基于最大似然频率精细估计的载波捕获算法

High-accurate Carrier Acquisition Based on Maximum Likelihood Estimation of Refined Frequency

深空通信中,星上对载波的主动捕获主要利用频率估计的方法。在实际载波捕获电路中,精确的频率估计值导入锁相环,使得锁相环捕获带余量充足。在锁相环带宽一定的情况下,估计精度的提高可以减少FFT实现点数。在FFT频率粗估计的基础上,通过频率精细估计算法可提高估计精度。为获得估计精度更高的频率精细估计算法,利用最大似然泛函不变性推导了频率精细估计的最大似然算法。载噪比在5 dB时,估计精度可以提高到FFT分辨率的10-4。仿真结果表明,该算法估计性能优于其他频率精细估计算法。

The carrier initiative acquisition on board is mainly based on the frequency estimation in deep space communications. With the aid of data, the estimator performs well at low Signal-to-Noise Ratio（SNR）. In the design of carrier acquisition, the accurate estimation of frequency aids the Phase Locked Loop（PLL）. If the ac- quisition bandwidth of PLL is fixed, accurate estimation value helps to decrease Fast Fourier Transform（FFF） size. The refined estimation after FFT coarse estimation is applied to improve estimation accuracy. In order to achieve higher estimation accuracy, a Maximum Likelihood（ML） algorithm of refined estimation is derived via functional invariance. The estimation accuracy can achieve 10- 4 when SNR is 5 dB. The simulation results pre- sent that the proposed algorithm outperforms other algorithms.