Information rates of next-generation long-haul optical fiber systems using coded modulation

G. Liga, A. Alvarado, E. Agrell, P. Bayvel

Research output: Contribution to journalArticleAcademicpeer-review

42 Citations (Scopus)
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A comprehensive study of the coded performance of long-haul spectrally-efficient WDM optical fiber transmission systems with different coded modulation decoding structures is presented. Achievable information rates are derived for three different square QAM formats and the optimal format is identified as a function of distance and specific decoder implementation. The four cases analyzed combine hard-decision (HD) or soft-decision (SD) decoding together with either a bit-wise or a symbol-wise demapper, the last two suitable for binary and nonbinary codes, respectively. The information rates achievable for each scheme are calculated based on the mismatched decoder principle. These quantities represent true indicators of the coded performance of the system for specific decoder implementations and when the modulation format and its input distribution are fixed. In combination with the structure of the decoder, two different receiver-side equalization strategies are also analyzed: electronic dispersion compensation and digital backpropagation. We show that, somewhat unexpectedly, schemes based on nonbinary HD codes can achieve information rates comparable to SD decoders and that, when SD is used, switching from a symbol-wise to a bit-wise decoder results in a negligible penalty. Conversely, from an information-theoretic standpoint, HD binary decoders are shown to be unsuitable for spectrally-efficient, long-haul systems.
Original languageEnglish
Pages (from-to)113-123
Number of pages11
JournalJournal of Lightwave Technology
Issue number1
Early online date6 Jun 2016
Publication statusPublished - 2017


  • Achievable information rates
  • coded modulation
  • forward error correction
  • generalized mutual information
  • hard-decision decoding
  • mutual information
  • nonbinary codes
  • optical communications
  • soft-decision decoding


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