the impact of the breakdown of given type on said innovation vector.

5. The process as claimed in claim 4, in which the impact of the breakdown of given type on said innovation is estimated by determination, from data provided by the Kalman filter (3), of a dynamic innovation matrix, and estimation of the amplitude of the breakdown of given type on a sliding estimation window corresponding to a given number (N) of incrementations of the Kalman filter (3), the dynamic innovation matrix representing a link between the amplitude of the breakdown and the spread caused by the breakdown on the innovation.

6. The process as claimed in claim 5, in which the given number (N) of incrementations of the Kalman filter (3) corresponds to a duration lasting less than a predetermined detection period (T).

7. The process as claimed in claim 6, in which the estimation of the amplitude of the breakdown of given type is done on the sliding estimation window by a minimisation method by the least-squares method or else by a Kalman filter.

8. The process as claimed in claim 7, in which the estimation of the impact of the breakdown on the hybrid navigation solution comprises determination, by the Kalman filter (3), of a dynamic navigation matrix, and estimation of an amplitude and a covariance of the breakdown of given type on a sliding estimation window corresponding to a given number (N) of incrementations of the Kalman filter, the dynamic navigation matrix representing a link between the amplitude of the breakdown and the spread caused by the breakdown on the hybrid navigation solution.

9. The process as claimed in claim 8, in which two (Ir, Ir′

) probability ratios are determined for each satellite, a (Ir) ratio being associated with a hypothetical breakdown of bias type and the other ratio (Ir′

) being associated with a hypothetical breakdown of ramp type.

10. The process as claimed in claim 9, in which, when a breakdown of bias type is declared during the declaration step, the estimation step of the impact of the breakdown on the hybrid navigation solution is conducted on a sliding estimation window from the moment of declaration of the breakdown of bias type.

11. The process as claimed in claim 10, in which, when a breakdown of ramp type is declared, the estimation step of the impact of the breakdown on the hybrid navigation solution is conducted on the sliding estimation window preceding the moment of declaration of the breakdown of ramp type.

12. The process as claimed in claim 11, in which, when several sums of (Ir, Ir′

) probability ratios are greater than their associated threshold value, a single breakdown is declared during the declaration step, said breakdown corresponding to the greater of the sums of probability ratios.

13. A hybridisation device comprising a virtual platform (2) capable of calculating inertial measurements, a Kalman filter (3) designed to devise a hybrid navigation solution from inertial measurements and raw measurements of signals emitted by constellations of satellites delivered by a satellite-positioning system (GNSS), characterised in that it comprises:

a detection module (41) configured to determine for each satellite at least one (Ir, Ir′

) probability ratio between a hypothetical breakdown of a given type by ratio and hypothetical absence of breakdown of the satellite and to declare a breakdown of given type as a function of the (Ir, Ir′

) probability ratio associated with the breakdown of given type is of a threshold value,

an accommodation module (5) configured to estimate an impact of the declared breakdown on the hybrid navigation solution devised by the Kalman filter, and to correct the hybrid navigation solution as a function of the estimation of the impact of the declared breakdown.

14. The device as claimed in claim 13, also comprising a device (42) for managing satellite signals configured to exclude raw measurements of signals emitted by any satellite declared in breakdown by the detection module.