Comparison of performance limits by mutual information and practical realizations for optical long-haul coded modulation communication systems

Mutual information (MI) is derived as an information-theoretical figure of merit to assess the performance bounds of an optical long-haul communication system when forward error correction is used. This limit, which is valid for any optical channel model, is compared with a trellis coded modulation (TCM) system and with a regular low-density parity-check (LDPC) code in order to evaluate the gap in performance due to imperfection in the code design.