Dual-Layered MIMO Transmission for Increased Bandwidth Efficiency

A dual-layered downlink transmission scheme is proposed for intrinsically amalgamating multiple-input-multiple-output (MIMO) spatial multiplexing (SMX) with spatial modulation (SM). The proposed scheme employs a classic SMX transmission that is known to offer superior bandwidth efficiency (BE) compared with SM. We exploit receive-antenna-based SM (RSM) on top of this transmission as an enhancement of the BE. The RSM here is applied to the combined spatial and power-level domain not by activating and deactivating the RAs but rather by choosing between two power levels {P
₁
, P
₂
} for the received symbols in these antennas. In other words, the combination of symbols received at a power level P
₁
carries information in the spatial domain in the same manner as the combination of nonzero elements in the receive symbol vector carries information in the RSM transmission. This allows for the coexistence of RSM with SMX, and the results show increased BE for the proposed scheme compared with both SMX and SM. To characterize the proposed scheme, we carry out a mathematical analysis of its performance, and we use this to optimize the ratio between P
₁
and P
₂
for attaining the minimum error rates. Our analytical and simulation results demonstrate significant BE gains for the proposed scheme compared with conventional SMX and SM.