Turbo-like codes for the block-fading channel

We consider the coded modulation family of block-wise concatenated codes (BCC). The blocks are separately interleaved and fed to binary inner encoders. Finally, the output of each component inner code is mapped onto a sequence of signal components by the modulator mapping. The proposed BCCs significantly outperform conventional serial and parallel turbo codes in the block-fading channel. Differently from the AWGN and fully-interleaved fading cases, iterative decoding performs very close to ML on the block-fading channel, even for relatively short block lengths. Moreover, at constant decoding complexity per information bit, BCCs are shown to be weakly good, while standard block codes obtained by trellis-termination of convolutional codes have a gap from outage that increases with the block length: this is a different and more subtle manifestation of the so-called "interleaving gain" of turbo-like codes.