Information-Theoretic Treatment of Space Modulation MIMO Systems

In space modulation techniques (SMTs), data bits are transmitted through modulating spatial and signal symbols. Signal symbols are ordinary complex symbols drawn from an arbitrary constellation diagram, such as quadrature amplitude modulation. Yet, spatial symbols represent the different channel paths from multiple transmit antennas to all receive antennas in a multiple-input multiple-output (MIMO) system. At each particular time instant, one or more of these channel paths is used to transmit the signal symbol and all other paths remain inactive. The receiver jointly determines the transmitted symbol and the considered channel paths to retrieve the information bits. This is unlike any conventional wireless communication technique, and special information-theoretic treatment is needed. In this paper, the theoretical channel capacity of SMTs is deduced. The conditions under which such capacity can be achieved are derived and discussed. Mutual information results for space shift keying, spatial modulation, generalized spatial modulation, and quadrature spatial modulation, as illustrative examples of SMTs, over several fading channels are reported and thoroughly discussed. The obtained Monte Carlo simulation results validate the accuracy of the conducted analysis. It is demonstrated that SMTs can achieve substantial gains as compared to the conventional MIMO systems. Such gains are attainable with proper design of signal symbols for each specific fading channel.