Information Theoretic Treatment for SMTs

Most existing studies derive space modulation techniques (SMTs) capacity by following conventional multiple‐input multiple‐output (MIMO) capacity derivation. Spatial information symbols are represented by the indexes of the different transmit antennas, while signal symbols are drawn from arbitrary signal constellation diagram. This chapter discusses the information theoretic treatment of SMTs. It is shown that the mutual information of SMTs approaches the capacity limit if the distribution of the signal constellation symbols multiplied by the spatial constellation symbols follows a complex Gaussian distribution. The capacity for SMTs should be calculated by maximizing over the spatial and signal symbols instead of the antenna indexes and signal symbol. The presence of channel estimation errors were shown to degrade the performance of typical MIMO systems. The chapter presents a mutual information performance comparison between spatial modulation (SM), quadrature spatial modulation (QSM), and spatial multiplexing (SMX) for Rayleigh and Nakagami fading channels.