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Soft-Decision-Aided, Maximum-Likelihood Carrier Phase Estimation for Coherent Optical QAM

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2 Author(s)
Ming-Wei Wu ; Dept. of Electr. & Comput. Eng., Nat. Univ. of Singapore, Singapore, Singapore ; Pooi-Yuen Kam

A novel, soft-decision-aided, maximum likelihood (SDA-ML) phase estimator is derived for carrier phase estimation in coherent optical communication. For estimating the carrier phase of the current symbol, SDA-ML uses both the feedback of earlier soft data decisions and the feedforward of later soft data decisions. The estimator is applicable to arbitrary 2-D modulations, where the symbols can have unequal energies and unequal a priori probabilities, and the constellation can be asymmetrical. An iterative SDA-ML algorithm and a simplified DA-SDA-ML algorithm with a reduced computational complexity are proposed. Both algorithms have no phase ambiguity. The data detector does not require to estimate the phase explicitly. Simulations show that SDA-ML and DA-SDA-ML outperform the Mth power and DA-ML in the presence of strong linear laser phase noise.

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Lightwave Technology, Journal of  (Volume:31 ,  Issue: 22 )