Iterative SOMA-Based SU-MIMO Receivers with Extrinsic-Information Adaptive Front-Ends

In this paper we present reduced-complexity high-performance iterative receivers for single-user MIMO systems that employ OFDM with bit-interleaved coded modulation. The proposed inner-outer decoder structures exploit the Soft-Output M algorithm (SOMA) to calculate bit-likelihood estimates via a limited search on a tree. A key element of the proposed designs is the way the SOMA front-end adapts at each iteration to new extrinsic information. This front-end defines the tree, both in terms of the order in which symbols are considered, as well as in terms of the subspaces used in the likelihood calculations at each depth in the tree. The proposed SOMA front-ends are different from the conventional QR-decomposition front-ends and provide a systematic way to adapt both the order and the subspaces at each iteration in an iterative decoding structure. Simulations for 4 × 4 16 QAM systems show that the proposed iterative receivers can yield significant performance gains over receivers using non-adaptive conventional front-ends.