Improving the Diversity of Spatial Modulation in MISO Channels by Phase Alignment

The performance of spatial modulation (SM) is known to depend on the minimum Euclidean distance in the received SM constellation. In this letter, a symbol scaling technique is proposed for spatial modulation in the multiple-input-single-output (MISO) channel that enhances this minimum distance. It achieves this by aligning the phase of the relevant channels so that the received symbol phases are distributed in uniformly spaced angles in the received SM constellation. In contrast to existing amplitude-phase scaling schemes that are data-dependent and involve an increase in the transmitted signal power for ill conditioned channels, here a phase-only shift is applied. This allows for data-independent, fixed per-antenna scaling and leaves the symbol power unchanged. The results show an improved SM performance and diversity for the proposed scheme compared to existing amplitude-phase scaling techniques.