Coordinated Beamforming for Downlink Visible Light Communication Networks

Visible light communication (VLC) is an emerging short-range optical wireless communication technology that is driven by the widespread deployment of light-emitting diodes (LEDs). Indoor VLC users may experience noticeable interference when independent transmitters utilizing wide-beam luminaires are closely located. In this paper, a coordinated beamforming (CB) scheme is proposed for downlink interference mitigation among the coexisting VLC attocells utilizing multi-luminaire transmitters. Compared to joint transmission (JT) schemes, wherein the data and channel state information are shared among transmitters of different attocells, the proposed CB scheme places lower requirements on the network in terms of backbone traffic, and is easier to implement in a practical deployment, though at the cost of compromised performance. In this paper, we investigate the downlink transmission of coordinated VLC attocells and focus on its transmitter design. The weighted sum mean square error (WSMSE) is adopted as the performance metric to take into consideration interference, noise, and fairness among users in system optimization. The WSMSE minimization problem is considered with linear beamforming restricted by amplitude constraints. Such constraints arise from the dynamic range limitations in typical LEDs. Moreover, we extend our design method to take into account possible mismatches in channel information available to the transmitters. Numerical examples are provided to illustrate the performance of the proposed CB scheme in typical VLC scenarios. We also quantify the performance gap among several coordination schemes including JT and CB.