Estimation de canal à évanouissement rapide utilisant le modèle d’expansion sur bases orthogonales (BEM) dans les systèmes OFDM.

Abstract

In this thesis we have discussed the estimation of the multipath fast fading channel in OFDM systems. Channel estimation requires a large number of pilots, which reduces the number of subcarriers dedicated to the useful data transmission. In this thesis, our main goal is to carry out channel estimation algorithms aiming to achieve the best combination of estimation performance and maximum spectral efficiency, using the basis expansion model (BEM). In particular, we focus on the development of a reduced PDR (Pilot to useful Data Ratio) estimation techniques by proposing two techniques in order to improve the spectral efficiency while maintaining an acceptable estimation performance in terms of Mean Square Error (MSE), and Binary Error Rate (BER), in high mobility situations. Our contribution is mainly based on exploiting additional clustered pilots carried by adjacent OFDM symbols, in complement of those contained in the symbol under investigation. The proposed adjacent pilot-based method leads us to consider the two followings cases, according to the assumed channel hypothesis : 1) In the first case, we consider a doubly selective channel, based on a comb pilot structure with the BEM (basis expansion model) approximation. In such scenarios, certain statistical properties of the channel are assumed to be a priori known. 2) In the second case, we consider a high mobility situation along with another type of channel, known as multipath channel with sparse taps. This type of channel exhibits a fast variation of the taps delay interspacing, which causes a very large delay spread between the different taps.