Apparatus and method for autonomous positioning of a vehicle

Abstract

A positioning device (110) for determining a position of a stationary or moving vehicle on a road of a given network (300) from positioning signals broadcast by satellites in at least one satellite constellation (200), comprising:-a first unit (111) determining a plurality of possible current positions and a plurality of timestamps, configured to: o generate a local copy of the positioning signals; o, receiving positioning signals broadcasted by one or more satellites (201) in the field of view; o, for each possible current location and timestamp, processing a correlation function between the received positioning signal and the local replica; a second unit (112): o determining a common error of all satellites, o using said common error to correct the correlation result, o determining a multi-satellite likelihood for each possible current position of the vehicle; and o, determining the position and the timestamp by comparing the multi-satellite likelihoods.

Description

Technical Field

[0001] The present invention relates generally to positioning systems and, more particularly, to apparatus and methods for self-locating a vehicle using positioning signals provided by at least one satellite constellation without requiring a prior time position or train motion. Background Art

[0002] Rail transport has become an effective solution for moving people and delivering goods. For example, rail transport has the advantages of being cost-effective, more environmentally friendly, capable of carrying large loads and more reliable compared to road transport, as trains do not share tracks with the public as trucks do with roads. As a direct result of these advantages, the deployment of rail networks has grown rapidly over the past two decades, especially in countries that have made significant social and / or economic progress. In order to meet the growing demand for more efficient, faster and cleaner rail transport, the number of trains sharing the same rail network and their speeds are constantly increasing. Therefore, the management of rail networks has become a vital task to ensure a certain level of safety, especially when it comes to passengers. A fundamental requirement for the efficient management of a rail network is the ability to accurately locate every train traveling or stopped on the tracks of the rail network in real time.

[0003] A known solution for determining the position of a train running on a railway network track is to deploy electronic beacons (also called transponders) along the track, which are wirelessly or wired to a central control unit. The working principle of the electronic beacon is to detect any train passing by through a mechanical or electronic mechanism. When a train is detected, the electronic beacon immediately sends a detection signal, which contains an identifier of the electronic beacon and may contain information about the passing train. In some cases, the electronic beacon can be configured to interact with the passing train, that is, to exchange signals. In these cases, the passing train can transmit the detection signal to the central control unit. The deployment and maintenance of this solution will soon become costly because a large number of electronic beacons are required in both high-speed railway networks (the distance between adjacent stations is usually more than a few kilometers) and subway networks (although the distance between adjacent stations is short, the subway network has a high requirement for high accuracy). The disadvantage of this solution is that it is only compatible with moving trains when it is necessary to locate a stationary train. In addition, using this solution, it is impossible to locate whether the train between two adjacent electronic beacons is running or stationary.

[0004] Another known solution for determining the position of a moving or stationary train on a railway network track is to use a global navigation satellite system (GNSS), that is, to equip each train with a GNSS receiver. This solution can overcome the difficulties caused by the requirement to deploy beacons along the track. Typically, a GNSS receiver operates independently of the railway network by calculating the three-dimensional (3D) position (latitude, longitude and altitude) of the corresponding train relative to a ground reference system. In order to calculate the accurate 3D position of the corresponding train, the GNSS receiver needs to be in an unobstructed line of sight with three or more GNSS satellites. However, in railway transportation, trains travel between mountains and buildings and cross bridges and tunnels, in which case this requirement is difficult to maintain for a long time. The presence of these obstacles blocks the GNSS signals from reaching the GNSS receiver, resulting in inaccurate positioning of the train. In addition, even if there are no obstacles between the GNSS satellite and the GNSS receiver, accurate positioning of the train requires precise time synchronization between the clock on the GNSS satellite that controls the generation of the GNSS signal and the clock on the GNSS receiver that correctly decodes the received GNSS signal. Typically, GNSS satellites carry very stable atomic clocks, while GNSS receivers use less stable and less accurate clocks that may drift in time. For example, a 1μm time drift in a GNSS receiver's clock can result in an error of tens of meters in the positioning of the corresponding train. This level of inaccuracy makes simple GNSS receivers incompatible with rail transport, which requires high precision, such as determining on which track a train is stationary at a station.

[0005] Therefore, there is a need for an improved positioning device which does not have the disadvantages of the prior art. Summary of the invention

[0006] To address these and other issues, a positioning device is provided, which is configured to determine the position of a vehicle based on positioning signals broadcast by at least one satellite constellation, wherein the vehicle is stationary or moving on a road of a given network. The positioning device includes:

[0007] a first unit configured to determine a plurality of possible current positions of a vehicle at a given measurement time and to determine a plurality of time stamps, the plurality of time stamps being determined within a given time interval, the first unit being further configured to:

[0008] o generating a local copy of the positioning signal for each possible current position of the vehicle, each local copy being associated with an early point, an early point, and a late point of one of a plurality of time stamps and being associated with a satellite in at least one satellite constellation;

[0009] o At each of the plurality of timestamps, receiving a signal received by at least one satellite constellation

[0010] Positioning signals broadcast by at least three satellites in view;

[0011] o for each possible current position of the vehicle, each timestamp in the plurality of timestamps, and each satellite in view, processing a correlation function between the received positioning signal and the corresponding generated local copy at an early point, an immediate point, and a late point;

[0012] - A second unit, which is configured to:

[0013] oFor each satellite, use the correlation results to determine the common / shared error for all satellites,

[0014] o for each satellite, each position and each timestamp, determining a corrected correlation result using the common error and the early, current and late points of the correlation result,

[0015] o For each possible current position of the vehicle, determine the multi-satellite likelihood, each multi-satellite likelihood is the sum of the squares of the corrected correlation results for a given timestamp

[0016] Determined;

[0017] oDetermine the most likely location and the most likely timestamp.

[0018] According to some embodiments, the step of determining the common error of all satellites comprises:

[0019] -For each satellite:

[0020] o determine the possible locations with the most relevant results,

[0021] o From the possible position, draw a line perpendicular to the axis pointing to the satellite,

[0022] o measure the minimum distance from each location to the line, and

[0023] o multiplying the minimum distance by the cosine of the satellite elevation angle to obtain the time distance, or

[0024] -For each satellite and each possible position:

[0025] o Newton interpolation of the correlation results at the early, immediate and late points with the timestamp of the maximum result,

[0026] o determine the temporal distance between the instantaneous position of the timestamp and the maximum value of the interpolated correlation,

[0027] - Determine the possible positions for each satellite having the closest temporal distance and calculate the common error as the average of the temporal distances of the satellites for said possible positions.

[0028] According to some embodiments, for each possible current position of the vehicle and each timestamp of a plurality of timestamps, processing a correlation function between positioning signals received at early, immediate, and late points and correspondingly generated local copies includes accumulating a plurality of correlation results calculated within a finite time interval surrounding said early, immediate, and late points of the timestamp.

[0029] According to some embodiments, the positioning device may further include a map database including location information of roads of a given network, and the second unit is further configured to determine the road portion where the vehicle is located by accessing the map database and using the determined most likely position.

[0030] According to some embodiments, the map database may also include a representation of the road surroundings of a given network.

[0031] According to some embodiments, the first unit may be further configured to access a map database to determine one or more propagation characteristics of each received positioning signal, the first unit further configured to exclude one or more positioning signals from the base likelihood calculation based on their propagation characteristics.

[0032] According to some embodiments, the first unit may be configured to determine a plurality of possible current locations by combining a plurality of positioning signals using PVT techniques while the vehicle is moving.

[0033] According to some embodiments, when the vehicle is stationary on a parking road among a plurality of adjacent parking roads, the first unit may be configured to determine a plurality of possible current positions by assigning a possible current position to each of the adjacent parking roads.

[0034] According to some embodiments, the first unit may be further configured to determine the given time interval based on a time integrity protection radius associated with the at least one satellite constellation.

[0035] According to some embodiments, the first unit may be further configured to determine a plurality of time stamps by periodically sampling within a given time interval.

[0036] According to some embodiments, the first unit may be configured to receive positioning signals from two or more satellite constellations, the first unit may be further configured to separately process the positioning signals broadcast by each satellite constellation, the second unit may be configured to determine the most probable position and the most probable timestamp for each satellite constellation, and the second unit may be further configured to determine a final most probable position among the determined most probable positions.

[0037] According to some embodiments, the second unit may be configured to determine the final most likely position using a selection criterion selected from the following selection criteria:

[0038] - the number of satellites in each constellation involved in determining each most likely position, with the final most likely position being determined by the maximum number of satellites in view; or

[0039] -Time, determining the final most likely position using the satellite constellation associated with the shortest given time interval.

[0040] According to some embodiments, the second unit may further be configured to generate an alarm notification if the most likely position of the vehicle cannot be determined within the predefined time interval.

[0041] The present invention also provides a method for determining the position of a vehicle using a positioning signal broadcast by at least one satellite constellation. The method comprises the following steps:

[0042] - determining a plurality of possible current positions of the vehicle and determining a plurality of time stamps within a given time interval;

[0043] - generating a local copy of the positioning signal for each possible current position of the vehicle, each local copy being associated with an early point, a current point, and a late point of one of a plurality of time stamps and being associated with a satellite in at least one satellite constellation;

[0044] - at each of a plurality of time stamps, receiving a positioning signal broadcast by at least three satellites within at least one satellite constellation;

[0045] - for each possible current position of the vehicle, each time stamp of the plurality of time stamps and each satellite in view, processing a correlation function between the received positioning signal and the correspondingly generated local copies at the earlier point, the immediate point and the later point;

[0046] -Use the correlation results to determine the common errors of all satellites;

[0047] - for each satellite, each position and each timestamp, correcting (406) the correlation result using the common error and the early, immediate and late points of the correlation result, determining a multi-satellite likelihood for each possible current position of the vehicle, each multi-satellite likelihood being determined for a given timestamp based on the sum of squares of the corrected correlation results, and determining, by comparing the multi-satellite likelihoods, a most probable position and a most probable timestamp among a plurality of possible current positions and among a plurality of timestamps, respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments of the invention and, together with the general description of the invention given above and the detailed description of the embodiments given below, serve to explain embodiments of the invention.

[0049] Figure 1 represents a vehicle positioning system according to some embodiments of the present invention;

[0050] Figure 2 The structure of the positioning device according to some embodiments of the present invention is schematically shown;

[0051] Figure 3 The acquisition of a positioning signal according to an embodiment of the present invention is shown;

[0052] Figure 4 is a flow chart illustrating a positioning process according to one embodiment of the present invention. DETAILED DESCRIPTION

[0053] Figure 1 A vehicle positioning system 10 that can use a positioning device 110 according to some embodiments of the present invention is shown. The vehicle positioning system 10 includes a number of roads belonging to a given network 300, which are arranged according to a given architecture. The vehicle positioning system 10 also includes one or more vehicles 100, each of which is restricted to traveling only on the roads of the given network 300. For example, the roads of the given network 300 can represent tracks of a railway transportation system. In such an example, the vehicle 100 is a railway vehicle 100, which can be but is not limited to a train or a subway. Each vehicle 100 includes a positioning device 110, which can be configured to determine the instantaneous position of the corresponding vehicle by using an externally provided positioning signal.

[0054] The vehicle positioning system 10 also includes a satellite constellation 200, which includes a plurality of satellites 201. The number of satellites 201 forming the constellation and their orbital characteristics can be predetermined to ensure that each positioning device 110 is covered by at least one satellite in the constellation at any time. This allows the positioning device 110 to always receive the positioning signal provided by at least one satellite in the constellation 200. It should be noted that the positioning signals transmitted by the satellites of the constellation 200 may be subjected to various distortions, such as multipath interference, before reaching the positioning device 110. These distortions may be caused by a variety of phenomena, including diffraction by natural obstacles or buildings. Some of these distortions may be deterministic, in which case these distortions can only be compensated by the positioning device 110. However, some other distortions are probabilistic and require high processing complexity to correctly decode the positioning signal. In addition, each satellite 201 in the constellation 200 includes an onboard clock, which is configured to control the generation of the positioning signal. Advantageously, the onboard clock in each satellite in the constellation 200 can be an atomic clock, which exhibits more stable and more accurate characteristics compared to other types of clocks.

[0055] A given network 300 includes a number of switches 304 interposed between roads, configured to direct vehicles 100 from one road to another. The use of switches 304 allows vehicles 100 to share common roads 302. In the example of a railway network 300, a switch is a mechanical device that can be used to direct a railway vehicle 100 from one track to another.

[0056] The given network 300 also includes a number of parking roads 301 for parking vehicles 100 when the vehicles 100 are not providing services and / or are out of service. In addition, some parking roads 301 can be arranged in parallel and connected to the public road 302 by means of turnouts. Generally, the parking road can be regarded as the starting point or end point of one or more corresponding vehicles 100. Each parking road 301 can be assigned a unique identifier. In some embodiments, the positioning device 110 can be configured to determine the parking road on which the corresponding vehicle is stationary by feeding back the unique identifier of the parking road when the corresponding vehicle is stationary on the parking road.

[0057] The given network 300 also includes several public roads 302, and multiple vehicles 100 can travel continuously on these public roads 302. In the example of the railway network 300, several railway vehicles 100 can travel on the same track along a common direction of travel. In addition, each public road 302 can be regarded as an association of multiple sections, each section being assigned a unique identifier. In some embodiments, the positioning device 110 can be configured to determine the section of the public road 302 on which the corresponding vehicle is positioned by feeding back the unique identifier of the section of the public road when the corresponding vehicle moves on the public road 302.

[0058] A given network 300 may also include one or more stations, for example, where a vehicle may temporarily stop at a station to pick up passengers. In addition, each station may include several parallel station lanes 303; each station lane 303 may be associated with a platform, for example. Advantageously, each station lane 303 may be assigned a unique identifier. In some embodiments, the positioning device 110 may be configured to determine the station lane on which the corresponding vehicle is moving when the corresponding vehicle enters the station, for example, by feeding back the unique identifier of the station lane.

[0059] In some embodiments of the present invention, the positioning device 110 may be configured to determine a parking road, a section of a public road 302 or a station road of a corresponding vehicle by utilizing one or more positioning signals provided by the satellite constellation 200 and utilizing the architecture of a given network 300 .

[0060] Figure 2The structure of the positioning device 110 according to some embodiments of the present invention is shown. The positioning device 110 will be described below with reference to the railway network 300. Those skilled in the art will readily appreciate that the positioning device 110 according to various embodiments of the present invention can be easily extended to other types of transportation networks, wherein the vehicle 100 is restricted to travel only on the roads of a given network 300. Advantageously, the positioning device 110 includes a first unit 111, which is configured to determine several possible current positions of the railway vehicle at a given measurement time. The possible current position of the railway vehicle can be determined based on one or more parameters, such as the state of the railway vehicle (e.g., stationary or moving), the last known position of the railway vehicle, the speed of the railway vehicle, etc. For example, when the railway vehicle is parked on one of several adjacent parking tracks 301, the first unit 111 can be configured to determine the possible current position of the railway vehicle by assigning a possible current position to each adjacent parking track 301. In another example where the railway vehicle travels on the common track 302 of the railway network 300, the first unit 111 may be configured to determine the possible current position of the railway vehicle by assigning a possible current position to each section of the common track 302. Considering the length of the railway vehicle, the possible current position of the railway vehicle may accurately correspond to the possible current position of its locomotive.

[0061] The positioning device 110 also includes a clock that controls the decoding of positioning signals provided by the satellite constellation 200. In one embodiment of the present invention, the positioning device 110 is equipped with a clock that is synchronized with an onboard clock of the satellite constellation 200 that controls the generation of the positioning signals. In such an embodiment, the first unit 111 is further configured to determine a timestamp that may correspond to a given measurement time.

[0062] In another embodiment of the present invention, the clock equipped with the positioning device 110 is not synchronized with one or more clocks on the satellites 201 of the constellation. In such an embodiment, the first unit 111 can be configured to determine a given time interval based on the timing mismatch between the two clocks. The first unit 111 can also be configured to determine multiple timestamps within a given time interval. For example, the timestamps can be obtained by linearly sampling the given time interval. The given time interval can also be determined as a function of the speed of the railway vehicle. For example, the higher the speed of the railway vehicle, the shorter the given time interval. The special case is that when the railway vehicle is stationary, the given time interval can be as long as possible according to the predefined positioning time requirement.

[0063] The first unit 111 may also be configured to generate one or more local copies of the positioning signal for each possible current position of the railway vehicle, each local copy of the positioning signal being associated with a timestamp at an early point, an instant point and a late point and with a satellite in view of the satellite constellation 200. The local copy of each positioning signal is generated by the first unit 111 based on the position of the corresponding satellite in view, which is assumed to be accurately known by the first unit 111 of the positioning device 110. Typically, the received navigation message includes an ephemeris field containing information related to the position of the satellite transmitting the positioning signal, and the received navigation message may also include an almanac field containing information related to the orbit of each satellite of the constellation.

[0064] The first unit 111 may also be configured to receive, at each of a plurality of time stamps, positioning signals broadcast by at least three satellites 201 of a constellation that are visible to the positioning device 110. Each positioning signal may consist of a navigation message modulated by a spreading sequence, which is typically a pseudo-random noise (PN). The positioning signals may be subjected to various distortions before arriving at the positioning device 110. Advantageously, the first unit 111 may also be configured to compensate for such distortions before utilizing the positioning signals to determine the position of the corresponding railway vehicle.

[0065] The first unit 111 may also be configured to calculate, for each possible current position of the railway vehicle, a correlation between the positioning signal and its local copy at an early point, an immediate point and a late point of a given timestamp among the plurality of timestamps, taking into account a satellite in view of a given satellite constellation 200 .

[0066] Advantageously, each of these correlations may be a coherent or incoherent accumulation of a plurality of correlations between the positioning signal and its local copy for a plurality of timestamps within a given time interval around a given timestamp. The size of the given time interval may depend on the speed of the train, so that the position of the vehicle does not change significantly during the given time interval. Thus, the given time interval may be several (several) minutes when the railway vehicle is not moving and may be hundreds of nanoseconds when the railway vehicle is moving at full speed. This step of accumulating the results of the correlations performed in time intervals when the movement of the railway vehicle is not significant helps to reduce the noise level of the measurement, thereby improving the quality of the position measurement.

[0067] The positioning device 110 further includes a second unit 112, which is configured to receive the association result calculated by the first unit 111 and the possible current position and a timestamp. In addition, the second unit 112 may be configured to:

[0068] -determine the common error for each satellite from the correlation results,

[0069] - using said common error to correct the correlation results, and

[0070] - using the corrected association result to determine a most probable current position among possible current positions and a most probable timestamp among the plurality of timestamps.

[0071] The positioning device 110 may also include a map database 113, which includes a representation of the railway network 300. For example, the map database 113 may include the 3D coordinates of the center line of each track of the railway network 300. Advantageously, only samples of the center line of the track may be included in the map database 113. This greatly reduces the amount of data contained in the database. In addition, the minimum distance between two adjacent samples of the center line may vary depending on whether there is a track ambiguity problem that needs to be solved. For example, when a railway vehicle is located on a parking track in several (several) adjacent parking tracks 301, a track ambiguity problem will occur. In this example, the minimum distance can be selected to be less than the minimum distance between two adjacent tracks, for example, less than four meters. In the absence of a track ambiguity problem, for example, when a railway vehicle is traveling on a common track 302, the minimum distance between two adjacent samples of the center line can be determined based on a predefined accuracy threshold.

[0072] In one embodiment of the invention, the map database 113 may also include a representation of the environment 400 surrounding the tracks of the railway network 300. Such a representation may involve elements of the surrounding environment 400 that may affect the positioning signal (i.e., distort the positioning signal) before the positioning signal reaches the positioning device 110. For example, only elements of the surrounding environment 400 that are located within a predefined interval centered on the track level may be considered. More precisely, for each considered element, the map database 113 may contain several characteristics, which may include geometric characteristics (length, height, width, distance from the center line of the track, etc.).

[0073] In another embodiment of the present invention, the second unit 112 may also be configured to determine the track where the railway vehicle is located by accessing the map database 113 and inputting the most likely position that has been determined. For example, in the case where the railway vehicle is parked on a parking track among the plurality of parking tracks 301, the second unit 112 may be configured to determine the unique identifier of the parking track where the railway vehicle is parked. In another case where the railway vehicle travels on the common track 302, the second unit 112 may be configured to determine the section of the common track 302 on which the railway vehicle is located.

[0074] In one embodiment of the present invention, the first unit 111 of the positioning device 110 may be configured to determine multiple possible current positions using a PVT (position-velocity-time) technique, which includes determining the distance between the positioning device 110 and each satellite 201 in view, such distances being referred to as "pseudoranges". When three pseudoranges are calculated, the first unit 111 may be configured to determine the 3D coordinates of the first unit knowing the positions of the satellites 201, the 3D coordinates representing the possible current position of the railway vehicle. When four or more pseudoranges are calculated, the first unit 111 may be configured to determine the corresponding possible current position of the railway vehicle from each combination of the three pseudoranges. In addition, the first unit 111 of the positioning device 110 may also be configured to access a map database 113 to reduce the number of possible current positions of the railway vehicle, since the railway vehicle is restricted to traveling only on the tracks of the railway network 300.

[0075] In another embodiment of the present invention, the first unit 111 of the positioning device 110 can be configured to determine a plurality of possible current positions by using a model and / or assumption that controls the movement of the railway vehicle on the track of the railway network 300. Advantageously, the determination of the plurality of possible current positions can also take into account externally provided information provided by other devices equipped to the railway vehicle. Such externally provided information may include the instantaneous speed of the train, the approximate position of the railway vehicle determined by an inertial measurement unit (IMU), and / or the position of the railway vehicle previously determined. In addition, the first unit 111 of the positioning device 110 can also be configured to access a map database 113 to reduce the number of possible current positions of the railway vehicle, since the railway vehicle is restricted to running only on the track of the railway network 300.

[0076] The first unit 111 of the positioning device 110 may be configured to determine a given time interval for a given satellite constellation 200 based on a time integrity protection radius, which may be calculated from time data of a RAIM function integrated in the positioning device 110 or external to the positioning device 110 .

[0077] In one embodiment of the present invention, the positioning device 110 may be configured to receive positioning signals provided by satellites 201 belonging to two or more satellite constellations 200 at a given measurement time. In such an embodiment, the positioning device 110 may be configured to independently process the positioning signals provided by each satellite constellation 200, as described above with respect to a single satellite constellation 200, thereby determining the most likely current position for each satellite constellation 200. In addition, the positioning device 110 may be configured to select a final most likely current position among a plurality of determined most likely current positions. Such a selection operation may be performed, for example, based on a selection criterion. The selection criterion may be, for example, the number of satellites 201 in view involved in determining the corresponding most likely position. In this case, the most likely position determined using the largest number of satellites 201 may be used as the final most likely position.

[0078] In another embodiment of the present invention, the selection criterion used by the positioning device 110 to determine the final most likely position among multiple most likely positions may be the duration of a given time interval. In this case, the most likely current position associated with the shortest given time interval may be used as the final most likely position.

[0079] In one embodiment of the present invention, the positioning device 110 may be configured to implement integrity monitoring to generate an alarm notification when the corresponding railway vehicle cannot be located within a predefined measurement time interval, which is measured from a given measurement time. This may occur, for example, when the railway vehicle enters an area with poor coverage and / or in bad weather conditions. The duration of the predefined measurement time interval may depend on whether the railway vehicle is stationary or moving. The generated alarm notification may be transmitted, for example, to the driver of the railway vehicle.

[0080] Figure 3The acquisition of positioning signals according to one embodiment of the present invention is shown. The positioning device 110 receives positioning signals from two in-view satellites 201 belonging to a common satellite constellation 200. The positioning signal broadcast by one of the two satellites 201 reaches the positioning device 110 according to line-of-sight propagation, that is, the positioning signal propagates along a direct path from the satellite to the positioning device 110. The positioning signal broadcast by the other satellite is subject to multipath propagation before reaching the positioning device 110. The first unit 111 of the positioning device 110 can be configured to access the map database 113 and determine the propagation characteristics of each received positioning signal, such as but not limited to understanding the position of the corresponding satellite, the possible current position of the railway vehicle, and the characteristics of the surrounding environment 400 provided by the map database 113. The first unit 111 can also be configured to exclude one or more positioning signals from the basic likelihood calculation based on their propagation characteristics. For example, the first unit 111 can only include the positioning signals that reach the positioning device 110 according to line-of-sight propagation into the correlation calculation, thereby improving the accuracy of the positioning of the railway vehicle.

[0081] Figure 4 4 is a flow chart showing a railway vehicle positioning process that can be implemented at the positioning device 110 according to an embodiment of the present invention. At step 401, multiple possible current positions of a railway vehicle moving on the track of the railway network 300 are determined at a given measurement time. The position or train movement at a previous time is not required. The multiple possible current positions can be determined using PVT technology in combination with multiple positioning signals broadcast by satellites 201 of at least one satellite constellation 200. Step 401 also includes determining multiple timestamps, and the timestamps are determined within a given time interval. For example, the multiple timestamps can be determined by sampling the given time interval regularly or irregularly. In addition, the given time interval can be predetermined based on the time integrity protection radius associated with the at least one satellite constellation 200.

[0082] At step 402, a local copy of the positioning signal is generated for each possible current position of the railway vehicle, each local copy is associated with an early point, an instant point, and a late point of a timestamp in the plurality of timestamps, and is associated with a satellite in view of the at least one satellite constellation 200. The early point and the late point have an equal absolute time offset from the instant point of the timestamp. For example, the early point can be obtained with a time offset of -100ns from the instant point, and the late point can be obtained with a time offset of +100ns from the instant point.

[0083] At step 403, a positioning signal broadcast by a satellite 201 in view of the at least one satellite constellation 200 is received at each of the plurality of timestamps.

[0084] At step 404, for each possible current position of the railway vehicle, for each timestamp of the plurality of timestamps and for at least three satellites of the at least one satellite constellation 200, a correlation function is calculated between the positioning signals transmitted by the satellite and received at the early point, the instant point and the late point and the corresponding generated local copies.

[0085] Advantageously, in one embodiment, each correlation corresponds to an accumulation of correlations performed within a given time interval around each early, immediate and late time points of the timestamp. The accumulation can be coherent or incoherent. It helps to reduce the noise level of the measurement, thereby improving the accuracy of positioning.

[0086] At step 405, the common error for each satellite is calculated from the correlation results. In practice, for each satellite, the error affecting the measurement is:

[0087] - receiver timing error, which is the error due to the deviation between the satellite clock and the railway vehicle clock,

[0088] - the balise position error, which corresponds to the distance between the railway vehicle and the possible position,

[0089] - Residual propagation delay, which is the deviation between the ionospheric and tropospheric delays provided by a model (eg, the Klobuchar model) and their actual delays.

[0090] The residual propagation delays of all satellites tend to be similar, and the receiver timing errors of all satellites are exactly the same. The maximum correlation can be observed at each possible position of the railway vehicle when the transponder position error is close to the residual propagation delay minus the receiver timing error. This means that for each satellite, the transponder position error is equal to their maximum correlation point.

[0091] Therefore, the common error of each satellite can be calculated based on the position of each satellite with the greatest correlation.

[0092] In one embodiment, the common error is calculated graphically: for each satellite, the possible position with the maximum correlation result is determined. From this position, a line is drawn perpendicular to the line connecting the possible positions and the satellite. This line corresponds to an approximation of a circular arc equidistant from the satellite: all points on this line show the same maximum correlation result.

[0093] For each possible position and each satellite in view, measure the minimum distance to the line of maximum correlation. Multiply this spatial distance by the cosine of the satellite elevation angle to convert to a temporal distance.

[0094] The best possible position of the railway vehicle corresponds to the possible position with the shortest temporal distance to each satellite, that is to say to the possible position that minimizes the difference between the maximum and minimum temporal distances to each satellite. For this best possible position, a common error can be calculated, which is equal to the average of the temporal distances to each satellite.

[0095] In another embodiment, the early, immediate, and late correlation results are used to determine the common error. For each satellite, each possible position, and timestamp corresponding to the maximum correlation result, the early, immediate, and late correlation results are interpolated (e.g., by Newton interpolation) to determine the exact correlation maximum. The exact correlation maximum is offset from the immediate correlation by a time distance equal to the possible position.

[0096] As in the previous embodiment, the best possible position of the railway vehicle corresponds to the possible position with the shortest temporal distance to each satellite, that is to say the possible position that minimizes the difference between the maximum and minimum temporal distances to each satellite. From this best possible position, a common error can be calculated, which is equal to the average of the temporal distances to each satellite.

[0097] The correlation result calculated for each possible satellite and each possible timestamp is corrected using the common error at step 406. The corrected correlation result may be found by interpolating the early, instantaneous and late correlation results for each possible position, each timestamp and each satellite using, for example, Newton interpolation, the corrected correlation value being given by the interpolated correlation results at an instantaneous position equal to the timestamp offset by the common error value.

[0098] Then, a multi-satellite likelihood is calculated for each possible current position and each possible timestamp as the sum of the squares of the corrected correlation results for each satellite. Finally, by comparing the multi-satellite likelihoods, the most likely position among the multiple possible current positions and the most likely timestamp among the multiple timestamps are determined, respectively. For example, the most likely position and the most likely timestamp may correspond to the maximum value of the multi-satellite likelihoods. If the positioning signal is broadcast from a satellite 201 belonging to a common satellite constellation 200, the most likely position is the final most likely position.

[0099] This position is unique because the correlation results used to determine the position have been corrected for common errors.

[0100] In one embodiment of the present invention, the positioning process may further include the following steps: if the railway vehicle is stationary, determining the parking track on which the railway vehicle is parked by accessing the map database 113 .

[0101] In another embodiment of the present invention, the positioning process may further include the following steps: if the railway vehicle is moving, determining the section of the track on which the railway vehicle is positioned by accessing the map database 113 .

[0102] It should be noted that the functions, actions and / or operations specified in the flow chart, sequence diagram and / or block diagram can be reordered, processed continuously and / or processed simultaneously according to the embodiments of the present invention. In addition, any flow chart, sequence diagram and / or block diagram may include more or less blocks than those shown according to the embodiments of the present invention.

[0103] Although embodiments of the present invention have been illustrated by the description of various examples, and these embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative methods, and illustrative examples shown and described.

Claims

1. A positioning device (110) configured to determine the position of a vehicle from a positioning signal broadcast by at least one satellite constellation (200), the vehicle being stationary or moving on a road of a given network (300), the positioning device (110) comprising: - a first unit (111) configured to determine a plurality of possible current positions of a vehicle at a given measurement time and to determine a plurality of time stamps, the plurality of time stamps being determined within a given time interval, the first unit (111) being further configured to: o generating a local copy of the positioning signal for each possible current position of the vehicle, each local copy being associated with an early point, a current point, and a late point of each of the plurality of time stamps and being associated with an in-view satellite of the at least one satellite constellation (200); o receiving, at each of the plurality of timestamps, a positioning signal broadcast by at least three in-view satellites (201) of the at least one satellite constellation (200); o for each possible current position of the vehicle, for each timestamp of the plurality of timestamps and for each satellite in view, processing a correlation function between the positioning signals received at an early point, an immediate point and a late point and the corresponding generated local copies; - a second unit (112) configured to: oFor each satellite, use the correlation results to determine the common error for all satellites, o for each satellite, each position and each timestamp, determining a corrected correlation result using the common error and the early, current and late points of the correlation result, o for each possible current position of the vehicle, determining a multi-satellite likelihood, each multi-satellite likelihood being determined from the sum of squares of the corrected correlation results for a given timestamp; o By comparing the multi-satellite likelihoods, a most likely position among the multiple possible current positions and a most likely time stamp among the multiple time stamps are determined respectively.

2. The positioning device (110) according to claim 1, wherein: The steps to determine the common error for all satellites include: -For each satellite: o determine the possible locations with the most relevant results, o from the possible position, draw a line perpendicular to the axis pointing to the satellite, o for each position measure the minimum distance to the line, and o multiplying the minimum distance by the cosine of the satellite elevation angle to obtain the time distance, or -For each satellite and each possible position: o Newton interpolation of the correlation results at the early, immediate and late points of the timestamp with the maximum correlation result, o determine the temporal distance between the instantaneous position of the timestamp and the maximum value of the interpolated correlation, - For each satellite the possible position with the shortest temporal distance is determined and the common error is calculated as the mean of the temporal distances of all satellites for said possible position.

3. The positioning device (110) according to one of the preceding claims, wherein: For each possible current position of the vehicle and for each of the multiple timestamps, processing the correlation function between the positioning signals received at the early point, the instant point and the late point and the corresponding generated local copies includes accumulating multiple correlation results calculated within a given time interval around the early point, the instant point and the late point of the timestamp.

4. The positioning device (110) according to one of the preceding claims, wherein: The positioning device also includes a map database (113) including location information of roads of a given network (300), and the second unit (112) is further configured to determine the section of the road where the vehicle is located by accessing the map database (113) and using the determined most likely location.

5. The positioning device (110) according to claim 4, wherein: The map database (113) also includes a representation of the surrounding environment (400) of the roads of a given network (300).

6. The positioning device (110) according to claim 5, wherein: The first unit (111) is further configured to access the map database (113) to determine one or more propagation characteristics of each received positioning signal, and the first unit (111) is further configured to exclude one or more positioning signals from the basic likelihood calculation based on their propagation characteristics.

7. The positioning device (110) according to one of the preceding claims, wherein: The first unit (111) is configured to determine the plurality of possible current positions by combining a plurality of positioning signals using a PVT technique when the vehicle is moving.

8. The positioning device (110) according to any one of claims 5 to 7, wherein: The first unit (111) is configured to determine a plurality of possible current positions by assigning a possible current position to each adjacent parking road (301) when the vehicle is stationary on a parking road among the plurality of adjacent parking roads (301).

9. The positioning device (110) according to one of the preceding claims, wherein: The first unit (111) is further configured to determine the given time interval based on a time integrity protection radius associated with the at least one satellite constellation (200).

10. The positioning device (110) according to one of the preceding claims, wherein: The first unit (111) is further configured to determine the plurality of time stamps by periodically sampling during a given time interval.

11. The positioning device (110) according to one of the preceding claims, wherein: The first unit (111) is configured to receive positioning signals from two or more satellite (201) constellations (200), the first unit (111) is further configured to process the positioning signals broadcast by each satellite (201) constellation (200), respectively, the second unit (112) is configured to determine a most likely position and a most likely timestamp for each satellite (201) constellation (200), and the second unit (112) is further configured to determine a final most likely position among the determined most likely positions.

12. The positioning device (110) according to claim 12, wherein: The second unit (112) is configured to determine the final most likely position using a selection criterion, the selection criterion being selected from the following selection criteria: - determining the number of satellites (201) of each constellation (200) involved in each most likely position, using the maximum number of satellites (201) in view to determine the final most likely position; or - Given the duration of the time intervals, determining the final most likely position using the satellite constellation (200) associated with the shortest given time interval.

13. The positioning device (110) according to one of the preceding claims, wherein: The second unit (112) is further configured to generate an alert notification if the most likely position of the vehicle cannot be determined within the predefined time interval.

14. A method for determining the position of a vehicle using positioning signals broadcast by at least one satellite constellation (200), the method comprising the steps of: - determining (401) a plurality of possible current positions of the vehicle and determining a plurality of time stamps within a given time interval; - generating (402) a local copy of the positioning signal for each possible current position of the vehicle, each local copy being associated with an early point, an immediate point and a late point of each of the plurality of timestamps and being associated with a satellite in view of the at least one satellite constellation (200); - receiving (403) at each of said plurality of timestamps a positioning signal broadcast by at least three in-view satellites (201) of said at least one satellite constellation (200); - for each possible current position of the vehicle, for each timestamp of the plurality of timestamps and for each satellite in view, processing (404) a correlation function between the positioning signal points received at an early point, an immediate point and a late point and the corresponding generated local copies; - using the correlation results to determine (405) the common error for all satellites; - for each satellite, each position and each timestamp, correcting (406) the correlation result using the common error and an early point, a current point and a late point of the correlation result, determining a multi-satellite likelihood for each possible current position of the vehicle, determining each multi-satellite likelihood from the square of the corrected correlation result for a given timestamp, and determining, by comparing the multi-satellite likelihoods, a most probable position among the multiple possible current positions and a most probable timestamp among the multiple timestamps, respectively.

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