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Advanced Signal Processing Algorithms for GNSS/OFDM Receiver

Damien Serant 1
1 SIGNAV - ENAC Equipe TELECOM-SIGNAV
TELECOM - ENAC - Equipe télécommunications
Abstract : 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.
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Damien Serant. Advanced Signal Processing Algorithms for GNSS/OFDM Receiver. Signal and Image processing. INPT, 2012. English. ⟨NNT : 2012INPT0006⟩. ⟨tel-01786809⟩

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