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Four-Dimensional Coded Modulation with Bit-wise Decoders for Future Optical Communications

Alvarado, A; Agrell, E; (2015) Four-Dimensional Coded Modulation with Bit-wise Decoders for Future Optical Communications. Journal of Lightwave Technology , 33 (10) pp. 1993-2003. 10.1109/JLT.2015.2396118. Green open access

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Abstract

Coded modulation (CM) is the combination of forward error correction (FEC) and multilevel constellations. Coherent optical communication systems result in a four-dimensional (4D) signal space, which naturally leads to 4D-CM transceivers. A practically attractive design paradigm is to use a bit-wise decoder, where the detection process is (suboptimally) separated into two steps: soft-decision demapping followed by binary decoding. In this paper, bit-wise decoders are studied from an information-theoretic viewpoint. 4D constellations with up to 4096 constellation points are considered. Metrics to predict the post-FEC bit-error rate (BER) of bit-wise decoders are analyzed. The mutual information is shown to fail at predicting the post- FEC BER of bit-wise decoders and the so-called generalized mutual information is shown to be a much more robust metric. For the suboptimal scheme under consideration, it is also shown that constellations that transmit and receive information in each polarization and quadrature independently (e.g., PM-QPSK, PM- 16QAM, and PM-64QAM) outperform the best 4D constellations designed for uncoded transmission. Theoretical gains are as high as 4 dB, which are then validated via numerical simulations of low-density parity check codes.

Type: Article
Title: Four-Dimensional Coded Modulation with Bit-wise Decoders for Future Optical Communications
Open access status: An open access version is available from UCL Discovery
DOI: 10.1109/JLT.2015.2396118
Publisher version: https://doi.org/10.1109/JLT.2015.2396118
Language: English
Additional information: Copyright © 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
Keywords: Bit-interleaved coded modulation, bit-wise decoders, channel capacity, coded modulation, fiber-optic communications, nonlinear distortion, low-density parity-check codes
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
URI: https://discovery.ucl.ac.uk/id/eprint/1461283
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