Capacity and nonuniform signaling for discrete-time Poisson channels

The Poisson photon-counting model is accurate for optical channels with low received intensity, such as long-range intersatellite optical wireless links. This work considers the computation of the channel capacity and the design of capacity-approaching, nonuniform signaling for discrete-time Poisson channels in the presence of dark current and under-average and peak amplitude constraints. Although the capacity of this channel is unknown, numerical computation of the channel capacity is implemented using a particle method. A nonuniform mapper is coupled to a low-density parity check code and a joint demapper-decoder is designed based on the sum-product algorithm. Simulations indicate near-capacity performance of the proposed coding system and significant gains over information rates using traditional uniform signaling. A key observation of this work is that significant gains in rate can be achieved for the same average power consumption by using optical transceivers with nonuniform signaling and a modest increase in peak power.