Spatial modulation for massive MIMO

Multiple-input multiple-output (MIMO) systems can increase wireless link capacity without requiring additional bandwidth and power. On the one hand, MIMO systems heavily depend on channel state information (CSI) at the receiver. It has also been shown that CSI at the transmitter (CSIT) can improve the link capacity and reliability considerably but with the disadvantage of extra feedback and computational costs. On the other hand, energy efficiency of MIMO systems could adversely increase with the number of antennas in the link. Therefore, there are considerable interests in energy efficient practical transmission schemes for MIMO links without CSIT. In this study, an emerging wireless communication concept which is termed as spatial modulation (SM) is considered for large scale MIMO. The results show that in information-theoretic viewpoint, SM achieves capacity comparable to the open-loop MIMO capacity even though a subset of transmit antennas is activated in every channel use. The reason is both the channel coefficients and input symbols carry information in SM. As a result, SM regains (compensates) the loss of information capacity due to activating a subset of antennas by modulating information in the antenna index. This means that the sum information rate remains high.