An optimized-hierarchy-aided approximate log-MAP detector for MIMO systems

Abstract—In this paper we propose a novel Space Division Multiplexing (SDM) detection method. The proposed technique constitutes a list search method and may be regarded as an advanced extension of the Sphere Decoder (SD). Our method may be employed in the so-called over-loaded scenario, where the number of transmit antenna elements exceeds that of the receive antenna elements. Furthermore, it is suitable for highthroughput, non-constant modulus modulation schemes, such as 16 and 64-QAM. We introduce a series of optimization rules which facilitate a substantial reduction in computational complexity. More specifically, we demonstrate that the method proposed, which we refer to as the Soft-output OPtimized HIErarchy (SOPHIE)-aided SDM detector exhibits the near-optimum performance of Log-MAP SDM detector in all considered scenarios. The associated computational complexity, which we control using two complexity-control parameters, is substantially lower than that imposed by all previously proposed methods. Index Terms—Bell Labs layered space-time (BLAST), fading channels, maximum likelihood (ML) detection, smart antennas, sphere decoding, turbo codes, wireless communications