Spherical quasi-physical model-based color-shift keying for visible light communication

In this paper, the new family of spherical color-shift keying (SCSK) constellations is proposed for visible light communication (VLC) systems. Specifically, the constant-intensity constraint (CIC) for conventional color-shift keying (CSK) schemes, which originates from the requirement of non-flickering illumination, confines the constellation symbols on a two-dimensional (2D) plane of the three-dimensional (3D) intensity space. To fully utilize the potential degree of freedom offered by the 3D intensity space, we propose to expand the envelope of CSK constellations by replacing the constant intensity with a new spherical intensity constraint, aiming to maximize the minimum Euclidean distance (MED). More explicitly, we design the robust SCSK constellations with and without white color balance (CB), respectively. Particularly, we transform the constellation design problem to the so-called spherical circle packing (SCP) problem, which is resolved based on the spherical quasi-physical (SQP) model. Then, we propose the so-called spherical heuristic quasiphysical algorithm (SHQPA) integrating the binary search algorithm (BSA) and the configuration update algorithms (CUA) to obtain the optimal SCSK constellations. Furthermore, we also study the corresponding bit-to-symbol mapping rules for the generated SCSK constellations. Simulation results show that the new family of SCSK constellations outperforms the conventional CSK counterparts.