US-12625220-B2 - Method for determining a corrected distance

US12625220B2US 12625220 B2US12625220 B2US 12625220B2US-12625220-B2

Abstract

A method determines a corrected distance between a mobile transceiver fastened to a vehicle and a fixed transceiver. The method includes: identification, among a set of predetermined path segments, of the segment on which the vehicle is currently found on the basis of the last position determined for this vehicle, then selection of a correction function specifically associated with the identified segment using a table that associates, with each path segment, a respective correction function, then execution of the identified correction function to obtain a current correction coefficient for correcting a raw distance computed from transmission and reception times of the radio signals exchanged between the fixed and mobile transceivers, then correction of the last raw distance computed using the current correction coefficient to obtain the corrected distance.

Inventors

Christophe Villien

Assignees

Commissariat à l'Energie Atomique et aux Energies Alternatives

Dates

Publication Date: 20260512
Application Date: 20221118
Priority Date: 20211118

Claims (10)

1 . A method for determining a corrected distance between a mobile transceiver fastened to a vehicle and a fixed transceiver, said method comprising the following steps when the vehicle is moving along a path segment belonging to a countable set of a plurality of predetermined path segments: exchanging, by the mobile transceiver, radio signals with a fixed transceiver, acquisition, by an electronic computer, of transmission and reception times of the radio signals exchanged between the fixed and mobile transceivers, computation, by the electronic computer, of a raw distance between the fixed and mobile transceivers solely from the acquired transmission and reception times of the exchanged radio signals, then determination, by the electronic computer, of a position of the vehicle, wherein the method comprises: identification, among the set of predetermined path segments, of the predetermined segment on which the vehicle is currently found on the basis of the last position determined for said vehicle, then selection of a correction function specifically associated with the identified segment using a table that associates, with each path segment, a respective correction function, each of these correction functions being able, when it is executed, to deliver a correction coefficient for correcting the raw distance, then execution of the identified correction function to obtain a current correction coefficient, then correction of the last raw distance computed using the current correction coefficient to obtain the corrected distance, wherein the determination, by the electronic computer, of the position of the vehicle is based at least partially on the obtained corrected distance.
2 . The method according to claim 1 , wherein: each correction function: is parametrized by a first physical quantity so that the delivered correction coefficient varies as a function of a value of said first physical quantity even when the vehicle remains inside the same predetermined segment, said first physical quantity being chosen from a group made up: of the distance between the fixed and mobile transceivers, and of a physical quantity representative of the power of the received radio signals, and is different from at least one of the other correction functions in that, for a given value of the first physical quantity, it delivers a different correction coefficient, the method comprises obtaining the current value of the first physical quantity, and the execution of the identified correction function comprises execution of the identified correction function parametrized with the obtained current value of the first physical quantity to obtain the current correction coefficient.
3 . The method according to claim 2 , wherein the first physical quantity is the distance between the fixed and mobile transceivers.
4 . The method according to claim 2 , wherein the method comprises a calibrating phase in which, for each predetermined path segment and for various positions of the vehicle on said predetermined path segment: a raw distance between the fixed and mobile transceivers is computed solely from the acquired transmission and reception times of the exchanged radio signals, and for the same vehicle position, an accurate distance is measured using another sensor that allows a distance measurement that is more accurate than the raw distance to be obtained without using the acquired transmission and reception times of the exchanged radio signals, then determination of the correction function that approximates the variation in the error between the computed raw distance and the measured accurate distance depending on the value of the first physical quantity, and association of said correction function with said predetermined path segment.
5 . The method according to claim 1 , wherein each correction function is defined by the following relationship: f sn ( d ) = a sn · d d 0 , sn 2 + d 2 + b sn where a sn , b sn and d 0,sn are three constants that entirely define the correction function, values of the constants a sn , b sn and d 0,sn minimize a difference between a precise distance measured without using a sensor and an error between the precise distance and the raw distance.
6 . The method according to claim 1 , wherein the radio signals are ultra-wideband signals.
7 . The method according to claim 1 , further comprising: acquisition, by the electronic computer, of a measurement of a second physical quantity that varies as a function of the position of the vehicle, said measurement being taken by a sensor independent of the fixed and mobile transceivers, then determination, by the electronic computer, of the position of the vehicle from the acquired measurement of the second physical quantity and from the determined corrected distance.
8 . The method according to claim 7 , wherein the acquisition of a measurement of the second physical quantity comprises acquisition of a measurement chosen from the group made up: of a first measurement of an acceleration of the vehicle, taken by an inertial navigation system, and of a second measurement of the position or speed of the vehicle, taken by a satellite geolocation unit.
9 . The method according to claim 8 , wherein: the acquisition of a measurement of the second physical quantity comprises: acquisition of a third measurement of an angular velocity of the vehicle, taken by the inertial navigation system, and the method in addition comprises determination, by the electronic computer, of the orientation of the vehicle from the acquired measurements of the acceleration and angular velocity of the vehicle and of the determined corrected distance.
10 . A system for determining a corrected distance between a mobile transceiver fastened to a vehicle and a fixed transceiver, said system comprising an electronic computer configured to execute the following steps when the vehicle is moving along a path segment belonging to a countable set of a plurality of predetermined path segments: exchanging, by the mobile transceiver, radio signals with a fixed transceiver, acquisition, by the electronic computer, of transmission and reception times of the radio signals exchanged between the fixed and mobile transceivers, computation, by the electronic computer, of a raw distance between the fixed and mobile transceivers solely from the acquired transmission and reception times of the exchanged radio signals, then determination, by the electronic computer, of a position of the vehicle, wherein the electronic computer is also configured to execute the following operations: identification, among the set of predetermined path segments, of the predetermined segment on which the vehicle is currently found from the last position determined for said vehicle, then selection of a correction function specifically associated with the identified segment using a table that associates, with each segment of the path, a respective correction function, each of these correction functions being able, when it is executed, to deliver a correction coefficient for correcting the raw distance, then execution of the identified correction function to obtain a current correction coefficient, then correction of the last raw distance computed using the current correction coefficient to obtain the corrected distance, wherein the determination, by the electronic computer, of the position of the vehicle is based at least partially on the obtained corrected distance.

Description

The invention relates to a method for determining a corrected distance between a mobile transceiver fastened to a vehicle and a fixed transceiver. The invention also relates to: a method for locating a vehicle implementing the method for determining a corrected distance, anda system for determining a corrected distance. Such distance-determining methods are for example implemented in methods for locating a vehicle. Such a locating method is for example described in the following article: V. Di Pietra et al.: “Loosely Coupled GNSS and UWB with INS Integration for Indoor/Outdoor Pedestrian Navigation”, Sensors, May 11, 2020. More precisely, in such locating methods, the distance between the fixed and mobile transceivers is used to correct a position of the vehicle estimated using other sensors. Thus, the more accurate the distance, the more accurate the position of the vehicle. The distance between the fixed and mobile transceivers is obtained from the transmission and reception times of radio signals exchanged between these transceivers. These radio signals are electromagnetic waves that propagate at the speed of light. Thus, even a very small error in the measurement of these transmission and reception times results in an error of several tens of centimetres in the determined distance. To overcome this problem, it has been proposed to correct a raw distance, computed solely from the measured transmission and reception times, by adding a correction coefficient thereto. The difficulty is then that the value of this correction coefficient depends on a plurality of parameters, notably including: the relative orientation of the antenna of the mobile transceiver with respect to the antenna of the fixed transceiver,the presence on the path of the exchanged radio signals of any elements, notably metal elements, able to perturb propagation of the signal, andthe power of the radio signals received by the fixed and mobile transceivers. A variation in the power of the radio signals received by the fixed and mobile transceivers generally induces a variation in time lags in the mechanism for detecting arrival time within the receiver. It is therefore difficult to construct a correction function that returns the value of such a correction coefficient given the current position and orientation of the vehicle with respect to the fixed transceiver. As a result, there are mainly two possible strategies. The first strategy consists in using a correction function that is complex and accurate but that is difficult to implement and time-consuming to execute. In particular, such a correction function is difficult to implement because it has very many parameters and because it is difficult to accurately adjust each of these parameters. The second strategy consists, conversely, in using a correction function that is simple to implement and rapid to execute. However, simplification of the implementation of the correction function comes at the price of a lower accuracy. Prior art relative to these issues may be found in the following documents: Whenda ZHAO et al.: “Learning-based Bias Correction for Time Difference of Arrival Ultra-wideband Localization of Resource constrained Mobile Robots”, Cornell University Library, Feb. 3, 2021,WO2021143920A1, andUS2003216865A1. The invention aims to overcome this contradiction by providing a method for determining the distance between fixed and mobile transceivers, in which the correction function may be implemented both simply and rapidly without however requiring the accuracy of the determined distance to be decreased. One subject thereof is therefore such a method for determining a distance. Another subject of the invention is a method for locating a vehicle implementing the above method for determining a distance. Lastly, another subject of the invention is a system for determining a distance. The invention will be better understood on reading the following description, which is given solely by way of non-limiting example, with reference to the drawings, in which: FIG. 1 is a schematic illustration of a vehicle constrained to move along a path, FIG. 2 is a schematic illustration of a system for locating the vehicle of FIG. 1; FIG. 3 is a schematic illustration of various software modules implemented in the system of FIG. 2; FIG. 4 is a flowchart of a method for locating the vehicle of FIG. 1 using the system of FIG. 2. In these figures, the same references have been used to designate elements that are the same. In the remainder of this description, features and functions well known to those skilled in the art are not described in detail. In particular, with respect to the general knowledge of those skilled in the art of devices for locating a vehicle using an inertial navigation system, the reader is referred, for example, to the following thesis: S. Godha, “Performance Evaluation of Low Cost MEMS-Based IMU Integrated With GPS for Land Vehicle Navigation Application”, PhD report, 2006. Below