【作者】 张迪；

【导师】 王殊；

【作者基本信息】 华中科技大学 ， 信息与通信工程， 2022， 博士

【摘要】 在“东数西算”战略工程中,数据中心集群内部数据超高速传输多采用基于四电平脉冲幅度调制(PAM4)的强度调制直接检测(IMDD)数据中心光纤通信系统,基于PAM4调制的信号相较于不归零码型调制的信号对系统非线性损伤更为敏感。结构简单、低成本的光载射频(ROF)通信系统为大量移动用户高速访问数据中心网络提供可能的解决方案,噪声水平和线性度是ROF通信系统最为关键的性能指标。长距离、大容量的相干光通信系统用于算力网络8个枢纽节点间的数据互连,光纤的非线性损伤是限制高速光信号长距离传输的重要因素,针对系统中光纤非线性损伤的补偿技术的研究尤为重要。本论文围绕光纤通信系统中非线性补偿技术的研究展开,分别对基于PAM4的IMDD光纤通信系统、ROF通信系统及长距离相干光通信系统的非线性补偿技术进行了研究。论文具体完成了以下工作:(1)在高速IMDD光纤通信系统中非线性失真会导致接收PAM4信号眼图异常,进而劣化接收信号的误码率性能。针对柱状图中不同电平方差不一致的问题,提出了局部高斯拟合非线性动态判决算法。接收光功率为0 d Bm时,接收信号的误码率由1.5e-4提升至1.51e-5。针对非线性导致的眼图歪斜,提出了分眼图的非线性补偿算法。接收光功率为-1 d Bm时,相比于传统复杂度更高的Volterra非线性补偿算法,该算法将接收信号的误码率由1.2e-5提升至6.6e-6。针对IMDD光纤通信系统中接收信号经均衡算法后高频噪声放大使接收信号性能劣化的问题,提出了利用前后符号噪声相关性抑制高频噪声的算法,该算法将接收信号的灵敏度由-0.2 d Bm提升至-5.2 d Bm。(2)在ROF光纤通信系统中,链路的各类非线性失真以及噪声是劣化接收信号误码率性能的关键因素。针对通道间串扰以及链路噪声导致信道矩阵条件数偏大的问题,提出了一种简化的单环格基规约迫零算法,相较于传统的迫零算法,四个通道光接收灵敏度提升均大于0.9 d B。此外,提出了联合K均值聚类与单环格基规约迫零算法的非线性补偿技术,接收光功率大于-2 d Bm时,该技术可有效提升光载射频通信系统抵抗非线性损伤的能力。(3)在长距相干光通信系统中光纤的非线性效应会导致接收信号的Q~2因子与误码率性能劣化。传统的微扰法可有效缓解光纤非线性效应对信号性能的影响,但该算法的计算复杂度高,其复杂度主要来自微扰项的计算和数量。本论文对微扰项的计算和选取进行了优化,提出了一种硬判决查找表微扰算法。在四波长波分复用系统中,所提算法微扰项的计算复杂度仅为传统无简化微扰法计算复杂度的1/21,且各通道Q~2因子劣化仅为0.04 d B。更多还原

【Abstract】 In the strategic project of"Eastern Data and Western Computing",the ultra-high-speed transmission of data within the data center cluster mostly adopts the intensity modulation direct detection(IMDD)data center optical fiber communication system based on four-level pulse amplitude modulation(PAM4),while signals acquired through PAM4 modulation are more sensitive to channel nonlinear impairment than traditional NRZ modulation.The architecture of radio-over-fiber(ROF)system is simple,the low-cost ROF communication system provides a possible solution for a large number of mobile users to access the data center network at high speed,the noise level and linearity are the most critical technical indicators.The long-distance,high-capacity coherent optical communication system is used for the data interconnection between the eight hub nodes of the computing power network.Nonlinear effect caused by optical fiber is the factor limiting the performance of signals received.Therefore,it is necessary to overcome such shortcomings of optical fiber communication system.This thesis focuses on the study of nonlinear compensation techniques for IMDD short-distance optical fiber communication systems,ROF systems and long-distance coherent communication systems.Contributions of the thesis are as follows.(1)In high-speed IMDD short-distance optical fiber communication systems,the nonlinear distortions can cause unequal eye height and eye skew,and degrade BER performance of received signals.A nonlinear dynamic slicer algorithm is proposed to eliminate the nonlinearity of PAM4 signal.By using the proposed algrorithm,the BER performance has been improved from 1.5e-4 to 1.51e-5 when the received optical power is set at 0 d Bm.To eliminate the eye skew distortion,an eye dependent nonlinear compensation algorithm is proposed.When the received optical power is-1 d Bm,the Bit Error Rate(BER)performance is improved from 1.2e-5 to 6.6e-6 with the help of the proposed algorithm,in comparison with the traditional volterra nonlinear equalization algorithm.A low-complexity error-based feedforward equalizer is proposed to lessen the impacts of FFE-enhanced in-band high frequency noise and improve the receiver sensitivity performance from-0.2 d Bm to-5.2 d Bm.(2)In the ROF optical fiber communication system,both nonlinear distortion and noise of the system are the key factors that reduce the BER performance of the received signals.To cope with the channel interference and noise that deteriorate the condition number performance of the Multi-input Multi-output(MIMO)channel,a simplified MIMO demodulation algorithm based on lattice reduction zero-forcing(LR-ZF)is formulated.Power penalty larger than 0.9 d B is achieved by using the proposed LR-ZF algorithm,compared to the commonly used zero-forcing algorithm.Moreover,a joint K-means clustering and single-ring LR-ZF nonlinear compensation algorithm is proposed,which can strengthen the capability to resist the nonlinear distortion of ROF systems when the received optical power exceeds-2 d Bm.(3)For long-distance coherent optical fiber communication system,nonlinear effects in the optical fiber can degrade the performance of Q~2 factor and BER of the received signals.It is able to relieve the degradation owing to optical fiber nonlinearity effectively by applying the conventional perturbative nonlinearity compensation(PNC)algorithm,which,however,is quite intricate to perform in aspects of both calculation and selection of the perturbation terms.In the thesis,a hard-slicer look-up table perturbation nonlinear compensation algorithm is proposed to deal with the mentioned disadvantages.Compared with the traditional PNC algorithm,the complexity of the proposed simplified algorithm is reduced to 1/21 with the Q~2 factor of each channel degradated by only 0.04 d B in the wavelength division multiplexing system.更多还原