相干光OFDM/OQAM系统相位噪声机理及抑制方法研究

Coherent optical orthogonal frequency division multiplexing with Offset Quadrature Amplitude Modulation (CO-OFDM/OQAM) is one key technology for the next-generation high spectrum efficiency and flexible optical networks. However, CO-OFDM/OQAM is very sensitive to optical phase noise, which hinders its application. In previous studies of CO-OFDM/OQAM, there is no comprehensive investigation of the mechanism of optical phase noise effect in the CO-OFDM/OQAM system, and the performance of inter-symbol-interference (ISI) suppression and inter-channel-interference (ICI) suppression in the CO-OFDM/OQAM system under the impact of optical phase noise is poor. In this project, we propose to conduct research on the mechanism of optical phase noise effect in the CO-OFDM/OQAM system and develop effective methods for optical phase noise suppression. We will derive the closed-form expression of the impact of optical phase noise on the ISI/ICI that exist in the real-orthogonality based CO-OFDM/OQAM system, and present a comprehensive expression of the mechanism of optical phase noise effect in CO-OFDM/OQAM system for the first time. We will develop novel and high-performance time/frequency domain optical phase noise suppression algorithms and high-accuracy time domain algorithms for joint estimation of optical phase noise/channel, and analyze the impact of the time/frequency localization characteristic of prototype filter on its tolerance to optical phase noise. We will present the principle of algorithms and conduct experimental investigation of their feasibility in a high speed (no less than 400Gb/s) CO-OFDM/OQAM communication system based on low-cost lasers of large linewidths (no less than 1MHz). This project is of great value for promoting the application of the high spectrum efficiency CO-OFDM/OQAM system in future optical networks.

交错正交幅度调制的相干光正交频分复用（相干光OFDM/OQAM）是构建下一代高光谱效率、弹性光网络的关键技术。但是，相干光OFDM/OQAM对光相位噪声的高敏感性极大地限制了其应用。已有的研究缺乏对其光相位噪声机理的完整分析，对光相位噪声扰动下的符号间串扰（ISI）和子载波间串扰（ICI）抑制效果不佳。本课题研究相干光OFDM/OQAM中光相位噪声机理及高效抑制方法。我们将解析分析光相位噪声对实数正交体系中固有的复数域ISI/ICI的扰动，首次完整阐明光相位噪声机理，并提出新颖的时域/频域高效光相位噪声抑制算法，以及光相位噪声/信道时域联合估计算法，分析原型滤波器的时频聚焦特性对光相位噪声容忍度的影响。我们将阐明算法原理，在采用低成本大线宽光源（不低于1MHz）高速（不低于400Gb/s）实验系统中验证算法可行性。本课题对推动高光谱效率相干光OFDM/OQAM在未来网络中应用具有重要价值。

基于多载波通信的交错正交幅度调制相干光正交频分复用（相干光OFDM/OQAM）是实现高光谱效率及弹性光网络的重要物理层技术。但是，相干光OFDM/OQAM系统对光相位噪声特别敏感。在采用高阶调制格式以及符号周期-光源线宽乘积较大的系统中，光相位噪声导致的性能劣化尤为严重。为提高多载波相干光OFDM/OQAM通信系统对光相位噪声的容忍度，我们在基于数字信号处理的光相位噪声抑制方面开展了深入研究，分析光相位噪声对实数正交体系中固有的复数域ISI/ICI的扰动，并在此基础上提出高性能的相位噪声抑制算法，包括：(1) 提出了既具有低建模误的时域直接展开次符号算法。构建时域次符号相位噪声估计理论框架，在该理论框架下研究时域直接展开的次符号光相位噪声抑制算法，通过将单个符号在时域分割成若干次符号，实现对光相噪的高分辨率估计,并研究导频分布与算法复杂度的优化。该算法具有低复杂度，其性能由于传统算法；(2) 构建了频域基底展开相位噪声抑制理论框架，揭示了传统傅里叶正交基底的缺陷，利用最小均方误差准则推导获得了新颖的非正交基底，实现了高性能的相噪抑制,验证了其性能忧于传统正交基底算法，且对残余频差敏感度低。课题的研究成果对推动相干光OFDM/OQAM在低成本相干接入网/城域网的应用具有重要的意义。