On the mutual information of the VLC channel in the presence of external ambient lighting

Visible Light Communications (VLC) represent a new frontier of communication allowing high data-rate Internet access, specially in indoor environments, where the use of Light Emitting Diodes is growing as a viable alternative to traditional illumination. As a result, by properly modulating light, it is possible to guarantee coexistence with illumination. One of the key challenges is the limited modulation bandwidth of sources that is typically tens of MHz. In this context, when VLC link must be optimized by using, for example, adaptive modulations, channel capacity is evaluated according to the hypothesis of Gaussian distributed input. In this paper we derive the mutual information expression when thermal noise, shot noise and ambient lighting are present so as to show the difference with the conventional Gaussian approach. More, we show the numerically evaluated mutual information when different input distributions have been taken into account.