EM-based semi-blind estimation of time-varying channels

OFDM systems traditionally perform channel coefficients estimation relying on known training sequences. However in wireless systems, performance and mobility can be further enhanced either by operating semi-blind channel estimation refinement or variation tracking between reference symbols. In this paper we propose an EM-based channel tracking method using a simple order 1 AR modelling of the channel variations. The proposed approach is applicable to both single carrier and OFDM systems. Simulation results presented in the context of 5 GHz WLAN show that this new algorithm allows us to reach the performance of a receiver having a perfect knowledge of the channel coefficients even in the mobile environment (3 m/s).