Post-FEC BER Benchmarking for Bit-Interleaved Coded Modulation with Probabilistic Shaping

Tsuyoshi Yoshida (Corresponding author), Alex Alvarado, Magnus Karlsson, Erik Agrell

Research output: Contribution to journalArticleAcademicpeer-review

4 Citations (Scopus)


Accurate performance benchmarking after forward error correction (FEC) decoding is essential for system design in optical fiber communications. Generalized mutual information (GMI) has been shown to be successful at benchmarking the bit-error rate (BER) after FEC decoding (post-FEC BER) for systems with soft-decision (SD) FEC without probabilistic shaping (PS). However, GMI is not relevant to benchmark post-FEC BER for systems with SD-FEC and PS. For such systems, normalized GMI (NGMI), asymmetric information (ASI), and achievable FEC rate have been proposed instead. They are good at benchmarking post-FEC BER or to give an FEC limit in bit-interleaved coded modulation (BICM) with PS, but their relation has not been clearly explained so far. In this article, we define generalized L-values under mismatched decoding, which are connected to the GMI and ASI. We then show that NGMI, ASI, and achievable FEC rate are theoretically equal under matched decoding but not under mismatched decoding. We also examine BER before FEC decoding (pre-FEC BER) and ASI over Gaussian and nonlinear fiber-optic channels with approximately matched decoding. ASI always shows better correlation with post-FEC BER than pre-FEC BER for BICM with PS. On the other hand, post-FEC BER can differ at a given ASI when we change the bit mapping, which describes how each bit in a codeword is assigned to a bit tributary.
Original languageEnglish
Article number9079569
Pages (from-to)4292 - 4306
Number of pages15
JournalJournal of Lightwave Technology
Issue number16
Publication statusPublished - 15 Aug 2020


  • Bit error rate
  • bit-interleaved coded modulation
  • bitwise decoding
  • forward error correction
  • generalized mutual information
  • modulation
  • mutual information
  • optical fiber communication
  • probabilistic shaping


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