Selection of modulation and codes for deep-space optical communications

Abstract

We describe several properties of deep space optical channels that lead to an appropriate selection of modulation format, pulse position modulation (PPM) order, error control code rate, and coding scheme. The selection process is motivated by capacity considerations. We compare the Shannon limit to the performance of Reed-Solomon codes and convolutional codes concatenated with PPM and show that, when iteratively decoded, concatenated convolutional codes operate approximately 0.5 dB from capacity over a wide range of signal levels, about 2.5 dB better than Reed-Solomon codes.