星载AIS信号的频偏估计

星载自动识别系统(AIS)中信号存在严重的多普勒频偏,影响信号的正确解调,而传统的基于快速傅里叶变换(FFT)的频偏估计算法其估计范围无法满足需要.为此,提出了一种改进的自相关-FFT频偏估计算法,通过构造辅助函数以确定信号频偏的正负号,在此基础上对基于FFT的频偏估计算法进行改进,从而扩大频偏估计范围,实现对大的多普勒频移的估计.仿真和实验结果均表明,改进算法的频偏估计范围扩大为原来的2倍,具有很高的估计精度,十分接近修正后的克拉美罗界,且算法简单、易于实现.

Frequency estimation of satellite-based AIS signals

In a satellite-based automatic identification system( AIS) ,demodulation of signal is affected by se-rious Doppler frequency offset, while the traditional frequency estimation algorithm based on fast Fourier transform( FFT) can not satisfy the need. To solve the problem,an improved self-correlation-FFT algorithm is proposed. The sign of frequency offset is determined by auxiliary function. The improved algorithm is ob-tained on the basis of frequency offset estimation algorithm based on FFT and sign of frequency offset,and it enlarges the frequency offset estimation range and realizes the large Doppler frequency offset estimation. The simulation and experimental results show that the frequency offset estimation range of the improved algorithm is twice times of the original. The improved algorithm,with high estimation precision,is simple and easy to implement and its estimated performance is very close to the modified Cramer-Rao bound( CRB) .