Date Added: Oct 2010
Orthogonal modulation is a natural choice for free-space optical links due to the relatively simple modulation and demodulation options that are available. In particular, Pulse-Position Modulation (PPM) takes advantage of the inherent average power limitations of some optical transmitters. In practical implementations, two types of optical PPM receivers are of interest: photon counting receivers and optical pre-amplified receivers. The differences between the two implementations result in different performance as well as different methods of analysis. In this paper, the authors consider error-correction coding options for both photon counting and pre-amplified versions of M-ary PPM, where M is the cardinality of the signal set.