Optical PPM Demodulation from Slot-Sampled Photon Counting Detectors

A scheme for the demodulation of an optical PPM signal from the sampled output of a photon counting detector is presented. The receiver operates on a time-series of samples, one sample per slot, from the bandlimited output of a photon counting detector operating in a photon starved channel. Algorithms to estimate the photon arrivals, interpolate the slot statistics, and estimate the slot phase in the presence of a sample to slot clock frequency offset are given, and the system performance is evaluated for a deep space optical communications link.