De par le développement de nombreux services et d’applications de localisation (positionnement des téléphones mobiles, aide à la personne…), le positionnement urbain et à l’intérieur des bâtiments représente aujourd’hui un marché important. Cependant, ces environnements sont très contraignants pour les systèmes de positionnement par satellites, à cause du blocage du signal par les bâtiments, des multitrajets, des interférences, etc. Même si des adaptations du système de positionnement par satellites existent pour réduire ces problèmes (récepteur haute-sensibilité, Assisted-GPS, évolutions système), elles ne permettent pas d’atteindre une disponibilité, une continuité et une précision suffisantes en ville et à l’intérieur des bâtiments. Quelques alternatives au positionnement par satellites permettent de compléter ce dernier dans ces environnements difficiles. Ce sont, par exemple, d’autres capteurs de position (accéléromètres, magnétomètres, gyroscopes, odomètres, laser, vidéo), ou des systèmes radio dédiés (pseudolites, RFID, UWB) ou encore des signaux d’opportunités (SO). Les SO sont des signaux de communication (par exemple : des signaux téléphonie mobile, radio, TV, Wifi) qui sont utilisés opportunément pour faire du positionnement. Bien que ces signaux ne soient pas prévus pour de telles applications, ils ont l’avantage d’être nombreux et variés dans les villes et à l’intérieur des bâtiments. De plus, ils permettent, de par leur nature, une bonne intégration des services de positionnement et de communication. Parmi tous les SO envisageable, cette thèse se concentre sur ceux basés sur la modulation « Orthogonal Frequency Division Multiplexing » (OFDM), qui apparait comme un choix évident, du fait de son incroyable popularité parmi les standards de communication actuels et futurs (Wi-Fi, WiMAX, LTE, DVB-T/H/SH, DAB, T-DMB, ISDB-T, MediaFLO utilisent tous la modulation OFDM). Parmi tous les standard existants basés sur la modulation OFDM, le standard européen « Digital Video Broascasting – Terrestrial » de télévision numérique terrestre, a été choisi comme cas d’étude dans cette thèse car sa structure est relativement simple, permettant la réutilisation du travail pour d’autres standards basés sur la modulation OFDM et qu’il est déjà opérationnel et déployé en Europe, rendant possible des tests sur signaux réels. Une méthode de mesure de pseudodistance basée sur des mesures de temps de propagation et utilisant les signaux DVB-T a été développée. Cette méthode utilise des boucles à verrouillage de retard (DLL) et prend en compte la spécificité des canaux de propagation terrestres (nombreux multitrajets, signal direct parfois absent, évanouissement du signal reçu…). Les performances de cette méthode ont été déterminées théoriquement et validées par simulation, dans un cas idéal (canal de propagation gaussien). Cette étude théorique montre notamment un écart-type de l’erreur d’estimation de la pseudodistance de l’ordre du mètre pour des SNR supérieurs à -20 dB, soit 30 à 40 dB en dessous du SNR requis pour décoder le signal TV. Les performances dans un canal réaliste ont été déterminées empiriquement grâce à des tests sur signaux réels. Un banc de test à été développé . Il permet la réception de signaux TV avec deux antennes indépendantes et est muni d’un récepteur GPS pour avoir une référence de position et fournir une référence de temps au reste du banc de test. Des mesures sur signaux réels on été réalisées dans plusieurs environnements (rural, urbain et à l’intérieur de bâtiments) en utilisant un émetteur TV synchronisé sur le temps GPS ou deux émetteurs en réseau mono-fréquence (SFN). Les résultats des mesures sur signaux réels ont montré des écart-types de l’erreur d’estimation de pseudodistance de l’ordre de la dizaine de mètres, avec de meilleures performances en environnement rural (car moins de multitrajets) et une amélioration de la performance lors de l’utilisation de la diversité d’antenne. / The recent years have shows a growing interest in urban and indoor positioning with the development of applications such as car navigation, pedestrian navigation, local search and advertising and others location-based-services (LBS). However, in urban and indoor environment the classical mean of positioning, the Global Positioning Satellite System (GNSS) has limited availability, accuracy, continuity and integrity due to signal blockage by building, intense multipath conditions and interferences from the other signals, abundant in metropolitan areas. Even some improvements of GNSS can reduce these issues (high-sensitivity receiver, assisted-GNSS, multi-constellation GNSS…), they do not permit to reach sufficient performance in deep urban and indoor environments. However, some alternatives to GNSS allow complementing it in difficult environments. They are, for example, additional sensors (accelerometers, gyrometers, magnetometers, odometers, laser, and video), radiofrequency systems dedicated to positioning (pseudolites, RFID, UWB) or signals of opportunity (SoO). SoO are telecommunication signals (as mobile phone, TV, radio, Wi-Fi) that are used opportunely to provide a positioning service. Even if these signals are not designed for such application, they have the advantages to be many and varied in urban and indoor environments. In addition they allow, by definition, a good integration of communication and positioning services. Among all the SoO available, this thesis focuses on the one based on the Orthogonal Frequency Division Multiplexing (OFDM) modulation. This choice is motivated by the important popularity of this modulation, that has been chosen in several actual and future telecommunication and broadcasting standards (Wi-Fi, WiMAX, LTE, DVB-T/H/SH, DAB, T-DMB, ISDB-T, MediaFLO…). Among this standard using the OFDM modulation, the European standard for digital television called “Digital Video Broadcasting – Terrestrial” (DVB-T) has been selected to be studied in this thesis. The choice is motivated by the relatively simple definition of this standard, allowing reuse of the work for other OFDM standards, and also because it is already operational in Europe, allowing tests on real signals. A method to obtain ranging measurements based on timing synchronization using DVB-T signals has been developed. This method uses delay lock loops (DLL) and takes into account the specificity of the terrestrial propagation channel (many multipathes, direct signal sometimes absent, quick variation of received power…). The performance of the method has been determinate theoretically and validated by simulation, in an ideal case (i.e.; with a Gaussian propagation channel). This theoretical study has proven than the ranging error standard deviation has an order of magnitude of 1 meter, for signal to noise ratio of about -20 dB, a SNR 40 dB under the demodulation threshold of the TV signal. The performance in a realistic propagation channel has been determined on real signal. For that purpose a test bench has been developed. It allows to receive and record TV signals on two synchronized antennas and it includes and GPS receiver to record a reference position and provide a GPS time reference to the test bench. Tests on real signals have been realized in several environments (sub-urban, urban and indoor) using 1 emitter synchronized on GPS time and 2 emitters in a signal frequency network (SFN). The results of these tests on real signals showed a precision of the ranging estimation of about 10 meters with a better performance in rural environment and an improvement of the ranging estimate using antenna diversity. Finally, the thesis proves the feasibility of positioning with signal using the OFDM modulation, with a technique that can be easily tailored to other OFDM signal than DVB-T.

<div> <div> <p>Global Navigation Satellite System Reflectometry (GNSS-R) has presented a great potential as an important approach for ocean remote sensing. Numerous studies have demonstrated that the shape of a code-correlation waveform of forward-scattered Global Positioning System (GPS) signals may be used to measure ocean surface roughness and related geophysical parameters such as wind speed. Recent experiments have extended the reflectometry technique to transmissions from communication satellites. Due to the high power and frequencies of these signals, they are more sensitive to smaller scale ocean surface features, which makes communication satellites a promising signal of opportunity (SoOp) for ocean remote sensing. Recent advancements in fundamental physics are represented by the new scattering model and bistatic radar function developed by Voronovich and Zavorotny based on the SSA (Small Slope Approximation). This new model allows the partially coherent scattering in low wind conditions to be correctly described, which overcomes the limitations of diffuse scattering inherited in the conventional KA-GO (Kirchhoff Approximation-Geometric Optics) model. Furthermore, exploration and practice using spaceborne platforms have become a primary research focus, which is highlighted by the launch of CYGNSS (Cyclone Global Navigation Satellite System) in 2016. CYGNSS is a NASA (National Aeronautics and Space Administration) Earth Venture Mission consisting of an 8 micro-satellite constellation of GNSS-R instruments designed to observe tropical cyclones.</p><p>However, in spite of the significant achievements made in the past 10 years, there are still a variety of challenges to be addressed currently in the ocean reflectometry field. To begin with, the airborne demonstration experiments conducted previously for S-band reflectometry provided neither sufficient amount of data nor the desired scenarios to assess high wind retrieval performance of S-band signals. The current L-band empirical model function theoretically does not also apply to S-band reflectometry. With respect to scattering models, there have been no results of actual data processing so far to verify the performance of the SSA model, especially on low wind retrievals. Lastly, the conventional model fitting methods for ocean wind retrievals were proposed for airborne missions, and new approaches will need to be developed to satisfy the requirement of spaceborne systems.<br></p><p>The research described in this thesis is mainly focused on the development, application and evaluation of new models and algorithms for ocean wind remote sensing. The first part of the thesis studies the extension of reflectometry methods to the general class of SoOps. The airborne reception of commercial satellite S-band transmissions is demonstrated under both low and high wind speed conditions. As part of this effort, a new S-band geophysical model function (GMF) is developed for ocean wind remote sensing using S-band data collected in the 2014 NOAA (National Oceanic and Atmospheric Administration) hurricane campaign. The second part introduces a dual polarization L- and S-band reflectometry experiment, performed in collaboration with Naval Research Lab (NRL), to retrieve and analyze surface winds and compare the results with CYGNSS satellite retrievals and NOAA data buoy measurements. The problems associated with low wind speed retrieval arising from near specular surface reflections are studied. Results have shown improved wind speed retrieval accuracy using bistatic radar cross section (BRCS) modeled by the SSA when compared with KA-GO, in the cases of low to medium diffuse scattering. The last part focuses on the contributions to the NASA-funded spaceborne CYGNSS project. It shows that the accuracy of CYGNSS ocean wind retrieval is improved by an Extended Kalman Filter (EKF) algorithm. Compared with the baseline observable methods, preliminary results showed promising accuracy improvement when the EKF was applied to actual CYGNSS data.<br><br></p></div></div>