Energy-efficient Modulation for Visible Light SCMA System with Signal-dependent Noise

In this paper, we investigate the problem of constellation design for a multi-user visible light communication (VLC) system based on sparse code multiple access (SCMA). The design goal is to maximize energy efficiency of the system and at the same time guarantee the lighting constraints, such that the benefit of SCMA to support massive connectivity is fully exploited. With signal-dependent noise (SDN) considered, we conclude that the conventional minimum Euclidean distance (MED) based criterion is far from optimal, based on which we introduce the rotated MED (R-MED) as the optimization objective to mitigate the constellation shape distortion caused by the SDN. A non-convex optimization is establish accordingly, which is relaxed to a convex problem by iterative linearization. Simulation results show that our design leads to non-trivial performance gain over the MED-based designs for systems where power of the SDN is non-negligible.