Design of Non-Uniform Capacity-Approaching Signaling for Optical Wireless Intensity Channels

Analysis and design of near capacity approaching non-uniform signaling for optical intensity pulse amplitude modulation (PAM) channels is presented. A discrete nonuniform source distribution with quantized-level probabilities is presented. The proposed source distribution approaches the channel capacity while remaining practical for implementation. A significant gap in the mutual information between the nonuniform quantized-level distributions and uniform $M$-ary PAM is obtained. For example, at low SNR, non-uniform binary signalling has over four times the rate of uniform constellations. Multilevel coding and multistage decoding are proposed to approach the rate gains due to non-uniform signaling.