Accelerated Linear EM-MAP Algorithm for OFDM Channel Estimation

OFDM systems traditionally perform channel estimation relying on known training sequences. However in wireless systems, performance and mobility can be further enhanced by operating semiblind channel estimation refinement between reference symbols. A channel tracking method based on a maximum a posteriori (MAP) version of the expectation-maximization (EM) algorithm and on a block representation of the channel variations has been proposed. It performs better than already existing recursive algorithms with the additional advantage of a linear arithmetic complexity. In this paper, we study the matrix governing the behaviour of this method. This leads to a practical rule for choosing optimally (with respect to the convergence rate) the unique parameter of the method. The proposed iterative procedure is applicable to both single carrier and OFDM systems. Simulations are presented in the context of 5 GHz WLANs, showing the practical interest of the method.