An Experimental Comparison of Coded Modulation Strategies for 100 Gbit/s Transceivers

TL;DR

This paper compares two coded modulation strategies, TTCM and BICM LDPC, for 100 Gbit/s optical transceivers, showing TTCM's performance advantage over BICM LDPC in long-distance transmission.

Contribution

It provides an information-theoretic comparison and experimental performance evaluation of TTCM and BICM LDPC for high-speed optical communication.

Findings

TTCM outperforms BICM LDPC by about 0.4 dB at 100 Gbit/s over 1000 km.

Ideal BICM LDPC incurs less than 0.1 dB penalty compared to TTCM.

BICM LDPC's simplicity makes it popular despite slight performance loss.

Abstract

Coded modulation is a key technique to increase the spectral efficiency of coherent optical communication systems. Two popular strategies for coded modulation are turbo trellis-coded modulation (TTCM) and bit-interleaved coded modulation (BICM) based on low-density parity-check (LDPC) codes. Although BICM LDPC is suboptimal, its simplicity makes it very popular in practice. In this work, we compare the performance of TTCM and BICM LDPC using information-theoretic measures. Our information-theoretic results show that for the same overhead and modulation format only a very small penalty (less than 0.1 dB) is to be expected when an ideal BICM LDPC scheme is used. However, the results obtained for the coded modulation schemes implemented in this paper show that the TTCM outperforms BICM LDPC by a larger margin. For a 1000 km transmission at 100 Gbit/s, the observed gain was 0.4 dB.