Bayesian Inference of GNSS Failures

International audienceThe probability of failure (failure rate) is a key input parameter to integrity monitoring systems used for safety, liability or mission critical applications. A standard approach in the design of Global Positioning System (GPS) integrity monitoring is to utilize the service commitment on the probability of major service failure, often by applying a conservative factor. This paper addresses the question of what factor is appropriate by applying Bayesian inference to real and hypothetical fault histories. Global Navigation Satellite System (GNSS) anomalies include clock or signal transmission type faults which are punctual (may occur at any time) and incorrect ephemeris data which are broadcast for a nominal two hours. These two types of anomaly, classified as continuous and discrete respectively are addressed. Bounds on the total probability of failure are obtained with given confidence levels subject to well defined hypotheses relating past to future performance. Factors for the GPS service commitment of 10-5 per hour per satellite are obtained within the range two to five with high confidence (up to 1-10-9)

GNSS Multipath Error Model for Aircraft Surface Navigation Based on Canonical Scenarios for Class F Airports

International audienceIn this study, the GNSS multipath simulator for aircraft navigation on the airport surface from [1] is used to derive a multipath pseudo¬range error model. First the principle of this deterministic¬statistical multipath simulator is reminded. A numerical validation of the electromagnetic multipath prediction is made by establishing the channel transfer function and comparing it to the one obtained with an electromagnetic software, FEKO, using the Method of Moments. To illustrate the outputs of such simulator, a comparison to measurements performed at ENAC is given. Then, after reminding the multipath pseudo¬range error model that was established in [2], a multipath pseudo¬range error model is adapted to ICAO code F airport layouts [3]. This model is based on the identification of canonical scenarios representing the taxi operation phase. The power spectral density of the multipath pseudo¬range errors is over¬bounded by a first order Gauss¬Markov spectral density. An example of application for the taxi on stand taxilane sub¬phase is proposed. In this example, the over¬bounding distribution fits quite well the power spectral density of the estimated multipath pseudo¬range errors

Multipath study on the airport surface

International audienceAirport Navigation will require more stringent localization performance requirements than in-flight navigation [1]. GNSS signals (Global Navigation Satellites Systems) can be envisaged to elaborate the aircraft estimate position on the airport surface. To improve the performance of localization on the airport, the errors on GNSS signals particular to the airport environment must be characterized. Most of these errors are well known such as ionosphere error, troposphere error, etc, and do not depend on the airport environment. But to achieve the expected sub-metric performance, it is necessary to better model multipath error for which a model already exists but is valid for operations from en-route down to CAT I only. In this paper, an analysis of real GPS measurements (using code pseudo range measurement, carrier phase measurement, Doppler measurement and the estimate C/N0 ratio measurement) during taxiing operation on the airport surface is conducted. The goal of this paper is to evaluate when multipath occurs and to compare the multipath model (elaborated from the standard deviation of the measurement errors due to multipath) based on those collected measurements in the airport with different models proposed in the literature (not necessary proposed for airport navigation)

Contrôle d intégrité appliqué à la réception des signaux GNSS en environnement urbain

L intégrité des signaux GNSS est définie comme la mesure de la confiance qui peut être placée dans l exactitude des informations fournies par le système de navigation. Bien que le concept d intégrité GNSS a été initialement développé dans le cadre de l aviation civile comme une des exigences standardisées par l Organisation de l Aviation Civile Internationale (OACI) pour l utilisation du GNSS dans les systèmes de Communication, Navigation, et Surveillance / Contrôle du Trafic Aérien (CNS/ATM), un large éventail d applications non aéronautiques ont également besoin de navigation par satellite fiable avec un niveau d intégrité garanti. Beaucoup de ces applications se situent en environnement urbain. Le contrôle d intégrité GNSS est un élément clé des applications de sécurité de la vie (SoL), telle que l aviation, et des applications exigeant une fiabilité critique comme le télépéage basé sur l utilisation du GNSS, pour lesquels des erreurs de positionnement peuvent avoir des conséquences juridiques ou économiques. Chacune de ces applications a ses propres exigences et contraintes, de sorte que la technique de contrôle d intégrité la plus appropriée varie d une application à l autre. Cette thèse traite des systèmes de télépéage utilisant GNSS en environnement urbain. Les systèmes de navigation par satellite sont l une des technologies que l UE recommande pour le Service Européen de Télépéage Electronique (EETS). Ils sont déjà en cours d adoption: des systèmes de télépéage pour le transport poids lourd utilisant GPS comme technologie principale sont opérationnels en Allemagne et en Slovaquie, et un système similaire est envisagé en France à partir de 2013. À l heure actuelle, le contrôle d intégrité GPS s appuie sur des systèmes d augmentation (GBAS, SBAS, ABAS) conçus pour répondre aux exigences de l OACI pour les opérations aviation civile. C est la raison pour laquelle cette thèse débute par une présentation du concept d intégrité en aviation civile afin de comprendre les performances et contraintes des systèmes hérités. La thèse se poursuit par une analyse approfondie des systèmes de télépéage et de navigation GNSS en milieu urbain qui permets de dériver les techniques de contrôle d intégrité GNSS les plus adaptées. Les algorithmes autonomes de type RAIM ont été choisis en raison de leur souplesse et leur capacité d adaptabilité aux environnements urbains. Par la suite, le modèle de mesure de pseudodistances est élaboré. Ce modèle traduit les imprécisions des modèles de correction des erreurs d horloge et d ephemeride, des retards ionosphériques et troposphériques, ainsi que le bruit thermique récepteur et les erreurs dues aux multitrajets. Les exigences d intégrité GNSS pour l application télépéage sont ensuite dérivées à partir de la relation entre les erreurs de positionnement et leur effets dans la facturation finale. Deux algorithmes RAIM sont alors proposés pour l application péage routier. Le premier est l algorithme basé sur les résidus de la solution des moindres carrés pondérés (RAIM WLSR), largement utilisé dans l aviation civile. Seulement, un des principaux défis de l utilisation des algorithmes RAIM classiques en milieux urbains est un taux élevé d indisponibilité causé par la mauvaise géométrie entre le récepteur et les satellites. C est pour cela que un nouvel algorithme RAIM est proposé. Cet algorithme, basé sur le RAIM WLSR, est conçu de sorte à maximiser l occurrence de fournir un positionnement intègre dans un contexte télépéage. Les performances des deux algorithmes RAIM proposés et des systèmes de télépéage associés sont analysés par simulation dans différents environnements ruraux et urbains. Dans tous les cas, la disponibilité du nouvel RAIM est supérieure à celle du RAIM WLSR.Global Navigation Satellite Systems (GNSS) integrity is defined as a measure of the trust that can be placed in the correctness of the information supplied by the navigation system. Although the concept of GNSS integrity has been originally developed in the civil aviation framework as part of the International Civil Aviation Organization (ICAO) requirements for using GNSS in the Communications, Navigation, and Surveillance / Air Traffic Management (CNS/ATM) system, a wide range of non-aviation applications need reliable GNSS navigation with integrity, many of them in urban environments. GNSS integrity monitoring is a key component in Safety of Life (SoL) applications such as aviation, and in the so-called liability critical applications like GNSS-based electronic toll collection, in which positioning errors may have negative legal or economic consequences. At present, GPS integrity monitoring relies on different augmentation systems (GBAS, SBAS, ABAS) that have been conceived to meet the ICAO requirements in civil aviation operations. For this reason, the use of integrity monitoring techniques and systems inherited from civil aviation in non-aviation applications needs to be analyzed, especially in urban environments, which are frequently more challenging than typical aviation environments. Each application has its own requirements and constraints, so the most suitable integrity monitoring technique varies from one application to another. This work focuses on Electronic Toll Collection (ETC) systems based on GNSS in urban environments. Satellite navigation is one of the technologies the directive 2004/52/EC recommends for the European Electronic Toll Service (EETS), and it is already being adopted: toll systems for freight transport that use GPS as primary technology are operational in Germany and Slovakia, and France envisages to establish a similar system from 2013. This dissertation begins presenting first the concept of integrity in civil aviation in order to understand the objectives and constraints of existing GNSS integrity monitoring systems. A thorough analysis of GNSS-based ETC systems and of GNSS navigation in urban environments is done afterwards with the aim of identifying the most suitable road toll schemes, GNSS receiver configurations and integrity monitoring mechanisms. Receiver autonomous integrity monitoring (RAIM) is chosen among other integrity monitoring systems due to its design flexibility and adaptability to urban environments. A nominal pseudorange measurement model suitable for integrity-driven applications in urban environments has been calculated dividing the total pseudorange error into five independent error sources which can be modelled independently: broadcasted satellite clock corrections and ephemeris errors, ionospheric delay, tropospheric delay, receiver thermal noise (plus interferences) and multipath. In this work the fault model that includes all non-nominal errors consists only of major service failures. Afterwards, the GNSS integrity requirements are derived from the relationship between positioning failures and toll charging errors. Two RAIM algorithms are studied. The first of them is the Weighted Least Squares Residual (WLSR) RAIM, widely used in civil aviation and usually set as the reference against which other RAIM techniques are compared. One of the main challenges of RAIM algorithms in urban environments is the high unavailability rate because of the bad user/satellite geometry. For this reason a new RAIM based on the WLSR is proposed, with the objective of providing a trade-off between the false alarm probability and the RAIM availability in order to maximize the probability that the RAIM declares valid a fault-free position. Finally, simulations have been carried out to study the performance of the different RAIM and ETC systems in rural and urban environments. In all cases, the availability obtained with the novel RAIM improve those of the standard WLSR RAIM.TOULOUSE-INP (315552154) / SudocSudocFranceF

Review and classification of vision-based localisation techniques in unknown environments

International audienceThis study presents a review of the state-of-the-art and a novel classification of current vision-based localisation techniques in unknown environments. Indeed, because of progresses made in computer vision, it is now possible to consider vision-based systems as promising navigation means that can complement traditional navigation sensors like global navigation satellite systems (GNSSs) and inertial navigation systems. This study aims to review techniques employing a camera as a localisation sensor, provide a classification of techniques and introduce schemes that exploit the use of video information within a multi-sensor system. In fact, a general model is needed to better compare existing techniques in order to decide which approach is appropriate and which are the innovation axes. In addition, existing classifications only consider techniques based on vision as a standalone tool and do not consider video as a sensor among others. The focus is addressed to scenarios where no a priori knowledge of the environment is provided. In fact, these scenarios are the most challenging since the system has to cope with objects as they appear in the scene without any prior information about their expected position

FUNTIMES – Future Navigation and Timing Evolved Signals

International audienceThe European Galileo system moves clear steps forward towards the completion of its space and ground segment infrastructures, after starting providing early services in 2016 and with the plan to achieve the full operational capability (FOC) in 2020. Also the user segment is rapidly expanding, with the increasing introduction of mass market chipsets fully supporting Galileo in a constantly growing number of smartphones. In this context a strong need for R&D activities in the field of navigation signal engineering has been identified by various Programme's stakeholders. Considering the long process required for introducing new signals and features in a system that is already deployed and finds itself in the exploitation phase, early R&D activities become essential to investigate potential evolutions and new concepts to improve the Galileo signals and services in the short, medium and long term. The Future Navigation and Timing Evolved Signals (FUNTIMES) project is a European GNSS mission evolution study funded by the European Commission within the Horizon 2020 Framework for Research and Development. It aims at identifying, studying and recommending mission evolution directions and at preliminary supporting the definition, design and implementation of the future generation of Galileo signals. The project is led by Airbus Defence and Space as prime contractor, supported by Ecole Nationale de l‘Aviation Civile (ENAC) and Istituto Superiore Mario Boella (ISMB) as subcontractors and was run under the supervision of the European Commission and its Joint Research Centre. The research activities were conducted according to the following high level evolution directions: - Improve the Galileo OS reliability by providing an enhanced authentication service based on both navigation message authentication and spreading code authentication, in such a way that the two solutions can take advantage of their combination. - Improve the sensitivity and/or reduce the complexity of the acquisition of the Galileo OS signals, e.g. by studying the potential introduction of a new signal component for this purpose. - Make use of new concepts and techniques for the delivery of the data messages, to improve the time-to-data performance and robustness. - Consider options for providing an effective high data rate component suitable for satellite navigation purposes, e.g. in view of a possible evolution of the signals providing the Galileo Commercial Service. The project started by defining the key elements characterizing GNSS signals, describing the current signal plans of the major global and regional satellite systems and carrying out a literature survey on the various proposals for the evolution and optimization of navigation signals. A key role in the project was then played by a specific task on the definition of signal user requirements, which, besides providing by themselves an added-value to the project outcomes, were taken into account to select and consolidate the R&D topics defined at the beginning of the study. For what concerns the core navigation signal R&D activity, various solutions belonging to the following areas were considered: new and evolved modulations and multiplexing techniques, new concepts and techniques for the data message, solutions providing services with higher reliability, solutions for improved navigation performance. In the followings, some highlights about the main project tasks are provided. *Adding New Signal Components to Galileo E1 OS* Due to backward compatibility constraints, the Galileo legacy signals defined in the current SIS-ICD do not offer much space for further modifications. The possibility to add new signal components to the Galileo E1 signal was investigated with the goals of providing a fast and reliable authentication service and better acquisition performance while keeping the complexity of the acquisition process low. Various options were investigated, considering new components centered at E1 or ones presenting a carrier offset. The options were studied in terms of ranging performance, compatibility with other signals in E1/L1, multiplexing efficiency and backward compatibility. The outcome of this task was then combined with the other solutions investigated during the project and briefly introduced in the followings. *Signal User Requirements Survey* This task aimed at identifying and understanding the current and future needs of various GNSS user groups in order to derive requirements and evolution directions for the Galileo signals. The work logic followed was based on a 3-step approach: - Definition of the user communities - Analysis of available documentation and state-of-the-art for each user communities to extract high level and, if possible, low level requirements - Consultation of representative of the various user communities by means of questionnaire on signal user requirements. The considered user communities are representative of 7 classes of users: - Traditional Safety-of-Life Applications (Navigation of Civil Aviation aircrafts, Train Control) - Automotive Location-Based Charging (LBC) and Vehicle Motion Sensing (VMS) - Mobile Location-Based Services (LBS) - Surveying - Timing and Synchronization - Search and Rescue - Remotely-Piloted Aircraft Systems (RPAS). As mentioned above, the consortium prepared a questionnaire which was distributed to companies and organizations representative of various GNSS user communities. After collecting the answers, personal interviews were conducted to deepen the outcomes of the survey and collect more details about their expectations. From the received answers, the following points were considered particularly relevant for the identification/consolidation of signal evolution directions: - The need for integrity and authentication is present also in non-safety of life applications (e.g. precise positioning) - Very wide-spread need for fast authenticated PVT (fast data and pseudo-range authentication) - Interest in fast Time-To-First-Fix (TTFF) Data, or in other words, fast provision of the Clock error corrections and satellites Ephemeris Data (CED). - Need for precise clock and orbit data, freely accessible through the navigation message transmitted through conventional signals (at L1/E1 or L5/E5) - Importance of stand-alone operation mode despite the increasing number of connected users (network connection still judged not reliable enough). - Need for multipath/NLOS resistant signals - Need for RFI resistant signals - Interest for an alert/emergency service. *Reed-Solomon Codes for the Improvement of the I/NAV Message* Despite the growing number of connected user devices, the reception of the clock and ephemeris data (CED) is still a major factor impacting the TTFF. The current approach for the dissemination of these data can be defined as "data carouseling": the data are repeatedly sent to the users with a certain repetition rate. For example the repetition rate of the CED contained in the Galileo E1 OS message is equal to 1 every 30 s. A different approach is offered by Maximum Distance Separable (MDS) codes like Reed-Solomon codes, whose erasure correction capability allows to retrieve the entire information contained in k data blocks from any combination of k received blocks of the codeword. During the project, the performance of Reed-Solomon codes when applied to the Galileo I/NAV message as proposed in [1] were studied, in terms of Time-to-Data, with extensive simulations in the AWGN and mobile channel. The results were then compared with the legacy implementation and with the performance of the GPS L1C signal and showed a very significant improvement, with a reduction of the Galileo E1 OS TTFF by up to 50% in difficult urban environments. Also received processing scheme and complexity aspects were taken into account in the work. *Spreading Code Authentication Techniques* The increasing awareness concerning the vulnerability of GNSS signals to potential spoofing attacks suggested to dedicate an important part of the project R&D activities to investigating new concepts and ideas to improve the reliability of the provided PNT service. This need was also confirmed by the conducted user requirements survey. The investigation of possible authentication techniques has been carried out on the basis of both quantitative results and qualitative analyses, considering a set of criteria useful to weight the overall performance of different options in realistic scenarios. The methodology used to trade-off different options took into account four main criteria: - the authentication performance, aiming to assess the techniques mainly in terms of Time Between Authentications (TBA) and Time To Alarm (TTA) metrics; - the spoofing robustness, that measures the level of resilience to different specific spoofing attacks; - the implementation readiness, that assesses the level of complexity required both at the system and receiver levels and the backward compatibility; - the legacy signal valorization, with the objective to assess the level of reuse and valorization of today’s signal and messages structures, e.g. considering the current Galileo plans to provide navigation message authentication for his Open Service. When considering authentication solutions, it is important not to focus only on the benefits of future participant users, i.e., those able to exploit the features of the authenticated signals, but also to take into account the possible impact on the existing satellites, ground segment, and other receivers (i.e. non-participant users). Therefore the activities included the assessment of the impact of authentication schemes on user receivers. In detail, the analysis covered the possible degradation of the performance of non-participant users, in terms of C/N0 degradation and impact on acquisition and tracking, and the evaluation of the performance of participant users in relation with the authentication technique parameters. In addition, a novel high-level concept for spreading code authentication, based on the idea of reusing the E1-B OS NMA data, was investigated. The proposed concept, already anticipated in [2], foresees the use of two types of SCA bursts, inserted in the open Pseudo-Random Noise (PRN) code sequence at different rates: - “Slow rate” SCA bursts, which are intended for a robust a-posteriori verification with moderate latency (i.e., TBA of about 10 seconds); - “Fast rate” SCA bursts, potentially suitable to improve the authentication performance (e.g. TBA of about 2 seconds) under a wide set of spoofing attacks. The proposed solution can potentially exploit the information received from all the in-view satellites by means of a two-steps authentication procedure. *CSK Modulation and Channel Codes for a High Data Rate Component* The Code Shift Keying (CSK) modulation is an orthogonal M-ary modulation (M orthogonal symbols are used in order to transmit U =log_2?(M) bits) which was specially designed to increase the bandwidth efficiency of a DS-SS signal, i.e. the bit rate to signal bandwidth ratio, without affecting the PRN code structure. The usage of CSK for the improvement of GNSS data delivery was already investigated in the past (e.g. in [3]). Within the FUNTIMES project the main scope of this task was to prove the expected benefits of this technique by applying it to a number of signal design options, considering various data rates, power distributions between data and pilot components and demodulation strategies at the receiver. The first advantage of CSK is the possibility to increase the bit rate of a DS-SS signal without increasing the PRN code number of bits and without increasing the signal chip rate (and thus signal bandwidth). The increased data rate could be used to increase the number of services provided by the signal and/or to improve the services already available, e.g. by sending correction data. The second benefit is enhanced flexibility of the signal bit rate as the CSK modulation allows to change the number of symbols of the modulation alphabet from one codeword to another one. This allows the GNSS signal to provide more robustness to fundamental data and less robustness to less relevant or optional data since the bit rate is directly relate to the demodulation sensitivity. The third major benefit of a CSK modulation is the possibility of implementing a non-coherent demodulation process that does not require the estimation of the incoming signal carrier phase. Therefore, when in degraded environments and/or for high dynamic users, the PLL cannot be in lock for a certain time, the GNSS receiver could still be able to demodulate the data signal. The results obtained in terms of signal availability and reduced Time-to-First-Fix are very promising and bring a significant improvement when compared with the data delivery performance of today's navigation signals. For what concerns the study of channel codes that could be best suited for high data rate transmission and, especially, in combination with a CSK scheme, the investigation focused on LDPC codes with a bit interleaved coded modulation (BICM/BCIM-ID). As Galileo transmits a navigation signal intended to deliver value-added data in a significant amount (high accuracy service through the E6-B signal), it was decided to study a potential application of the studied CSK schemes to a similar use case. From the results obtained, depending on the C/N0 value considered, an increase of the information bit rate from the current 500 bps up to 5000 bps can be feasible, while still reaching a WER equal to 10-3 for a signal component C/N0 equal to 37 dB-Hz. The project allowed to study new elements in the field of GNSS signal engineering and to consolidate solutions that were already investigated in the recent literature, paving the way to the evolution of the Galileo signal plan but also offering elements and ideas that can be adopted by any other GNSS. The variety of solutions proposed presents different levels of maturity. In some cases the solutions are ready to be implemented in the currently deployed systems, while in other cases they would require a corresponding evolution of the space and ground segments. Where deemed necessary, specific recommendations for future R&D work in the areas studied in the project were provided

Impact of the on-board magnitude error on the centroiding accuracy: GAIA Report to ESA, PDH2-1210-TN-002.1 (GAIA-CA-TN-OPM-CM-002-1)

International audienc

Impact of the on-board magnitude error on the centroiding accuracy: GAIA Report to ESA, PDH2-1210-TN-002.1 (GAIA-CA-TN-OPM-CM-002-1)

International audienc

Etude de l'applicabilité des techniques de lever d'ambiguïté de la mesure de phase gps aux approches de précision

The US Global Positioning System (GPS) provides an accurate positioning service anywhere in the world at any time, but its features are far from being sufficient for it to constitute the Global Navigation Satellite System (GNSS) expected by the civil aviation community. The horizontal accuracy is below 100 m 95% of the time, which is adequate for oceanic, enroute and non precision approaches phases of flight, although additional autonomous integrity monitoring is required to improve safety. The position estimate is computed by measuring the distance to all the visible satellites of the constellation, from the observations of pseudo random noise code modulations. When corrected using a ground reference station, the GPS code pseudorange measurements should provide an accuracy of a few meters. This is sufficient for low accuracy precision approaches (Category I), but guidance during the high accuracy precision approaches (Category II and III) requires the use of a sub-meter positioning system with a high integrity. Since the beginning of the years 1980s, the GPS carrier phase measurements have been used in geodetic applications to pinpoint the location of the survey sites with a centimeter accuracy, after res- olution of the intrinsic ambiguities of these measurements. Such techniques are attractive to the civil aviation community as they appear to have the accuracy required for its most demanding applications. However, as the ambiguity resolution process appears to be fragile especially in real-time kinematic applications, several questions remain unanswered about the reliability of these specific techniques, called AROF (Ambiguity Resolution On-the-Fly) procedures. The aim of this study is to contribute to the analysis of the feasibility of using GPS carrier phase measurements ambiguity resolution procedures during precision aircraft landings. The starting point of this analysis is the presentation of the requirements for a GNSS based precision landing system, and the determination of a model for the carrier phase measurements. Then, the data pre-processing oper- ations are reviewed, and the resulting quality of the data is assessed. Then, a classification of AROF procedures is proposed, and theoretical principles of several techniques, including the new MAPAS procedure developed during this study, are described. Next, the characteristics of AROF procedures are identified, enabling the determination of the requirements of AROF procedures. Afterwards, the difficulty of the determination of theoretical performance is discussed, and mathematical expressions of the performance parameters of MAPAS are presented. Next, the performance of AROF procedures is evaluated on a practical basis using simulated measurements, using measurements collected from a Nortel GPS signal generator, and using field measurements. Finally the characteristics are checked against the constraints, and a conclusion is drawn from this study.Le système américain GPS (Global Positioning System) fournit à tout utilisateur dans le monde entier un service de positionnement précis, mais ses caractéristiques sont trop éloignées de celles d’un GNSS (Global Navigation Satellite System) pour l’aviation civile. La précision atteinte est inférieure à 100 m 95 % du temps, et est suffisante pour les phases de vol océanique, en route, et pour les approches de non précision, mais une surveillance autonome complémentaire de l’intégrité est nécessaire pour améliorer la sécurité. L’estimation de position est effectuée en utilisant les mesures de distance entre l’utilisateur et les satellites visibles de la constellation GPS, obtenues grâce à l’observation des modulations de code pseudo-aléatoires du signal émis par les satellites. Après correction grâce aux données d’une station de référence, ces mesures de pseudo-distance de code devraient permettre un positionnement d’une précision de quelques mètres. Ceci est suffisant pour les approches de faible précision (Catégorie I), mais le guidage des avions pendant les approches de haute précision (Catégorie II et III) requiert l’utilisation d’un système de positionnement sub- métrique ayant une très grande intégrité. Depuis le début des années 80, les mesures de phase de la porteuse du signal GPS sont utilisées lors des applications géodésiques pour déterminer précisément la position des points de mesure, avec une précision centimétrique après la résolution des ambiguïtés intrinsèques aux mesures de phase. De telles techniques sont attirantes pour l’aviation civile, puisqu’elles semblent avoir la précision néces- saire pour ses applications les plus exigeantes. Cependant, le processus de résolution des ambiguïtés s’avère fragile, surtout dans les applications dynamiques en temps réel, et des questions subsistent concernant la fiabilité des ces techniques spécifiques, appelées méthodes AROF (Ambiguity Resolu- tion On-the-Fly). Le but de cette étude est d’apporter une contribution à l’analyse de l’applicabilité des méthodes de lever d’ambiguïté de la mesure de phase GPS au guidage des avions en phase d’atterrissage de précision. Le point de départ de cette analyse est constitué par les exigences opérationnelles des systèmes d’atterrissage de précision basés sur un système GNSS, et par un modèle mathématique des mesures de phase GPS. Puis, les opérations de pré-traitement des mesures sont présentées, et la qualité des données obtenues est évaluée. Ensuite, on propose une classification des méthodes AROF, et on décrit les principes théoriques de plusieurs techniques, y compris de la méthode MAPAS, développée au cours de cette thèse. Puis, les caractéristiques des procédures AROF sont identifiées, permet- tant l’établissement des exigences. Puis, la difficulté de l’établissement des performances théoriques de ces méthodes est analysée, et des expressions mathématiques des performances de MAPAS sont présentées. Enfin, les performances de MAPAS sont évaluées sur un plan pratique, en utilisant des mesures simulées, des mesures collectées sur un générateur de signaux GPS Nortel, et des mesures réelles en situation aéroportuaire. Finalement, les caractéristiques de ces procédures sont comparées aux contraintes, et une conclusion est tirée de cette analys

Degraded Modes Resulting From The Multi Constellation Use Of GNSS

Actuellement, on constate dans le domaine de la navigation, un besoin croissant de localisation par satellites. Apres une course a l'amelioration de la precision (maintenant proche de quelques centimetres grace a des techniques de lever d'ambiguite sur des mesures de phase), la releve du nouveau defi de l'amelioration de l'integrite du GNSS (GPS, Galileo) est a present engagee. L'integrite represente le degre de confiance que l'on peut placer dans l'exactitude des informations fournies par le systeme, ainsi que la capacite a avertir l'utilisateur d'un dysfonctionnement du GNSS dans un delai raisonnable. Le concept d'integrite du GNSS multi-constellation necessite une coordination au niveau de l'architecture des futurs recepteurs combines (GPS-Galileo). Le fonctionnement d'un tel recepteur dans le cas de passage du systeme multi-constellation en mode degrade est un probleme tres important pour l'integrite de navigation. Cette these se focalise sur les problemes lies a la navigation aeronautique multiconstellation et multi-systeme GNSS. En particulier, les conditions de fourniture de solution de navigation integre sont evaluees durant la phase d'approche APV I (avec guidage vertical). En disposant du GPS existant, du systeme Galileo et d'un systeme complementaire geostationnaire (SBAS), dont les satellites emettent sur des frequences aeronautiques en bande ARNS, la question fondamentale est comment tirer tous les benefices d'un tel systeme multi-constellation pour un recepteur embarque a bord d'un avion civil. En particulier, la question du maintien du niveau de performance durant cette phase de vol APV, en termes de precision, continuite, integrite et disponibilite, lorsque l'une des composantes du systeme est degradee ou perdu, doit etre resolue. L'objectif de ce travail de these est donc d'etudier la capacite d'un recepteur combine avionique d'effectuer la tache de reconfiguration de l'algorithme de traitement apres l'apparition de pannes ou d'interferences dans une partie du systeme GNSS multiconstellation et d'emettre un signal d'alarme dans le cas ou les performances de la partie du systeme non contaminee ne sont pas suffisantes pour continuer l'operation en cours en respectant les exigences de l'aviation civile. Egalement, l'objectif de ce travail est d'etudier les methodes associees a l'execution de cette reconfiguration pour garantir l'utilisation de la partie du systeme GNSS multi-constellation non contaminee dans les meilleures conditions. Cette etude a donc un interet pour les constructeurs des futurs recepteurs avioniques multiconstellation.The International Civil Aviation Organization (ICAO) has defined the concept of Global Navigation Satellite System (GNSS), which corresponds to the set of systems allowing to perform satellite-based navigation while fulfilling ICAO requirements. The US Global Positioning Sysem (GPS) is a satellite-based navigation system which constitutes one of the components of the GNSS. Currently, this system broadcasts a civil signal, called L1 C/A, within an Aeronautical Radio Navigation Services (ARNS) band. The GPS is being modernized and will broadcast two new civil signals: L2C (not in an ARNS band) and L5 in another ARNS band. Galileo is the European counterpart of GPS. It will broadcast three signals in an ARNS band: Galileo E1 OS (Open Service) will be transmitted in the GPS L1 frequency band and Galileo E5a and E5b will be broadcasted in the same 960-1215 MHz ARNS band than that of GPS L5. GPS L5 and Galileo E1, E5a, E5b components are expected to provide operational benefits for civil aviation use. However, civil aviation requirements are very stringent and up to now, the bare systems alone cannot be used as a means of navigation. For instance, the GPS standalone does not implement sufficient integrity monitoring. Therefore, in order to ensure the levels of performance required by civil aviation in terms of accuracy, integrity, continuity of service and availability, ICAO standards define different systems/algorithms to augment the basic constellations. GPS, Galileo and the augmentation systems could be combined to comply with the ICAO requirements and complete the lack of GPS or Galileo standalone performance. In order to take benefits of new GNSS signals, and to provide the service level required by the ICAO, the architecture of future combined GNSS receivers must be standardized. The European Organization for Civil Aviation Equipment (EUROCAE) Working Group 62, which is in charge of Galileo standardization for civil aviation in Europe, proposes new combined receivers architectures, in coordination with the Radio Technical Commission for Aeronautics (RTCA). The main objective of this thesis is to contribute to the efforts made by the WG 62 by providing inputs necessary to build future receivers architecture to take benefits of GPS, Galileo and augmentation systems. In this report, we propose some key elements of the combined receivers' architecture to comply with approach phases of flight requirements. In case of perturbation preventing one of the needed GNSS components to meet a phase of flight required performance, it is necessary to be able to switch to another available component in order to try to maintain if possible the level of performance in terms of continuity, integrity, availability and accuracy. That is why future combined receivers must be capable of detecting the impact of perturbations that may lead to the loss of one GNSS component, in order to be able to initiate a switch. These perturbations are mainly atmospheric disturbances, interferences and multipath. In this thesis we focus on the particular cases of interferences and ionosphere perturbations. The interferences are among the most feared events in civil aviation use of GNSS. Detection, estimation and removal of the effect of interference on GNSS signals remain open issues and may affect pseudorange measurements accuracy, as well as integrity, continuity and availability of these measurements. In literature, many different interference detection algorithms have been proposed, at the receiver antenna level, at the front-end level. Detection within tracking loops is not widely studied to our knowledge. That is why, in this thesis, we address the problem of interference detection at the correlators outputs. The particular case of CW interferences detection on the GPS L1 C/A and Galileo E1 OS signals processing is proposed. Nominal dual frequency measurements provide a good estimation of ionospheric delay. In addition, the combination of GPS or GALILEO navigation signals processing at the receiver level is expected to provide important improvements for civil aviation. It could, potentially with augmentations, provide better accuracy and availability of ionospheric correction measurements. Indeed, GPS users will be able to combine GPS L1 and L5 frequencies, and future GALILEO E1 and E5 signals will bring their contribution. However, if affected by a Radio Frequency Interference, a receiver can lose one or more frequencies leading to the use of only one frequency to estimate the ionospheric code delay. Therefore, it is felt by the authors as an important task to investigate techniques aimed at sustaining multi-frequency performance when a multi constellation receiver installed in an aircraft is suddenly affected by radiofrequency interference, during critical phases of flight. This problem is identified for instance in [NATS, 2003]. Consequently, in this thesis, we investigate techniques to maintain dual frequency performances when a frequency is lost (L1 C/A or E1 OS for instance) after an interference occurrence.TOULOUSE-INP (315552154) / SudocSudocFranceF