K-Best Sphere Detection for the Sphere Packing Modulation Aided SDMA/OFDM Uplink

Recently, the turbo-detected sphere packing (SP) aided space-time block-coding (STBC) STBC-SP scheme was demonstrated to provide useful performance improvements over conventionally-modulated orthogonal design based STBC schemes in the context of single-user multiple-input multiple-output (SU-MIMO) systems. Hence, in this treatise we extend its employment to the multi-user MIMO (MU-MIMO) scenario. For the sake of achieving a near maximum a posteriori (MAP) performance while imposing a moderate complexity, we specifically design the K-best sphere detection (SD) scheme for supporting the operation of the SP-modulated system, since the conventional SD cannot be directly applied to such a system. Consequently, with the aid of our modified SD, a significant performance gain can be achieved by the SP-modulated system over its conventionally-modulated counterpart in the context of MU-MIMO systems. For example, a performance gain of 3.5 dB can be achieved by the proposed 256-SP over the identical-throughput 16-QAM benchmark system in the scenario of a four-receive-antenna SDMA uplink (UL) system supporting two users both employing Alamouti´s G₂ space-time code, given a target BER of 10^-4.