EM Based MAP Channel Estimation for Turbo/Convolutional Coded SFBC/STBC-OFDM Systems

We consider the design of turbo receiver structures for space-frequency block coded (SFBC/STBC) OFDM systems in unknown frequency selective fading channels. The turbo receiver structures for SFBC/STBC-OFDM systems under consideration consist of an iterative MAP expectation/maximization (EM) channel estimation algorithm, soft MMSE SFBC/STBC decoder and a soft MAP outer-channel-code decoder. MAP-EM employs iterative channel estimation and it improves receiver performance by re-estimating the channel after each decoder iteration. Moreover, the MAP-EM approach considers the channel variations as random processes and applies the Karhunen-Loeve (KL) orthogonal series expansion. The performance of the proposed approaches is studied in terms of mean square error and bit-error rate. Through experimental results, the effect of a pilot spacing on the channel estimator performance and sensitivity of turbo receiver structures on channel estimation error are studied