A Moment Generating Function Formulation for an Optically Preamplified PPM Intersatellite System

Abstract

A scheme for the utilisation of optically preamplified pulse position modulation (PPM) receivers in intersatellite laser communications is presented. To facilitate higher bit-rate operation an analysis is presented for a PPM system employing a receiver which integrates over a time slot and compares the result with a fixed threshold. When operating at the SITM-1 bit-rate of 155 Mbit/s and using conservative parameters our model demonstrates a possible receiver sensitivity of 50.7 photons/bit (at a BER of 10 -6 ) in the presence of background noise, indicating the potential of this receiver configuration for use in satellite communications. The analysis is facilitated by the use of a moment generating function approach which enables the use of tight upper bounds on the bit error probability to be derived using Chernoff bound (CB) techniques. We compare results obtained from this technique with those obtained by applying a Gaussian approximation (GA) and find that the GA is consistently less conservative for the cases considered (by 0.5 dB) at a BER of 10 -6 . This nevertheless suggests a reasonable level of accuracy and such a GA could be a useful tool for obtaining a first order approximation.