Improved carrier phase estimation algorithms for optical coherent systems

To enhance the performance of Viterbi-Viterbi phase estimation for optical coherent transmission systems, two effective approaches are investigated in this paper, as adding one stage of normalization and using weighted average filter in the algorithm. The simulation results for QPSK, 8PSK and 16-QAM show that: (1) Triangle window can enlarge the range of permitted block length over 1.5 times in VVPE for three modulation formats, which means the ability of adaptive is enhanced for receiver with respect to laser linewidth; (2) Improved algorithm achieves smaller SNR penalty due to laser phase noise. For the linewidth per laser of 9MHz (QPSK), 2MHz (8PSK), and 1MHz (square 16-QAM), the SNR penalty is 0.8dB.