Reduced-Complexity Approx-Log-MAP and Max-Log-MAP Soft PSK/QAM Detection Algorithms

In this paper, we propose to reduce the complexity of both the Approx-Log-MAP algorithm as well as of the Max-Log-MAP algorithm conceived for generalized PSK/QAM detection, where only a reduced-size subset of the PSK/QAM constellation points is taken into account for producing a single soft-bit output. Although the detectors of Gray-labelled low-order PSK/QAM schemes generally produce near-horizontal EXIT curves, our proposed detectors exploit the a priori LLRs gleaned from a channel decoder in order to retain the optimum detection capability for all PSK/QAM constellations. Furthermore, we demonstrate in this paper that the widely applied MIMO schemes including V-BLAST and STBC, which invoke the proposed soft PSK/QAM detectors may also benefit from our reduced-complexity design. Our simulation results confirm that a near-capacity performance may be achieved by the proposed detectors at a substantially reduced detection complexity.