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Mise en oeuvre d'un système de communication OFDM-haut débit dédié aux trains à grandes vitesses

Abstract : THe 4th generation of wireless communication systems (LTE, IEEE.802.16m and IEEE.802.20) is developed in the rail to provide information services, maintenance, reservation services and Internet access. In a context of high mobility (i.e. the TGV), the consequences of the Doppler Effect on the performance of such systems are important : it's impossible to use high data rate modulations. Our objective is to propose solutions to minimize this damage. It covers an efficient estimation of a time-varying channel in an OFDM system. In order to estimate the channel, which is essential for the equalization of data, pilots sub-carriers are inserted into the OFDM symbol. The channel is estimated in the time domain and temporal variations of each path are modeled by a set of functions (BEM Modeling Basis expansion). The channel is obtained by the corresponding base coefficients. A pilot structure is proposed, it consists to vary the positions of pilot sub-carriers from a symbol to another. The positions of the pilot sub-carriers are allocated dynamically during the transmission of OFDM symbols. We talk about the dynamic allocation of pilots sub-carriers (ADP). The estimated time-varying channel is better and therefore the system performance is improved compared to the Doppler effect. In a multiuser OFDM system, we propose to exploit the idea of ADP to create a frequency diversity. Each user is identified by a unique combination of pilot sub-carriers. Using the cooperation between different users (frequency diversity), the estimated time-varying channel is improved and the fatal effects of the Doppler Effect is reduced.
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https://hal-uphf.archives-ouvertes.fr/tel-03416058
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Submitted on : Friday, November 5, 2021 - 9:19:41 AM
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  • HAL Id : tel-03416058, version 1

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Boudali Ouarzazi. Mise en oeuvre d'un système de communication OFDM-haut débit dédié aux trains à grandes vitesses. Micro et nanotechnologies/Microélectronique. Université de Valenciennes et du Hainaut-Cambrésis, 2011. Français. ⟨NNT : 2011VALE0028⟩. ⟨tel-03416058⟩

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