Joint-Mapping-Based Variable Active Antenna Spatial Modulation

Spatial modulation (SM) maps information to both spatial dimensions (active antenna indices) and conventional 2D M-ary symbols. The existing SM schemes use fixed number of active antennas in each transmit vector as varying them causes detection ambiguity. Motivated by this, we introduce a new joint-mapping based variable active antenna spatial modulation scheme, which varies the number of active antennas in each transmit vector. It alleviates detection ambiguity by jointly mapping information to the complete 3D constellation consisting of active antenna indices (spatial dimension) and the 2D M-ary symbols. This is unlike the existing SM schemes which separately map information to the active antenna indices and the 2D symbols. This idea enables us to i) avoid detection ambiguity; and ii) achieve low bit error rate and comparable maximum likelihood detection complexity as that of existing SM schemes.