Optimal power efficiency of spatial multiplexing in optical wireless MIMO channels

This paper investigates the problem of power efficiency for spatially multiplexed multiple-input multiple-output (MIMO) visible light communication (VLC) system. In this system, it combines the optical communication with illumination, but the offset power, which is used to satisfy the nonnegative constraint of the transmitter-side signal after precoding, leads to the reduction of power efficiency. In this paper, a negative inverse diagonal(NID) matrix based on optimal maximum likelihood (ML) criterion and suboptimal criterion is designed to minimise the offset power consumption, which has no effect in the conventional power allocation. We theoretically derive the detection signal at receiver with multiplying by the same NID matrix. The focus of this paper is the capacity and average power efficiency performance of the system. Simulation results show that our proposed method improves power efficiency significantly. Furthermore, we show that our scheme provides higher capacity of the system than the method without designing the NID matrix.