DocumentCode :
24996
Title :
Performance Investigation of Pilot-Aided Log-Likelihood Ratios for LDPC Coded CO-OFDM
Author :
Shengjiao Cao ; Pooi-Yuen Kam ; Changyuan Yu ; Xiaofei Cheng
Author_Institution :
A*STAR Inst. for Infocomm Res., Singapore, Singapore
Volume :
33
Issue :
10
fYear :
2015
fDate :
May15, 15 2015
Firstpage :
1961
Lastpage :
1970
Abstract :
Pilot-subcarrier and pilot-tone aided log-likelihood ratios (PA-LLR, PT-LLR), proposed for LDPC coded coherent optical OFDM (CO-OFDM) system, is reviewed in this paper. The knowledge of common phase error based on pilot-subcarriers or pilot-tone is incorporated into the new PA-LLR or PT-LLR metric, which eliminates the need for prior common phase error estimation and compensation. The formulation of both metrics is presented in a unified way. The performance of both metrics, in their approximate versions, is compared against the approximate conventional LLR (AC-LLR) for different modulation formats using different LDPC codes in a back-to-back case. APA-LLR or APT-LLR outperforms AC-LLR for higher-order QAM, with smaller number of pilot-subcarriers (PSCs) or at smaller pilot-tone-to-signal power ratios (PSRs). A time-domain blind intercarrier interference (BL-ICI) mitigation algorithm is employed to improve the performance, which eliminates the error floor at large laser linewidth. Furthermore, we examine the tolerance of different LLR metrics to linear fiber impairment (chromatic dispersion) or nonlinear phase noise (self-phase modulation), in which case, our metrics still outperform the conventional one. Iterative demodulation using new tentative-decision-based phasor offers almost 1-dB OSNR improvement for smaller number of PSCs. Finally, we also analytically prove that APA-LLR or APT-LLR converges to AC-LLR as the number of PSCs or PSR value increases. The optimal OSNR for calculating noise power is found to be around 10 dB for actual OSNR values beyond 10 dB in either the back-to-back case or after 13 600-ps/nm/km dispersion with channel compensation. APA-LLR and APT-LLR offer better performance than AC-LLR without any increase in complexity.
Keywords :
OFDM modulation; demodulation; intercarrier interference; light coherence; optical fibre communication; optical fibre dispersion; optical noise; parity check codes; phase noise; quadrature amplitude modulation; self-phase modulation; telecommunication channels; time-domain analysis; Iterative demodulation; LDPC coded CO-OFDM; LDPC coded coherent optical OFDM system; OSNR; channel compensation; chromatic dispersion; common phase error; higher-order QAM; laser linewidth; linear fiber impairment; modulation formats; noise power; nonlinear phase noise; pilot-subcarrier aided log-likelihood ratios; pilot-tone aided log-likelihood ratios; pilot-tone-signal power ratios; self-phase modulation; tentative-decision-based phasor; time-domain blind intercarrier interference mitigation algorithm; Decoding; Measurement; Modulation; OFDM; Parity check codes; Phase noise; Signal to noise ratio; Common phase error; LDPC coded CO-OFDM; common phase error; inter-carrier interference; intercarrier interference; linear phase noise; log-likelihood ratio; loglikelihood ratio; pilot-subcarrier aided; pilot-tone aided;
fLanguage :
English
Journal_Title :
Lightwave Technology, Journal of
Publisher :
ieee
ISSN :
0733-8724
Type :
jour
DOI :
10.1109/JLT.2015.2392772
Filename :
7014221
Link To Document :
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