The traditional fast Fourier transform based frequency offset estimation (FFT-FOE) estimates the frequency offset by searching the spectral peak of the signal after the fourth power operation, which is suitable for multiple modulation formats. But the accuracy of FOE is limited by the number of FFT points. In this paper, we propose a high accuracy and low complexity FOE algorithm based on all phase FFT (APFFT-FOE). The accuracy of FOE can be improved effectively with lower additional computational complexity. Simulation results show that the mean square error of APFFT-FOE is reduced by more than one order of magnitude compared with the FFT-FOE. Compared with other FOE algorithms that can achieve the same accuracy, the additional computational complexity required by APFFT-FOE is reduced by more than 50%\%. Finally, the APFFT-FOE is experimentally verified with 20 GBaud 16/64-QAM modulation signal. The experimental results show that the required OSNR for 16-QAM signal to reach 6.7%\% hard-decision forward-error correction is relaxed by 0.23 dB. For 64-QAM signal, the required OSNR at 20%\% soft-decision forward-error correction threshold is relaxed by 0.68 dB.

中文翻译：

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M-QAM相干光系统基于全相位FFT的高精度、低复杂度频偏估计方法


传统的基于快速傅里叶变换的频偏估计（FFT-FOE）通过搜索四次幂运算后信号的频谱峰值来估计频偏，适用于多种调制格式。但FOE的精度受到FFT点数的限制。在本文中，我们提出了一种基于全相位FFT（APFFT-FOE）的高精度、低复杂度FOE算法。可以有效提高FOE的精度，同时降低额外的计算复杂度。仿真结果表明，APFFT-FOE的均方误差较FFT-FOE降低了一个数量级以上。与其他能够达到相同精度的FOE算法相比，APFFT-FOE所需的额外计算复杂度降低了50%%以上。最后，利用20 GBaud 16/64-QAM调制信号对APFFT-FOE进行了实验验证。实验结果表明，16-QAM信号达到6.7%\%硬判决前向纠错所需的OSNR放宽了0.23 dB。对于 64-QAM 信号，20%\% 软判决前向纠错阈值所需的 OSNR 放宽 0.68 dB。