Block encoding and decoding for the optical PPM channel (Corresp.)

Pulse position modulation (PPM) is a popular signaling format in pulsed optical communication links. PPM encoding is extended to include block pulse encoding over multiple PPM frames. Maximum likelihood decoding operations associated with this encoding are developed for both shot-noise limited and thermal-noise limited optical receiver models. Both ideal (Poisson) and avalanche photodetectors are considered, and it is shown that optimal block decoders involve combinations of linear and quadratic operations. Error probability bounds are presented, showing the relative improvement in detectability that appears possible by resorting to block encoding over multiple frames.