Method and device for identifying a faulty satellite among a set of satellites

Abstract

The present invention relates to a method and device for identifying a failed satellite among a set of satellites S1,…,SN based on pseudo-distances (PR) between a mobile and the satellites S1,…,SN. In particular, the method comprises, following satellite failure detection (FLT), the steps of: for each satellite Si in the set of satellites S1,…,SN: obtaining (S310) a set Pi of mobile positions, each position pi,j being determined from the pseudo-distances (PR) associated with the satellites S1,…,SN, excluding: satellite Si; and at least one other different satellite Sj for each position pi,j; determining (S320) a dispersion indicator σi of the positions in the set Pi; and identifying (S330) the failed satellite among the set of satellites S1,…,SN based on the dispersion indicators σ1,…,σN. Figure for the abstract: Fig. 6

Description

Title of the invention: Method and device for identifying a faulty satellite among a set of satellites Technical field

[0001] The present invention relates to the field of satellite navigation, also known as GNSS navigation (for "Global Navigation Satellite System" in English). In particular, the present invention relates to a method and a device for identifying a faulty satellite among a set of satellites, as well as an associated navigation system, an aircraft, and a computer program. The present invention finds a particularly advantageous, although in no way limiting, application for the implementation of satellite navigation systems for aircraft, ships, or land vehicles. Prior art

[0002] The invention falls within the particular context of satellite navigation systems. Embedded in a mobile device (e.g. an aircraft), such a navigation system uses the signals received from satellites to determine the position of the mobile, and potentially other navigation data of the mobile such as its speed and its orientation. To determine the position of a mobile, a satellite navigation system uses positioning measurements, called pseudo-distances ("pseudo-ranges" in English), provided by a GNSS receiver. These measurements characterize the distances between the mobile and the visible satellites of a constellation. In the context of the invention, the navigation systems considered can also use data from an inertial unit to determine the navigation data of the mobile, using for example a multi-sensor fusion algorithm based on a Kalman filter.

[0003] For certain applications such as aeronautics, the reliability of navigation data is crucial. Navigation systems must then satisfy certain requirements in terms of integrity. For example, the navigation system must be able to determine the position of the mobile with a given integrity risk, that is to say with a defined probability (in particular very low, for example 107) that the position error is greater than a protection radius (i.e. an alert terminal) without any alert being raised. For a satellite navigation system, the failure of a satellite leads to an alteration of the pseudo-distance associated with it, which may take the form of a bias, a drift, or an acceleration, which induces significant position errors which may increase over time. To guarantee the integrity of the navigation system, it is therefore necessary to be able to detect a satellite failure and, if necessary, to identify the faulty satellite so as to no longer use the pseudodistances associated with it.

[0004] In the current state of the art, some solutions use a plurality of Kalman filters to detect a satellite failure and identify the faulty satellite. Each filter excludes the pseudo-distances associated with one of the satellites so that the pseudo-distances used are different from one filter to another. For each filter, a statistical indicator is evaluated from the cross-innovation of the filter. By using the statistical indicators of the different filters, it is then possible to detect a satellite failure and identify the faulty satellite. Such a solution is for example presented in document FR2964468A1. However, for certain geometric configurations of the satellites, these solutions may exclude a functional (i.e. non-faulty) satellite instead of the faulty satellite.Such an exclusion error can notably lead to a loss of integrity, or a loss of availability of the navigation system, and must be avoided. In addition, these solutions present a high implementation complexity and require significant use of resources (e.g. computing and memory resources, processing time, etc.).

[0005] Furthermore, existing RAIM (Receiver Autonomous Integrity Monitoring) type solutions make it possible to identify a faulty satellite without using Kalman filters. These solutions use a least squares algorithm to determine the position of the mobile from the pseudo-distances associated with the different satellites. Document US10684375B2 illustrates such a solution. To detect a satellite failure, these solutions compare a statistic of the residuals to a threshold, i.e. they use the differences between the pseudo-distances provided by the GNSS receiver and pseudo-distances calculated from the position of the mobile estimated by the least squares algorithm. When a satellite failure is detected, the faulty satellite is identified from the amplitude of the residuals, in particular the faulty satellite corresponds to the satellite for which the residual is maximum.However, these solutions may erroneously exclude a functional satellite.

[0006] There is therefore a need for a solution making it possible to reliably identify a faulty satellite among a set of satellites from pseudodistances between a mobile and the different satellites. Statement of the invention

[0007] The present invention aims to remedy all or part of the drawbacks of the prior art, in particular those set out above.

[0008] According to one aspect of the invention, a method is proposed for identifying a faulty satellite among a set of satellites Si,.. .,SN from pseudo-distances between a mobile and the satellites Si,.. .,SN, the method comprising, following a detection of a satellite failure, steps of: - for each satellite Si of the set of satellites Si,.. .,SN: • obtaining a set P; of positions of the mobile, each position p ij of the set P; being determined from the pseudo-distances associated with the satellites Si,...,SN excluding: the satellite Si; and at least one other different satellite Sj for each position pLJ; • determination of a dispersion indicator o, of the positions of the set Pi; and - identification of the faulty satellite among the set of satellites Si,...,SN according to the dispersion indicators Oi,...,oN.

[0009] The present invention proposes, following the detection of a satellite failure, to identify the faulty satellite (denoted Sx hereinafter) by using the pseudo-distances provided by a satellite positioning receiver.

[0010] More precisely, for each satellite S; of a set of satellites Si,...,SN, a set Pi of positions of the mobile is obtained. Each position pij of the set Pi is estimated using the pseudo-distances associated with the satellites Sb...,SN with the exception of those associated with the satellite S; and with another satellite Sj (i^j). In other words, the positions of the set Pi are estimated using different combinations of satellites among the satellites Si,...,SN, all these combinations excluding the satellite Si. We must then distinguish two cases depending on whether the excluded satellite Si is the faulty satellite Sx or a functional satellite.

[0011] If the excluded satellite Si is the faulty satellite Sx, the positions of the set Px are obtained by excluding the pseudo-distance associated with the faulty satellite Sx. The positions of the set Px are estimated using only pseudo-distances associated with functional satellites. Since the faulty satellite Sx is not used to determine the positions of the set Px, these positions are healthy (i.e. reliable) and have low dispersion (i.e. low variability).

[0012] On the other hand, if the excluded satellite Si is a functional satellite (i^x), the positions of the set P; are obtained by using the pseudo-distance associated with the faulty satellite Sx, with the exception of the position pi>x. Since the faulty satellite Sx is used to determine the positions of the set P; (except the position pi>x), these positions are faulty (i.e. unreliable) and have a high dispersion (i.e. significant variability). Also, only the position pijX is healthy, while the other positions of the set P; are faulty.

[0013] The present invention proposes to use the dispersion indicators ab...,oN to identify the faulty satellite Sx among the set of satellites Sb...,SN. The indicators Oi,.. ,,oN respectively characterize the dispersion (i.e. the variability) of the positions of the sets Pi,...,PN.

[0014] In particular, the identified faulty satellite Sx corresponds to the satellite of the set of satellites Si,.. .,SN for which the dispersion indicator ox is minimum. Indeed, the dispersion indicator ox, determined by excluding the faulty satellite Sx, is representative of a low dispersion of the positions of the set Px. Conversely, the other dispersion indicators o, (i^x), determined by excluding a functional satellite S;, are representative of high dispersions.

[0015] Thus, the present invention makes it possible to reliably identify a faulty satellite among a set of satellites from the pseudo-distances between a mobile and the different satellites.

[0016] Compared to the existing solutions described above, it should be noted that the present invention makes it possible to identify a faulty satellite more reliably and more quickly. In particular, the proposed solution has minimal implementation complexity and requires less use of resources (e.g. computing and memory resources, processing time, etc.).

[0017] According to one embodiment, the step of determining the dispersion indicator oi comprises steps of: - determination of an average position P; from the positions of the set E; - determination of a set D; of distances between the positions of the set Pi and the average position Pj; and - determination of the dispersion indicator o, from the set D;, the dispersion indicator o, being equal to a standard deviation of the distances of the set D;.

[0018] In this embodiment, it is proposed to use the standard deviation of the distances to the average position as an indicator of dispersion o, of the positions of the set P;. This embodiment makes it possible to precisely measure the dispersion of the positions of the set P; and requires few computing and memory resources. It thus contributes to providing a solution making it possible to identify a faulty satellite among a set of satellites reliably, and with minimal implementation complexity.

[0019] According to one embodiment, each set of positions P; comprises Nl positions of the mobile, and each position p;j of the set P; is determined from the pseudo-distances associated with the satellites Si,...,SN excluding: the satellite Si; and another different satellite Sj for each position pLJ.

[0020] According to this embodiment, the positions of a set P; are determined using all possible combinations of N-2 satellites among the satellites Si,...,SN and excluding the satellite Si. The set P; therefore comprises the maximum number of positions determined from N-2 satellites excluding the satellite Si for each positions.

[0021] More precisely, the set Px here comprises N1 healthy (i.e. reliable) positions determined by excluding the faulty satellite Sx. The other sets P; with i4x comprise respectively: N-2 faulty (i.e. unreliable) positions determined using the faulty satellite Sx; and a single healthy position pi>x determined by excluding the faulty satellite Sx.

[0022] This embodiment makes it possible to obtain a significant difference between: the dispersion indicator ox determined by excluding the faulty satellite Sx; and the other dispersion indicators Oi(i^x) determined by using the faulty satellite Sx. In this way, this embodiment makes it possible to improve the reliability of the solution proposed for identifying a faulty satellite Sx among a set of satellites Si,...,SN.

[0023] According to one embodiment, the method comprises for each satellite Si of the set of satellites Si,.. .,SN, and for each satellite Sj of the set of satellites Si,.. .,SN with j>i: a determination of a position of the mobile from the pseudodistances associated with the satellites Si,...,SN excluding the satellite S; and the satellite Sj, the determined position being used to obtain the position pij of the set P; and the position pjj of the set Pj.

[0024] To describe this embodiment, consider the position pij of the set P;. This position pij is determined from the pseudo-distances associated with the satellites S i,.. ,,SN by excluding the satellites Si and Sj. This is also the case for the position pjj of the set Pj, so that the positions p;j and p,; are identical. In other words, the position pij of the set Pi and the position pj; of the set Pj are both obtained using the same combination of satellites. This embodiment then proposes to determine the position p;j and to use it for both the set P; and the set Pj.

[0025] According to this embodiment, a position common to several sets among Pi,...,PN is determined only once. This embodiment thus makes it possible to minimize the necessary computing and memory resources. It contributes to providing a solution making it possible to identify a faulty satellite with low implementation complexity.

[0026] According to one embodiment, the proposed method for identifying a faulty satellite further comprises a step of detecting the satellite failure. More particularly, this step of detecting the satellite failure may comprise each of the steps of a method for detecting a satellite failure according to the invention and described below.

[0027] According to one aspect of the invention, a method is proposed for detecting a satellite failure from pseudo-distances between a mobile and a set of satellites Si,.. „SN., the method comprising a step of detecting the satellite failure comprising stages of: - obtaining a set P of positions of the mobile, each position p; of the set P being determined from the pseudo-distances associated with the satellites Si,.. .,SN by excluding a different satellite Si for each position p; ; - determination of a dispersion indicator o of the positions of the set P; and - satellite failure detection based on the dispersion indicator o.

[0028] The present invention proposes to detect a satellite failure using the pseudodistances provided by a satellite positioning receiver.

[0029] To do this, it is proposed to obtain a set P of positions of the mobile using different combinations of satellites among the satellites Si,...,SN. More precisely, each position p; of the set P is estimated using the pseudodistances associated with the satellites Si,...,SN with the exception of that associated with the satellite Si.

[0030] If all the satellites Si,.. .,SN are functional, the positions of the set P are determined using only pseudo-distances associated with functional satellites. The positions of the set P are therefore healthy (i.e. reliable) and have a low dispersion.

[0031] On the other hand, if a satellite Sx among the set of satellites Si,.. .,SN is faulty, only the position px is healthy since it is determined using only pseudo-distances associated with functional satellites. The other positions p; (i^x) of the set P are determined using the pseudo-distance associated with the faulty satellite Sx, and are therefore faulty. For this reason, in the event of a satellite failure, the positions of the set P have a high dispersion.

[0032] To detect a satellite failure, the present invention thus proposes using the indicator o characterizing the dispersion of the positions of the set P. In particular, a satellite failure is detected at least as a function of a comparison of the dispersion indicator o with a threshold.

[0033] Thus, the present invention makes it possible to reliably detect a satellite failure from the pseudo-distances between a mobile and a set of satellites.

[0034] In addition, the proposed solution makes it possible to detect a satellite failure more reliably and more quickly than existing solutions. In particular, the proposed solution has low implementation complexity.

[0035] According to one embodiment, the step of determining the dispersion indicator o comprises steps of: - determination of an average position P from the positions of the set P; - determination of a set D of distances between the positions of the set P and the average position P; and - determination of the dispersion indicator o from the set D, the dispersion indicator o being equal to a standard deviation of the distances of the set D.

[0036] According to this embodiment, the standard deviation of the distances to the average position is used as an indicator of dispersion o of the positions of the set P. This embodiment makes it possible to precisely measure the dispersion of the positions of the set P and requires few computing and memory resources. This embodiment thus contributes to detecting a satellite failure reliably and with minimal implementation complexity.

[0037] According to one embodiment, several iterations kb... ,kM of the detection step are implemented for pseudo-distances acquired at different times. Furthermore, in this embodiment, the satellite failure is detected during the iteration kM if: - the dispersion indicator o of the iteration kM is greater than a threshold; and if - a variation Ao of the dispersion indicator o during the iterations kb... ,k M is greater than another threshold.

[0038] The failure of a satellite Sx causes an alteration of the pseudo-distance associated with it, which may take the form of a bias (i.e. a step), a drift (i.e. a ramp), or an acceleration. As a result, the positions of the mobile determined from this pseudo-distance will present, over time, a sudden variation or a progressive drift. By using the variation Ao, in addition to the dispersion indicator o, this embodiment makes it possible to improve the reliability of detection of a satellite failure.

[0039] According to one embodiment, the positions of the mobile are determined using a Bancroft algorithm.

[0040] This embodiment is advantageous in that it makes it possible to determine, precisely and quickly, the position of the mobile from the pseudo-distances associated with the satellites. In particular, in comparison with a Kalman filter, the Bancroft algorithm has a low implementation complexity.

[0041] It should be noted that the Bancroft algorithm can be used: when detecting a satellite failure, to determine the positions p; of the set P; and / or when identifying a faulty satellite, to determine the positions p;j of the sets P;.

[0042] According to one aspect of the invention, there is proposed a device for identifying a faulty satellite among a set of satellites Si,.. .,SN from pseudo-distances between a mobile and the satellites Si,.. .,SN, the device comprising an identification module configured for, following detection of a satellite failure: - for each satellite S; of the set of satellites Si,.. .,SN: • obtain a set Pj of positions of the mobile, each position pij being determined from the pseudo-distances associated with the satellites Si,...,SN excluding: the satellite Si and; at least one other different satellite Sj for each position pij; • determine a dispersion indicator o, of the positions of the set Pi; and - identify the faulty satellite among the set of satellites Sb.. .,SN according to the dispersion indicators Oi,...,oN.

[0043] The device for identifying a faulty satellite may be configured to implement any of the embodiments of a method according to the invention. In particular, this identification module may be configured to implement each of the steps of a method according to the invention.

[0044] According to one embodiment, the proposed device for identifying a faulty satellite further comprises a module for detecting a satellite failure. In particular, this detection module can be configured to implement each of the steps of a method for detecting a satellite failure according to the invention.

[0045] According to one aspect of the invention, there is provided a device for detecting a satellite failure from pseudo-distances between a mobile and a set of satellites Si,..,,SN, the device comprising a detection module configured to: - obtain a set P of positions of the mobile, each position p; of the set P being determined from the pseudo-distances associated with the satellites Si,..,,SN by excluding a different satellite Si for each position p;; - determine a dispersion indicator o of the positions of the set P; and - detect the satellite failure according to the dispersion indicator o.

[0046] The device for detecting a satellite failure may be configured to implement any of the embodiments of a method according to the invention. In particular, for each step of a method according to the invention, the proposed device for detecting a satellite failure may be configured to implement said step.

[0047] According to another aspect of the invention, there is provided a navigation system intended to be embedded in a mobile comprising: - a satellite positioning receiver configured to provide pseudo-distances between a mobile and a set of satellites; and - a device for detecting a satellite failure in accordance with the invention and / or a device for identifying a faulty satellite in accordance with the invention.

[0048] The navigation system may also comprise a navigation device configured to determine navigation data of the mobile from: pseudodistances provided by the satellite positioning receiver; and data from an inertial unit.

[0049] The proposed navigation system can, for example, be installed in an aircraft, a ship, or a land vehicle.

[0050] According to one aspect of the invention, there is provided a mobile machine comprising a navigation system according to the invention.

[0051] According to one embodiment, the mobile machine is an aircraft. Alternatively, the mobile machine may be a ship or a land vehicle.

[0052] According to one aspect of the invention, there is provided a computer program comprising instructions for implementing the steps of a method according to the invention, when the computer program is executed by at least one processor or computer.

[0053] The computer program may be formed of one or more sub-parts stored in the same memory or in separate memories. The program may use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other desirable form.

[0054] According to one aspect of the invention, there is provided a computer-readable information medium comprising a computer program in accordance with the invention.

[0055] The information carrier may be any entity or device capable of storing the program. For example, the carrier may comprise a storage means, such as a non-volatile memory or ROM, for example a CD-ROM or a microelectronic circuit ROM, or a magnetic recording means, for example a floppy disk or a hard disk. Furthermore, the storage medium may be a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by a telecommunications network or by a computer network or by other means. The program according to the invention may in particular be downloaded onto a computer network. Alternatively, the information carrier may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question.

[0056] The proposed device for identifying a faulty satellite, the navigation system, the aircraft, the computer program and the information medium have the advantages described above in connection with the proposed identification method. Brief description of the drawings

[0057] Other characteristics and advantages of the present invention will emerge from the description provided below, illustrating embodiments of the invention given by way of example and without any limiting character, with reference to the attached drawings:

[0058] [Fig.l] represents the hardware architecture of an aircraft according to one embodiment of the invention;

[0059] [Fig.2] represents the functional architecture of a device according to an embodiment of the invention comprising a module for detecting a satellite failure and a module for identifying a faulty satellite;

[0060] [Fig.3] represents steps of a method according to an embodiment of the invention for detecting a satellite failure and identifying a faulty satellite;

[0061] [Fig.4] represents steps of a method according to an embodiment of the invention for detecting a satellite failure;

[0062] [Fig.5] represents values ​​of a dispersion indicator o determined by a method according to one embodiment of the invention for detecting a satellite failure;

[0063] [Fig.6] represents steps of a method according to an embodiment of the invention for identifying a faulty satellite; and

[0064] [Fig.7] represents values ​​of dispersion indicators ob.. ,,oN determined by a method according to an embodiment of the invention for identifying a faulty satellite. Description of the embodiments

[0065] The present invention applies, in particular, to satellite navigation systems for aircraft. The following description of the invention will refer to this particular context of application, which is given only as an illustrative example and should not limit the invention. The latter applies to satellite navigation for any type of carrier, mobile machine or vehicle.

[0066] [Fig.l] represents the hardware architecture of an aircraft according to an embodiment of the invention. In particular, [Fig.l] is described below to introduce the present invention and to exemplify a context of application thereof.

[0067] The aircraft AC illustrated in [Fig.l] is equipped with a navigation system SYS. In the context of the invention, the term aircraft designates any device capable of rising and moving in the air, such as an airplane, a helicopter, a drone, etc.

[0068] The SYS navigation system comprises a satellite positioning RX receiver (i.e. a GNSS receiver); and an APP device.

[0069] The RX receiver is configured to receive signals transmitted by the satellites Si ,.. ,,SN. The satellites Sb...,SN belong for example to the satellite constellation of the GPS system, or of the Galileo system. In addition, the RX receiver is configured to determine, from the signals received from the satellites Sb...,SN, the pseudo-distances PR between the RX receiver of the aircraft AC and the satellites Sb.. .,SN. The RX receiver provides these pseudo-distances to the APP device. We also designate by "pseudo-distance between the aircraft and a satellite" a pseudo-distance between the RX receiver of the aircraft AC and a satellite Si.

[0070] For a given acquisition instant, and for each satellite Si among the set of satellites Si,...,SN, the RX receiver provides the pseudo-distance pp between the RX receiver and the satellite Si. We hereinafter denote PR={pri,...,prN] the set of pseudo-distances PR associated with the satellites Si,...,SN, and acquired at a given instant. In particular, the number of satellites N is greater than or equal to 6.

[0071] The navigation system APP is configured to determine navigation data of the aircraft AC from the pseudo-distances PR provided by the receiver RX. By “navigation data”, we mean here data relating to the position, and / or the movement of the aircraft AC, such as geographical coordinates (e.g. latitude, longitude, altitude), speed, attitudes.

[0072] Furthermore, the navigation system SYS may comprise an inertial unit and implement hybrid inertial-GNSS navigation. In other words, the navigation system SYS may determine the navigation data of the aircraft AC using both the pseudo-distances PR provided by the receiver RX; and the data from an inertial unit.

[0073] The APP device is configured to: detect a satellite failure; and / or identify a faulty satellite from the PR pseudo-distances provided by the RX receiver.

[0074] Furthermore, the APP device can be configured to implement the navigation solution of the SYS system, i.e. it can be configured to determine the navigation data of the aircraft AC. However, within the scope of the invention, the navigation solution of the SYS system could also be implemented by another device (distinct from the APP device).

[0075] The APP device comprises, according to the embodiment illustrated by [Fig.l]: at least one processing unit or processor PROC; and at least one memory MEM.

[0076] More particularly, the APP device has, according to one embodiment, the hardware architecture of a computer. The memory MEM constitutes an information medium in accordance with the invention, readable by a computer and by the processor PROC, on which is recorded a computer program PROG in accordance with the invention. The program PROG comprises instructions for carrying out steps of a method in accordance with the invention, when the program PROG is executed by the processor PROC. The program PROG defines the functional modules represented in [Fig. 2] of the APP device, which rely on or control the hardware elements of the latter.

[0077] As illustrated in [Fig.l], the APP device has a COM communication module configured to communicate with the RX receiver. No limitation is attached to the nature of the communication interfaces between these devices, which can be wired or wireless, and can implement any known protocol of the person skilled in the art.

[0078] The architecture of the APP device having been introduced, we describe below its operation with reference to the following figures.

[0079] [Fig.2] and [Fig.3] respectively represent the functional architecture of a device according to an embodiment of the invention and steps of a method according to an embodiment of the invention.

[0080] As illustrated in [Fig.2], the APP device comprises: a DET module for detecting a satellite failure; and / or an ID module for identifying a faulty satellite. The operation of these modules is described below with reference to the steps of [Fig.3].

[0081] The term module can correspond to a software component, a hardware component or a set of hardware and software components. A software component itself corresponds to one or more computer programs or any element of a program capable of implementing a function or a set of functions. In the same way, a hardware component corresponds to any element of a hardware assembly capable of implementing a function or a set of functions.

[0082] As illustrated by [Fig.3], the proposed method comprises (all or part) of the steps S100 to S400 described below and implemented by the APP device to detect a satellite failure FLT and / or identify a faulty satellite Sx.

[0083] Note that the proposed method may comprise a plurality of iterations of each of its steps. The steps of the method may be repeated at a given frequency, for example every second.

[0084] In step S100, the device APP obtains the pseudo-distances PR associated with the satellites Si,...,SN provided by the satellite positioning receiver RX.

[0085] In step S200, the detection module DET of the device APP detects the presence or absence of a satellite failure FLT from the pseudo-distances PR between the receiver RX and the satellites Si,.. .,SN. The implementation of step S200 is described in more detail with reference to [Fig.4].

[0086] If an FLT satellite failure is detected in step S200, then the method continues to step S300; otherwise, the method repeats steps S100 and S200.

[0087] Thus, according to one embodiment, the proposed method comprises several iterations ki,.. .,kM of the detection step S200. The iterations ki,.. .,kM of this step are implemented for pseudo-distances PR respectively acquired at times q,.. ,,tM.

[0088] In step S300, following the detection of a satellite failure FLT, the identification module ID of the APP device identifies the faulty satellite Sx among the set of satellites Si,.. .,SN from the pseudo-distances PR between the receiver RX and the satellites Si,.. .,SN. The implementation of step S300 is described in more detail with reference to [Fig.6].

[0089] In step S400, the APP device excludes the satellite Sx identified as faulty. More precisely, the pseudo-distances prx associated with the satellite Sx will no longer be used by the navigation system SYS to determine the navigation data of the aircraft AC.

[0090] The proposed solution described here makes it possible to detect a satellite failure FLT and to identify the faulty satellite Sx among the set of satellites Si,.. .,SN. Thus, the proposed method and device APP make it possible to exclude the faulty satellite Sx so that the navigation system SYS no longer uses the pseudo-distances prx associated with it.

[0091] It is important to emphasize that the APP device uses only the PR pseudodistances provided by the satellite positioning receiver RX (i.e. GNSS data), i.e. it does not use data from an inertial unit. Advantageously, the proposed solution can be implemented independently of the navigation solution used by the SYS system.

[0092] [Fig.4] represents steps of a method according to an embodiment of the invention. More specifically, this figure details the implementation of step S200 of detecting an FLT satellite failure, previously introduced with reference to [Fig.3].

[0093] According to the embodiment illustrated by [Fig.4], step S200 of detecting an FLT satellite failure comprises steps S210 to S230 described below.

[0094] In step S210, the device APP obtains a set P of positions of the aircraft AC. The set P comprises N positions pb...,pN. Each position p; of the set P is determined from the set of pseudo-distances PR;={pri,...,prN}\pr;. In other words, the position p; is resolved by excluding the satellite Si. More precisely, we designate by "position of the aircraft" a position of the receiver RX on board the aircraft AC.

[0095] According to one embodiment, the positions pi,..., pN of the set P are respectively determined using a Bancroft algorithm, for example using N Bancroft algorithms in parallel. The details of implementing a Bancroft algorithm, for resolving the position of a mobile from pseudo-distances associated with a set of satellites, are for example presented in the following document: S. Bancroft, “An Algebraic Solution of the GPS Equations”, IEEE Transactions on Aerospace and Electronic Systems, January 1985.

[0096] However, within the scope of the invention, embodiments could also be envisaged in which other algorithms are used to resolve the positions of the aircraft AC, for example a least squares algorithm, or a Kalman filter.

[0097] Note that, in certain exceptional cases, a Bancroft algorithm may fail to resolve a position p; of the aircraft AC. If this is the case, then the implementation implementation of step S200 of detecting a satellite failure is interrupted, and the method can resume at step S100.

[0098] In step S220, the device APP determines a dispersion indicator o of the positions of the set P. The dispersion indicator o measures the variability of the positions of the set P.

[0099] For this purpose, and according to the embodiment of [Fig.4], step S220 comprises steps S221 to S223 described below.

[0100] In step S221, the device APP determines an average position P from the positions of the set P. In particular, the average position p=Â^ p.

[0101] In step S222, the device APP determines a set D of distances between the positions of the set P and the average position P. Specifically, the set of distances D={di,...dN] with the distance || p.-p || •

[0102] In step S223, the device APP determines the dispersion indicator o from the set of distances D. In particular, the dispersion indicator o is equal to a standard deviation of the distances of the set D, i.e. rE^cHEA)2

[0103] Within the scope of the invention, embodiments could also be envisaged in which other dispersion indicators o are used to measure the variability of the positions of the set P. For example, the variance of the positions of the set P could be used.

[0104] In step S230, the APP device detects the presence or absence of a satellite FLT failure as a function of the dispersion indicator o. The APP device can, for example, detect a satellite FLT failure if the dispersion indicator o is greater than a threshold Xo.

[0105] More particularly, the APP device detects, according to one embodiment, an FLT satellite failure in the following manner. We consider the iteration kM of the detection step S200. In addition to the dispersion indicator o, the APP device determines a variation Ao of the dispersion indicator o during the previous iterations ki,...,kM. It then detects an FLT satellite failure if (and only if): the dispersion indicator o is greater than a threshold Xo and the variation Ao is greater than a threshold XAo. The thresholds Xo and kAo can in particular be set according to a given false alarm probability.

[0106] The variation Ao is determined from the values ​​of the indicator o determined during all or part of the iterations kb.. .,kM. The variation Ao may for example correspond to a slope coefficient determined by a linear regression of values ​​of the indicator o determined during the iterations ki,...,kM. According to other examples, the variation Ao may correspond to a derivative of the indicator o over time, or to a difference between values ​​of the indicator o determined during the iterations kB.. .,k M. The calculation of the variation Ao may further involve filtering operations, for example using a low-pass filter to eliminate rapid variations in the indicator o over time.

[0107] The proposed solution makes it possible to reliably detect a FLT satellite failure from the pseudo-distances PR between the receiver RX and the satellites Si,.. .,SN. We describe this point in more detail with reference to the following figure.

[0108] [Fig.5] represents values ​​of a dispersion indicator o determined by a method according to an embodiment of the invention for detecting a satellite failure.

[0109] This figure illustrates the values ​​of the dispersion indicator o during the iterations of the FLT satellite failure detection step S200. It therefore illustrates the evolution of the dispersion indicator o over time.

[0110] The time at which the FLT satellite failure occurs is indicated by dotted lines in this figure. Note that the values ​​of the dispersion indicator o are relatively low before the FLT satellite failure occurs, and that they then increase over time.

[0111] At a given time, if the satellites Si,.. .,SN are all functional, then the positions of the set P are determined using only pseudo-distances associated with functional satellites and are said to be healthy. The positions of the set P are therefore relatively close to the real position of the aircraft AC and have low variability. In this case, the value of the dispersion indicator o is low.

[0112] On the other hand, if a satellite Sx among the set of satellites Si,.. .,SN is faulty, only the position px is healthy, since it is determined using only pseudo-distances associated with functional satellites. The other positions p; (i^x) of the set P are determined using the pseudo-distance prx associated with the faulty satellite Sx and are corrupted by this erroneous pseudo-distance prx. These positions p; (i^x) are said to be faulty and move away from the real position of the aircraft AC. In addition, the faulty positions p; (i^x) have significant variations between them. In the event of a FLT satellite failure, the positions of the set P have a high variability and the value of the dispersion indicator o is significant.

[0113] For this reason, it is notably proposed to compare the dispersion indicator o with the threshold Xo to detect an FLT satellite failure.

[0114] Furthermore, it should be mentioned that the failure of the satellite Sx causes an alteration of the pseudo-distance prx associated with it over time, which may take the form of a bias, a drift, or an acceleration. As a result, the values ​​of the dispersion indicator o will present, over time, a sudden variation or a progressive increase as illustrated by [Fig.5].

[0115] Therefore, by jointly using the dispersion indicator o and the variation Ao, the proposed solution makes it possible to reliably detect an FLT satellite failure at from pseudo-distances PR between the RX receiver and the satellites Si,.. .,SN.

[0116] Following the detection of a satellite failure Sx, the proposed APP device identifies the faulty satellite Sx among the set of satellites Si,...,SN, to then exclude this faulty satellite Sx and no longer use the pseudo-distances associated with it. We describe the step S300 of identifying the faulty satellite Sx with reference to figures 6 and 7.

[0117] [Fig.6] represents steps of a method according to an embodiment of the invention. This figure details the implementation of step S300 of identifying the faulty satellite Sx, introduced above with reference to [Fig.3].

[0118] According to the embodiment illustrated by [Fig.6], step S300 of identifying the faulty satellite Sx comprises steps S310 to S330 described below.

[0119] As illustrated by [Fig.6], the step S300 of identifying the faulty satellite Sx is triggered by the detection of a satellite FLT failure. It is important to emphasize that the proposed method may comprise the step S200 of detecting the satellite FLT failure described above.

[0120] However, within the framework of the invention, embodiments could also be envisaged in which the FLT satellite failure is detected by another device (distinct from the APP device), which triggers the implementation of the steps described below.

[0121] For each satellite Si of the satellites Si,...,SN, the APP device implements steps S310 and S320. Steps S310-S320 can be implemented in parallel (i.e. concomitantly) for the different satellites Si,...,SN.

[0122] In step S310, the device APP obtains a set P; of positions of the aircraft AC. The set of positions P; comprises Nl positions. Each position p;j of the set P; is determined from the set of pseudo-distances PR;j={pri,.. .,prN}\{pr;, pq] with i4j- In other words, each position pij is resolved by excluding: the satellite Si; and another different satellite Sj for each position pLJ.

[0123] According to one embodiment, the positions of the set P; are respectively determined using a Bancroft algorithm. However, embodiments could be envisaged in which other algorithms are used to resolve these positions.

[0124] The sets Pb.. .,PN comprise a total of N(Nl) positions. However, it is not necessary to implement N(Nl) Bancroft algorithms. Some positions are common to several sets. For example, the position pij of the set Pi and the position p,. of the set Pj are identical. These two positions are both determined from the pseudo-distances {pn,.. .,prN}\{pri,prj}, i.e. excluding the satellites S; and Sj.

[0125] For this reason, according to one embodiment, the APP device obtains the sets of positions Pb.. .,PN in the following way. For any i F [ 1,N 1 , and for any je [[ 1 ,N ] such that j>i, the APP device resolves a position p;j of the aircraft AC from the pseudo-distances {pri,...,prN}\{pr;,prj}. It then uses the determined position pij for both the set P; and the set Pj. As a result, the APP device determines only N(Nl) / 2 positions of the aircraft AC, for example using N(Nl) / 2 Bancroft algorithms in parallel. This embodiment thus makes it possible to minimize the computational resources required to implement the proposed solution.

[0126] Note that, in certain exceptional cases, one of the Bancroft algorithms may fail to resolve a position pij of the aircraft AC. If this is the case, then the implementation of step S300 of identifying the faulty satellite is interrupted, and the method can resume at step S100.

[0127] In step S320, the APP device determines a dispersion indicator o, of the positions of the set P;. The dispersion indicator o, measures the variability of the positions of the set P;.

[0128] For this purpose, and according to the embodiment of [Fig.6], step S320 comprises steps S321 to S323 described below.

[0129] In step S321, the device APP determines an average position P; from the positions of the set P;. In particular, the average position _ 1 yN . Pi-N-1 ~ j=l ,j iPjj

[0130] In step S322, the device APP determines a set D; of distances between the positions of the set P; and the average position [Ë Precisely, for all j F | 1,NJ such that ji, the distance dij of the set D; is defined by Il Pij-Pi II •

[0131] In step S323, the device APP determines the dispersion indicator o, from the set of distances D;. The dispersion indicator o, is here equal to a standard deviation of the distances of the set D;. We therefore have n 2-jLy N fd___lv n d. vi “N-1 * i\Nl ^-u=l,u * iL Lu /

[0132] Alternatively, embodiments of the invention could be envisaged in which other types of dispersion indicators o, are used to measure the variability of the positions of the set P;.

[0133] In step S330, the APP device identifies the faulty satellite Sx among the set of satellites Si,...,SN according to the dispersion indicators ob..,,oN. The faulty satellite Sx identified by the APP device corresponds here to the satellite of the set of satellites Si,.. .,SN for which the dispersion indicator ox is minimum, i.e. ox= minto, oN).

[0134] The proposed solution makes it possible, in the event of a satellite failure, to identify the faulty satellite Sx from the pseudo-distances PR between the receiver RX and the satellites Si,..,SN. We present with reference to the following figure the reasons why the proposed solution makes it possible to reliably identify the faulty satellite Sx.

[0135] [Fig.7] represents values ​​of dispersion indicators ob.. .,oN determined by a method according to an embodiment of the invention for identifying a faulty satellite.

[0136] This figure illustrates, as an example, the evolution of the dispersion indicators ob..., o N over time. In this example, the number of satellites N is equal to 12, and the faulty satellite Sx is satellite S3.

[0137] The FLT satellite failure occurs at the instant indicated by dotted lines in the figure. Before the FLT satellite failure occurs, the values ​​of the dispersion indicators o, ,...,Oi2 are low. Then, the values ​​of these indicators all increase over time, with the exception of the dispersion indicator o3 determined by excluding the faulty satellite S3.

[0138] The dispersion indicator o3 is determined by excluding the faulty satellite S3. More precisely, the positions of the set P3 are obtained by excluding the pseudorange pr3 associated with the faulty satellite S3. Thus, the positions of the set P3 are estimated using only pseudoranges associated with functional satellites. Since the faulty satellite S3 is not used, the positions of the set P 3 are all healthy and have low variability. The value of the dispersion indicator o3 is therefore low

[0139] Conversely, the other dispersion indicators o, (i^3) are respectively determined by excluding a functional satellite Si. The positions of the set P; are obtained by using the pseudo-distance associated with the faulty satellite S3, with the exception of the position pi>3. The set P; then comprises 10 (i.e. N-2) faulty positions and a healthy position pi3. For this reason, the positions of the set P; present a strong variability and the value of the dispersion indicator o, is important.

[0140] By identifying the satellite Sx from the set of satellites Sb.. .,SN for which the dispersion indicator ox is minimum, the proposed solution makes it possible to reliably identify the faulty satellite from the set of satellites Sb...,SN.

[0141] Advantageously, the solution proposed above makes it possible to detect a satellite failure and to identify the faulty satellite using only pseudodistances provided by a satellite positioning receiver, i.e. without using inertial data. The proposed solution can in particular be implemented independently of the navigation solution used by the SYS system for the AC aircraft.

[0142] Additional variants: It should be noted that the order in which the steps of a method according to the invention, in particular with reference to the attached drawings, constitutes only an example of embodiment without any limiting character, variants being possible. In particular, a method according to the invention may comprise one or more iterations of the steps described above, in particular with reference to the attached drawings. Furthermore, the reference signs do not limit the scope of the protection, their sole function being to facilitate the understanding of the claims.

[0143] A person skilled in the art will understand that the embodiments and variants described above constitute only non-limiting examples of implementation of the invention. In particular, a person skilled in the art will be able to envisage any adaptation or combination of the embodiments and variants described above in order to meet a very specific need.

Claims

Claims

1. Method for identifying a faulty satellite among a set of satellites Si,.. .,SN from pseudo-distances (PR) between a mobile (AC) and the satellites Si,...,SN, the method comprising, following a detection (S200) of a satellite failure (FLT), steps of: - for each satellite S; of the set of satellites Si,.. .,SN: • obtaining (S310) a set R of positions of the mobile (AC), each position pij being determined from the pseudo-distances (PR) associated with the satellites Si,...,SN excluding: the satellite S; ; and at least one other different satellite Sj for each position pij; • determining (S320) a dispersion indicator o, of the positions of the set P; ; and - identifying (S330) the faulty satellite among the set of satellites Si,...,SN as a function of the dispersion indicators 01,...,¾.

2. Method according to claim 1, in which the step of determining (S320) the dispersion indicator o, comprises steps of: - determining (S321) an average position P; from the positions of the set R; - determining (S322) a set D; of distances between the positions of the set R and the average position P; ; and - determining (S323) the dispersion indicator o, from the set D;, the dispersion indicator o, being equal to a standard deviation of the distances of the set D;.

3. Method according to claim 1 or 2, in which each set of positions P; comprises Nl positions of the mobile (AC), and each position Pij of the set P; is determined (S310) from the pseudo-distances (PR) associated with the satellites Si,...,SN excluding: the satellite Si; and another different satellite Sj for each position pLJ.

4. Method according to claim 3, comprising for each satellite Si of the set of satellites Si,...,SN, and for each satellite Sj of the set of satellites Si,...,SN with j>i: a determination of a position of the mobile (AC) from the pseudo-distances (PR) associated with the satellites Si,...,SN excluding the satellite Si and the satellite Sj, the determined position being used to obtain (S310) the position p;j of the set P; and the position pj4 of the set Pj.

5. Method according to any one of claims 1 to 4, further comprising a step of detecting (S200) the satellite failure (FLT), the detection step (S200) comprising steps of: - obtaining (S210) a set P of positions of the mobile (AC), each position p; being determined from the pseudodistances associated with the satellites Si,...,SN by excluding a different satellite Si for each position p;; - determining (S220) a dispersion indicator o of the positions of the set P; and - detecting (S230) the satellite failure (FLT) as a function of the dispersion indicator o.

6. Method according to claim 5, wherein the step of determining (S220) the dispersion indicator o comprises steps of: - determining (S221) an average position P from the positions of the set P; - determining (S222) a set D of distances between the positions of the set P and the average position P; and - determining (S223) the dispersion indicator o from the set D, the dispersion indicator o being equal to a standard deviation of the distances of the set D.

7. Method according to claim 5 or 6, comprising several iterations ki ,.. .,kM of the detection step (S200), the iterations kb...,kM being implemented for pseudo-distances (PR) acquired at different times, and in which the satellite failure (FLT) is detected (S230) during the iteration kM if: - the dispersion indicator o of the iteration kM is greater than a threshold; and if - a variation Ao of the dispersion indicator o during the iterations ki,...,kM is greater than another threshold.

8. Method according to any one of claims 1 to 7, wherein the positions of the mobile (AC) are determined (S210, S310) using a Bancroft algorithm.

9. Device (APP) for identifying a faulty satellite among a set of satellites Si,.. .,SN from pseudo-distances (PR) between a mobile (AC) and the satellites Si,...,SN, the device (APP) comprising an identification module (ID) configured to, following detection (S200) of a satellite failure (FLT): - for each satellite Si of the set of satellites Si,.. .,SN: • obtain (S310) a set P; of positions of the mobile (AC), each position pij being determined from the pseudo-distances (PR) associated with the satellites Si,...,SN while excluding: the satellite Si; and at least one other different satellite Sj for each position pLJ; • determine (S320) a dispersion indicator o, of the positions of the set Pi; and - identify (S330) the faulty satellite among all its tellites Si,...,SN according to the dispersion indicators Oi,.. .,oN.

10. Navigation system (SYS) intended to be embedded in a mobile (AC) comprising: - a satellite positioning receiver (RX) configured to provide pseudo-distances between the mobile (AC) and a set of satellites; and - a device (APP) according to claim 9.

11. Mobile machine (AC) comprising a navigation system (SYS) according to claim 10.

12. Computer program (PROG) comprising instructions for implementing the steps of a method according to any one of claims 1 to 8, when said computer program (PROG) is executed by at least one processor (PROC).

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