Multi-cell VLC: Multi-user downlink capacity with coordinated precoding

This paper studies the multi-user performance of multi-cell visible light communication (VLC) systems with coordinated precoding among cells. Practically, separated LED arrays are employed to properly illuminate a large room/office. This configuration enables a multi-cell VLC system, which is analogous to that in mobile cellular networks. In such multi-cell systems supporting multiple users, the received signal at a user can severely be degraded not only by the interference caused by the signals that are intended to other users within the cell (intra-cell interference) but also by interference from signals of the other cells (inter-cell interference). In order to remove these interferences, we propose a coordinated precoding technique which allows coordination between VLC cells. We then investigate the optimal precoding matrix design to maximize the achievable sum capacity of users. The maximization problem is formulated as a convex optimization problem which can be solved efficiently by using standard software packages. Numerical results show that the proposed coordinated precoding outperforms the non-coordinated one.