Capacity lower bounds of IM/DD AWGN optical wireless channels based on Fano´s inequality

Intensity modulation and direct detection (IM/DD) is the most commonly applied scheme in optical wireless communication systems. There is no exact channel capacity expression for optical wireless communication systems in IM/DD additive white Gaussian noise (AWGN) channels, but capacity bounds exist. In this letter, channel capacity for optical wireless communications in the IM/DD AWGN channel is analyzed based on Fano´s inequality, and peak-and-average optical power constraints are considered. New lower bounds, which are tight in the specific signal to noise ratio (SNR) region, are derived under two cases of peak-and-average optical power constraints. Besides, the lower bounds can be achieved in practical environment by using DC-biased M-ary pulse amplitude modulation (PAM) scheme.