Sphere Packing Modulation in the SDMA Uplink Using $K$-Best Sphere Detection

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 letter, we extend its employment to the multiuser 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.