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OFDM-Based Spatial Modulation for Optical Wireless Communications

Spatial modulation is a power and complexity efficient multiple-input-multiple-output (MIMO) method which uses the transmit unit indexes to encode information. This paper investigates two different spatial modulation (SM) methods for optical wireless communications (OWC) systems based on orthogonal frequency division multiplexing (OFDM). Moreover, a novel method is proposed to enhance the spectral efficiency of SM systems by mapping the data symbols in time domain rather than subcarrier. The bit error rate (BER) performance of the proposed method is studied and compared with conventional OFDM-based SM and repetition coding (RC) as a benchmark. Maximum-a-posteriori-probability (MAP) detection and zero-forcing (ZF) are considered which affect the BER performance under different channel correlation conditions. Computer simulations have shown that the proposed method outperforms both the conventional OFDM-based SM and RC. It is also confirmed that the proposed method performs better than the reference systems under highly correlated channel conditions.