Receiver Structure and Performance for Trellis-Coded Pulse-Position Modulation in Optical Communication Systems

This article describes a receiver structure for trellis-coded pulse-position modulation (T-PPM) for optical communication systems. Monte Carlo simulation results of the Viterbi decoding algorithm under realistic Webb modeling of the avalanche photodiode (APD)-based receiver are compared with asymptotic bounds on performance. These results show that T-PPM can reduce the loss in performance incurred by spreading of the PPM optical pulse. Specifically, when a PPM symbol-error rate of 0.001 is required, the average signal photon count per information bit is reduced by 5 photons per information bit, or 0.6 to 2.0 dB depending upon the background photon level, when T-PPM is used with the receiver parameters selected here. It is also shown that preserving only a small subset of slot statistics during the decoding process does not result in any significant loss in overall performance.