WO2007026098A1 - Device for checking the consistency of broadcast information, with no constraints on the clocks of the monitoring stations, for a satellite navigation system - Google Patents

Device for checking the consistency of broadcast information, with no constraints on the clocks of the monitoring stations, for a satellite navigation system Download PDF

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Publication number
WO2007026098A1
WO2007026098A1 PCT/FR2006/050820 FR2006050820W WO2007026098A1 WO 2007026098 A1 WO2007026098 A1 WO 2007026098A1 FR 2006050820 W FR2006050820 W FR 2006050820W WO 2007026098 A1 WO2007026098 A1 WO 2007026098A1
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satellite
sai
satellites
difference
scj
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PCT/FR2006/050820
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French (fr)
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Mathias Van Den Bossche
Antoine Clerino
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Alcatel Lucent
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/03—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers
    • G01S19/08—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers providing integrity information, e.g. health of satellites or quality of ephemeris data
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/02—Details of the space or ground control segments

Definitions

  • the invention relates to satellite navigation systems, and more specifically to the control of coherence between information contained in navigation messages, broadcast by the satellites of such systems, and measurements of pseudo-distances, made by radio stations. monitoring of these systems.
  • a satellite navigation system conventionally comprises, firstly, a constellation of satellites placed in orbit, responsible for transmitting signals making it possible to measure distances and to broadcast, in the direction of the Earth, navigation messages provided by the mission ground segment of the system and intended to inform the users of the respective positions of the satellites and their offsets, or a second part, a set of monitoring stations, located in places selected from the Earth or in spacecraft and responsible for collecting the navigation messages transmitted by satellites and to perform measurements relating to the pseudo-distances that separate them from satellites in view, and thirdly, a station of calculation (part of the mission ground segment) responsible, in particular, for checking the consistency between the information contained in the navigation messages broadcast by satellites and measurements of pseudo-distances made by the monitoring stations.
  • This consistency check is intended to validate, almost in real time (typically in a few seconds), the accuracy of the navigation messages broadcast by the various satellites of the constellation (and therefore the physical integrity of the users). It consists more precisely in verifying the adequacy of the orbital positions of the different satellites and the time offsets (or clock offsets) contained in the messages of navigation they broadcast, with the measurements relating to pseudo-distances made by the monitoring stations.
  • the overall performance of the consistency check depends on the resolution of the fit checks, which depends on the measurement errors on the pseudoranges.
  • a first solution is to use high precision atomic clocks in monitoring stations in order to minimize the contributions of hardware components to clock offsets.
  • the constraints imposed on the electronic components contribute to the increase of the costs of the monitoring stations and prevent to use the existing equipment with clocks less precise and noticeably less expensive. This is mainly because the consistency check is done almost in real time.
  • the consistency check is based on the use of near-instantaneous measurements, the number of which is fixed by the number of N sta monitoring stations (typically 1O.N sta ).
  • N sta is the number of monitoring stations in the system
  • its resolution should be approximately the order of that of the prediction of orbits, which is incompatible with the reduction in the number of monitoring stations imposed by their costs.
  • a second solution consists in estimating the different clock offsets ("synchronization") by means of a pre-processing software, before carrying out the consistency check.
  • the clock offsets of the monitoring stations are unknowns of the consistency check, the others are satellite orbit errors and satellite clock offsets.
  • the reason that the clock offsets of the monitoring stations can be estimated by means of a program before the consistency check results from the fact that their estimates can be made by means of filters (for example of the Kalman type) which are considered unsafe for the prediction of satellite orbit errors and satellite clock offsets.
  • the program introduces constraints that limit the performance of the consistency check. Indeed, this program is not optimal since the estimate it makes of clock offsets does not take into account satellite orbit errors and satellite clock offsets, which is a problem when of the consistency check phase itself.
  • the ability of the filters to improve the performance of the estimates is directly related to the possibility of modeling the physical phenomena objects of said estimates.
  • this requires very precise atomic clocks, whose behavior modeling is very delicate because of their stochastic nature and whose costs are very high.
  • an information coherence verification device for a station for calculating a mission ground segment of a satellite navigation system comprising a constellation of satellites emitting signals (intended to make pseudo measurements). -distances) and broadcasting navigation messages containing information to be verified, and a set (or network) of terrestrial or spatial monitoring stations determining pseudo-distances separating them from satellites in view from the broadcast navigation messages.
  • This information consistency verification device is characterized by the fact that it comprises processing means loaded, in the event of reception, of a first part, of representative data of pseudo-data. distances determined substantially simultaneously by each monitoring station relative to each satellite in view, a second part, navigation messages corresponding to these data, broadcast by the satellites, and thirdly, times of reception of these messages navigation:
  • each equation is the expression of a difference ( ⁇ p ⁇ ) between pseudo-range residues ( ⁇ ! y , ⁇ k J ) , relating to two satellites seen by the same monitoring station and each representing the difference between the pseudo-distance determined by this monitoring station relative to one of the two satellites in view and a distance determined from the data received, this difference between residues ( ⁇ p /)) being equal to the combination between a distance representative of an estimated clock offset difference between the two satellites, a difference between the projections, according to the directions linking the two satellites to the monitoring station, of geometrical errors of orbital positioning of the two satellites, and a difference between residual errors on the determined pseudo-distances es by connection with two satellite monitoring station and
  • the device according to the invention may comprise other characteristics that can be taken separately or in combination, and in particular:
  • its processing means may be responsible for defining at i) equations in which each difference between residues is equal to a combination in which are added to the distance representative of the estimated clock offset difference between the second satellite and the first satellite, on the one hand, the geometric error projection difference orbital positioning between the second satellite and the first satellite, and secondly, the residual error difference on the pseudo-distance between the first satellite and the second satellite;
  • its processing means may be responsible for performing a sum-type combination between the selected projection of the geometrical orbital positioning error of a satellite and the distance representative of the difference between the estimated clock offsets and predicted this satellite, in order to compare the result of this sum to the chosen threshold. ;
  • its processing means may be responsible for selecting at ii) the most unfavorable projection, on the terrestrial surface where the satellite is visible, of its geometrical orbital positioning error;
  • it may comprise storage means coupled to its processing means and suitable for storing the data received from the monitoring stations.
  • the invention also proposes a computing station (or coherence monitoring center), for a satellite navigation system, equipped with a coherence verification device of the type of that presented above.
  • the invention also proposes a terrestrial or spatial monitoring station, for a satellite navigation system comprising a computing station of the type of that presented above and satellites generating and broadcasting navigation messages containing information to be verified, and arranged to determine pseudo-distances substantially simultaneously with respect to each satellite it sees, from the navigation messages they broadcast.
  • the single figure schematically illustrates a part of a satellite navigation system comprising a computing station equipped with an exemplary embodiment of a coherence verification device according to the invention.
  • the attached drawing may not only serve to complete the invention, but also contribute to its definition, if any.
  • the satellite navigation system is the future GALILEO system. But, the invention is not limited to this system.
  • the SAi satellites are placed in orbit and are charged, in particular, to emit signals making it possible to make pseudo-range measurements and to diffuse in the direction of the Earth T navigation messages which are transmitted to them by the ground segment. mission, so that the information they contain is exploited by navigation receivers and SCj monitoring stations.
  • SCj monitoring stations are located in selected locations of the Earth T or in spacecraft, such as satellites. In particular, they are responsible for collecting the navigation messages transmitted by the satellites SAi of the constellation, and for measuring the pseudo-distances separating them from the SAi satellites in view.
  • the satellite SA1 is in view of the monitoring stations SC1, SC2 and SC3
  • the satellite SA2 is in view of the monitoring stations SC1, SC2, SC3 and SC4
  • the satellite SA3 is in view of the stations.
  • SC2, SC3 and SC4 monitoring More precisely, each monitoring station SCj periodically performs a measurement p, j of the pseudo-distance which separates it from the satellite in view SAi. This estimate is made from the difference between the instant of reception by the monitoring station SCj of a navigation message transmitted by the satellite in view SAi and the instant of transmission of this received navigation message, defined by the information it contains.
  • Each measurement p, j and the corresponding navigation message and its reception time are communicated by each monitoring station SCj to the computing station SG.
  • the computing station SG is generally located on the Earth T. It comprises a consistency checking device D equipped with a processing module MT loaded, in particular, to check the coherence between the pseudo-jacks Pi j and the information contained in the messages. (which are broadcast by the SAi satellites), which are communicated to it by the SCj monitoring stations.
  • the calculation station SG can also be responsible for predicting the trajectories and clock offsets of the satellites SAi from the pseudo-distances made by the monitoring stations SCj. These predictions of trajectories and clock offsets are used to generate the future navigation messages that are transmitted to SAi satellites for broadcasting.
  • the data that is processed by the processing module MT are collected from the monitoring stations SCj by the device D, or else transmitted to the device D by said monitoring stations SCj automatically or on request.
  • the device D comprises storage means MY, such as a memory or a database, in which it stores at least temporarily the data received (or collected) so that they can be processed.
  • the first step is to solve the equation system of pseudo-range residues (1), given below:
  • j is the distance prediction between a monitoring station SCj and a satellite in view SAi, which is determined by the processing module MT from the information (data) contained in the navigation message broadcast by the satellite SAi,
  • Atf c is the difference between the time given by the clock of the monitoring station SCj and a reference time. It is also called clock shift of the monitoring station,
  • Aff A and hJ ⁇ X SA are three unknowns to be estimated for each pair of monitoring station SCj and of satellite in view SAi.
  • the system of equations (1) thus has 4N SA + N sc unknown.
  • this system comprises about 400 equations and 160 unknowns, which leads to a so-called “over-determination” (or “over-determination”) report.
  • "- number of equations divided by the number of unknowns) equal to 2.5.
  • the second step of the consistency check is to perform the sum of the most unfavorable projection, on the surface of the Earth T where the satellite SAi is visible, of the geometric positioning error ⁇ X SA of the satellite SAi, with the result of the product of the constant "c" by the difference between the estimated value of the bias (or clock shift) ⁇ t £ f and the predicted value of this bias, which can be determined from the information contained in the navigation message transmitted by the satellite in view SAi, and then generates an alarm when this sum is greater than a chosen threshold.
  • the processing module MT must therefore determine the bias ⁇ f ⁇ of each monitoring station SCj to solve each system of equations (1), which amounts to determining the synchronization of the "network" of monitoring stations SCj with respect to the reference time of the system, even though these At ref SC 1 bias are not used in the second step of the consistency check.
  • the invention proposes to proceed differently from what has just been described. It is based on the observation that clock offsets Af ⁇ and
  • SAi are terms that appear in the system of equations (1) currently used to verify the coherence of the information broadcast by the satellites SAi, but that in a particular calculation configuration the estimate of the offsets of The clock of the monitoring stations SCj is not necessary for this verification of coherence which concerns in reality only satellite unknowns Af s ⁇ e and ⁇ ⁇ SX ⁇ .
  • the invention therefore proposes, first of all, that each monitoring station SCj substantially simultaneously performs the pseudorange measurements Pij relating to each SAi satellite that it sees.
  • all the py measurements of a monitoring station SCj are affected by the same monitoring station clock offset SCj Atf c (also called bias).
  • the processing module MT of the consistency checking device D can then operate in a mode that can be described as differential by making differences ⁇ p ⁇ between pseudo-range residues ⁇ !; 7 and ⁇ tj relative to two satellites SAi and SAk (with i ⁇ k) seen by the same monitoring station SCj.
  • the conventional system of equations (1) whose resolution is the subject of the first step performed by the processing module MT, is transformed into a new system of equations (2), of the type of the one given below, which no longer includes bias terms Af s e £ monitoring station SCj:
  • the processing module MT thus constitutes the system of equations (2) from the data received from the monitoring stations SCj (for example stored in the memory MY), and then it resolves this system of equations (2) by determining the unknowns ⁇ t £ f and ⁇ ⁇ r ⁇ X SA for each monitoring station SCj and each satellite SAi that it sees.
  • each bias ⁇ t £ f corresponds to the difference between the time of a satellite SAi tsAi and a reference time t ref , which is itself defined with respect to an origin of time.
  • N TM 1 - 1 For a given station SCj there are (N TM 1 - 1) independent combinations. Therefore, the total number of independent equations equals N SA x (N TM 1 - 1) +1 and the number of unknowns equals 4N SA .
  • the over-determination ratio is then typically equal to 3, and in the case of a GALILEO system comprising 100 monitoring stations this ratio becomes 7.5.
  • the combination that is indicated in the right-hand side of the system of equations (2) is a preferential combination. It may be subject to variations, provided that it is constituted from the appropriate sum (s) and / or subtraction (s) of at least the distance representative of the estimated clock offset difference between the first SAi and second satellite SAk, the geometric error projection difference of orbital positioning between the first SAi and second SAk satellites, and the difference in residual error on the pseudo-distance between the first SAi and second satellite SAk.
  • the second step of the consistency check is substantially identical to that performed by a conventional consistency checking device. It therefore consists, as indicated above, in carrying out the sum of the most unfavorable projection, on the surface of the Earth T where the satellite SAi is visible, of the geometric positioning error ⁇ X S ⁇ of the satellite SAi, with the result of the produces the constant "c" by the difference between the estimated value of Af s ⁇ e and its predicted value contained in the navigation message transmitted by the satellite in view SAi, and then generating an alarm when this sum is greater than a threshold selected.
  • the combination that serves in this second step is a preferential combination. It can be the subject of variants, since it consists of a sum and / or an appropriate subtraction between at least one selected projection of the geometrical orbital positioning error of a satellite SAi and a distance representative of the difference between the estimated and predicted clock offsets of the satellite SAi.
  • the coherence verification device D and in particular its processing module MT and its possible memory MY, can be realized in the form of electronic circuits, software (or computer) modules, or a combination of circuits. and software.
  • the invention offers many advantages, among which:
  • Atomic clocks of very high precision which makes it possible to significantly reduce their cost and to reuse existing navigation equipment, such as for example certain airport receivers used in LAAS (Local Area Augmentation System) systems. significantly improve the accuracy of location in small areas such as airports),
  • LAAS Local Area Augmentation System
  • the over-determination ratio increases faster than the linear increase in efficiency (typically 3 in the case of a GALILEO system comprising 40 monitoring stations, and 7.5 in the case of a GALILEO system comprising 100 stations monitoring).
  • the overdetermination ratio typically goes from 3 to 4 in the case of a GALILEO system with 40 monitoring stations, and from 7.5 to 10 in the case of a Galileo system. a GALILEO system with 100 monitoring stations),
  • a composite clock based on all the clocks of the satellites can be used as a reference time scale, so that an optimal time reference can be available since it is the time reference that the can be generated at the level of the system that is closest to that used by the users of the system,
  • the invention is not limited to device embodiments of coherence verification, monitoring station and computing station described above, only by way of example, but it encompasses all the variants that may be considered by those skilled in the art within the scope of the claims below.

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
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Abstract

The invention relates to a device (D) which is dedicated to checking the consistency of information broadcast by satellites (SA1-SA3) within a computing station (SG) of a satellite navigation system. The inventive device (D) comprises processing means (MT) and, upon reception of data representative of pseudo-distances which are determined essentially simultaneously by each monitoring station (SC1-SC4) of the system in relation to each satellite within sight and of corresponding navigation messages broadcast by said satellites and of the times at which they are received by the monitoring stations, said processing means (MT) are used to: i) define and solve a system of equations of the type having formula (I); and ii) generate an alarm each time the result of a combination between a selected projection of the geometric error in relation to the orbital positioning of a satellite (SA1) and a distance representative of the difference between the estimated clock offset and a predicted clock offset for said satellite (SA1) is above a selected threshold.

Description

DISPOSITIF DE VERIFICATION DE COHERENCE D'INFORMATIONS DIFFUSEES, SANS CONTRAINTE SUR LES HORLOGES DES STATIONS DE SURVEILLANCE, POUR UN SYSTEME DE NAVIGATION PAR SATELLITESDEVICE FOR VERIFYING COHERENCE OF DIFFUSE INFORMATION, WITHOUT CONSTRAINTS ON THE CLOCKS OF SURVEILLANCE STATIONS, FOR A SATELLITE NAVIGATION SYSTEM
L'invention concerne les systèmes de navigation par satellites, et plus précisément le contrôle de la cohérence entre des informations contenues dans des messages de navigation, diffusés par les satellites de tels systèmes, et des mesures de pseudo-distances, effectuées par des stations de surveillance de ces systèmes.The invention relates to satellite navigation systems, and more specifically to the control of coherence between information contained in navigation messages, broadcast by the satellites of such systems, and measurements of pseudo-distances, made by radio stations. monitoring of these systems.
Un système de navigation par satellites comporte classiquement, d'une première part, une constellation de satellites placés en orbite, chargés d'émettre des signaux permettant de faire des mesures de distance et de diffuser en direction de la Terre des messages de navigation fournis par le segment sol de mission du système et destinés à informer les usagers des positions respectives des satellites et de leurs décalages d'horloge (ou « dock offsets »), d'une deuxième part, un ensemble de stations de surveillance, situées en des endroits choisis de la Terre ou dans des engins spatiaux et chargées de collecter les messages de navigation transmis par les satellites et d'effectuer des mesures relatives aux pseudo-distances qui les séparent des satellites en vue, et d'une troisième part, une station de calcul (faisant partie du segment sol de mission) chargée, notamment, de vérifier la cohérence entre les informations contenues dans les messages de navigation diffusés par les satellites et les mesures de pseudo-distances effectuées par les stations de surveillance.A satellite navigation system conventionally comprises, firstly, a constellation of satellites placed in orbit, responsible for transmitting signals making it possible to measure distances and to broadcast, in the direction of the Earth, navigation messages provided by the mission ground segment of the system and intended to inform the users of the respective positions of the satellites and their offsets, or a second part, a set of monitoring stations, located in places selected from the Earth or in spacecraft and responsible for collecting the navigation messages transmitted by satellites and to perform measurements relating to the pseudo-distances that separate them from satellites in view, and thirdly, a station of calculation (part of the mission ground segment) responsible, in particular, for checking the consistency between the information contained in the navigation messages broadcast by satellites and measurements of pseudo-distances made by the monitoring stations.
Cette vérification de cohérence est destinée à valider, quasiment en temps réel (typiquement en quelques secondes), la justesse des messages de navigation diffusés par les différents satellites de la constellation (et donc l'intégrité physique des usagers). Elle consiste plus précisément à vérifier l'adéquation des positions orbitales des différents satellites et des décalages temporels (ou décalages d'horloge), contenus dans les messages de navigation qu'ils diffusent, avec les mesures relatives aux pseudo-distances effectuées par les stations de surveillance. La performance globale de la vérification de cohérence dépend de la résolution des vérifications d'adéquation, laquelle dépend des erreurs de mesure sur les pseudodistances.This consistency check is intended to validate, almost in real time (typically in a few seconds), the accuracy of the navigation messages broadcast by the various satellites of the constellation (and therefore the physical integrity of the users). It consists more precisely in verifying the adequacy of the orbital positions of the different satellites and the time offsets (or clock offsets) contained in the messages of navigation they broadcast, with the measurements relating to pseudo-distances made by the monitoring stations. The overall performance of the consistency check depends on the resolution of the fit checks, which depends on the measurement errors on the pseudoranges.
Comme le sait l'homme de l'art, l'un des principaux contributeurs aux erreurs de mesure est le décalage d'horloge des stations de surveillance. Par conséquent, si l'on souhaite effectuer une vérification de cohérence efficace, il est important de réduire autant que possible la contribution des décalages d'horloge. Deux solutions ont été proposées à cet effet.As known to those skilled in the art, one of the major contributors to measurement errors is the clock shift of the monitoring stations. Therefore, if it is desired to perform an effective consistency check, it is important to minimize the contribution of clock offsets as much as possible. Two solutions have been proposed for this purpose.
Une première solution consiste à utiliser dans les stations de surveillance des horloges atomiques de grande précision afin de réduire au maximum les contributions des composants matériels (« hardware ») aux décalages d'horloge. Les contraintes imposées aux composants électroniques contribuent à l'augmentation des coûts des stations de surveillance et empêchent d'utiliser les équipements existants avec des horloges moins précises et notablement moins chères. Cela résulte principalement du fait que la vérification de cohérence s'effectue quasiment en temps réel. En effet, contrairement aux prédictions d'orbites et de comportements d'horloge qui reposent sur la collecte pendant un long intervalle de temps (un arc de tarc heures) de milliers de mesures (typiquement tarc.12O. 1O.Nsta, où Nsta est le nombre de stations de surveillance du système), la vérification de cohérence repose sur l'utilisation de mesures quasi-instantanées dont le nombre est fixé par le nombre de stations de surveillance Nsta (typiquement 1O.Nsta). Or, pour que la vérification de cohérence soit optimale il faudrait que sa résolution soit approximativement de l'ordre de celle de la prédiction d'orbites, ce qui est incompatible avec la réduction du nombre de stations de surveillance imposée par leurs coûts.A first solution is to use high precision atomic clocks in monitoring stations in order to minimize the contributions of hardware components to clock offsets. The constraints imposed on the electronic components contribute to the increase of the costs of the monitoring stations and prevent to use the existing equipment with clocks less precise and noticeably less expensive. This is mainly because the consistency check is done almost in real time. In fact, contrary to the predictions of orbits and clock behaviors that rely on the collection for a long time interval (an arc of t arc hours) of thousands of measurements (typically t arc .12O .1O.N sta , where N sta is the number of monitoring stations in the system), the consistency check is based on the use of near-instantaneous measurements, the number of which is fixed by the number of N sta monitoring stations (typically 1O.N sta ). However, for the consistency check to be optimal, its resolution should be approximately the order of that of the prediction of orbits, which is incompatible with the reduction in the number of monitoring stations imposed by their costs.
Une seconde solution consiste à estimer les différents décalages d'horloge (« synchronisation ») au moyen d'un logiciel de pré-traitement, avant de procéder à la vérification de cohérence. Les décalages d'horloge des stations de surveillance sont des inconnues de la vérification de cohérence, les autres étant les erreurs d'orbites satellitaires et les décalages d'horloge des satellites. La raison pour laquelle les décalages d'horloge des stations de surveillance peuvent être estimés au moyen d'un programme avant la vérification de cohérence, résulte du fait que leurs estimations peuvent être effectuées au moyen de filtres (par exemple de type Kalman) qui sont considérés comme peu sûrs pour la prédiction des erreurs d'orbites satellitaires et des décalages d'horloge des satellites. Hélas, le programme introduit des contraintes qui limitent les performances de la vérification de cohérence. En effet, ce programme n'est pas optimal dans la mesure où l'estimation qu'il fait des décalages d'horloge ne tient pas compte des erreurs d'orbites satellitaires et des décalages d'horloge des satellites, ce qui pose problème lors de la phase de vérification de cohérence proprement dite. Par ailleurs, l'aptitude des filtres à améliorer les performances des estimations est directement liée à la possibilité de modéliser les phénomènes physiques objets desdites estimations. Or, cela nécessite des horloges atomiques très précises, dont la modélisation de comportement est très délicate du fait de leur caractère stochastique et dont les coûts sont très élevés.A second solution consists in estimating the different clock offsets ("synchronization") by means of a pre-processing software, before carrying out the consistency check. The clock offsets of the monitoring stations are unknowns of the consistency check, the others are satellite orbit errors and satellite clock offsets. The reason that the clock offsets of the monitoring stations can be estimated by means of a program before the consistency check results from the fact that their estimates can be made by means of filters (for example of the Kalman type) which are considered unsafe for the prediction of satellite orbit errors and satellite clock offsets. Alas, the program introduces constraints that limit the performance of the consistency check. Indeed, this program is not optimal since the estimate it makes of clock offsets does not take into account satellite orbit errors and satellite clock offsets, which is a problem when of the consistency check phase itself. Moreover, the ability of the filters to improve the performance of the estimates is directly related to the possibility of modeling the physical phenomena objects of said estimates. However, this requires very precise atomic clocks, whose behavior modeling is very delicate because of their stochastic nature and whose costs are very high.
Il est également possible de combiner les deux solutions décrites précédemment, mais cela n'est toujours pas satisfaisant.It is also possible to combine the two solutions described above, but this is still not satisfactory.
Aucune solution connue n'apportant une entière satisfaction, l'invention a donc pour but d'améliorer la situation.Since no known solution is entirely satisfactory, the purpose of the invention is therefore to improve the situation.
Elle propose à cet effet un dispositif de vérification de cohérence d'informations pour une station de calcul d'un segment sol de mission d'un système de navigation par satellites comprenant une constellation de satellites émettant des signaux (destinés à faire des mesures de pseudo-distances) et diffusant des messages de navigation contenant des informations à vérifier, et un ensemble (ou réseau) de stations de surveillance terrestres ou spatiales déterminant des pseudo-distances les séparant de satellites en vue à partir des messages de navigation diffusés.It proposes for this purpose an information coherence verification device for a station for calculating a mission ground segment of a satellite navigation system comprising a constellation of satellites emitting signals (intended to make pseudo measurements). -distances) and broadcasting navigation messages containing information to be verified, and a set (or network) of terrestrial or spatial monitoring stations determining pseudo-distances separating them from satellites in view from the broadcast navigation messages.
Ce dispositif de vérification de cohérence d'informations se caractérise par le fait qu'il comprend des moyens de traitement chargés, en cas de réception, d'une première part, de données représentatives de pseudo- distances déterminées sensiblement simultanément par chaque station de surveillance relativement à chaque satellite en vue, d'une deuxième part, de messages de navigation correspondants à ces données, diffusés par les satellites, et d'une troisième part, des instants de réception de ces messages de navigation :This information consistency verification device is characterized by the fact that it comprises processing means loaded, in the event of reception, of a first part, of representative data of pseudo-data. distances determined substantially simultaneously by each monitoring station relative to each satellite in view, a second part, navigation messages corresponding to these data, broadcast by the satellites, and thirdly, times of reception of these messages navigation:
- de définir et résoudre un système d'équations (éventuellement associé à une référence temporelle) dans lequel chaque équation est l'expression d'une différence (δΔp^ ) entre des résidus de pseudo-distances ( Δρ! y , Δρk J ), relatifs à deux satellites vus par une même station de surveillance et représentant chacun la différence entre la pseudo-distance déterminée par cette station de surveillance relativement à l'un des deux satellites en vue et une distance déterminée à partir des données reçues, cette différence entre résidus (δΔp/^ ) étant égale à la combinaison entre une distance représentative d'une différence de décalage d'horloge estimé entre les deux satellites, une différence entre les projections, suivant les directions liant les deux satellites à la station de surveillance, d'erreurs géométriques de positionnement orbital des deux satellites, et une différence entre des erreurs résiduelles sur les pseudo-distances déterminées par la station de surveillance relativement aux deux satellites, puisto define and solve a system of equations (possibly associated with a temporal reference) in which each equation is the expression of a difference (δΔp ^) between pseudo-range residues (Δρ ! y , Δρ k J ) , relating to two satellites seen by the same monitoring station and each representing the difference between the pseudo-distance determined by this monitoring station relative to one of the two satellites in view and a distance determined from the data received, this difference between residues (δΔp /)) being equal to the combination between a distance representative of an estimated clock offset difference between the two satellites, a difference between the projections, according to the directions linking the two satellites to the monitoring station, of geometrical errors of orbital positioning of the two satellites, and a difference between residual errors on the determined pseudo-distances es by connection with two satellite monitoring station and
- de générer une alarme chaque fois que le résultat d'une combinaison, entre une projection choisie de l'erreur géométrique de positionnement orbital d'un satellite et une distance représentative de la différence entre le décalage d'horloge estimé et un décalage d'horloge prédit de ce satellite, est supérieur à un seuil choisi.to generate an alarm whenever the result of a combination between a chosen projection of the geometrical orbital positioning error of a satellite and a distance representative of the difference between the estimated clock offset and an offset of predicted clock of this satellite, is greater than a chosen threshold.
Le dispositif selon l'invention peut comporter d'autres caractéristiques qui peuvent être prises séparément ou en combinaison, et notamment :The device according to the invention may comprise other characteristics that can be taken separately or in combination, and in particular:
- ses moyens de traitement peuvent être chargés de définir au i) des équations dans lesquelles chaque différence entre résidus est égale à une combinaison dans laquelle sont additionnées à la distance représentative de la différence de décalage d'horloge estimé entre le second satellite et le premier satellite, d'une part, la différence de projection d'erreur géométrique de positionnement orbital entre le second satellite et le premier satellite, et d'autre part, la différence d'erreur résiduelle sur la pseudo-distance entre le premier satellite et le second satellite ;its processing means may be responsible for defining at i) equations in which each difference between residues is equal to a combination in which are added to the distance representative of the estimated clock offset difference between the second satellite and the first satellite, on the one hand, the geometric error projection difference orbital positioning between the second satellite and the first satellite, and secondly, the residual error difference on the pseudo-distance between the first satellite and the second satellite;
- ses moyens de traitement peuvent être chargés d'effectuer au ii) une combinaison de type somme entre la projection choisie de l'erreur géométrique de positionnement orbital d'un satellite et la distance représentative de la différence entre les décalages d'horloge estimé et prédit de ce satellite, afin de comparer le résultat de cette somme au seuil choisi. ;its processing means may be responsible for performing a sum-type combination between the selected projection of the geometrical orbital positioning error of a satellite and the distance representative of the difference between the estimated clock offsets and predicted this satellite, in order to compare the result of this sum to the chosen threshold. ;
- ses moyens de traitement peuvent être chargés de choisir au ii) la projection la plus défavorable, sur la surface terrestre où le satellite est visible, de son erreur géométrique de positionnement orbital ;its processing means may be responsible for selecting at ii) the most unfavorable projection, on the terrestrial surface where the satellite is visible, of its geometrical orbital positioning error;
- il peut comprendre des moyens de mémorisation couplés à ses moyens de traitement et propres à stocker les données reçues des stations de surveillance.it may comprise storage means coupled to its processing means and suitable for storing the data received from the monitoring stations.
L'invention propose également une station de calcul (ou centre de surveillance de la cohérence), pour un système de navigation par satellites, équipée d'un dispositif de vérification de cohérence du type de celui présenté ci-avant.The invention also proposes a computing station (or coherence monitoring center), for a satellite navigation system, equipped with a coherence verification device of the type of that presented above.
L'invention propose également une station de surveillance terrestre ou spatiale, pour un système de navigation par satellites comprenant une station de calcul du type de celle présentée ci-avant et des satellites générant et diffusant des messages de navigation contenant des informations à vérifier, et agencée pour déterminer des pseudo-distances sensiblement simultanément relativement à chaque satellite qu'elle voit, à partir des messages de navigation qu'ils diffusent.The invention also proposes a terrestrial or spatial monitoring station, for a satellite navigation system comprising a computing station of the type of that presented above and satellites generating and broadcasting navigation messages containing information to be verified, and arranged to determine pseudo-distances substantially simultaneously with respect to each satellite it sees, from the navigation messages they broadcast.
D'autres caractéristiques et avantages de l'invention apparaîtront à l'examen de la description détaillée ci-après, et du dessin annexé, sur lequel l'unique figure illustre de façon très schématique une partie d'un système de navigation par satellites comprenant une station de calcul équipée d'un exemple de réalisation d'un dispositif de vérification de cohérence selon l'invention. Le dessin annexé pourra non seulement servir à compléter l'invention, mais aussi contribuer à sa définition, le cas échéant. Dans ce qui suit, on considère à titre d'exemple non limitatif que le système de navigation par satellites est le futur système GALILEO. Mais, l'invention n'est pas limitée à ce système. Elle concerne en effet tous les systèmes de navigation par satellites mettant en œuvre une vérification de cohérence (ou fonction de détermination de l'intégrité), et notamment les systèmes de type GPS (en particulier GPS III), et ses « surcouches » régionales ou locales d'intégrité basées sur des systèmes sol ou satellitaires, tels qu'EGNOS, le WAAS, le LAAS ou leurs analogues dans d'autres régions du monde.Other features and advantages of the invention will appear on examining the detailed description below, and the attached drawing, in which the single figure schematically illustrates a part of a satellite navigation system comprising a computing station equipped with an exemplary embodiment of a coherence verification device according to the invention. The attached drawing may not only serve to complete the invention, but also contribute to its definition, if any. In what follows, we consider as a non-limiting example that the satellite navigation system is the future GALILEO system. But, the invention is not limited to this system. It concerns indeed all satellite navigation systems implementing a consistency check (or integrity determination function), and in particular GPS-type systems (in particular GPS III), and its regional "overlay" or integrity systems based on ground or satellite systems, such as EGNOS, WAAS, LAAS or their analogues in other parts of the world.
Un système de navigation par satellites, comme par exemple celui qui est partiellement illustré sur l'unique figure, comprend une constellation de satellites SAi (ici i = 1 à 3, mais dans la réalité sa valeur maximale NSA est beaucoup plus grande, typiquement 30 dans le cas du système GALILEO), un ensemble de stations de surveillance (terrestres ou spatiales) SCj (ici j = 1 à 4, mais dans la réalité sa valeur maximale Nsc est beaucoup plus grande, typiquement de 40 à 100 dans le cas du système GALILEO), et une station de calcul SG.A satellite navigation system, as for example that which is partially illustrated in the single figure, comprises a satellite constellation SAi (here i = 1 to 3, but in reality its maximum value N SA is much larger, typically 30 in the case of the GALILEO system), a set of monitoring stations (terrestrial or spatial) SCj (here j = 1 to 4, but in reality its maximum value Nsc is much larger, typically 40 to 100 in the case the GALILEO system), and an SG computing station.
Schématiquement, les satellites SAi sont placés en orbite et sont chargés, notamment, d'émettre des signaux permettant de faire des mesures de pseudo-distances et de diffuser en direction de la Terre T des messages de navigation qui leurs sont transmis par le segment sol de mission, afin que les informations qu'ils contiennent soient exploitées par des récepteurs de navigation et par les stations de surveillance SCj.Schematically, the SAi satellites are placed in orbit and are charged, in particular, to emit signals making it possible to make pseudo-range measurements and to diffuse in the direction of the Earth T navigation messages which are transmitted to them by the ground segment. mission, so that the information they contain is exploited by navigation receivers and SCj monitoring stations.
Les stations de surveillance SCj sont situées en des endroits choisis de la Terre T ou dans des engins spatiaux, comme par exemple des satellites. Elles sont notamment chargées, d'une part, de collecter les messages de navigation transmis par les satellites SAi de la constellation, et d'autre part, d'effectuer des mesures relatives aux pseudo-distances qui les séparent des satellites SAi en vue. Dans l'exemple illustré, le satellite SA1 est en vue des stations de surveillance SC1 , SC2 et SC3, le satellite SA2 est en vue des stations de surveillance SC1 , SC2, SC3 et SC4, et le satellite SA3 est en vue des stations de surveillance SC2, SC3 et SC4. Plus précisément, chaque station de surveillance SCj effectue périodiquement une mesure p,j de la pseudo-distance qui la sépare du satellite en vue SAi. Cette estimation se fait à partir de la différence entre l'instant de réception par la station de surveillance SCj d'un message de navigation émis par le satellite en vue SAi et l'instant d'émission de ce message de navigation reçu, défini par les informations qu'il contient.SCj monitoring stations are located in selected locations of the Earth T or in spacecraft, such as satellites. In particular, they are responsible for collecting the navigation messages transmitted by the satellites SAi of the constellation, and for measuring the pseudo-distances separating them from the SAi satellites in view. In the illustrated example, the satellite SA1 is in view of the monitoring stations SC1, SC2 and SC3, the satellite SA2 is in view of the monitoring stations SC1, SC2, SC3 and SC4, and the satellite SA3 is in view of the stations. SC2, SC3 and SC4 monitoring. More precisely, each monitoring station SCj periodically performs a measurement p, j of the pseudo-distance which separates it from the satellite in view SAi. This estimate is made from the difference between the instant of reception by the monitoring station SCj of a navigation message transmitted by the satellite in view SAi and the instant of transmission of this received navigation message, defined by the information it contains.
Chaque mesure p,j et le message de navigation correspondant ainsi que son instant de réception sont communiqués par chaque station de surveillance SCj à la station de calcul SG.Each measurement p, j and the corresponding navigation message and its reception time are communicated by each monitoring station SCj to the computing station SG.
La station de calcul SG est généralement implantée sur la Terre T. Elle comprend un dispositif de vérification de cohérence D muni d'un module de traitement MT chargé, notamment, de contrôler la cohérence entre les pseudodistances Pij et les informations contenues dans les messages de navigation (qui sont diffusés par les satellites SAi), qui lui sont communiqués par les stations de surveillance SCj. La station de calcul SG peut également être chargée de prédire les trajectoires et décalages d'horloge des satellites SAi à partir des pseudo-distances effectuées par les stations de surveillance SCj. Ces prédictions de trajectoires et de décalages d'horloge servent à générer les futurs messages de navigation qui sont transmis aux satellites SAi afin qu'ils les diffusent.The computing station SG is generally located on the Earth T. It comprises a consistency checking device D equipped with a processing module MT loaded, in particular, to check the coherence between the pseudo-jacks Pi j and the information contained in the messages. (which are broadcast by the SAi satellites), which are communicated to it by the SCj monitoring stations. The calculation station SG can also be responsible for predicting the trajectories and clock offsets of the satellites SAi from the pseudo-distances made by the monitoring stations SCj. These predictions of trajectories and clock offsets are used to generate the future navigation messages that are transmitted to SAi satellites for broadcasting.
Les données qui font l'objet d'un traitement par le module de traitement MT (pseudo-distances p,j estimées, messages de navigation diffusés par les satellites SAi et instants de réception correspondants) sont collectées auprès des stations de surveillance SCj par le dispositif D, ou bien transmises au dispositif D par lesdites stations de surveillance SCj automatiquement ou sur requête. Par exemple, le dispositif D comporte des moyens de mémorisation MY, tels qu'une mémoire ou une base de données, dans lesquels il stocke au moins provisoirement les données reçues (ou collectées) afin qu'elles puissent être traitées.The data that is processed by the processing module MT (estimated pseudo-distances p, j estimated, navigation messages broadcast by the SAi satellites and corresponding reception instants) are collected from the monitoring stations SCj by the device D, or else transmitted to the device D by said monitoring stations SCj automatically or on request. For example, the device D comprises storage means MY, such as a memory or a database, in which it stores at least temporarily the data received (or collected) so that they can be processed.
Dans un dispositif de vérification de cohérence classique, la vérification de cohérence se fait en deux étapes.In a conventional consistency checking device, the consistency check is done in two steps.
La première étape consiste à résoudre le système d'équation de résidus de pseudo-distances (1), donné ci-dessous :The first step is to solve the equation system of pseudo-range residues (1), given below:
Δp,7 = p9 -R9 =c(At^ -Af;i)-ehJ.δXSA +δ<; (1 ), où :Δp, 7 = p 9 -R 9 = c (Δt -Af; i) -e hJ .ΔX SA + δ <; (1), where:
- i = 1 à NSA etj = 1 à Nsc,i = 1 to N SA andj = 1 to Nsc,
- R,j est la prédiction de distance entre une station de surveillance SCj et un satellite en vue SAi, qui est déterminée par le module de traitement MT à partir des informations (données) contenues dans le message de navigation diffusé par le satellite SAi,- R, j is the distance prediction between a monitoring station SCj and a satellite in view SAi, which is determined by the processing module MT from the information (data) contained in the navigation message broadcast by the satellite SAi,
- « c » est la vitesse de la lumière,- "c" is the speed of light,
- Atfc est l'écart entre le temps donné par l'horloge de la station de surveillance SCj et un temps de référence. Il est également appelé décalage d'horloge de la station de surveillance,Atf c is the difference between the time given by the clock of the monitoring station SCj and a reference time. It is also called clock shift of the monitoring station,
- Δt£f est l'écart entre le temps donné par l'horloge du satellite en vue SAi et le temps de référence. Il est également appelé décalage d'horloge du satellite,- Δt £ f is the difference between the time given by the satellite clock in view SAi and the reference time. It is also called satellite clock shift,
- ëι rδXSA est la projection, suivant la direction liant le satellite SAi à la station- ë ι r δX SA is the projection, following the direction linking the satellite SAi to the station
de surveillance SCj, de l'erreur géométrique de positionnement orbital δXSA du satellite SAi, etmonitoring SCj, the geometric positioning error δX SA of the satellite SAi, and
- δζj est l'erreur résiduelle sur les pseudo-distances p,j. Il s'agit d'un bruit de mesure de type aléatoire dépendant de nombreux paramètres.- δζj is the residual error on the pseudo-distances p, j . This is a random type of measurement noise depending on many parameters.
Atfc , AffA et ëhJδXSA sont trois inconnues à estimer pour chaque couple de station de surveillance SCj et de satellite en vue SAi.Atf c , Aff A and hJ δX SA are three unknowns to be estimated for each pair of monitoring station SCj and of satellite in view SAi.
Le système d'équations (1) comporte donc 4NSA + Nsc inconnues. Dans le cas d'un système de type GALILEO comportant 30 satellites SAi et 40 stations de surveillance SCj, ce système comprend environ 400 équations et 160 inconnues, ce qui conduit à un rapport dit de « sur-détermination » (ou « over-determination » - nombre d'équations divisé par le nombre d'inconnues) égal à 2,5.The system of equations (1) thus has 4N SA + N sc unknown. In the case of a GALILEO type system comprising 30 SAi satellites and 40 SCj monitoring stations, this system comprises about 400 equations and 160 unknowns, which leads to a so-called "over-determination" (or "over-determination") report. "- number of equations divided by the number of unknowns) equal to 2.5.
La seconde étape de la vérification de cohérence consiste à effectuer la somme de la plus défavorable projection, sur la surface de la Terre T où le satellite SAi est visible, de l'erreur géométrique de positionnement orbital δXSA du satellite SAi, avec le résultat du produit de la constante « c » par la différence entre la valeur estimée du biais (ou décalage d'horloge) Δt£f et la valeur prédite de ce biais, déterminable à partir des informations contenues dans le message de navigation transmis par le satellite en vue SAi, puis à générer une alarme lorsque cette somme est supérieure à un seuil choisi.The second step of the consistency check is to perform the sum of the most unfavorable projection, on the surface of the Earth T where the satellite SAi is visible, of the geometric positioning error δX SA of the satellite SAi, with the result of the product of the constant "c" by the difference between the estimated value of the bias (or clock shift) Δt £ f and the predicted value of this bias, which can be determined from the information contained in the navigation message transmitted by the satellite in view SAi, and then generates an alarm when this sum is greater than a chosen threshold.
Dans un dispositif de vérification de cohérence classique, le module de traitement MT doit donc déterminer le biais Af^ de chaque station de surveillance SCj pour résoudre chaque système d'équations (1), ce qui revient à déterminer la synchronisation du « réseau » de stations de surveillance SCj par rapport au temps de référence du système, alors même que ces biais At ref SC1 ne servent pas dans la seconde étape de la vérification de cohérence.In a conventional coherence verification device, the processing module MT must therefore determine the bias Δf ^ of each monitoring station SCj to solve each system of equations (1), which amounts to determining the synchronization of the "network" of monitoring stations SCj with respect to the reference time of the system, even though these At ref SC 1 bias are not used in the second step of the consistency check.
L'invention propose de procéder différemment de ce qui vient d'être décrit. Elle repose sur l'observation du fait que les décalages d'horloge Af^ etThe invention proposes to proceed differently from what has just been described. It is based on the observation that clock offsets Af ^ and
Afs{e , respectivement d'une station de surveillance SCj et d'un satellite en vueAf s {e, respectively SCj a monitoring station and a satellite in view
SAi, sont des termes qui apparaissent dans le système d'équations (1) utilisé actuellement pour procéder à la vérification de la cohérence des informations diffusées par les satellites SAi, mais que dans une configuration de calcul particulière l'estimation même des décalages d'horloge des stations de surveillance SCj n'est pas nécessaire à cette vérification de cohérence qui ne concerne en réalité que des inconnues satellitaires Afs{e et ë^SX^ .SAi, are terms that appear in the system of equations (1) currently used to verify the coherence of the information broadcast by the satellites SAi, but that in a particular calculation configuration the estimate of the offsets of The clock of the monitoring stations SCj is not necessary for this verification of coherence which concerns in reality only satellite unknowns Af s { e and ë ^ SX ^.
L'invention propose donc, tout d'abord, que chaque station de surveillance SCj effectue sensiblement simultanément les mesures de pseudodistance Pij relatives à chaque satellite SAi qu'elle voit. Ainsi, toutes les mesures py d'une station de surveillance SCj sont affectées par un même décalage d'horloge de station de surveillance SCj Atfc (également appelé biais).The invention therefore proposes, first of all, that each monitoring station SCj substantially simultaneously performs the pseudorange measurements Pij relating to each SAi satellite that it sees. Thus, all the py measurements of a monitoring station SCj are affected by the same monitoring station clock offset SCj Atf c (also called bias).
Le module de traitement MT du dispositif de vérification de cohérence D peut alors fonctionner dans un mode que l'on peut qualifier de différentiel en effectuant des différences δΔp^ entre des résidus de pseudo-distances Δρ!;7 et Δρt j relatifs à deux satellites SAi et SAk (avec i ≠ k) vus par une même station de surveillance SCj. En d'autres termes, le système d'équations (1) classique, dont la résolution fait l'objet de la première étape effectuée par le module de traitement MT, est transformé en un nouveau système d'équations (2), du type de celui donné ci-dessous, qui ne comporte plus de termes de biais Afs e£ de station de surveillance SCj :The processing module MT of the consistency checking device D can then operate in a mode that can be described as differential by making differences δΔp ^ between pseudo-range residues Δρ!; 7 and Δρ tj relative to two satellites SAi and SAk (with i ≠ k) seen by the same monitoring station SCj. In other words, the conventional system of equations (1), whose resolution is the subject of the first step performed by the processing module MT, is transformed into a new system of equations (2), of the type of the one given below, which no longer includes bias terms Af s e £ monitoring station SCj:
δΔp^ =APι J -ΔPij = -c(AtZ -Atsl )~KMsA +ekjXSA +K° -&£ (2).δΔp ^ = A Pι -Δ J ij = -c (ATZ -Atsl) ~ KMs A + e k jX SA + K ° - £ & (2).
Lors de la nouvelle première étape selon l'invention, le module de traitement MT constitue donc le système d'équations (2) à partir des données reçues des stations de surveillance SCj (par exemple stockées dans la mémoire MY), puis il résout ce système d'équations (2) en déterminant les inconnues Δt£f et ëι rδXSA pour chaque station de surveillance SCj et chacun des satellites SAi qu'elle voit.In the new first step according to the invention, the processing module MT thus constitutes the system of equations (2) from the data received from the monitoring stations SCj (for example stored in the memory MY), and then it resolves this system of equations (2) by determining the unknowns Δt £ f and ë ι r δX SA for each monitoring station SCj and each satellite SAi that it sees.
Il lui faut pour ce faire une équation supplémentaire qui précise où se trouve l'origine du temps. Celle-ci est en effet nécessaire du fait que chaque biais Δt£f correspond à la différence entre le temps d'un satellite SAi tsAi et un temps de référence tref, qui est lui-même défini par rapport à une origine de temps.To do this, he needs an additional equation that specifies where the origin of time is. This is indeed necessary because each bias Δt £ f corresponds to the difference between the time of a satellite SAi tsAi and a reference time t ref , which is itself defined with respect to an origin of time.
Pour une station donnée SCj il y a (N™1 - 1) combinaisons indépendantes. Par conséquent, le nombre total d'équations indépendantes est égal à NSA x (N™1 - 1) +1 et le nombre d'inconnues est égal à 4NSA. Dans le cas d'un système de type GALILEO comportant 30 satellites SAi et 40 stations de surveillance SCj, le rapport de sur-détermination est alors typiquement égal à 3, et dans le cas d'un système GALILEO comportant 100 stations de surveillance ce rapport devient égal à 7,5.For a given station SCj there are (N ™ 1 - 1) independent combinations. Therefore, the total number of independent equations equals N SA x (N ™ 1 - 1) +1 and the number of unknowns equals 4N SA . In the case of a GALILEO-type system comprising 30 SAi satellites and 40 SCj monitoring stations, the over-determination ratio is then typically equal to 3, and in the case of a GALILEO system comprising 100 monitoring stations this ratio becomes 7.5.
Il est important de noter que la combinaison qui est indiquée dans le membre de droite du système d'équations (2) est une combinaison préférentielle. Elle peut faire l'objet de variantes, dès lors qu'elle est constituée à partir de somme(s) et/ou de soustraction(s) appropriées d'au moins la distance représentative de la différence de décalage d'horloge estimé entre les premier SAi et second SAk satellites, la différence de projection d'erreur géométrique de positionnement orbital entre les premier SAi et second SAk satellites, et la différence d'erreur résiduelle sur la pseudo-distance entre les premier SAi et second SAk satellites.It is important to note that the combination that is indicated in the right-hand side of the system of equations (2) is a preferential combination. It may be subject to variations, provided that it is constituted from the appropriate sum (s) and / or subtraction (s) of at least the distance representative of the estimated clock offset difference between the first SAi and second satellite SAk, the geometric error projection difference of orbital positioning between the first SAi and second SAk satellites, and the difference in residual error on the pseudo-distance between the first SAi and second satellite SAk.
La seconde étape de la vérification de cohérence est sensiblement identique à celle effectuée par un dispositif de vérification de cohérence classique. Elle consiste donc, comme indiqué précédemment, à effectuer la somme de la plus défavorable projection, sur la surface de la Terre T où le satellite SAi est visible, de l'erreur géométrique de positionnement orbital δXSΛ du satellite SAi, avec le résultat du produit de la constante « c » par la différence entre la valeur estimée de Afs{e et sa valeur prédite contenue dans le message de navigation transmis par le satellite en vue SAi, puis à générer une alarme lorsque cette somme est supérieure à un seuil choisi.The second step of the consistency check is substantially identical to that performed by a conventional consistency checking device. It therefore consists, as indicated above, in carrying out the sum of the most unfavorable projection, on the surface of the Earth T where the satellite SAi is visible, of the geometric positioning error δX SΛ of the satellite SAi, with the result of the produces the constant "c" by the difference between the estimated value of Af s { e and its predicted value contained in the navigation message transmitted by the satellite in view SAi, and then generating an alarm when this sum is greater than a threshold selected.
Il est important de noter que la combinaison qui sert dans cette seconde étape est une combinaison préférentielle. Elle peut faire l'objet de variantes, dès lors qu'elle est constituée à partir d'une somme et/ou d'une soustraction appropriée entre au moins une projection choisie de l'erreur géométrique de positionnement orbital d'un satellite SAi et une distance représentative de la différence entre les décalages d'horloge estimé et prédit du satellite SAi.It is important to note that the combination that serves in this second step is a preferential combination. It can be the subject of variants, since it consists of a sum and / or an appropriate subtraction between at least one selected projection of the geometrical orbital positioning error of a satellite SAi and a distance representative of the difference between the estimated and predicted clock offsets of the satellite SAi.
Le dispositif de vérification de cohérence D selon l'invention, et notamment son module de traitement MT et son éventuelle mémoire MY, peuvent être réalisés sous la forme de circuits électroniques, de modules logiciels (ou informatiques), ou d'une combinaison de circuits et de logiciels.The coherence verification device D according to the invention, and in particular its processing module MT and its possible memory MY, can be realized in the form of electronic circuits, software (or computer) modules, or a combination of circuits. and software.
L'invention offre de nombreux avantages, parmi lesquels :The invention offers many advantages, among which:
- il n'est plus nécessaire d'estimer les décalages d'horloge des stations de surveillance, et donc de déterminer la synchronisation du réseau de stations de surveillance par rapport au temps de référence du système,it is no longer necessary to estimate the clock offsets of the monitoring stations, and therefore to determine the synchronization of the network of monitoring stations with respect to the reference time of the system,
- il n'est plus nécessaire d'utiliser dans les stations de surveillance des horloges atomiques de très grande précision, ce qui permet de réduire notablement leur coût et de réutiliser des équipements de navigation existants, comme par exemple certains récepteurs d'aéroports utilisés dans les systèmes de type LAAS (« Local area Augmentation System » - système permettant d'améliorer notablement la précision de la localisation dans des zones de dimensions restreintes telles que des aéroports),- it is no longer necessary to use in monitoring stations Atomic clocks of very high precision, which makes it possible to significantly reduce their cost and to reuse existing navigation equipment, such as for example certain airport receivers used in LAAS (Local Area Augmentation System) systems. significantly improve the accuracy of location in small areas such as airports),
- la vérification de cohérence ne requiert plus de modélisation du comportement des horloges atomiques, du fait qu'elle repose sur l'utilisation d'estimations quasi-instantanées,- consistency checking no longer requires modeling the behavior of atomic clocks, because it relies on the use of quasi-instantaneous estimates,
- le rapport de sur-détermination croît plus rapidement que l'augmentation linéaire d'efficacité (typiquement 3 dans le cas d'un système GALILEO comportant 40 stations de surveillance, et 7,5 dans le cas d'un système GALILEO comportant 100 stations de surveillance). En outre, si l'on utilise l'approximation consistant à fusionner, lors de la seconde étape, l'erreur temporelle des satellites (Δt£f ) avec la composante radiale de l'erreurthe over-determination ratio increases faster than the linear increase in efficiency (typically 3 in the case of a GALILEO system comprising 40 monitoring stations, and 7.5 in the case of a GALILEO system comprising 100 stations monitoring). In addition, if we use the approximation of merging, in the second step, the time error of the satellites (Δt £ f) with the radial component of the error
géométrique de positionnement orbital (δXSA ), appelée SISE (pour Signalorbital positioning geometry (δX SA ), called SISE (for Signal
In-Space Error) dans le cas d'un système GALILEO, le rapport de surdétermination passe typiquement de 3 à 4 dans le cas d'un système GALILEO comportant 40 stations de surveillance, et de 7,5 à 10 dans le cas d'un système GALILEO comportant 100 stations de surveillance),In-Space Error) in the case of a GALILEO system, the overdetermination ratio typically goes from 3 to 4 in the case of a GALILEO system with 40 monitoring stations, and from 7.5 to 10 in the case of a Galileo system. a GALILEO system with 100 monitoring stations),
- on peut utiliser comme échelle de temps de référence une horloge composite basée sur l'ensemble des horloges des satellites, si bien que l'on peut disposer d'une référence de temps optimale étant donné que c'est la référence de temps que l'on peut générer au niveau du système qui est la plus proche de celle que les usagers du système utilisent,a composite clock based on all the clocks of the satellites can be used as a reference time scale, so that an optimal time reference can be available since it is the time reference that the can be generated at the level of the system that is closest to that used by the users of the system,
- des parties d'erreurs, communes à toutes les mesures effectuées dans les stations de surveillance et dues i) aux biais introduits par les composants matériels du dispositif de mesure, ii) aux erreurs résiduelles troposphériques communes, et iii) aux erreurs de coordonnées des stations de surveillance, peuvent être supprimées.- parts of errors, common to all measurements made at monitoring stations and due to (i) biases introduced by the hardware components of the measuring device, (ii) common residual tropospheric errors, and (iii) coordinate errors of monitoring stations, can be deleted.
L'invention ne se limite pas aux modes de réalisation de dispositif de vérification de cohérence, de station de surveillance et de station de calcul décrits ci-avant, seulement à titre d'exemple, mais elle englobe toutes les variantes que pourra envisager l'homme de l'art dans le cadre des revendications ci-après. The invention is not limited to device embodiments of coherence verification, monitoring station and computing station described above, only by way of example, but it encompasses all the variants that may be considered by those skilled in the art within the scope of the claims below.

Claims

REVENDICATIONS
1. Dispositif de vérification de cohérence d'informations pour une station de calcul (SG) d'un système de navigation par satellites comprenant des satellites (SA) générant et diffusant des messages de navigation contenant des informations à vérifier, et des stations de surveillance (SC) déterminant des pseudo-distances les séparant de satellites en vue (SAi) à partir desdits messages de navigation diffusés, caractérisé en ce qu'il comprend des moyens de traitement (MT) agencés, en cas de réception de données représentatives de pseudo-distances déterminées sensiblement simultanément par chaque station de surveillance (SCj) relativement à chaque satellite (SAi) en vue, et des messages de navigation correspondants diffusés par lesdits satellites (SAi) et de leurs instants de réception, i) pour définir et résoudre un système d'équations dans lequel chaque équation est l'expression d'une différence entre des résidus de pseudo-distances, relatifs à deux satellites (SAi, SAk) vus par une même station de surveillance (SCj) et représentant chacun la différence entre la pseudo-distance déterminée par ladite station de surveillance (SCj) relativement à l'un des deux satellites (SAi1SAk) et une distance déterminée à partir desdites données reçues, ladite différence entre résidus étant égale à une combinaison entre une distance représentative d'une différence de décalages d'horloge estimés entre les deux satellites, une différence entre des projections, suivant les directions liant les deux satellites à ladite station de surveillance (SCj), d'erreurs géométriques de positionnement orbital des deux satellites, et une différence entre des erreurs résiduelles sur les pseudo-distances déterminées par ladite station de surveillance (SCj) relativement aux deux satellites, puis ii) pour générer une alarme chaque fois que le résultat d'une combinaison, entre une projection choisie de l'erreur géométrique de positionnement orbital d'un satellite (SAi) et une distance représentative de la différence entre le décalage d'horloge estimé et un décalage d'horloge prédit dudit satellite (SAi), est supérieur à un seuil choisi.An information coherency checking device for a satellite navigation system (SG) computing station including satellites (SA) generating and broadcasting navigation messages containing information to be checked, and monitoring stations. (SC) determining pseudo-distances separating them from satellites in view (SAi) from said broadcast navigation messages, characterized in that it comprises processing means (MT) arranged, in the event of reception of representative pseudo data -distances determined substantially simultaneously by each monitoring station (SCj) relative to each satellite (SAi) in view, and corresponding navigation messages broadcast by said satellites (SAi) and their reception times, i) to define and resolve a system of equations in which each equation is the expression of a difference between pseudo-distances residues, relative to two satelli (SAi, SAk) seen by the same monitoring station (SCj) and each representing the difference between the pseudo-distance determined by said monitoring station (SCj) relative to one of the two satellites (SAi 1 SAk) and a distance determined from said received data, said difference between residues being equal to a combination between a distance representative of a difference in estimated clock offsets between the two satellites, a difference between projections, according to the directions linking the two satellites to said monitoring station (SCj), geometrical errors of orbital positioning of the two satellites, and a difference between residual errors on the pseudo-distances determined by said monitoring station (SCj) relative to the two satellites, then ii) to generate an alarm whenever the result of a combination, between a selected projection of the geometric positioning error orbital of a satellite (SAi) and a distance representative of the difference between the estimated clock offset and a predicted clock offset of said satellite (SAi), is greater than a chosen threshold.
2. Dispositif selon la revendication 1 , caractérisé en ce que lesdits moyens de traitement sont agencés pour définir au i) des équations dans lesquelles chaque différence entre résidus est égale à une combinaison dans laquelle sont additionnées à la distance représentative de la différence de décalage d'horloge estimé entre le second satellite (SAk) et le premier satellite (SAi), la différence de projection d'erreur géométrique de positionnement orbital entre le second satellite (SAk) et le premier satellite (SAi), et la différence d'erreur résiduelle sur la pseudo-distance entre le premier satellite (SAi) et le second satellite (SAk).2. Device according to claim 1, characterized in that said processing means are arranged to define i) equations in wherein each difference between residues is equal to a combination in which is added to the distance representative of the estimated clock offset difference between the second satellite (SAk) and the first satellite (SAi), the geometric error projection difference orbital positioning between the second satellite (SAk) and the first satellite (SAi), and the residual error difference on the pseudo-distance between the first satellite (SAi) and the second satellite (SAk).
3. Dispositif selon l'une des revendications 1 et 2, caractérisé en ce que lesdits moyens de traitement sont agencés pour effectuer au ii) une combinaison de type somme entre ladite projection choisie de l'erreur géométrique de positionnement orbital d'un satellite (SAi) et ladite distance représentative de la différence entre les décalages d'horloge estimé et prédit dudit satellite (SAi), de manière à comparer le résultat de ladite somme au seuil choisi.3. Device according to one of claims 1 and 2, characterized in that said processing means are arranged to perform at ii) a sum-type combination between said selected projection of the geometrical orbital positioning error of a satellite ( SAi) and said distance representative of the difference between the estimated and predicted clock offsets of said satellite (SAi), so as to compare the result of said sum with the chosen threshold.
4. Dispositif selon l'une des revendications 1 à 3, caractérisé en ce que lesdits moyens de traitement sont agencés pour choisir au ii) la projection la plus défavorable, sur une surface terrestre où ledit satellite (SAi) est visible, de son erreur géométrique de positionnement orbital.4. Device according to one of claims 1 to 3, characterized in that said processing means are arranged to choose ii) the most unfavorable projection, on a terrestrial surface where said satellite (SAi) is visible, its error Geometric Orbital Positioning.
5. Dispositif selon l'une des revendications 1 à 4, caractérisé en ce que lesdits moyens de traitement sont agencés pour associer une référence temporelle audit système d'équations.5. Device according to one of claims 1 to 4, characterized in that said processing means are arranged to associate a temporal reference to said system of equations.
6. Dispositif selon l'une des revendications 1 à 5, caractérisé en ce qu'il comprend des moyens de mémorisation (MY) couplés auxdits moyens de traitement (MT) et propres à stocker lesdites données reçues desdites stations de surveillance (SCj).6. Device according to one of claims 1 to 5, characterized in that it comprises storage means (MY) coupled to said processing means (MT) and adapted to store said data received from said monitoring stations (SCj).
7. Station de calcul (SG) pour un système de navigation par satellites, caractérisée en ce qu'elle comprend un dispositif de vérification de cohérence d'informations (D) selon l'une des revendications précédentes.7. Computing station (SG) for a satellite navigation system, characterized in that it comprises an information consistency checking device (D) according to one of the preceding claims.
8. Station de surveillance (SCj) pour un système de navigation par satellites comprenant une station de calcul (SG) selon la revendication 7 et des satellites (SA) générant et diffusant des messages de navigation contenant des informations à vérifier, caractérisée en ce qu'elle est agencée pour déterminer des pseudo-distances sensiblement simultanément relativement à chaque satellite (SAi) qu'elle voit, à partir des messages de navigation qu'ils diffusent. 8. Monitoring station (SCj) for a satellite navigation system comprising a computing station (SG) according to claim 7 and satellites (SA) generating and broadcasting navigation messages containing information to be verified, characterized in that it is arranged to determine pseudo-distances substantially simultaneously relative to each satellite (SAi) it sees, from the navigation messages they broadcast.
PCT/FR2006/050820 2005-08-30 2006-08-29 Device for checking the consistency of broadcast information, with no constraints on the clocks of the monitoring stations, for a satellite navigation system WO2007026098A1 (en)

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FR0552597A FR2890265A1 (en) 2005-08-30 2005-08-30 Information broadcast consistency checking device for e.g. Galileo system, has processing unit generating alarm each time when combination between selected projection and distance representing difference between offsets is above threshold

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