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    Interface air pour systèmes de navigation en bande S : étude détaillée des signaux OFDM

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    Positioning in urban or indoor environment is a hot topic, either due to regulations such as the E911 requiring US mobile telecommunication operators to be able to locate their subscribers in case of emergency, or due to the market development, with the extension of location - based services targeting the mass market concentrated in metropolitan areas. In urban or indoor areas, it is generally recognized that satellite - based positioning systems are not suitable (alone) to provide a continuous, reliable and accurate position to the user. Therefore, alternative positioning techniques may be useful to complement or replace satellite positioning in these environments. This PhD study ha s studied the possibility of using a mobile TV system based on the DVB - SH standard as system of opportunity for positioning. The advantage s of using a DVB - SH system for positioning are multiple. First, such system has a good availability in metropolitan areas, including indoor. Secondly, the emitters are synchronized and their density should be sufficient to track signals from several emitters simultaneously. This opens the possibility of using timing measurements from several emitters to find a position by trilateration . Also, the large bandwidth of the TV signal, required for the transmission of video content, should be beneficial for the accuracy of the timing measurements and for the robustness against multipath . Therefore, DVB - SH system seems to be an interesting candidate as system of opportunity for positioning. However, several challenges are to be solved for such a solution to be relevant. First, the signals propagate in the urban environment, which creates challenging conditions for positioning su ch as strong power fading, blockage of the desired line - of - sight signal or large echoes. Secondly, the DVB - SH standard uses an OFDM modulation, which has not been studied for positioning purpose. Therefore, techniques for fine tracking of the first receive d signal replica will have to be developed. Finally, a particularity of modern broadcast system is the use of a Single Frequency Network, in which all emitters send the same signal on the same carrier frequency. Therefore emitter identification in a Single Frequency will be another issue to be solved. This PhD study has proved the feasibility of positioning using DVB - SH signals. The main contributions of this work are the propositions of (1) an OFDM signal delay tracking method working in urban propagation channels, and (2) a modification to the network deployment permitting emitter identification and (3) a first assessment of the position accuracy using the proposed algorithms. These two methods have very low impact on the initial TV broadcasting service if the right set of signal parameters is chosen: no signal modification is required and the network deployment modification uses a feature already present in the DVB - SH standard. The positioning method was simulated using real urban propagation channel measurements. The obtained position has root mean square error of 4 0m. The main error contribution comes from tracking a non - line - of - sight signal. Further work would be required to deal with this issue, which would lower the position root mean square error to 7 m, which has been locally observed in the simulation for good tracking conditionsLe positionnement en environnement urbain est un domaine de recherche actif, de par la croissance des services grand public liées à la localisation, et à cause de réglementations émergentes liées aux situations d'urgence (E911). En environnement urbain ou à l'intérieur des bâtiments, il est communément admis que les systèmes de positionnement basés sur des satellites ne sont pas suffisants pour fournir une position précise, fiable et de manière continue. Des techniques de positionnement alternatives sont donc développées afin de remplacer ou compléter les systèmes de positionnement par satellite. Cette thèse étudie la possibilité de fournir un service de positionnement utilisant un futur système de diffusion de télévison vers les mobiles basé sur le standard DVB-SH. Le principal attrait de ce système pour du positionnement est sa bonne couverture en milieu urbain, ainsi que l'utilisation d'un réseau d'émetteurs synchronisés. Il est donc possible d'employer des mesures de temps d'arrivée des signaux afin de réaliser une triangulation pour calculer la position d'un récepteur. Afin de fournir ce service innovant, des techniques spécifiques d'estimation de pseudo-distance et d'identification d'émetteurs ont été développées dans le cadre de cette thèse. Le principal résultat de cette étude est d'avoir montré la faisabilité du positionnement utilisant un système DVB-SH, ne nécessitant que de légères modifications du système qui n'apportent aucune dégradation auservice de diffusion TV. De premières simulations ont montré une précision de positionnement autour de 40m en utilisant des mesures réalistes de canal de propagation urbain
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