光接入网络中的数字信号处理技术

Digital Signal Processing for Optical Access Networks

采用先进的数字信号处理(DSP)技术,在发射机和接收机分别引入预处理和后处理,以提高光接入网络的频谱效率并延长传输距离。研究了一种基于光超奈奎斯特(Super-Nyquist)滤波的类9状态正交振幅调制(9QAM)信号多模均衡(MMEQ)后端DSP算法,使用这种方案,能够有效提高频谱效率,实现了频谱效率高达4 bps/Hz的正交移相键控(QPSK)信号传输;还研究了一种基于数字SuperNyquist信号前端预处理的方案,此方案的优点是不需要光预滤波即可达到相同的频谱效率。使用一个采用直接调制激光器(DML)、直接探测和数字均衡技术的高速无载波幅度相位-64状态正交振幅调制(CAP-64QAM)系统,在20 km标准单模光纤(SSMF)上实现了创纪录的60 Gbit/s CAP-64QAM信号传输;使用相干探测,实现了速率高达100 Gbit/s的64状态正交振幅调制-正交频分复用(16QAM-OFDM)实时传输系统,解决了实时OFDM信号处理中的关键问题。

In this paper, we investigate advanced digital signal processing（DSP） at the transmitter or receiver side for signal pre-equalization and post-equalization in order to improve the spectrum efficiency（SE） and transmission distance in an optical access network. A novel DSP scheme for this optical super-Nyquist filtering 9 QAM like signals based on multi-modulus equalization without post filter are proposed and experimentally demonstrated, which directly recovers the Nyquist filtered QPSK to a9-QAM-like signal. With this technique, SE can be increased to 4 bits/s/Hz for QPSK signals. A novel digital super-Nyquist signal generation scheme is also proposed to further suppress the Nyquist signal bandwidth and reduce channel crosstalk without using optical pre-filtering. Only optical couplers are needed for super-Nyquist WDM multiplexing. We extend the DSP for short-haul optical transmission networks by using high-order QAMs. We propose and experimentally demonstrate a high-speed CAP-64 QAM system using direct modulation laser based on direct detection and digital equalization. Decision-directed least mean square is used to equalize the CAP-64 QAM. Using this scheme, we generate and transmit up to 60 Gbit/s CAP-64 QAM over 20 km stand single-mode fiber based on the DML and direct detection. Finally,several key problems are solved for real time OFDM signal transmission and processing. Using coherent detection, up to 100 Gbit/s 16 QAM-OFDM real-time transmission is realized.