A multi-user joint constellation design of color-shift keying for VLC downlink broadcast channels

Abstract

While creating a required illumination, LED luminaries can be used as wireless access points by visible light communication (VLC) technology. Under normal conditions, there is more than one user who needs to be connected to the VLC network. Consequently, multiple access technique, e.g., time division multiple address (TDMA), is required to enable multiple users to share the network without interfering each other. To achieve a more efficient multi-user communication, we propose a multi-user joint constellation (JC) design for color-shift keying (CSK) by utilizing multiple LED luminaries equipped with multi-color LEDs. Unlike traditional multiple-input–multiple-output (MIMO) researches in which the symbols of different transmitters are independently generated from the constellations, the transmitted symbols are jointly generated in our design which takes the advantage of both multi-color and spacial resources in VLC systems. Considering the signal constraints in both optical and electric domains, the JC design is formulated with the objective function of maximizing the minimum Euclidean distance (MED) between different receiving constellation points. To make it easy to solve the non-convex optimization problem, we propose an iterative algorithm with the help of slack variable and Taylor expansion. Afterwards, a method of constellation mapping for the system is provided. In order to analyze the performance of the JC design, conventional TDMA and non-orthogonal multiple access (NOMA) scheme are introduced as comparisons and the simulation results illustrate that JC owns a better performance than both of them.