Which interleaver for turbo-equalization system on frequency and time selective channels for high order modulations?

The development engineer has to face the question of where to place an interleaver in a digital communication system. In this paper we propose to solve this problem according to the channel transmission characteristics in the particular case of turbo-equalization system. Using a state of the art in coded modulations and some simulation results, we deduce the best interleaver, among the coordinate, bit and symbol interleavers, depending on the channel time selectivity. The coordinate interleaver is then proposed as a trade-off between the two latter types of interleaver.