Enhanced spatial modulation with multiple constellations

Spatial modulation (SM) has recently drawn a great deal of attention, particularly due to the low complexity that it promises for both the transmitter and the receiver sides. However, this technique has a significant spectral efficiency loss with respect to spatial multiplexing (SMX) with the same number of transmit (Tx) antennas, and when the modulation order is increased to achieve the same spectral efficiency, it loses in terms of the bit error rate (BER). In this paper, a new type of SM (referred to as Enhanced SM) is proposed which increases the number of bits transmitted per channel use compared to conventional SM. Note that conventional MIσMO techniques including SMX and SM employ a fixed signal constellation. In our proposed technique, some information bits select not only the index(es) of the active antenna(s), but also the constellations to be transmitted from each of them. Both the closed-form analysis and the numerical results demonstrate that the proposed technique achieves better performance than conventional SM and that in most cases it also outperforms SMX.