中文摘要：

基于Viterbi-Viterbi算法原理，提出了一种适用于Squarem—QAM相干光通信系统载波相位估计的改进算法，能够充分利用所有符号的相位信息进行载波相位估计。仿真分析表明，改进算法比现有其它算法复杂度更低，相位噪声容限更大，当BER=10-3,SNR代价为2dB时，16-QAM和64-QAM允许的激光线宽分别为1．1MHz和0．25MHz。

英文摘要：

A modified carder phase estimation algorithm based on Viterbi-Viterbi phase estimation method is proposed for high-level QAM-based optical coherent systems, in which all of the received symbols are used to estimate the carrier phase in order to enhance the tolerance of laser phase noise. Compared to the other exist- ing algorithms, the computation complexity of the proposed algorithm is lower,the phase noise tolerance is bigger. The simulation results show that 2dB SNR penalty is induced at BER=10-3 with the laser linewidths of 1.1MHz and 0.25MHz for square 16-QAM and 64-QAM.