The spatial modulation (SM) concept combines, in a novel fashion, digital modulation and multiple antenna transmission for low complexity and spectrally efficient data transmission. The idea considers the transmit antenna array as a spatial constellation diagram with the transmit antennas as the constellation points. To this extent, SM maps a sequence of bits onto a signal constellation point and onto a spatial constellation point. The information is conveyed by detecting the transmitting antenna (the spatial constellation point) in addition to the signal constellation point. In this manner, inter-channel interference is avoided entirely since transmission is restricted to a single antenna at any transmission instance. However, encoding binary information in the spatial domain means that the number of transmit antennas must be a power of two. To address this constraint, fractional bit encoded spatial modulation (FBE—SM) is proposed. FBE–SMuses the theory of modulus conversion to facilitate fractional bit rates over time. In particular, it allows each transmitter to use an arbitrary number of transmit antennas. Furthermore, the application of SM in a multi-user, interference limited scenario has never been considered. To this extent, the average bit error rate (ABER) of SM is characterised in the interference limited scenario. The ABER performance is first analysed for the interference-unaware detector. An interference-aware detector is then proposed and compared with the cost and complexity equivalent detector for a single–input multiple–output (SIMO) system. The application of SM with an interference-aware detector results in coding gains for the system. Another area of interest involves using SM for relaying systems. The aptitude of SM to replace or supplement traditional relaying networks is analysed and its performance is compared with present solutions. The application of SM to a fixed relaying system, termed dual-hop spatial modulation (Dh-SM), is shown to have an advantage in terms of the source to destination ABER when compared to the classical decode and forward (DF) relaying scheme. In addition, the application of SM to a relaying system employing distributed relaying nodes is considered and its performance relative to Dh-SM is presented. While significant theoretical work has been done in analysing the performance of SM, the implementation of SM in a practical system has never been shown. In this thesis, the performance evaluation of SM in a practical testbed scenario is presented for the first time. To this extent, the empirical results validate the theoretical work presented in the literature.