Flexible decision-aided maximum likelihood phase estimation for optical coherent QAM signals

Abstract

提出相干光通信系统的弹性判决辅助式最大似然(DAML)相位估计算法,将弹性DAML相位估计算法从相移键控(PSK)系统扩展到正交幅度调制(QAM)系统,并进行相位估计误差推导。仿真结果表明,弹性DAML在不同块长度条件下存在误比特率(BER)下界,能消除传统DAML的块长度效应,可有效降低符号检测过程对信号相位波动的要求,进而放宽相干光系统对激光器线宽的限制。 Flexible decision-aided maximum likelihood (DAML) phase estimation method is proposed, which extends from the phase shifted keying (PSK) system to the quadrature amplitude modulation (QAM) system, and the phase estimation error is derived. Simulation results show that the flexible DAML has a lower bound of bit error ratio (BER) for different block lengths, which can eliminate the block length effect from the conventional DAML and effectively reduce the requirement of signal phase fluctuation in the process of signal detection, thereby it loosens the restriction on laser linewidth in coherent optical systems.