基于实虚交替导频的CO-OFDM-OQAM通信系统激光器相位噪声抑制方法

Laser phase noise suppression method for a CO-OFDM-OQAM communication system with real-imaginary-alternate pilots

针对偏移正交幅度调制的相干光正交频分复用(CO-OFDM-OQAM)通信系统,本文提出了一种基于实虚交替导频的相位噪声抑制算法。该算法利用激光器相位噪声的性质和固有虚部干扰(IMI)系数的对称性规律设计全新的实虚交替导频,结合线性拟合,能够准确估计每个频域符号的公共相位误差(CPE)。由于是在频域进行补偿,与时域相位噪声抑制算法相比,计算复杂度大幅下降。搭建了有效速率为65 GBits/s的偏振复用CO-OFDM-OQAM系统的数值仿真平台,研究了不同激光器线宽和子载波个数下系统的传输性能,考察了所提方法对相位噪声的抑制效果。获得的结果证实:OSNR固定为25 dB,子载波总数分别为256、512和1024时,误码率达到FEC极限时所需要的线宽分别为801.1、349和138.4 kHz。对于使用16-QAM调制格式、子载波个数为256或512的系统,能较好补偿激光器的相位噪声,而且不会影响功率峰均比。

A phase noise suppression algorithm based on real-imaginary-alternate pilots was proposed for a coherent optical orthogonal frequency division multiplexing communication system with offset quadrature amplitude modulation(CO-OFDM-OQAM).The algorithm uses the properties of laser phase noise and the intrinsic imaginary interference(IMI)symmetry law to design real-imaginary-alternate pilots.In combina-tion with a linear fitting,it can accurately estimate the common phase error(CPE)for CO-OFDM-OQAM.As the compensation was performed in the frequency domain,the computational complexity was signific-antly reduced compared to the time-domain phase noise suppression algorithms.A numerical simulation plat-form was built for a polarization multiplexed CO-OFDM-OQAM system with an effective bit rate of 65 GBits/s.Through it,the transmission performance of the system with different laser linewidths and num-bers of subcarriers was studied,and the suppression effect of the proposed method on phase noise was ex-amined.The results obtained confirm that the linewidths required to reach the FEC limit for BER are equal to 801.1,349,and 138.4 kHz for a fixed OSNR of 25 dB and a total number of subcarriers of 256,512,and 1024,respectively.For the system using a 16-QAM modulation format with 256 or 512 subcarriers,it com-pensates well for the laser phase noise without affecting the power peak-to-average ratio.