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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 26 — Dec. 10, 2012
  • pp: B171–B180

Ultrafast and low overhead training symbol based channel estimation in coherent M-QAM single-carrier transmission systems

Mohamed Morsy-Osman, Mathieu Chagnon, Qunbi Zhuge, Xian Xu, Mohammad E. Mousa-Pasandi, Ziad A. El-Sahn, and David V. Plant  »View Author Affiliations

Optics Express, Vol. 20, Issue 26, pp. B171-B180 (2012)

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We propose a training symbol based channel estimation (TS-EST) algorithm that estimates the 2 × 2 Jones channel matrix. The estimated matrix entries are then used as the initial center taps of the 2 × 2 butterfly equalizer. Employing very few training symbols for TS-EST, ultrafast polarization tracking is achieved and tap update can be initially pursued using the decision-directed least mean squares (DD-LMS) algorithm to mitigate residual intersymbol interference (ISI). We experimentally verify the proposed TS-EST algorithm for 112 Gbps PDM-QPSK and 224 Gbps PDM-16QAM systems using 10 and 40 training symbols for TS-EST, respectively. Steady-state and transient bit error rates (BERs) achieved using the TS-EST algorithm are compared to those obtained using the constant modulus algorithm (CMA) and the training symbol least mean squares (TS-LMS) algorithm and results show that the proposed TS-EST algorithm provides the same steady-state BER with a superior convergence speed. Also, the tolerance of the proposed TS-EST algorithm to laser phase noise and fiber nonlinearity is experimentally verified. Finally, we show by simulation that the superior tracking speed of the TS-EST algorithm allows not only for initial polarization tracking but also for tracking fast polarization transients if four training symbols are periodically sent during steady-state operation with an overhead as low as 0.57%.

© 2012 OSA

OCIS Codes
(060.1660) Fiber optics and optical communications : Coherent communications
(060.2330) Fiber optics and optical communications : Fiber optics communications

ToC Category:
Subsystems for Optical Networks

Original Manuscript: October 2, 2012
Revised Manuscript: November 8, 2012
Manuscript Accepted: November 8, 2012
Published: November 28, 2012

Virtual Issues
European Conference on Optical Communication 2012 (2012) Optics Express

Mohamed Morsy-Osman, Mathieu Chagnon, Qunbi Zhuge, Xian Xu, Mohammad E. Mousa-Pasandi, Ziad A. El-Sahn, and David V. Plant, "Ultrafast and low overhead training symbol based channel estimation in coherent M-QAM single-carrier transmission systems," Opt. Express 20, B171-B180 (2012)

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