相干光FBMC/OQAM系统的信道和载波频率偏移联合估计及补偿方法研究

Joint Channel and Carrier Frequency Offset Estimation and Correction for Coherent Optical FBMC/OQAM System

色散和激光器频率偏移能够对使用交错正交幅度调制格式的相干光滤波器组多载波(CO-FBMC/OQAM)系统产生严重影响。针对这个问题,重点研究了该系统的基于训练序列的信道和载波频率偏移联合估计及补偿方法。详细分析了CO-FBMC/OQAM系统的信道传输模型,对训练序列的结构进行了设计和优化,抑制了固有虚部干扰(IMI)的影响。为了消除信道噪声对估计过程的干扰,提出了基于不同帧之间频域平均的估计方法。该方法将实值导频的交叉关联函数在不同帧之间进行频域平均,取其相位后获得载波频率偏移估计值。信道响应也在不同帧之间进行频域平均后得到最终估计值。搭建了CO-FBMC/OQAM系统的数值仿真平台,并研究了激光器频率偏移不同时,经过1500km标准单模光纤传输后系统的误差幅度矢量和误码率。数值仿真结果表明:不管是在背靠背场景下,还是在1500km光纤传输后,该方法都能够抑制色散和激光器频率偏移的影响,有效提升系统的传输性能。

Chromatic dispersion and laser frequency offset have serious impact on coherent optical filter bank multicarrier systems with offset quadrature amplitude modulation（CO-FBMC/OQAM system）.Preamble-based joint estimation and correction algorithm of channel and carrier frequency offset（CFO）in CO-FBMC/OQAM system is investigated.The channel transmission model of CO-FBMC/OQAM system is theoretically elaborated,and the preamble structure is deliberately designed and optimized to suppress the impact of inherent imaginary interference（IMI）.In order to reduce the noise impact,an estimation method based on inter-frame averaging is proposed.In this method,the cross-correlation function within multiple frames is averaged and the laser frequency offset according to the phase of this average is estimated.Finally,we get the final channel response by averaging channel estimation results within multiple frames.The error amplitude vector and error rate of the system are numerically demonstrated through 1500 km standard single-mode fiber transmission with different CFO values.The results show that the proposed method can suppress the influence of chromatic dispersion and laser frequency offset,and significantly enhance transmission performance in the back-to-back scenario or after 1500 km optical fiber transmission.