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Optimal Symbol Set Design for Generalized Spatial Modulations in MIMO VLC Systems

This paper investigates optimal symbol set selection for the generalized spatial modulation (GSM) in visible light communication (VLC) systems. Realizing that the optimal search involves a highly complex combinatorial problem, a symbol set generation tree is proposed. The tree allows assessment of the system performance at each node and can be terminated early to obtain near-optimal solutions with reduced complexity. It is observed that the proposed optimal symbol search provides performance improvement of many dBs over results obtained with averaged random sets. The benefit of the optimized symbol set design is found to increase with increasing number of pulse amplitude modulation levels. Our contributions also include integration of possible rotations of the array in the mathematical model, and the demonstration of the results to be robust to channel changes due to rotations and shifting of the array in the image plane. Finally, the results are validated through hardware experimental results.