Interleaved coded modulation for non-binary codes: a factor graph approach

This contribution deals with the problem of combining (non-binary) error-correcting codes with higher-order modulation schemes on AWGN and flat fading channels through interleaved coded modulation. We extend the idea of bit-interleaved coded modulation (BICM) to a more general form. With the aid of factor graph representations, we show how higher-order modulation can be combined with non-binary codes so that noniterative detection becomes optimal. This is in contrast with conventional BICM, for which non-iterative detection can be far from optimal. Through computer simulations, we compare an optimal non-iterative scheme with conventional BICM. It turns out that the gain due to optimal detection is outweighed by the loss in time-diversity as compared to BICM-ID.