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