基于高阶正交幅度调制(QAM)和大线宽相干光正交频分复用(CO-OFDM)系统, 提出了一种在时域进行无迹卡尔曼滤波(UKF)的相位噪声补偿算法。该算法在接收端基于训练符号频域卡尔曼滤波实现信道均衡, 用较小的频域导频数据开销进行频域扩展卡尔曼滤波, 先补偿公共相位误差(CPE)噪声, 然后将CPE噪声补偿之后的数据在时域进行载波间干扰(ICI)相位噪声粗补偿。对相位噪声粗补偿后的频域数据进行预判决, 结合接收端原始时域数据, 在时域对判决后的数据进行UKF以实现ICI相位噪声的精细补偿。对精细补偿之后的频域数据再进行相位噪声粗补偿并进行迭代运算, 极大地提高了相位噪声的补偿效果。对50 Gbit·s-1的CO-OFDM系统进行了传输距离为100 km的仿真, 与其他算法相比, 所提算法的频谱利用率极高, 且具有较好的补偿效果。对激光器线宽为700 kHz且调制方式为32QAM的传输信号进行二次迭代后, 所提相位噪声补偿算法的误码率性能仍可达到前向纠错上限。所提算法促进了大线宽CO-OFDM系统在长距离接入网和城域网中的应用。

A phase noise compensation algorithm, which carries out unscented Kalman filter (UKF) in time domain, is proposed based on high-order quadrature amplitude modulation (QAM) and large linewidth coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. The algorithm realizes channel equalization based on the training symbol frequency domain Kalman filter at the receiver, and less frequency domain pilot data overhead is used to carry out frequency domain extended Kalman filter. The common phase error (CPE) noise is compensated first. Then, inter-carrier interference (ICI) phase noise coarse compensation is carried out on the data after CPE noise compensation in time domain. Initial pre-decision is performed on the frequency domain data after phase noise coarse compensation. Combining with the primary time domain data at the receiver, UKF is applied to the decision data in time domain to achieve fine compensation of ICI phase noise. Phase noise coarse compensation is performed for frequency domain data after fine compensation, and iterative operation is carried out, which greatly improves the compensation effect of phase noise. Simulations with transmission distance of 100 km are carried out based on 50 Gbit·s-1 CO-OFDM system. Compared with other algorithms, the proposed algorithm has higher spectral efficiency and better compensation effect. After two iterations of the transmission signal with laser linewidth of 700 kHz and modulation format of 32QAM, the bit error rate performance of proposed phase noise compensation algorithm can still reach the upper limit of forward error correction. The proposed algorithm promotes the application of large linewidth CO-OFDM systems in long distance access networks and metropolitan area networks.