Turbo detection for MIMO systems: bit labeling and pre-coding

Bit-interleaved coded modulation with iterative detection for MIMO systems demands an efficient APP detector that delivers soft information about the coded bits. The list-sequential detector is a reduced-complexity approximation to an exhaustive APP detector. It uses a tree search employing the stack algorithm to find dominant terms of the log-likelihood ratio. The commonly used symbol-by-symbol Gray labeling is not necessarily the best approach to good performance of iterative systems. We therefore consider different bit labelings and differential pre-coding adapted to MIMO systems. With the help of EXIT charts and BER simulations, we show that symbol-by-symbol Gray labeling in combination with an outer Turbo code is a good compromise for fast convergence and low error floor of MIMO systems with iterative detection. Part of the material in this article was published at the 5th International ITG Conference on Source and Channel Coding (SCC) at Erlangen, Germany (January 14th–16th, 2004). April 30, 2004 DRAFT