The Effect of the Choice of the Mapping on the Performance of Map Equalizer

In this paper, we propose to study the effect of the choice of the mapping on the performance of iterative receivers for frequency selective channels. We use at the transmitter a BICM (Bit Interleaved Coded Modulation) based scheme obtained by the concatenation of a binary code and a modulator separated by an interleaver. Because of the interleaving, the optimal receiver is too complex. We consider here an iterative receiver composed of a Maximum A Posteriori (MAP) equalizer and a MAP decoder. During the iterations, the equalizer and the decoder exchange extrinsic information and use them as a priori in order to improve their performance. An optimization of the mapping is required to obtain a gain by using the iterative receivers. In order to make the mapping choice easier, we propose to perform an analysis based on the Gaussian approximation. This analysis relies on only one simulation of the equalizer.