Dimming Scheme Analysis for Pulse Amplitude Modulated Visible Light Communications

IEEE 802.15.7 is the first global standard for visible light communications (VLC). In this standard, dimming support is one of the main challenges for VLC. In this paper, we investigate the dimming schemes for pulse amplitude modulated (PAM) VLC. Unlike previous dimming schemes that only change probability or intensity of the PAM constellation points, this paper develops a hybrid dimming scheme for VLC, which performs dimming control by jointly optimizing the probability and the intensity of the PAM constellation points. By solving a simple iteration algorithm, the desired source distribution and the mutual information are derived. Numerical results show that the optimal intensity shift percentage in our scheme is zero, which indicates that the intensity in the PAM constellation should not be shifted with the dimming target, and the dimming control can be implemented by only changing the probability of the PAM constellation points.