Superposition constellation design for multi-user multi-chip visible light communication systems

In this paper, we study a multi-user multi-chip visible light communication (VLC) system. The superposition constellation is proposed for the system to achieve an efficient multi-user communication. Specifically, the constellation design is formulated to maximize the minimum Euclidean distance between users' symbols with the constraint of illuminance, chromaticity and the dynamic range of light-emitting diodes (LEDs). It is proved the users' performance is determined by the minimum Euclidean distance of the constellation. We then transform the constellation design into a convex optimization problem by Taylor series and get an iterative algorithm. In addition, a kind of modulation and demodulation methods is provided for the system. Simulation results illustrate that the proposed method outperforms the conventional time division multiple address (TDMA) scheme.