Pilot-tone assisted log-likelihood ratio for LDPC coded CO-OFDM system

Shengjiao Cao, Pooi Yuen Kam, Changyuan Yu, Xiaofei Cheng

Research output: Journal article publicationJournal articleAcademic researchpeer-review

11 Citations (Scopus)


Pilot-tone assisted log-likelihood ratio (PT-LLR) is derived for low-density parity-check coded, coherent optical orthogonal frequency division multiplexing systems in the presence of linear phase noise. The knowledge of common phase error (CPE) obtained from the pilot-tone is incorporated into the new LLR metric, which eliminates the need for prior CPE estimation and compensation. We compare our metric with the conventional LLR (C-LLR) through extensive simulation using their approximate versions (APT-LLR, AC-LLR). APT-LLR has the same order of complexity as AC-LLR while it outperforms AC-LLR for higher order modulation formats (16-QAM, 64-QAM) at smaller pilot-tone-to-signal power ratios. In addition, we show that with the help of time-domain blind intercarrier interference mitigation, both metrics perform better in the presence of larger laser linewidth.
Original languageEnglish
Article number6826532
Pages (from-to)1577-1580
Number of pages4
JournalIEEE Photonics Technology Letters
Issue number15
Publication statusPublished - 1 Aug 2014
Externally publishedYes


  • common phase error
  • LDPC coded OFDM
  • linear phase noise
  • log-likelihood ratio
  • Pilot-tone assisted

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics
  • Electrical and Electronic Engineering


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