大波特率、高阶调制格式信号的广泛应用使相干光通信系统对收发机中存在的硬件损伤更加敏感,因此迫切需要相应的损伤估计方法。提出了一种新的基于数字信号处理的收发机损伤联合估计方案,该方案可同时监测因光发射机和光接收机硬件不完美引起的光信号同相/正交(IQ)分量幅度、相位不平衡和时钟偏移。该方案首先使用Godard定时误差检测器和施密特正交化法估计并补偿了接收机损伤;接着使用最大似然的独立成分分析法和级联的判决引导最小均方(DDLMS)算法分别实现了对发射机损伤不敏感的偏振解复用和载波相位恢复;最后从DDLMS的抽头系数中估计出发射机损伤。得益于对发射端IQ不敏感的偏振解复用和载波相位恢复,该方案实现了宽范围的损伤监测。仿真结果表明,与传统数字信号处理方案相比,所提方案对发射端幅度、相位不平衡的估计范围分别提升了约100%和33%。

The wide use of high baudrate and high-order modulation format signals makes coherent optical communication systems more sensitive to hardware impairment in the transceiver, so there is an urgent demand for corresponding impairment estimation scheme. This paper proposes a new joint estimation scheme for transceiver impairment based on digital signal processing, which can simultaneously monitor in-phase/quadrature (IQ) amplitude, phase imbalance, and time skew caused by the hardware imperfections of the optical transmitter and optical receiver. First, the Godard timing error detector and Gram-Schmidt orthogonalization method are used to estimate and compensate for the receiver impairment. Then, the maximum likelihood-based independent component analysis method and cascaded decision-direct least mean square (DDLMS) algorithm are used to achieve polarization de-multiplexing and carrier phase recovery which are insensitive to transmitter impairment. Finally, the transmitter impairment is estimated from the tap coefficients of DDLMS algorithm. The scheme achieves wide range impairment monitoring, which is attributed to polarization de-multiplexing and carrier phase recovery that are insensitive to the IQ of the transmitter. Simulation results demonstrate that the estimation ranges of the amplitude and phase imbalances of the proposed scheme are improved by about 100% and 33% compared with that of the conventional digital signal processing scheme, respectively.