Channel capacity for dimmable visible light communications

The transmitted optical intensity in visible light communications (VLC) system is represented by a nonnegative input, which is corrupted by an additive white Gaussian noise. In this paper, we consider that the transmitted optical intensity signal must satisfy the illumination constraint to fulfill the illumination support in VLC system. So the average transmitted optical intensity is constrained by a target illumination intensity which is determined by the nominal optical intensity of light source devices and the dimming target. The derivation of the upper bound is based on signal space geometry via a sphere-packing argument. The lower bound is derived through the maximum mutual information between the channel input and output, which is determined by the source entropy maximization. Both the bounds are presented in terms of the closed forms. The numerical results show that the presented bounds are very tight at the application zone of dimmable VLC links.