Distance-Range-Oriented Constellation Design for VLC-SCMA Downlink with Signal-Dependent Noise

In this letter, the constellation design for a sparse code multiple access-based visible light communication downlink is studied. The noise at the receiving avalanche photodiode is dependent on the signal intensity, and the associated design problems are typically intractable. We point out that for such a system, both the minimum Euclidean distance (MED) and rotated-MED-based methods are not the optimal optimization objective, and propose a distance-range-oriented (DRO) modulation, where a linear combination of the minimum and maximum Euclidean distance is considered. We observe in the simulation results that the proposed DRO-based scheme outperforms the MED and rotated-MED-based ones across a wide range of signal and noise levels.