相干光正交频分复用系统中射频导频和扩展卡尔曼滤波联合的相位噪声补偿算法

Joint Phase Noise Compensation Algorithm Using RF-Pilot and Extended Kalman Filter in CO-OFDM Systems

针对大线宽和高阶圆形正交幅度调制(C-QAM)的相干光正交频分复用(CO-OFDM)系统,提出一种基于射频导频(RF-Pilot)和时域扩展卡尔曼滤波相结合的相位噪声补偿算法。该算法通过在接收端预设的RF-Pilot进行时域相位噪声粗补偿,并进行信道估计和均衡。再对信道均衡后的频域数据进行预判决,结合判决后的时域数据和信道均衡后的时域数据,进行扩展卡尔曼滤波,实现相位噪声的最终补偿。基于传输速率为50Gb·s^(-1)和传输距离为100km的CO-OFDM系统在C-16QAM和C-32QAM两种调制格式下进行了算法的仿真验证。仿真结果表明,该算法相较于原RF-Pilot算法,具有较好的相位噪声补偿效果,且频谱利用率并未显著降低,算法复杂度并未显著增加。激光器线宽为2.1MHz,且使用C-32QAM时,该相位噪声算法补偿的误码性能可达到前向纠错上限,从理论上证明使用该算法可提高CO-OFDM系统对激光器线宽的容忍度,线宽较宽的廉价分布式反馈激光器可作为CO-OFDM系统的发射端光源和接收端本地振荡。该算法能扩展大线宽CO-OFDM系统在长距离接入网和城域网中的应用。

We propose a phase-noise compensation algorithm by using radio frequency pilot（RF-Pilot）method in combination with extend Kalman filter（EKF）in time domain for the coherent optical orthogonal frequency division multiplexing（CO-OFDM）system with large linewidths and high-order circular quadrature amplitude modulation（C-QAM）.We realize the coarse phase-noise compensation in time domain by setting a RF-Pilot at the receiver,and then complete the channel evaluation and channel balance.After accomplishing the initial pre-decision in the frequency domain,we use EKF to realize the final phase noise compensation,according to the judged temporal signal and the channel equalization temporal signal.We numerically verify the algorithm by transforming in a 50 Gb·s^（-1） CO-OFDM system with 100 km transmission distance under C-16QAM and C-32QAM.The results show that compared with original RF-Pilot phase-noise compensation algorithms,the proposed method has better performance on the phase noise compensation while has no obvious decrease of frequency utilization,and the complexity is not increased significantly.For CO-OFDM systems with C-32QAM and a laser linewidth of 2.1 MHz,the bit error rate achieves the upper limit of forward error correction.It theoretically confirms that the proposed algorithm can improve the tolerance of laser linewidth on the CO-OFDM system.We can use the inexpensive distributed feedback lasers with relatively large linewidth as the source of the object and the oscillator of the receiver.The proposed phase-noise compensation algorithm is beneficial to the application of CO-OFDM system in long distance access network and metropolitan area network.