Robust MMSE Linear Precoding for Visible Light Communication Broadcasting Systems

In this paper, we study an indoor visible light communication (VLC) downlink system with multiple LED fixtures and multiple single-photodiode users. We assume that VLC transmission over a subset of fixtures can be coordinated through a power line communication backbone network. Hence, we have a multiple-input VLC system, for which we derive the optimal linear precoding transmitter according to the minimum mean-squared error (MMSE) criterion. Different from similar problems in RF wireless communication, we need to take constraints resulting from the LED linearity region and its use as an illumination device into account. Since the precoder design requires channel knowledge at the transmitter, usually provided through a low-rate RF or infrared feedback channel, we further extend our derivations to the practically relevant case of imperfect channel estimation. Numerical results for VLC with different system parameters are presented to illustrate the performance of the proposed transmitter designs.