Channel estimation for MIMO-OFDM systems in mobile wireless channels

A channel estimation method is proposed for multiple-input multiple-output orthogonal frequency division multiplexing(MIMO-OFDM)systems in time-varying fading channels.In this method,a decision-directed space-alternating generalized expectation-maximization(SAGE)algorithm is introduced to the tracking of time-varying fading.In order to improve the estimation performance of the SAGE algorithm,a low rank approximation method is presented by using the signal subspace of the channel frequency autocorrelation matrix.The study reveals that this method can be incorporated into the SAGE algorithm.Furthermore,a modified fast subspace tracking algorithm is given to adaptively estimate the signal subspace by utilizing training OFDM blocks sent at regular interval.Simulation results demonstrate the considerable benefits of the proposed channel estimation method.