Enhanced Complex-Valued CSK-OOFDM System for Visible Light Communication

In this paper, we jointly consider the problems of constellation design and automatic modulation recognition (AMR) for color shift keying (CSK) and optical orthogonal frequency division multiplexing (OOFDM) in visible light communication (VLC) systems. Specifically, we conceive a solution based on the proposed enhanced complex-valued CSK (ECCSK) aided OOFDM (ECCSK-OOFDM) framework for multi-target-color communication (MTCC) scenarios. Firstly, we devise a complex-valued CSK constellation design method under given color/illumination constraints. The new method not only eliminates the color balance distortion issue, but also achieves a better normalized minimum Euclidean distance (NMED). Secondly, an expectation maximization (EM) based ECCSK constellation recognition algorithm is proposed, which enables the system to automatically identify the ECCSK constellation with unknown symbol timing offset (STO) and noise variance. Simulation results demonstrate the effectiveness of the new ECCSK constellation design method and the EM-based AMR algorithm. It shows that the proposed system can provide a performance close to the ideal benchmark scheme in MTCC scenarios.