Coded Spatial Modulation applied to Optical Wireless Communications in Indoor Environments

Spatial Modulation (SM) is a combined multiple-input-multiple-output (MIMO) and digital modulation technique which besides common signal modulation conveys additional information bits in the spatial domain. To this end, only one transmitter is active at any time instance. The actual index of each emitter represents a unique spatial constellation point and thus conveys additional information. As a consequence, SM completely avoids inter-channel interference (ICI) and provides low detection complexity. Like for any MIMO scheme, the performance of SM is degraded in the presence of high channel correlation. Therefore, Trellis Coded Spatial Modulation (TCSM) applies coding techniques to the bits conveyed in the spatial domain to assist the detection of the active transmitter. As optical wireless communications (OWC) in indoor environments is subject to high spatial correlation and low channel distinctness, we evaluate the performance of coded SM applied to indoor OWC. For this purpose, we propose an enhanced coded SM technique which jointly encodes the bits conveyed in the signal and spatial domains. It is found in this paper that our enhanced coded SM technique can achieve gains in signal to noise ratio (SNR) of about 1 - 3 dB compared to the originally proposed TCSM scheme.