Pilot symbol initiated iterative channel estimation and decoding for QAM modulated OFDM signals

In this paper, we consider the iterative channel estimation and decoding algorithms for quadrature amplitude modulation (QAM) modulated orthogonal frequency division multiplexing (OFDM) signals. We first describe the optimal sequence estimation based on the expectation-maximization (EM) algorithm. Using some approximations, we propose a sub-optimal iterative channel estimation and decoding algorithm, which is shown to have reduced computational complexity. The bit error rate (BER) performances of the proposed algorithm are evaluated using computer simulations. The results show that the proposed algorithm performs nearly as well as the optimal EM algorithm, and outperforms the conventional minimum mean square error (NMSE) estimator.