Coding Options for the Degraded Optical PPM Channel

Considerable work has been done in developing efficient error-control coding schemes for the ideal optical PPM channel under self-noise limited conditions in the absence of either dark current or background thermal noise effects. In this work we consider corresponding coding options for the degraded PPM channel operating in the presence of dark current but no thermal noise. Coding options studied include use of non-binary Reed-Solomon (RS) codes operating in an errors-erasures mode as well as non-binary convolutional codes utilizing Viterbi maximum likelihood (ML) decoding. We also describe the performance and complexity of a novel concatenated coding scheme employing non-binary convolutional inner codes and RS outer codes. The results provide a first step in providing an assessment of coding options for the more general optical PPM channel which includes background thermal noise as well as dark current.