On Precoding for Optical Wireless MISO Broadcasting—An Information Theoretic Perspective

The multiple-input-single-output (MISO) Gaussian broadcast channel (BC) under per-emitter peak-amplitude constraint arises in naturally indoor optical wireless communication (OWC) applications due to the availability of many luminaires and simple photo receivers. In this paper, we study the achievable rate region of the two-user peak-amplitude constrained MISO BC with the goal of increasing the rate region beyond the one achieved using zero-forcing (ZF) precoding. To this end, a novel precoding scheme is proposed that combines a type of discrete-state dirty paper channel (DPC) studied recently and ZF precoding for the MISO BC, termed the DPC-ZF precoding. We derive the achievable rate region of the proposed precoding scheme, and compare it with the one achieved by ZF precoding numerically by simulating a two-user indoor OWC broadcasting system. Numerical results show a significant improvement in the achievable rate region through DPC-ZF precoding compared to ZF precoding, implying the existence of more powerful interference management schemes for OWC broadcasting.