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Canal de propagation 5G et mécanisme de contrôle d'intégrité : application à la localisation sûre des rames dans un tunnel

Abstract : System level simulations are crucial in the development phase of any emerging wireless technology. It allows to identify the key factors that affect the transmission quality and to define the network limits. The used simulators must then be based on accurate and realistic channel models to better predict the system performances. In this context, several researches had been interested to the development of new models that take into account the emerging propagation scenarios introduced by the fifth generation of mobile communications (5G) that will be commercialized by 2020. In order to optimize the spectral and energetic resources use, the mobile terminals of this next generation should be constantly aware of their environment. This relies on the implementation of a location system, especially in constrained environments where satellite positioning systems are not available. In the field of transport, a rather recurrent example of these scenarios is that of tunnels. Although they are indoor environments, this type of environment is characterized by the phenomenon of wave guiding due to its geometric structure and the properties of the materials of its walls. Thus, an extension of the propagation models developed for the 5G systems is then necessary, in order to take into account this use case. We propose in this thesis a hybrid approach to reproduce the effect of the channel in a localization system. First, we calculate the propagation parameters by a ray-tracing simulator. It accurately describes the behavior of the radio waves inside the tunnel; nevertheless, it is expensive in terms of computing time. Then we analyze the obtained deterministic data to identify their statistical laws, and we store both of them in a database to stochastically generate the channel coefficients needed for our ranging system, namely the amplitude and the delay relative to each path. The impulse response of the channel will finally be used to estimate the distance between the two transmission antennas. Depending on the propagation conditions as well as the position of the receiver, three sources of error can compromise the accuracy of this distance. For a ranging system based on the time metric, they are related to the bandwidth, the detection threshold, and the obstruction of the direct path. The implementation of an integrity control mechanism seems to be a promising solution to improve the performance of our system. It then consists of identifying the outliers that do not meet the constraints imposed by the application, then excluding or correcting them according to the strategy adopted by the receiver. In this context, we propose to exploit the spatial diversity of a SIMO (Single Input Multiple Output) system with two reception antennas in order to identify the propagation conditions of the channel. The first step of our approach aims to increase the temporal resolution of the two impulse responses of the system. Being sparse, they are reconstructed in the frequency domain over a very wide band using a compressed sensing technique. Then we classify them according to a temporal criterion, which represents the time difference of propagation of the signal in each channel, and we obtain it by the inter-correlation of reconstructed impulse responses. The proposed approach not only improves the reliability of the ranging information in the tunnel, but also reduces the error related to the limited bandwidth of the system and the obstruction of the direct path. An experimental implementation of the ranging system based on OFDM signals gives rise to distance estimation errors at least six times lower than those reported by the classical approach, or even to those issued from other identification techniques based on statistical tests. This algorithm and the hybrid model of the channel are then the two major contributions of this thesis work [...]
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Submitted on : Thursday, June 11, 2020 - 6:15:10 PM
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Camelia Skiribou. Canal de propagation 5G et mécanisme de contrôle d'intégrité : application à la localisation sûre des rames dans un tunnel. Electromagnétisme. Sorbonne Université; Université Cadi Ayyad (Marrakech, Maroc), 2018. Français. ⟨NNT : 2018SORUS343⟩. ⟨tel-02865510⟩



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