Method for determining the position and/or speed of a guided vehicle and associated system
View Patent ↗A method for selecting usable satellites from among the satellites of a localization constellation, to determine an instantaneous kinematic state of a train, is provided. The method includes determining a measured value and an estimated value of a Doppler coefficient and/or a pseudo-range, then comparing the measured and estimated values and, in case of divergence, deleting the satellite from the usable satellites. The estimated value results from a dynamic model of the train, which uses only a kinematic state at a past moment to calculate an estimated instantaneous kinematic state and that uses a mapping of the track on which the guided vehicle moves.
1. A method for calculating, at a present moment, a kinematic state of a guided vehicle from signals emitted by a set of satellites from a constellation of localisation satellites, the method being performed by a programmed calculator on board the guided vehicle, the method comprising:
selecting a set of usable visible satellites from among a set of visible satellites of a constellation of localisation satellites comprising, for each satellite of the set of visible satellites:
calculating an instantaneous measured value for a quantity between a Doppler coefficient and a pseudo-range, from the signal received from said visible satellite;
determining an instantaneous estimated value for the quantity, based on a dynamic model of the guided vehicle that uses only a kinematic state of the guided vehicle determined at a past moment to estimate an estimated kinematic state at the present moment and that uses a map of the track on which the guided vehicle moves;
comparing the instantaneous measured and estimated values according to a criterion, and in case of noncompliance with the criterion; and
deleting the satellite from a set of usable visible satellites; and
calculating the kinematic state of the guided vehicle at the present moment only from the signals received from the satellites of the set of usable visible satellites.
2. The method as recited in claim 1 wherein the determining of an instantaneous estimated value for the quantity includes using an ephemeris making it possible to estimate a relative position and speed between one satellite of the set of visible satellites and the guided vehicle in the estimated kinematic state at the present moment.
3. The method as recited in claim 1 wherein the criterion used when comparing the instantaneous measured and estimated values is based on a deviation between the instantaneous measured and estimated values and/or a covariance between the instantaneous measured and estimated values.
4. The method as recited in claim 3 wherein the criterion includes verifying that the deviation is smaller than a threshold deviation and/or that the covariance is below a threshold covariance.