Performance of Convolutional Codes in a Direct-Detection Optical PPM Channel

Several strategies for combining convolutional codes (CC's) and pulse position modulation (PPM) in a direct-detection optical channel are considered, including binary and 2^n-ary PPM with a rate-1/n CC. In the latter case, Massey's concept of coding of L separate component channels constituting a 2^L-ary PPM erasure channel is extended to a channel having background radiation. The analysis is carried out for both the ideal photon counting, and the avalanche photodetection (APD) cases, providing a comparative evaluation of the various strategies in terms of bit error probability and achievable coding gain for different code structures and decoding schemes.