Precoding Technique for Ill-Conditioned Massive MIMO-VLC System

Visible light communications (VLC) has lately emerged as a viable supplement to existing radio frequency (RF) based communication systems, and is an integral component of future communication systems. The possibility of deploying massive arrays of light emitting diodes (LED) and photo-detectors (PD), which translates to a massive array of multiple input multiple output (MIMO) system for VLC, have been recently proposed. However, massive-MIMO in VLC has the following drawbacks which limit its practical deployment: a) high condition number of the channel matrix, which negatively affects the robustness of traditional channel-inversion based detection, and b) high interference in a multi-user setting due to correlated columns of the overall MIMO channel matrix. In this paper, the multi-user (MU) massive-MIMO in VLC is considered, and a precoding technique is proposed that induces diverse effective channel matrices for different users, and hence facilitates MU detection using ordered successive interference cancellation. Further, it is shown that the proposed precoding technique maximizes an upper bound of the overall sum-rate of the MU massive-MIMO system. Lastly, simulations have been performed for MU massive LED and PD arrays demonstrating that the proposed precoding technique outperforms existing precoding techniques, and hence is a viable solution for massive-MIMO in VLC.