Method for locating a vehicle on a predefined trajectory, computer program and associated device

Abstract

The invention relates to a method for locating a train (4) moving on a set of tracks (V1,V2) on which virtual beacons defined by their geographical coordinates are distributed and equipped with an on-board satellite receiver receiving geopositioning signals from satellites S1, … ; Ss for each beacon Bj, j = 1 to N and each satellite Sk, k = 1 to s: calculation of the correlation delay, between the geostationary signal received by the satellite receiver from Sk and the theoretical geostationary signal calculated as having to be received from Sk in Bj; a representative value of the correlation delay is converted into a distance, by multiplying this representative value by c and dividing it by the cosine elk of the elevation of Sk;A maximum spatial bias is determined, and the values ​​j = 1 to N are compared to a predefined threshold MSBREF: following this comparison, if only one beacon has a maximum spatial bias less than MSBREF, this beacon is then detected as the one at which the train is located. Figure for the abbreviation: Fig. 1;

Description

Title of the invention: Method for localizing a vehicle on a predefined trajectory, computer program and associated device. Technical field

[0001] The present invention relates to the field of position estimation carried out by satellite geolocation, by a satellite positioning system also designated by the acronym GNSS (for Geolocation and Navigation by a Satellite System). Previous technique

[0002] Two categories of GNSS positioning are distinguished: absolute positioning, where location is determined solely by GNSS pseudo-distances without any external information, and differential or relative positioning, where positioning is determined relative to a reference (ground reference stations). The latter includes solutions such as PPP (Precise Point Positioning), RTK (Real-Time Kinematic Positioning), or SB AS (Satellite Complement to a GNSS System).

[0003] To achieve the required Safety Integrity Level performance levels, SIL4, a ground infrastructure is currently required (including actual beacons).

[0004] The applicant has previously developed a positioning solution based on a correlation calculation between a received GNSS signal and a predicted PRN code for a known position on georeferenced virtual beacons: without errors, a maximum correlation power should be observed for the assumption of the position closest to the receiver, allowing the detection of the possible positions of the virtual beacons closest to the receiver.

[0005] The absolute accuracy of a position obtained by a position determination system, traditionally by triangulation of data from satellites and received by a satellite receiver, is subject to errors which can be expressed and summed as follows:

[0006] UERE2 = (E_SIS)2 + (E_Tropo) 2+ (E_Iono)2 +(E_Rx)2 +(E_Multitrajet)2 where

[0007] the UERE (“User Equivalent Range Error”) is the user equivalent range error;

[0008] E_sis represents the errors of the "Signal In Space" i.e. coming from the satellites (satellite clock, trajectory...)

[0009] E_Tropo, respectively E_lono, are the errors related to interferences due to reflections of the SIS on the tropospheric layer, respectively ionospheric layer;

[0010] E Rxsont are the errors specific to the satellite receiver, typically due to measurement noise, phase center and clock bias of the receiver;

[0011] E_Multitrajet are errors due to reflections of the satellite signal on obstacles before reaching the satellite receiver.

[0012] The position error can be modeled and therefore estimated by assuming that all satellites transmit correctly and as a function of the signal-to-noise ratio (SNR); however, this remains a statistical value.

[0013] The types of errors in the satellite-receiver link are also classified as follows, according to where they occur: - "Satellite" errors, due to: clock drift (desynchronization), orbit description (ephemerides), phase center (antenna polarization); - "Propagation" errors, due to: ionospheric delay (layer of the atmosphere from ~80 to 1,000 km altitude, effects related to the presence of free charges), tropospheric delay (layer from 0 to ~80km altitude, effects mainly related to meteorological conditions); - "Reception" errors, due to: measurement noise, phase center, clock bias; - “Local” errors due to: multipathing, decoying.

[0014] There is a need for a reliable location solution that is applicable in particular to the constraints of the railway sector. Summary of the invention

[0015] According to a first aspect, the present invention describes a method for locating a vehicle adapted to move along a set of predefined trajectory(ies),

[0016] a satellite receiver onboard the vehicle being adapted to receive at a instant t of geopositioning signals from a satellite system comprising at least s satellites Sk, k=l to s and s greater than or equal to 3;

[0017] an electronic processing unit comprising a database storing the geographic coordinates Pj of virtual beacons Bj, j = 1 to N, distributed along the trajectories of said set of trajectory(ies);

[0018] said method comprising the following steps implemented by the electronic processing unit at a given time t of location:

[0019] it / for each tag Bj, j = 1 to N:

[0020] - for each satellite Sk for k = 1 to s: • Calculation of the delay between the geostationary signal received by the satellite receiver at time t from the Sk satellite and the theoretical geostationary signal calculated as expected to be received from the satellite Sk at time t at the position of the virtual beacon Bi as defined by the geographical coordinates Pj of Bj in the database, said delay being called correlation delay, X ( S& Bj); a representative value of the correlation lag X ( Bj ) is converted into a corresponding distance, called spatial bias, by multiplying this value represents the correlation delay X(Bj) by c, velocity of light in a vacuum and dividing it by cos elk, where elk is the elevation of the

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027] Sk satellite; - for each beacon Bj, j = 1 to N, a maximum spatial bias MSBbj is determined: MSB gy = MAX^Jà^s*} i2 / The maximum spatial biases MSB^y, j= 1 to N are compared to a predefined threshold MSBref: following this comparison, if only one beacon has a maximum spatial bias If MSBb is less than MSBref, this tag is then detected as the one at the level of which the device is located at the time of location. The proposed innovation uses the principle of correlation with estimation of the best position based on correlation delay measurements. This approach thus guarantees autonomous measurement integrity, i.e., without any additional sensors or installations other than the GNSS receiver, and is therefore perfectly suited to railway navigation. The advantage conferred by the use of correlation delays is that, rather than identifying the nearest beacon as the one maximizing the correlation power (for example via ArgmaxB^k=lCorr(Sh Bj, where Corr^S^, Bj, t ) 2est 'c maximum of the correlation signal power), we This eliminates the bias due to the fact that the level of correlation depends on the power received, while the correlation lag is independent of it. The invention therefore proposes a reliable positioning solution, allowing to reduce errors and it also takes into account a protection radius defining a maximum limit of tolerable precision error. In some embodiments, such a process will further include at least one of the following features: - one of the following provisions is also implemented by the processing block in step i2: - i2_l / if only two tags have their largest spatial bias less than MSBREpet, since they are adjacent on the same road, it is considered that the device is located between the two beacons; - i2_2 / if more than one tag has a greater maximum lower spatial bias to MSBREF (optionally outside the case just above): an ambiguity situation is detected and it is considered that localization cannot be performed; - i2_3 / if only two tags have their greatest spatial bias less than If MSBREpet and they are adjacent on the same track, it is considered that the device is located between the two beacons; outside of this case, if more than one beacon has a greater maximum spatial bias less than MSBj^p, it is considered that the localization cannot be carried out; - c i2_4 / if no beacon has a greater maximum spatial bias MSBgy pos less than MSBRFFj this indicates the existence of defective satellites, an ambiguity situation is thus detected and it is considered that localization cannot be carried out;

[0028] - steps i1 and i2 are iterated relative to each subset of satellites comprising s-1 of the s satellites instead of the s satellites considered in the previous iteration for s>5, when, following said comparison of the previous iteration, only one beacon had a maximum spatial bias MSBgj less than MSBRFF and

[0029] if at the current iteration, for each of the subsets of satellites, the comparison step detects the same single beacon as at the previous iteration corresponding to a given level of integrity, said beacon is considered to have been detected with said given level of integrity increased by one;

[0030] - steps i1 and i2 are iterated relative to each subset of satellites comprising s-1 of the s satellites instead of the s satellites considered in the previous iteration for s>5, and if in the previous iteration, no beacon had a greater maximum spatial bias MSB^L!X,s less than MSBRu and in the current iteration, only one beacon has a maximum spatial bias MSBgj less than MSBRFF, this beacon is then detected as the one at which the craft is located at the time of localization and the satellite seme is identified as faulty;

[0031] - said representative value of the correlation lag X(S Bj) is equal to the difference between said correlation lag X(Bj) and a bias named BCBj, which is an estimate of the temporal bias associated with the Bj beacon and common to all satellites and allowing to minimize MSB^y;

[0032] said representative value of the correlation lag X ( SBj ) is equal to the difference between said correlation lag X ( Bj ) and a bias named BCBj = ^k=ï A BJ^k '

[0033] The processing block implements one of the following provisions ila, ilb, ilc, to, considering the tag Bi, implement the step il of calculating the delays, X(Sk, Br t) for k= 1 to s:

[0034] ila / calculation of the correlation between said received geostation signal and said theoretical geostation signal calculated in B;, said delay B(, t) being calculated as a function at least of said calculated correlation;

[0035] ilb / the delay X^*, Bh l) is calculated, by translation, using the following formula:

[0036] X(SÆ, B{, t) = Bq, t) + g respectively SjA, is the distance between satellite Sj, and a reference beacon Bo, respectively the distance between satellite Sk and beacon B,.

[0037] O is the delay between the geolocation signal received by the receiver satellite at time t from satellite Sk and the theoretical geostationary signal calculated as being received from satellite Sk at time t at the position of the virtual beacon Bo as defined by the geographic coordinates PO of Bo in the database,

[0038] c is the speed of light in a vacuum;

[0039] ilc / the delay Bp t) is calculated, by translation, using the following formula:

[0040] X(Bp t) = x(Sh Bq t) + ds^o^eQ / 0.3

[0041] where Boest is a reference tag,

[0042] Ala = latitude (Bo) - latitude (B;), Alo = longitude (B0) - longitude (B;) a = arctan (Ala / (Alo * cos (latitude (Bo) ))

[0043] [3 = azk + a

[0044] ds = d * sin([3]

[0045] where latitude(), longitude() are the coordinates in an orthogonal frame in the local tangent plane;

[0046] - the processing unit implements at least one of the following provisions 4.1, 4.2:

[0047] 4.1 by implementing provision ila, X(SÂ, Bm, t) and XfS^, B02, t) are calculated; then considering BOi as a reference beacon and by implementing one of the formulas in ilb or ilc, the delay in #02 is determined this time by translation considering Boi as a reference beacon and is named X^S^ S02, t)01;

[0048] and depending on at least the difference between X(S^, B02, t) and X / S^ ÆO23)oi, the satellite Sk is excluded from the set of satellites taken into consideration for step i3 of estimating the location of the craft as a function of said representative values ​​of differences between said calculated delays;

[0049] 4.2 perform the next step for tags Bi, i = 1 to r:

[0050] by implementing one of the formulas in ilb or île: a first delay Bp t)01 is determined by considering BOi as a reference beacon and a second delay X( Bp l ) 02 is determined by considering B02 as a reference beacon;

[0051] and depending on at least the differences between X(Bp t) 01 and X(Bp t) 02 i = 1 to r, the satellite Sk is excluded from the set of satellites taken into consideration for step i3 of estimating the location of the craft as a function of said representative values ​​of differences between said calculated delays;

[0052] - each beacon considered is spaced from its nearest neighbors by a distance D equals the distance between two neighbouring lanes and the predefined threshold MSBREF is taken as equal to D / 2.

[0053] According to another aspect, the invention describes a computer program intended to be stored in the memory of an electronic device further comprising a microcomputer, said computer program comprising instructions which, when executed on the microcomputer, implement the steps of a process according to the invention.

[0054] According to another aspect, the invention describes an electronic processing block for the localization of a vehicle adapted to move on a set of predefined trajectory(ies) and carrying a satellite receiver to receive at a time t geopositioning signals from a satellite system comprising at least s satellites Sk, k=l to s and s greater than or equal to 3;

[0055] the electronic processing unit comprising a database storing the geographic coordinates Pj of virtual beacons Bj, j = 1 to N, distributed along the trajectories of said set of trajectory(s);

[0056] said electronic processing unit being adapted to implement the following operations, at a given time t of location:

[0057] it / for each tag Bj, j = 1 to N:

[0058] - for each satellite Sk for k = 1 to s:

[0059] calculation of the delay, between the geostationary signal received by the satellite receiver at time t from the satellite Sk and the theoretical geostationary signal calculated as having to be received from the satellite Sk at time t at the position of the virtual beacon Bi as defined by the geographic coordinates Pj of Bj in the database, said delay being named correlation delay, X ( Bj );

[0060] a representative value of the correlation lag X ( Bj ) is converted into a corresponding distance, called spatial bias, by multiplying this value representative of the correlation delay X ( Bj ) by c, speed of light in a vacuum and dividing it by cos elk, where elk is the elevation of the satellite Sk;

[0061] - for each tag Bj, j = 1 to N, a maximum spatial bias MSBgj is determined: 100621 MSBb,=

[0063] i2 / the maximum spatial biases MSBgy, j= 1 to N are compared to a predefined threshold MSBref: following this comparison, if only one beacon has a maximum spatial bias MSBb / less than MSBref, this beacon is then detected as the one at which the device is located at the time of localization. Brief description of the drawings

[0064] The invention will be better understood and other features, details and advantages will become clearer from the following description, given by way of non-limiting reason, and from the accompanying figures, given by way of example.

[0065] [Fig-1] Fig.1 schematically represents a railway system putting in works a method of embodiment of the invention;

[0066] [Fig.2] The [Fig.2] represents steps of a position determination method 100 in an embodiment of the invention;

[0067] [Fig.3] Figure 3 illustrates the relationship between temporal bias ATgj (= X ( S& Bj, t ) ) and spatial error";

[0068] [Fig.4] Fig.4 represents the values ​​taken by a correlation function in an example;

[0069] [Fig.5] The [Fig.5] represents steps of a position determination method 100 in an embodiment of the invention;

[0070] [Fig.6] The [Fig.6] illustrates the geometric model considered;

[0071] [Fig.7] Fig.7 also illustrates the geometric model under consideration;

[0072] [Fig.8] Fig.8 represents a local tangent frame of reference used in one of the modes of realization of the invention;

[0073] [Fig.9] The [Fig.9] illustrates the determination of spatial biases for a beacon as considered in step 105;

[0074] [Fig. 10] The [Fig. 10] illustrates the common bias correction for a beacon and the maximum spatial bias determined for this beacon as considered in step 105;

[0075] [Fig. 11] The [Fig. 11] is a flowchart defining the sequence of TESTS 1, 2 and 3 in an embodiment of the invention;

[0076] [Fig. 12] The [Fig. 12] represents "correlation lines";

[0077] [Fig. 13] The [Fig. 13] illustrates the grouping of the beacons into trajectories in one implementation mode of the invention;

[0078] [Fig. 14] The [Fig. 14] schematically represents a treatment carried out in the case of a moving train (so-called dynamic case).

[0079] Identical references may be used in different figures when they refer to identical or comparable elements. Description of the implementation methods

[0080] With reference to [Fig. 1], a railway system 1 in an embodiment of the invention comprises one or more trains, including train 4 shown in [Fig. 1], which are adapted to move along a predefined trajectory or various predefined trajectories. Each of these trajectories is represented by a series of track segments (for example, left-hand rail segments, right-hand rail segments, or even virtual segments arranged between the left-hand and right-hand rails...).

[0081] Train 4 includes an on-board electronic processing unit 10, which comprises: - an Rx unit 11 including a standard GNSS satellite global positioning system, - an electronic location block 121, - a topographic database 13.

[0082] In [Fig.1], segments of r respective channels Vj, V2, ..., Vr are represented.

[0083] Hereafter, a position will be called a "virtual beacon" or simply a "beacon", B. predetermined, or reference point, whose spatial coordinates are precisely known. The beacons are distributed on the track segments, for example on the line centered between the 2 track rails, or close to the track, for example less than 50 cm from this line.

[0084] For example, the distance between two neighbouring lanes being equal to D, the beacons are spaced from their nearest beacons on the same lane by a distance equal to D, with D here equal to 4 m for example (in other embodiments, this distance is less than 4 m, for example equal to 2 m).

[0085] The track segments and markers are finite in number. Their 3D geographic position (relative to a terrestrial reference frame) and their characteristics are known and are referenced in the topographic database 13. These characteristics include, for example: segment identifier, marker identifier, segment length, segment heading (also called track heading), association between segment identifier and identifier of markers located on (or in the immediate vicinity of) the segment, value of geometric parameters, for example, clothoid or spline, chaining characteristics in the railway network (for example: identifier of successor and predecessor segments).

[0086] The Rx 11 block, onboard train 4, is adapted to receive geopositioning signals from a synchronized local time base, emitted by a set 20 of GNSS geopositioning satellites: Si 20_l, ..., Ss 20_s, in Visibility of block Rx 11. Depending on the embodiment, s = 1 or s > Nsat, with Nsat equal to 2, 3, 4 or 5.

[0087] GNSS satellites include, for example, satellites of the American GPS (Global Positioning System) and / or the European GALILEO system and / or the Russian Glonass system, and / or the Chinese Beidou system or any other equivalent system. The positions of the satellites, which may change over time, are predetermined and known to the Rx 11 receiver (via ephemeris data).

[0088] In a known manner, the GNSS receiver in the Rx 11 block is adapted to perform a baseband frequency downsampling from the received signals, to demodulate the signal and extract a geopositioning signal comprising the repetition of a 1023 Hz code. It is this signal in this form which is then referred to as the "received signal" below and which is used, for example, for correlation calculations.

[0089] For example, in a known way, the GNSS receiver is further adapted to extract time and delay information from PRN code (Pseudo Random Noise, used on Galileo and GPS) and to calculate, for each satellite in sight, from this received information, an estimate of the distance between the geolocation device itself and the satellite in sight, also called pseudo-distance.

[0090] The pseudo-distance differs from the actual distance between the satellite in question and the geolocation device due to the errors mentioned above: propagation time estimation errors, due, for example, to atmospheric conditions in the troposphere and ionosphere, and the synchronization error of the geolocation receiver's internal clock. However, it is possible to eliminate common errors (including the receiver's time bias) by relying on information transmitted by a plurality of separate satellites.

[0091] For example, the PRN code of the C / A (Coarse Acquisition) signal in the case of GPS is a digital signal composed of 1023 chips and repeats every millisecond. It should be noted that the term "chip" used in GNSS techniques is distinct from the term "bit," which is used to define a unit of information. The code has a given code length, denoted L(C!A). Its temporal length is 1 ms, and therefore its spatial length is 1 ms * c, where c is the speed of light. From this, we deduce a temporal chip length of 1 ms / 1023.

[0092] The localization block 121 is adapted to estimate the position of the train 4 considered at time t.

[0093] Depending on the embodiment, this location estimation takes different forms. For example, in one embodiment, it includes determining the position of the estimated beacon closest to train 4 and / or the coordinates geographical of the receiver Rx; in one embodiment it allows the validation or not of a previously determined positioning hypothesis; in one embodiment it allows the identification of the track segment on which the train is a priori positioned (being certain of the train's track is indeed a major safety element to avoid accidents).

[0094] The location estimation is carried out, according to the invention, based in particular on the satellite positioning signals received by the Rx 11 block in its position to be estimated, and furthermore, in embodiments, based for example on measurements from an on-board inertial measurement unit and / or based on measurements by an odometer.

[0095] Method for determining position according to the invention, based on correlations between predicted signals relating to virtual beacons and received signals

[0096] With reference to [Fig.2], a method 100 for determining the position of the train 4 at time t is implemented by the processing block 10; it comprises a set of steps 101 to 105, exploiting the received GNSS signal and the prior knowledge of the positions of the fixed and predetermined virtual beacons B provided by the topographic database 13.

[0097] Such a process exploits the fact that the trajectory of train 4 necessarily follows the segments of railway track, which are known and on which there are markers.

[0098] The processing is implemented by correlation of the GNSS signal received, by the Rx block 11, at the local reference date t of the GNSS receiver, from the various visible satellites Sk, k = 1 to s (s being, according to the embodiments, the maximum number of available satellites or a subset), with each of the expected code signals (replica code signals) from these satellites at the same local reference date t of the GNSS receiver, and calculated for the position P; of a virtual beacon B;.

[0099] Depending on the case, the beacons considered B;, i = 1 to N, are either the set of beacons B, or a strict subset of this set of beacons B (therefore comprising a reduced number of beacons and determined taking into account certain basic assumptions considered known: train 4 located on a stopping track or a departure track or a running track, in a restricted geographical area, etc.). The beacon B; is located at P;, a 3D geographical position, recorded, in association with B;, in the base 13.

[0100] In one embodiment, the processing block 10 comprises a processor and a memory, in which software instructions are stored, which, when executed on the processor, implement the steps of the process 100.

[0101] Thus, in step 101, the theoretically received signals (replica signals) at time t at the level of each considered beacon B;, Cca}cBiSk(t) ■> from each satellite Sk in view of the beacon are predicted by the localization block 121 (because as the position of the beacon is known, the travel time of the satellite signal to the beacon is known).

[0102] During the generation of local GNSS replicas of the expected codes, errors are taken into account using available error models, i.e., the known clock error, ionospheric error, and tropospheric error models. These error models can be provided by the onboard GNSS receiver or via an assist link, and allow errors in the expected satellite distances to be reduced to a few meters.

[0103] It is assumed that the residual errors on the code delay after application of the corrections are centered Gaussian (in one embodiment, the validity of this assumption is then tested in an integrity proof).

[0104] In step 102, at time t, the RX11 block receives, in its current position, the signals (O sent by the Sk satellites, k = 1 to s and provides them to the location block 121.

[0105] In step 103, for beacon B; and each satellite Sk, the correlations between predicted signals Cca[c ( t ) and signals C^xsk ( ^ ) received at time t by the Rx block 11 are calculated by the localization block 121.

[0106] Correlation functions are calculated for beacon B; and for satellite Sk - at least for a number of values ​​taken by T: [01 ° 7] pg( T ) =

[0108] (the integration interval is for example fixed at the value T, typically equal to at least the duration of a navigation bit, i.e. 20 ms or 20 PRN code lengths).

[0109] In step 104, for beacon B; and for satellite Sk, the localization block 121 then estimates the value of T in which the correlation function t ) reaches its maximum; this value, which is the correlation lag between the two signals ccalcBiyM and signals C^kiest named B,, t).

[0110] The code delay X(Sk. B,, t ) thus obtained is actually composed of a propagation error term and residual error term, as well as a geometric term dependent on the distance between the beacon and the receiver, and on the azimuth and elevation of the satellite considered.

[0111] In step 105, based on the code delays at time t considered, thus estimated X(Sk. Bk t) for the considered beacons B, i = 1 to N and for the considered satellites Sk, k = 1 to s: the localization block 121 estimates the location of train 4, in the manner described below, named MSP solution (from the English "Maximal Spatial Protection"), after the presentation of elements relating to the geometric model and the measurement model which are used by this solution.

[0112] Example of position search when the train is stopped, on a siding or departure track (so-called static case):

[0113] In such a case, for the implementation of algorithm 100, only the markers (or a subset of these markers) of base 13 that are identified therein as being located on segments of sidings or departure tracks are considered. These subsets of markers are therefore, in this case, the markers B;, i=l to N.

[0114] Fig. 4 presents a one-dimensional graphical representation, as a function of time represented on the abscissa, of a correlation function mentioned above, schematically represented on the one hand in the form of a triangle, although in reality, under the impact of noise, this function takes on the appearance of a curve represented by a dotted line and considered as a parabola (parabolic interpolation) in the area of ​​vertex 26.

[0115] The duration 24 is typically the duration of a chip of a GNSS code sequence (typically for GPS one chip corresponds to Ips, i.e. 300m).

[0116] This correlation function has a maximum 26, as determined, with abscissa tijk, which is therefore the code delay. In some embodiments, an interpolation is further performed to better estimate the position of the maximum.

[0117] In embodiments, when calculating the values ​​of the correlation function for the beacon B; and the satellite Sk, i = 1 to N and k = 1 to s, the following steps are carried out (using in particular three multiplier modules and three integrator modules): - a convolution product is performed: the received satellite signal C^xk (D is multiplied by the replica signal Ccalc ( t ) which is the a priori replica perfectly aligned with the code (if the train is positioned at Pi and in the absence of uncompensated errors), then the result is integrated: the output value, named Prompt (P), is representative of the correlation between these two signals; - The received satellite signal Cft\k(t) is multiplied by the advanced replica signal Cculc Bik (^ + ^). The result is then integrated: the output value, named Early (E), is representative of the correlation between these two signals; for example, the positive value 5 is equal to 7.5 ns (the idea being to have a predefined Early-Late interval that is representative of the required accuracy, particularly for channel detection; the channels being considered

[0118]

[0119]

[0120]

[0121]

[0122]

[0123]

[0124]

[0125]

[0126]

[0127]

[0128] spaced 4m apart, i.e. 15ns in temporal terms, we choose here for example a gap of 15ns between the Early and Late points). - The received satellite signal C^xk(O) is multiplied by the delayed replica signal Ccalc Bik(J) and then the result is integrated: the output value, named Late (L) is representative of the correlation between these two signals; - in embodiments, in order to obtain more points of the correlation function, additional advanced and delayed replica signals of the offset values ​​<51, <52, are for example also multiplied and integrated. In what follows, we assume that Doppler is perfectly understood. Geometric model The correlation delay X ( S^. Bj, t ) corresponds to the code delay measured between the signal received by the receiver Rx from the satellite Sk and the signal predicted at the level of a beacon Bj considered. In the absence of propagation error, satellite error, receiver error and local errors, X(5„ t) is therefore the difference in travel time between the satellite-beacon path and the satellite-receiver path. We then have vZ in ., i / oncr» j for the Sk satellite and the Bj beacon. With X ( Bj, t ) = ë{SkBj - SkKx)r From a geometric perspective, this relationship can be expressed to the first order as a function of the distance between the receiver and the beacon. With reference to [Fig. 6], by naming: - Hk the orthogonal projection of the position of Sk in the local plane tangent to the earth at the location considered (and for example associated with the NED (“North, East, Down”) or ENU (“East (E), North (N), Up (Z)” frame: see in [Fig.8]), - elk is the elevation of the Sk satellite and azk' is the relative azimuth of the Sk satellite with respect to the line between the Bj beacon and the Rx receiver, we have: I z \ HkBrHkRx B, c being the speed of light in a vacuum. Applying Al-Kashi's theorem to triangle HkBkRk, we obtain: HkRx = r x b s 1 +

[0129] The radical expands to the first order, which gives: HtRx « H^j-co^az^^Bf

[0130] and now considering the equation above for X ( Sk, Bj, t):

[0132] This approximation can be physically considered as an equality given the difference in order of magnitude between the distances SkBj and RxBj. It follows that the delay of the received signal relative to the predicted signal can then be written as:

[0133]

[0134] cos^az'^-RxBj £008¼)

[0135] Case of relative azimuth:

[0136] The relative azimuth, TTïF, can be expressed as a function of the azimuth azk of the OZk - BjBx, BjHk Satellite Sk and runway heading # if the Rx receiver is located on the same track as the beacon Bp azk = 0 - azk (see [Fig.7]).

[0137]

[0138] X^Bj, t) = cos((?-a^ M

[0139]

[0140] This expressed form can be written using a dot product as follows: coslaz\RxB 1 1---s»--a— X ( t ) = = ^BJR^OSsk

[0141] where LOSsk is the line of sight vector (“Line Of Sight”), of unit norm, starting from the beacon Bj (or the receiver Rx, given the distances) and pointing towards the satellite Sk. Measurement model

[0142] The measurement of X(Bj, t) (i.e., the result of the calculation performed in step 104 as a function of the received signal) is affected by errors related to signal prediction and the correlator, coming from several sources including:

[0143] - error in correcting / modeling the propagation of the received signal (ionosphere, troposphere);

[0144] - satellite errors (orbits and satellite clock) impacting weather prediction of emission and satellite position;

[0145] - receiver errors (clock, group delay) for time estimation emission;

[0146] - local errors (multipath, spoofing) lengthening the signal propagation time received ;

[0147] - correlator sensitivity / resolution and correlation noise.

[0148] These errors have spatial and temporal properties that differ, and influence the value of X ( Bj, t) differently.

[0149] The ionospheric and tropospheric correction errors add directly to the difference in geometric travel time, and are locally the same for all beacons.

[0150] By grouping together on one side the errors related to the receiver common to all satellites (brec) and on the other side, the errors specific to each satellite (orbit, satellite clock, ionospheric and tropospheric model error, multipath, ...) which we call bsk and calling X^S^, Bj, t ) the measured value (i.e. calculated from the measurements of the received signal and therefore integrating the errors):

[0151] XtS^t) =iB]RxIÔS^k+brec + bsk

[0152] Principles on which the MSP process is based

[0153] The MSP method is based on the concept of equivalence between the temporal domain and the spatial / geometric domain.

[0154] In what follows, we consider the delay values, X(S^ B j, t), supplied at the output of step 104 for the considered set of beacons Bj, j = 1 to N and the considered set of satellites Sk, k = 1 to r, for a location determination instant t.

[0155] The delay value, X ( S^, Bj, t ) , between the received signal and the predicted signal from the satellite Sk at the level of a beacon Bj, is a temporal bias; it is renamed ATÿj. It can be 'projected' and thus converted into a distance in the plane of the trajectories, which will be called "spatial bias" AS^j^k-. This spatial bias is a distance which is a function of the position of the satellite Sk in the sky (with an elevation, denoted eld) and the speed of light c (on the one hand, the relation Speed ​​= Distance / Time is exploited; on the other hand, taking into account a cos(elk) applies a correction to take into account the sensitivity of the error as a function of the elevation of the satellite).

[0156] It is defined by the following equation in the case of a Bj beacon and a Sk satellite:

[0157] AÇ

[0158] Figure 3 graphically illustrates this relationship, with train 4, whose position is being sought, located at Bo. Aspects relating to satellite Si are represented by solid lines, those relating to satellite S2 are represented by dashed lines.

[0159] On this [Fig.3]:

[0160] - AT g lçj represents t), the time delay between the maximum of correlation for the received signal and the predicted signal for the Si satellite at the Bi beacon;

[0161] - PI belonging to the line of maximum correlation of SI, a correlation maximum for SI is measured in PI, i.e. the delay between predicted signal and received signal is zero;

[0162] - represents the spatial bias associated with the measured temporal bias AT

[0163] MSP Solution

[0164] The process implemented in step 105 by the localization block 121 according to the invention, called the MSP process (for reference, from the English "Maximum Spatial Protection"), comprises the operation of determining, as a function of the correlation delays determined Bj, t), at time t, for i=laNetk=làs, the beacon closest to the receiver as being that of the beacons satisfying the following conditions:

[0165] - the beacon must correspond to a distance (spatial bias) less than a threshold predefined, lines of maximum correlation after correction of a bias assumed to be common to all satellites.

[0166] - the beacon must also be the only one, among the beacons, to ensure a distance below the predefined threshold, lines of maximum correlation, after correction of a bias assumed to be common to all satellites.

[0167] The predefined threshold, referred to here as MSBref, is for example set at half the distance D separating two adjacent beacons (the threshold value is considered the positioning protection range; for a cold start, it must be equal to half the distance between the track and its adjacent track, to determine the track safely). In the case considered here, MSBref is equal to 2m.

[0168] With reference to [Fig.5], in an embodiment of the MSP process executed in step 105, a first test, named TEST 1, is carried out during a step 1051.

[0169] During this step 1051, substeps 1051_1 to 1051_5 are implemented by the localization block 121 (this amounts to studying each hypothesis corresponding to "each beacon is the one in which the receiver 11 is positioned").

[0170] In substep 1051_1, for each BjConsidérée beacon, the value, named BCBj, of the temporal bias associated with the beacon and common to all satellites allowing to minimize the largest corresponding residual spatial bias, is estimated.

[0171] In substep 1051_2, for each BjConsidérée beacon, the residual spatial bias (after common bias correction), named for each satellite Sk, is determined: 101721 A cc <ATBjSk-BQyj, pour k = 1 à s co^

[0173] In substep 1051_3, for each BjConsidérée tag, the distance corresponding to the largest residual spatial bias (after correction of the common bias), named MSBBj (for the English "Maximum Spatial Bias") is now determined: 101741 MSB gy = MAX fcl JàS w ]

[0175] In substep 1051_4, the largest residual spatial biases of the MSBgj tags are compared to the predefined threshold MSBref (among the set of tags, only one, Bj_pos, is assumed to have a larger residual spatial bias MSBgj poS lower than MSBref).

[0176] In substep 1051_5, test TEST 1 is performed to validate the correct correspondence between bias detection and topography geometry (base 13): - if only one beacon, Bj pos has a greater residual spatial bias MSB^y less than MSBref, this beacon is then considered to be the one at which the receiver 11 is located at time t (successful beacon detection situation); and in one embodiment, the following TEST is performed if the number of satellites currently considered is greater than or equal to 5, to obtain a higher level of integrity where appropriate; - if no beacon has a greater maximum spatial bias less than MSBref the position of receiver 11 cannot be determined in this way (in this case, there was therefore no detection of beacon); in one embodiment it is considered that one or two satellites are faulty and in another embodiment the following TEST is carried out if the number of satellites currently considered is greater than or equal to 5; - in one embodiment, it is considered that if only two beacons have their greatest spatial bias less than MSBREF and they are adjacent on the same track, it is considered that train 4 is located between the two beacons (this corresponds to the case (or other) in the legend in [Fig. 11]); - in one embodiment, if more than one beacon has a maximum spatial bias less than MSBref (optionally outside the case just above): an ambiguity situation is thus detected and it is considered that localization cannot be carried out (this situation typically indicates an unsatisfactory satellite distribution).

[0177] Different methods are applicable for determining the common bias of substep 1051_1, for the Bj beacon. In one embodiment, the common bias BCBj is taken to be equal to the average, calculated over all satellites, of the temporal bias for the Bj beacon: BCBi = VS a • In another embodiment, all the values possible integers of common temporal bias are tested (the range of possible values ​​extends from the minimum ATg^k to the maximum ATg^k, among the AT^sk- k = 1 to s); for each common bias hypothesis, the residual temporal biases are converted into spatial biases; then, the maximum spatial bias is retained; subsequently, the algorithm retains the hypothesis of temporal bias which allows to minimize the maximum spatial bias (MSBBj).

[0178] Substeps 1051_1 and 1051_2 are optional.

[0179] In one embodiment of the MSP process, with reference to [Fig.5], the test following TEST1, named TEST 2, is carried out: during a step 1052, the corresponding previously carried-out steps 1051_1 to 1051_5 are then repeated, this time considering one by one each of the subgroups of satellites having one less satellite than the set of satellites considered for 1051_1 to 1051_5 relating to TEST 1.

[0180] In addition, it is verified that all these subsets of satellites detect the same beacon as in the previous test where applicable, otherwise there is a situation of ambiguity and TEST 2 is considered unsuccessful (i.e. location not detected).

[0181] If no beacon was detected in the previous level test, but a beacon is correctly detected in TEST 2 by removing a satellite, that satellite is considered to be faulty and the detection is considered to be successful with an integrity of level 1.

[0182] If no subset satisfies the 2m criterion, then the test fails.

[0183] In one embodiment of the MSP process, with reference to [Fig. 5], another test, TEST 3, is performed during step 1053, after step 1052 relating to TEST 2, for s initially considered greater than or equal to 6, and if the result of test 2 concluded with the detection of zero, or only one, beacon with MSB < 2m. The principle is the same as for TEST 2, but the subsets of satellites considered comprise s-2 satellites and no longer s-1 satellites.

[0184] A flowchart of an example of the sequence of tests 1, 2, 3 is shown in [Fig.1 1], in an embodiment of the invention, for an MSBref = 2 m.

[0185] The MSP solution ensures a protection radius of MSBref value, (here equal to 2 m) around each beacon.

[0186] The verification of satisfaction of the protection radius criterion (equal to MSBref here 2m) is common to the 3 successive test levels considered in the described embodiment: it aims to verify whether there is indeed a single, unique beacon whose satellite correlation lines are at a distance of less than 2m (after, in the considered embodiment, correction of the assumed common bias). Test levels 2 and 3 are variants with the addition of detection consistency for all satellite subgroups.

[0187] In the embodiment described above, tag detection is associated with a confidence level regarding integrity. Indeed, the MSP process considered here consists of a maximum of 3 successive tests. For each test, there are actually 3 possible results, not just a binary KO or OK result; the 3rd result is where no beacon verifies that its MSB <2m; or, in short: - Result 1: "Success" (= test OK): when there is only one beacon with MSB < MSBref or when only two successive beacons (e.g., along the track) have MSB < MSBref - Result 2: "Ambiguity" (= KO test): when more than two tags (not corresponding to the previous case) have MSB < MSBref - Result 3: "Overflow" (indicating the existence of defective satellite(s)): when no beacon with MSB < MSBREf

[0188] In step 1051 of test 1, it is only in this case of 3rd outcome and in the OK case, that we proceed to test 2.

[0189] In Test 2, the processing of satellite subsets must yield the same result for all subsets. Successful detection of a subset increases the integrity of the detection and proceeds to Test 3. If ambiguous cases are detected, processing is stopped at integrity level 1. If an Overflow result occurred in Test 1, and if, for a subset of s-1 satellites, only one beacon is found with MSB < MSBref, this indicates that a defective satellite is detected (the one among the s satellites not belonging to this subset of s-1 satellites). This provides a method for detecting defective satellites. If a defective satellite is detected, processing continues with Test 3. If, for all subsets considered in Test 2, MSB > MSBref, this indicates the existence of two defective satellites, and processing continues with Test 3.

[0190] The integrity level of the output solution depends on the number of successful test stages (i.e., those that resulted in detection): - Integrity level 1 corresponds to 1 successful test; - Integrity level 2 corresponds to 2 successful tests (2 tests = OK results in at integrity level 2; for example, we can have test1=OK; test2=No tag<2m and test3=OK if two failing satellites compensate for their errors; - integrity level 3 corresponds to 3 successful tests.

[0191] In other embodiments, only one or two of the three tests are considered.

[0192] If the number of available satellites is sufficient, the MSP solution in the embodiment implemented here also makes it possible to detect and protect against satellite failure, for example against 1 failing satellite (test 2) to 2 failing satellites (test 3).

[0193] Figure 9 illustrates the determination of spatial biases for a beacon as considered in step 105: the beacon considered is beacon numbered 1727 and it is represented the spatial biases for this beacon relative to each of the Sb S2, S3 satellites.

[0194] The MSBREF size protection radius is further shown around the numbered beacon 1523.

[0195] Fig. 10 illustrates the maximum spatial bias determined for the numbered beacon 1727 after correction of the common bias as considered in step 105.

[0196] Figures 9 and 10 represent the tracks in top view, with markers numbered 1522 to 1527 on one track, markers numbered 1724 to 1729 on another track, and markers numbered 404 to 409 on yet another track.

[0197] A complete GNSS positioning solution for the railway industry must include the following features:

[0198] - coldstart (starting position): recover the initial position of the train with identification of the lane;

[0199] - main track positioning: positioning of the train along the track when it travels on the identified lane;

[0200] - resolve the ambiguity of the switch: to identify the track used when a The switch point has been crossed;

[0201] - Retrieve position: Retrieve the position upon exiting the inaccessible area. GNSS, with or without availability of the train's previous position.

[0202] The MSP positioning solution described above was described under the assumption of a stationary train (cold start) with, for example, in one embodiment, the following main steps, as a reminder:

[0203] - correlation calculation, for each beacon considered and each satellite considered, between the received signals and the predicted signals (steps 101-103);

[0204] - for each tag considered, calculate the correlation lag (= temporal bias) of the satellite signal for each satellite (aTr cJ = X(S B- t) (step 104);

[0205] - apply the MSP algorithm (step 105) based on a common error mechanism to detect the position of the train and the problematic satellites.

[0206] For this last step, an accurate measurement of Bj, t) is a prerequisite for good detection; in the case of cold start, good accuracy depends on the following characteristics:

[0207] - the stationary nature of the train allows for a long correlation integration up to a few seconds (or even minutes) to mitigate the impact of noise in order to obtain a stable and reliable correlation result;

[0208] - a list of predefined time offsets with a sufficiently small range to ensure the accuracy of the interpolation.

[0209] The method according to the invention described above is adapted to the static case, for consolidating channel detection at initialization, to the "cold start," and to the dynamic case, provided that the integration times for correlation calculations are adjusted. The time of passage over the beacon in the dynamic case could be an additional parameter to refine position detection. A robust and simple version can do without this by taking into account regular and fixed detection times, and thus the nearest beacon is detected for a similarly estimated position detection time.

[0210] Example of position search when the train is moving on a track (dynamic case):

[0211] In such a case, in one embodiment, only the beacons (or a subset thereof) of base 13 identified therein as being located on train tracks are considered for the implementation of algorithm 100 (this subset can be further reduced by retaining only the beacons located on tracks on which the train is likely to be located, this assessment being determined, for example, based on a maximum displacement evaluated according to measurements from an on-board inertial measurement unit and a previous reliable position of the train). These subsets of beacons are therefore, in this case, the beacons B, i=1 to N, considered.

[0212] In one embodiment, the dynamic case differs from the static case in that, in addition, the correlation is calculated at different times, with the correlation being maximum when the train is at the beacon. Indeed, in addition to beacon detection (maximum spatial correlation), it is also necessary to detect the time at which this correlation is maximum (which is not necessary in the static case).

[0213] Dynamic positioning:

[0214] Dynamic correlation integration time:

[0215] When the train is in motion, the received GNSS signal is collected by the receiver Rx 11 from different positions. For the received GNSS signals, in addition to the impact of noise / interference, a new ambiguity regarding the signal collection position is thus introduced.

[0216] An appropriate correlation integration time must be well defined to balance the following aspects:

[0217] - the duration of the integration time must be as long as possible to mitigate the impact of noise in order to obtain a sufficiently accurate correlation result;

[0218] - the duration of the integration time must be as short as possible to reduce the ambiguity of the signal collection position.

[0219] In parallel, taking into account that in dynamic positioning, to resolve the ambiguities of the switches and the recovery of the position of the moving train, It is generally necessary to distinguish between paths; 2 meters is defined as the threshold value for signal collection range, that is:

[0220] Correlation integration time Tint = 2 m / Vtrain (Vtrain: speed of the train)

[0221] According to the above formula, the typical integration time is: 1.3 s for 5 km / h, 400 ms for 20 km / h, 120 ms for 60 km / h, 60 ms for 120 km / h, 40 ms for 180 km / h.

[0222] As summarized above, with a dynamic correlation integration time, the same algorithm can be used for dynamic positioning.

[0223] Track detection when the train is moving:

[0224] Sometimes, signals lasting several tens of milliseconds are insufficient to mitigate the impact of noise. In one embodiment, the following method is implemented by the localization block 121 to further mitigate the random signal error by averaging the MSP information:

[0225] - the tags considered and their associated positions defined in the database, (the tags considered correspond to the only candidate positions in an embodiment, for example the only beacons within the circle of uncertainty such as 100 meters around the PVT position of the train) are grouped into different trajectories (routes) near the localized track (in other words, we are only looking for possible positions relative to a track / position known reliably) as illustrated on [Fig. 13] partially representing the circle of uncertainty, the beacons (small circles), grouped into routes 0, 1 and 2, the arrow indicating the direction of movement to be determined;

[0226] - the correlation calculation (step 103) for the considered tags with a time defined integration is performed;

[0227] - for each considered tag B;, the correlation lag ATgjsJ = X ( Bj t ) is calculated for each satellite

[0228] - for each possible route (route k):

[0229] - the tag with a minimum maximum spatial bias (MSB) is determined and is defined as the most likely position on this route;

[0230] - for this most probable position (corresponding to the Bjoroutek beacon), the bias spatial relative to each satellite AS'gjoroute k = 1 to s, is recorded and averaged over the last N measurement instants considered: cf. illustration on [Fig. 14], the current detection is referenced 200, the last N detections are identified by the brace 201;

[0231] - among the average spatial biases for each satellite above, choose the maximum, which is then defined as the MSB of the route;

[0232] - on this basis apply a decision logic analogous to the MSP method (step 105 described above) to determine the new track after passing a switch (here, only when the possible routes are again at least 4m apart):

[0233] - there must be only one MSB below the threshold defined as half of the distance between 2 lanes (typically 2m); this will be considered the true road;

[0234] - if no MSB satisfies the threshold defined as half the distance between 2 routes, so we cannot solve the path and we wait for the next iteration;

[0235] - if 2 or more MSBs satisfy the threshold, then there is a situation of ambiguity (due to biased satellites): the path cannot be solved; the test is performed at the next iteration.

[0236] The method can be used to detect the track to resolve ambiguity in turnouts, as well as to distinguish the track for train movement. It can also be used to improve the integrity of the main track positioning with the determined track.

[0237] Alternative solutions for determining the values ​​of delay X^^ B^ t )

[0238] There are different solutions for determining the values ​​of delay ^(¾ Bk t).

[0239] One of these solutions was described in steps 101 to 104 considering the tag Bi and the set of satellites Sk, k= 1 to s according to which the correlation of the signals received and theoretically received at Bj is calculated, and the delay ^(¾ B,. t) is deduced from this calculated correlation. Typically, if we consider P possible positions (i.e. P beacons), S satellites and 5 time offsets for the correlation, then we will have P*S*5 correlation points to calculate (with for each correlation point a calculation of the predicted code and the correlation with the signal actually received, then for each position and each satellite, a delay Xmax is calculated based on the result of the correlation of 5 time offsets using a parabolic interpolation: thus a large volume of computation is implemented.

[0240] In one embodiment, the invention implements, instead, a solution for determining the delay values ​​^(¾ Br t) according to one of the two approaches described below, exploiting the relationship between the delays relative to one beacon and the delays relative to another beacon, and thus allowing the correlation to be calculated only for a reference beacon.

[0241] Two approaches are proposed here.

[0242] Approach 1:

[0243] The correlation calculated with respect to one of the beacons, for example the Bb beacon for the Sk satellite, can be expressed as follows:

[0244] fro+Tmr -I ro CRXSk ( ^ ) ■ ^calc B ISk U /

[0245] It follows that between two beacons, Bb B2, the correlation difference is simply the difference in predicted signals Cci^c (t), C^ic ÿ^Sk (O ' all the beacons using the same error correction for predicted signals from Sk, it

[0246] It follows that: Q« / c BÏSk (O - Cealc B2Sk ( O = ^(SfBl -

[0247] c is the speed of light in a vacuum; where SkBb respectively, is the distance between satellite % and beacon Bb respectively the distance between satellite Sk and beacon B2.

[0248] Using this approach, the location block 121 determines the delay A»0 of any beacon B by "translation", instead of steps 101 to 104, from the delay determined for a reference beacon Bo:

[0249] X(SY B;, t) = Bq, t) +

[0250] where S^Bq, respectively SkB{, is the distance between the satellite Sk and the beacon Bo, respectively the distance between the satellite Sk and the beacon B,.

[0251] Approach 2:

[0252] This approach 2 is based on the concept of a correlation line. According to the correlation formula, at positions (i.e., between beacons) that are equidistant from the Sk satellite, there is the same predicted signal and therefore the same correlation result. These positions (beacons) lie on the same line on the ground, called the correlation line. The difference between the relative delays of any two beacons is, in fact, the distance between these correlation lines on which these two beacons are located. Figure 12 illustrates, among the set of points indicating beacon positions, the correlation line on which beacon Bo is located and the correlation line on which another beacon, B, is located; and the distance, ds, between these two correlation lines.

[0253] Using this approach, instead of steps 101 to 104, the location block 121 determines the delay Bh t) of any beacon B; by "translation" from the delay determined for a reference beacon Bo using the following formula

[0254] X(Sk, B, t) = X(Sfc B^ t) +dv*co^ / J / 0.3

[0255] where

[0256] azk, elk: azimuth angles, respectively elevation angles of the Sk satellite;

[0257] a: angle between the line passing through Bo and B; and the axis E;

[0258] [3 : angle between the line passing through Bo and B; and the correlation line passing through B; ;

[0259] d: distance between the Bo, B beacons;;

[0260] ds: distance along the line of the satellite Sk in the plane, between the beacons Bo, B; (in other words, it is the projection of d along SkB0)

[0261] the following calculations being performed:

[0262] Ala = latitude(B0) - latitude(B;), Alo = longitude(B0)- longitude(B;), the coordinates called longitude(), latitude() of the Bo, B; be given in a NED frame (or in any orthogonal frame also in the local tangent plane);

[0263] a = arctan(Ala / (Alo *cos(latitude(B0)

[0264] [3 = azk + a

[0265] ds = d * sin([3]

[0266] and finally: X^ Bb t) = X(^ t ) + ds*coielk)l0.3-

[0267] Implementing either of these two approaches makes it possible to reduce in a significant way the computational load required to implement the localization solution according to the invention.

[0268] Tests were carried out using real signals collected from the channels, allowing the correlation delay X() to be deduced for seven beacons by "translation" from another reference beacon. The difference between the delays obtained by translation and those actually measured by correlation calculation was calculated: it is approximately 0.1 m on average and a maximum of 0.39 m, and the two approaches give comparable results with an average difference of 0.02 m and a maximum difference of 0.1 m.

[0269] Furthermore, it is necessary to use precise values ​​for the correlation delays in the localization solution according to the invention. However, the accuracy of the correlation delay X() obtained based on correlation calculations using received signal measurements and calculations of theoretical signals at the beacons is unknown. The inaccuracy may arise from noise or interference on the GNSS signal and / or interpolation errors.

[0270] The translated values ​​of correlation delay are used to evaluate the accuracy of the "measured" correlation delays and to validate / invalidate satellites: see the two examples of embodiments described below.

[0271] For example, considering two beacons BOi, B02 (13.5 m apart), the X(Sfc Bp t) "measured", i = 01, 02, is determined by effective correlation calculation (from measurements at these beacons) relative to these beacons, by implementing steps 101 to 104.

[0272] In a first validation method, the comparison of the correlation delays at one or more tags obtained by translation (by one of the two approaches described above) and those actually "measured" at this / these tag(s) (by steps 101 to 104) is used to evaluate the accuracy of the "measured" correlation delays and Validate / invalidate satellites. Starting from this calculated (measured) Bp t), i = 01, by translation this time from the reference beacon BOi, a translated X(Sft, Bp t ) i=02 is determined. The differences between the measured and translated X( Bj, t ) are then compared, and if the difference exceeds a predetermined threshold, Sk is excluded from the set of satellites used by the localization block 121 to implement the localization determination in step 105.

[0273] In a second validation mode, each of the BOi, B02 tags is used as a reference tag by the locating block 121 to calculate by translation, by one of the two approaches described above, the correlation delay X^ # / ,!),] = 1 tor.

[0274] So for each beacon Bj, j = 1 to r, the location block 121 obtains a first value X( Bj, t ) Oi by translation from the measured BOi, t) and a second value X ( Bj, t ) 02 by translation from the measured X( S^, B01, t ), The differences between X(Bj, t) and X(S^, Bj, t) O2 translated are then compared, j = 1 to r and if the difference exceeds a predetermined threshold (specific to the satellite Sk or common to different satellites), Sk is excluded from the set of satellites used by the location block 121 to implement the location determination in step 105.

[0275] It should also be noted that measurements of the codes in the positioning signals have been described above. The invention can also be implemented by measuring, instead of or in addition to the code measurements, the phases of the carriers of the positioning signals.

[0276] Method 100 can be implemented by executing software instructions on a processor, as described above. Alternatively, either and / or both can be implemented by dedicated hardware, typically a digital integrated circuit, either specific (ASIC) or based on programmable logic (e.g., FPGA / Field Programmable Gate Array).

[0277] The method according to the invention is of course usable, beyond the railway field, in any system in which it is necessary to estimate the position of a vehicle whose movement is only possible on a predetermined and finite set of trajectories, a database storing the geo-referencing of virtual beacons located on the trajectories.

Claims

1. Demands Method for locating a device (4) adapted to move on a set of predefined trajectory(ies) (VI,V2), a satellite receiver on board the device being adapted to receive at a time t geopositioning signals from a satellite system comprising at least s satellites Sk, k=l to s and s greater than or equal to 3; an electronic processing unit (10) comprising a database (13) storing the geographic coordinates Pj of virtual beacons Bj, j = 1 to N, distributed along the trajectories of said set of trajectories; said process comprising the following steps implemented by the electronic processing unit (10) at a location time t: it / for each beacon Bj, j = 1 to N: - for each satellite Sk for k = 1 to s: • calculation of the delay, between the geostationary signal received by the satellite receiver at time t from the satellite Sk and the theoretical geostationary signal calculated as having to be received from the satellite Sk at time t at the position of the virtual beacon Bi as defined by the geographic coordinates Pj of Bj in the database, said delay being called correlation delay, X(Bj); • a representative value of the correlation lag X(S^ Bj) is converted into a corresponding distance, ASgj^, called spatial bias, by multiplying this representative value of the correlation lag X ( S& Bj ) by c, the speed of light in a vacuum and dividing it by cos elk, where elk is the elevation of the satellite Sk; - for each beacon Bj, j = 1 to N, a maximum spatial bias MSBgj is determined: i2 / The maximum spatial biases MSBgy, j= 1 to N are compared to a predefined threshold MSBrep: following this comparison, if only one beacon has a maximum spatial bias MSBgy lower than MSBrep, that beacon

2.

3. is then detected as the one at which the device is located at the moment of localization. A localization method according to claim 1, wherein one of the following provisions is further implemented by the processing block in step i2: - i2_l / if only two tags have their greatest spatial bias less than MSD^ and they are adjacent on the same track, it is considered that the device is located between the two beacons; - i2_2 / if more than one tag has a greater spatial bias maximum less than MSBREF (optionally outside the case just above): an ambiguity situation is detected and it is considered that localization cannot be performed; - i2_3 / if only two tags have their greatest spatial bias less than MSB^pet and they are adjacent on the same track, it is considered that the device is located between the two beacons; outside of this case, if more than one beacon has a greater maximum spatial bias less than MSBREF, it is considered that the localization cannot be carried out; - c i2_4 / if no beacon has a greater maximum spatial bias MSB^yp(W less than MSBREp this indicates the existence of defective satellites, an ambiguity situation is thus detected and it is considered that the localization cannot be carried out. A localization method according to claim 1 or 2, wherein steps 11 and 12 are iterated with respect to each subset of satellites comprising s-1 of the s satellites in place of the s satellites considered in the previous iteration for s>5, when, following said comparison of the previous iteration, only one beacon had a maximum spatial bias MSBgj less than MSBREF and If at the current iteration, for each of the satellite subsets, the comparison step detects the same single beacon as at the previous iteration corresponding to a given integrity level, said beacon is considered to have been detected with said given integrity level increased by one.

4. A localization method according to claim 1 or 2 or 3, wherein steps 11 and 12 are iterated with respect to each subset of satellites comprising s-1 of the s satellites in place of the s satellites considered in the previous iteration for s>5, and if in the previous iteration, no beacon had a greater maximum spatial bias MSBgy^ less than MSBREFet than in the current iteration, only one beacon has a maximum spatial bias MSBgy less than MSBREF, this beacon is then detected as the one at which the craft is located at the time of localization and the seme satellite is identified as faulty.

5. A localization method according to any one of the preceding claims, wherein said representative value of the correlation delay X(Bj) is equal to the difference between said correlation delay X(Bj) and a bias named BCBj, which is an estimate of the temporal bias associated with the beacon Bj and common to all satellites and allowing to minimize MSB / jy.

6. Localization method according to any one of the preceding claims, wherein said representative value of the correlation lag X ( Bj ) is equal to the difference between said correlation lag X(S^ Bj) and a bias named BCBj =y5 .

7. A localization method according to any one of the preceding claims, wherein the processing block implements one of the following provisions i1a, i1b, i1c, for, considering the beacon Bi, implementing step i1 of calculating the delays, X(Sk, B, t) for k= 1 to s: i1a / calculation of the correlation between said received geostationary signal and said theoretical geostationary signal calculated at B;, said delay X(Sk, B, t) being calculated as a function of at least said calculated correlation; i1b / the delay X(Sk, B, t) is calculated, by translation, using the following formula: X(Sk, B, t) = X(Sk, B, t) + 1 / SkB(SkB) where SkB is the distance between satellite B and a reference beacon B0, respectively the distance between satellite Sk and beacon Bi, -^(¾ 0 is the delay between the geostationary signal received by the satellite receiver at time t from satellite Sk and the theoretical geostationary signal calculated as expected to be received from satellite Sk at time t at the position of the virtual beacon Bo as defined by the geographic coordinates PO of Bq in the database, c is the speed of light in a vacuum; the delay X(Si, Bj. t ) is calculated, by translation, using the following formula: BiA) =X(Sh 5(),1) +^;COs(dJ / 0.3 where B() is a reference beacon, Ala = latitude(Bo) - latitude(B;), Alo = longitude(B0)- longitude(B;)a = arctan(Ala / (Alo *cos(latitude(B0) )) 0 — azk + and ds = d * sin([3) where latitude(), longitude( ) are the coordinates in an orthogonal coordinate system in the local tangent plan.

8. A localization method according to claim 7, wherein the processing block implements at least one of the following provisions 4.1, 4.2: 4.1 by implementing the provision il a, S0], t) and X(^ 502, t) are calculated; then, considering BOi as the reference beacon and by implementing one of the formulas in ilb or ile, the delay in 502 is determined this time by translation, considering Boi as the reference beacon and is named B^, t)01; and as a function of at least the difference between X^j, 502, t ) and t)ob, the satellite Sk is excluded from the set of satellites taken into consideration for step i3 of estimating the location of the craft as a function of said representative values ​​of differences between said calculated delays; 4.2 perform the next step for tags Bi, i = 1 to r: by implementing one of the formulas in ilb or ile: a first delay X(5^ B,.t)01 is determined by considering BOi as the reference beacon and a second delay X( B^t ) 02 is determined by considering B02 as the reference beacon; and as a function of at least the differences between X(SG Bt, t)01 and X($GB^ t )02 i = 1 to r , the satellite Sk is excluded from the set of. satellites taken into consideration for step i3 of estimating the location of the craft based on said representative values ​​of differences between said calculated delays.

9. A localization method according to any one of the preceding claims, wherein each beacon considered is spaced from its nearest neighbors by a distance D equal to the distance between two neighboring lanes and the predefined threshold MSBREF is taken to be equal to D / 2.

10. Computer program, intended to be stored in the memory of an electronic locating device (121) and further comprising a microcomputer, said computer program comprising instructions which, when executed on the microcomputer, implement the steps of a method according to any one of the preceding claims.

11. Electronic processing unit (10) for the localization of a vehicle (4) adapted to move on a set of predefined trajectory(ies) (VI,V2) and carrying a satellite receiver (11) to receive at time t geopositioning signals from a satellite system comprising at least s satellites Sk, k=l to s and s greater than or equal to 3; the electronic processing unit (10) comprising a database (13) storing the geographic coordinates Pj of virtual beacons Bj, j = 1 to N, distributed along the trajectories of said set of trajectory(ies);said electronic processing block (10) being adapted to implement the following operations, at a location time t: it / for each beacon Bj, j = 1 to N: - for each satellite Sk for k = 1 to s: calculation of the delay, between the geostationary signal received by the satellite receiver at time t from the satellite Sk and the theoretical geostationary signal calculated as having to be received from the satellite Sk at time t at the position of the virtual beacon Bi as defined by the geographic coordinates Pj of Bj in the database, said delay being called correlation delay, X ( Bj ); a representative value of the correlation delay X ( Sk, Bj ) is converted into a corresponding distance, AS^j^, called spatial bias, by multiplying this representative value of the delay by; correlation X ( Bj ) by c, speed of light in a vacuum and dividing it by cos elk, where elk is the elevation of the satellite Sk; - for each beacon Bj, j = 1 to N, a maximum spatial bias MSBgj is determined: MSB By = MAX^^JaSb^J i2 / the maximum spatial biases MSBjÿj, j= 1 to N are compared to a predefined threshold MSBref: following this comparison, if only one beacon has a maximum spatial bias MSB^j less than MSBref, this beacon is then detected as the one at which the device is located at the time of localization.

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