Adaptive Modulation for Two Users in VLC

In visible light communications, it is common to have more than one light sources within the line of sight of a receiver. This paper proposes an adaptive modulation scheme for a system with two light sources and two receivers where two different data streams are sent to the two receivers. The transmitted powers of both light sources are optimized to reduce the bit error rate (BER) at the receivers. Although the optimization problem is non-convex, it can be transformed into a set of linear optimization problems. Analytical results show how to reduce the set and reduce the complexity of the optimization problem. Under various settings, our proposed scheme is compared with multi-user maximum likelihood, repetition coding, and linear zero-forcing precoding techniques. Simulation results show that the proposed scheme outperforms the other techniques in terms of BER.