On coded modulation for optical transmission

➤ Multi-dimensional coded modulation is useful in: • Filling the capacity gaps in a way to trade off between capacity and reach. • Enhancing the nonlinear tolerance by special encoding constraints. ➤ Most SD FEC schemes achieve the hard-decoding Shannon limit (or slightly better), there is still 1 to 1.5 dB worth mining. ➤ While the performance of many of the high-dimensional modulation formats examined is superior to conventional formats at BERs in the region of 10-3 and 10-2, the use of modern strong FEC codes remains a topic for further investigation. ➤ In general, gains in noise tolerance may be offset by worse nonlinear performance for novel formats, and detailed analysis of nonlinear performance is essential. ➤ Research activity on coded modulation will continue.