Non-data aided EM-Based channel estimation for OFDM systems with time-varying fading channels

Abstract

In this paper, a computationally efficient algorithm is presented for maximum a posteriori (MAP) channel estimation for OFDM systems employing M-PSK modulation scheme with additive Gaussian noise, based on the Expectation Maximization (EM) method. A non-data-aided scheme is considered for the estimation of a multipath time-varying channel by averaging over the M-PSK signal constellation. For this, an EM algorithm is derived which estimates the complex channel parameters of each subcarriers iteratively in frequency domain and which converges to the true MAP estimation of the Unknown channel, The algorithm requires a convenient representation of die discrete multipath fading channel based on the Karhumen-Loeve orthogonal expansion. The algorithm is applied to the QPSK modulated OFDM systems and efficiency of the method proposed is shown by the computer simulations.