Pilot-Tone Assisted Log-Likelihood Ratio for LDPC Coded CO-OFDM System

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.

[1]  Changyuan Yu,et al.  Pilot-aided log-likelihood ratio for LDPC coded M-QAM CO-OFDM system , 2014, OFC 2014.

[2]  William Shieh,et al.  1-Tb/s large girth LDPC-coded coherent optical OFDM transmission over 1040-km standard single-mode fiber , 2011, 2011 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference.

[3]  W. Shieh,et al.  Phase Estimation for Coherent Optical OFDM , 2007, IEEE Photonics Technology Letters.

[4]  Changyuan Yu,et al.  Pilot-Aided Log-Likelihood Ratio for LDPC Coded MPSK-OFDM Transmission , 2013, IEEE Photonics Technology Letters.

[5]  Pooi Yuen Kam,et al.  Log-Likelihood Ratios for LDPC Codes with Pilot-Symbol-Assisted BPSK Transmission over the Noncoherent Channel , 2009, 2009 IEEE Wireless Communications and Networking Conference.

[6]  Ivan B. Djordjevic,et al.  LDPC-coded OFDM in fiber-optics communication systems [Invited] , 2008 .

[7]  Ting Wang,et al.  40×117.6 Gb/s PDM-16QAM OFDM transmission over 10,181 km with soft-decision LDPC coding and nonlinearity compensation , 2012, OFC/NFOEC.

[8]  Ting Wang,et al.  On the LDPC-coded modulation for ultra-high-speed optical transport in the presence of phase noise , 2013, 2013 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference (OFC/NFOEC).

[9]  W. Shieh.  Maximum-Likelihood Phase and Channel Estimation for Coherent Optical OFDM , 2008, IEEE Photonics Technology Letters.

[10]  Changyuan Yu,et al.  Time-Domain Blind ICI Mitigation for Non-Constant Modulus Format in CO-OFDM , 2013, IEEE Photonics Technology Letters.

[11]  I. Morita,et al.  Coherent Optical 25.8-Gb/s OFDM Transmission Over 4160-km SSMF , 2008, Journal of Lightwave Technology.