Optimal Precoder for MIMO Schemes in Indoor Wireless VLC Systems

Abstract

In multiple-input multiple-output (MIMO) indoor visible light communication (VLC) systems, channel gains are highly correlated. As a result, the bit error rate (BER) of the system is degraded. To improve the BER performance of the system, we propose two precoders, namely, an optimal precoder and a diagonal precoder for MIMO schemes in VLC systems with $N_t$ light emitting diodes (LED) and $N_r$ photo detectors (PD). The optimal precoder maximizes the minimum euclidean distance of the received signal set under non-negativity and maximum power constraints. The diagonal precoder, on the other hand, induces transmit power imbalance to alleviate the degradation due to channel correlation. We compare the performance of spatial multiplexing (SMP), generalized spatial modulation (GSM), and spatial modulation (SM) MIMO schemes with and without precoding. Our simulation results show that MIMO schemes with the proposed precoders outperform the MIMO schemes without precoder by up to 49 dB at $10^{-4}$ BER, and that in the presence of precoding, SMP can outperform GSM and SM.