改进的16QAM载波频偏估计算法

Modified Carrier Frequency Offset Estimation Algorithm for Square-16QAM

针对QAM相干光传输系统中载波频偏估计算法存在估计范围小、计算复杂度高的问题,提出一种基于训练符号的FFT频偏估计算法。利用训练符号相位信息消除部分采样信号调制相位,取该部分信号的幅角进行FFT变换,最终得到频偏估计值。消除了原频偏估计算法中除以4的运算,从而扩大了频偏估计范围,同时由于减少了FFT长度进而降低计算复杂度。仿真结果表明,改进后的算法在QAM相干检测系统保持较高精度的频偏估计情况下,其估计范围可以达到±50%符号速率。

Aiming at the carrier frequency offset estimation algorithm with the small estimated range and the high computational complexity problem, a new FFT frequency offset estimation algorithm based on training symbols is proposed for QAM coherent optical transmission system, which removes the modulated phase information from the received signal accurately using training sequence. Then a estimation value by using the peak of a period gram, which is employing FFT transform is got. The computing divided by 4 in the original offset estimation algorithm is eliminated to expand the range of frequency offset estimation, and the computational complexity is reduced by decreasing the FFT transform length. The simulation results show that the improved algorithm has a higher frequency offset estimation accuracy and larger estimation range, and its estimation range is about 50% of the symbol rate.