EM-MMSE based Channel Estimation for OFDM Systems

Accurate estimation of time-varying wireless channels is a difficult task in orthogonal frequency division multiplexing (OFDM) systems. Pilot based techniques have normally been employed for channel estimation. However, for time varying channels, pilot symbols need to be transmitted periodically to overcome the effect of time selective fading. Expectation-maximization (EM) based technique may be used in such situations avoiding the need for periodic retransmission of pilot symbols. In order to reduce the complexity of EM algorithm, we propose an EM-MMSE based iterative procedure to estimate the time-varying channel. The proposed algorithm is not only computationally simpler than EM method but also yields performance improvement over conventional pilot based methods.