Iterative channel estimation and decoding of turbo-coded OFDM symbols in selective Rayleigh channel

This work deals with the detection of turbo-coded symbols in orthogonal frequency-division multiplexed (OFDM) systems. OFDM symbol detection requires channel estimation, which is often carried out using known pilots. In this paper, an iterative detector composed of a turbo decoder and a channel estimator is proposed. These modules perform jointly and exchange soft information through an iterative process. The decoder consists of the maximum a posteriori Bahl-Cocke-Jelinek-Raviv (MAP-BCJR) algorithm, and the channel estimator is based on the minimum mean-square error (MMSE) criterion. The proposed approach allows for the use of all available information, increases the quality of channel estimation, and improves the system performance. This paper also proposes a new expression of the channel reliability factor used by the MAP-BCJR decoding algorithm. This metric depends on signal-to-noise ratio and the channel estimation error variance. The effect of the channel reliability factor and of the channel estimation error are investigated.