Sum-rate maximization of multi-user MIMO visible light communications

This paper studies multi-user multiple-input multiple-output (MU-MIMO) visible light communications (VLC) for indoor broadcast systems. Transmitters, configured as multiple LED arrays, and multiple users equipped with multiple photodetectors (PD) are considered. The main challenge in such broadcast systems is the multi-user interference (MUI). In order to completely suppress the MUI, the block diagonalization (BD) precoding technique, originally utilized for radio frequency (RF) communications, will be adopted. Unlike RF counterpart the VLC signal is positive only leading to the modification of the precoding matrix, thus affecting the overall performance. The paper will investigate the lower bound for the sum-rate maximization of all users in the room scale scenario. Furthermore, the findings show that user's positions and PD's rotations considerably impact on the VLC system performance.