超奈奎斯特相干光传输系统载波频偏估计算法  

Carrier Frequency Offset Estimation Algorithm of Faster-than-Nyquist Coherent Optical Transmission Systems

作　　者：杨桃[1] 赵菁[1] 秦英凯 由家林 Yang Tao;Zhao Jing;Qin Yingkai;You Jialin(State Key Laboratory of Information Photonics and Optical Communications,Beijing University of Posts and Telecommunications,Beijing 100876,China)

机构地区：[1]北京邮电大学信息光子学与光通信国家重点实验室,北京100876

出　　处：《光学学报》2023年第4期18-27,共10页Acta Optica Sinica

基　　金：北京市自然科学基金(4214059);国家自然科学基金(62001045);信息光子学与光通信国家重点实验室(北京邮电大学)自主研究课题(IPOC2021ZT17);中央高校基本科研业务费项目(2022RC09)。

摘　　要：提出一种基于训练序列相位差+调频Z变换(CZT)的两级频偏估计算法。该方案采用设计的时域训练序列块并结合块内和块间多次平均平滑噪声影响,以较低开销实现频偏的稳定粗估计,并进一步基于第一级频偏粗估计设定第二级CZT估计范围,以较低计算复杂度完成最终高精度频偏估计。三载波128 GBaud偏振复用十六进制正交幅度调制(PM-16QAM)超奈奎斯特(FTN)波分复用(WDM)系统的仿真结果表明,加速因子为0.95、0.90、0.85时,所提算法训练开销仅为1.56%,即可实现-8~8 GHz范围内的稳定频偏估计,残余频偏分别为2、2.5、3 MHz左右。与估计精度基本相当的传统盲四次方FFT频偏估计算法相比,所提算法的总体计算复杂度显著降低,约为传统算法的8%。Objective In virtue of the computing power provided by advanced digital signal processing(DSP)technology,the fasterthan-Nyquist(FTN)optical transmission technology can compensate for impairments,which has recently been considered a potential approach in the field of large-capacity coherent optical transmission.However,the severe inter-symbol interference(ISI)caused by tight FTN filtering will lead to the heavy deterioration of accuracy and stability in frequency offset estimation(FOE),which needs to be combated to guarantee the system performance.At present,the 4th fast Fourier transform(4th-FFT)algorithm is usually used for FOE in FTN coherent optical systems.To obtain a more ideal estimation accuracy,the 4th-FFT algorithm requires a large number of estimated samples to obtain a high-resolution FFT spectrum,which will bring greater computational complexity.Thus,the conventional FOE algorithm in the DSP module of the receiver is faced with conflicting effectiveness and complexity,which significantly degrades the stability and accuracy of FOE.Aiming at the above problems,this paper proposes a two-stage FOE algorithm based on phase difference of training sequence and chirp Z-transform(CZT)for dual-polarization(DP)16QAM FTN-WDM systems.Methods This paper puts forward a two-stage FOE algorithm.In the first stage of the proposed scheme,the periodic multi-symbol structure of the training sequence is adopted to process multiple inter-and intra-period averaging to alleviate the influence of the noise on FOE,which can achieve stably rough FOE with low overhead.In the second stage,according to the rough frequency offset value f1 in the first stage,the CZT spectrum search range is set and the starting and ending frequency points(the lower and upper limit values of the FOE range)are determined.Specifically,with the rough frequency offset value f1 as the center point,the spectrum search of equal length is carried out to both sides respectively.According to the starting and ending frequency points and the preset frequency reso

关 键 词：光通信 超奈奎斯特 相干光传输 载波频偏估计 低复杂度 

分 类 号：O436[机械工程—光学工程]