Extended Receive Spatial Modulation MIMO scheme for Higher Spectral Efficiency

Spatial modulation (SM) schemes use the index of the transmit (resp. the receive) antenna to transmit additional data, and therefore allow for a new exploitation of the space dimension to increase the spectral efficiency of MIMO systems. The baseline of the proposed study relies on the so-called extended receive antenna shift keying (ERASK) concept consisting in transmitting the spatial bits by focusing the transmit energy towards subsets of receive antennas. With ERASK, the subsets of targeted antennas can be of any size leading to an amount of additional spatial bits directly equal to the number of receive antennas. However, an ON/OFF keying is used to carry the spatial symbols meaning that a zero power level is associated for non targeted antennas. Consequently, the transmission of additional IQ symbols in ERASK is not compatible with every spatial symbol configurations. In this paper, we propose a novel scheme referred to as Extended RSM (ERSM) that sends additional IQ modulated signals in ERASK, in order to increase the overall spectral efficiency. The key idea is to associate a non zero power levels for all spatial symbols. Two power levels are used to transmit the spatial and the IQ symbols, and an optimal ratio of the power is calculated. The theoretical performance of the proposed ERSM scheme is derived and then validated through simulations.