深空通信载波同步高精度FFT频偏估计算法

摘要

深空通信信道具有高动态、低信噪比的特点, 传统深空探测器应答机中采用的基于锁相环的载波同步算法, 在信噪比低于6dB时无法实现可靠同步.针对这一问题, 文章提出了一种基于插值的快速傅里叶变换 (FFT) 频偏估计算法.通过一次插值, 即可获得频偏的无偏估计值;插值后再进行二分搜索, 以提高靠近谱线位置频点的估计精度.文章对此算法的估计精度进行了仿真, 同时给出了其在某深空探测器应答机中的实现和验证情况.结果表明:此算法估计精度优于抛物线、Rife等插值算法;当二分搜索迭代次数等于5时, 能够实现整个频偏估计范围内的可靠载波恢复.基于算法设计的深空探测器应答机载波同步门限可达2dB, 相较于传统应答机, 载波同步门限降低4dB.%Due to the characteristic of high dynamic and low signal-to-noise ratio in deep space communication, carrier synchronization algorithm based on phase-locked loop in traditional deep space transponder reliable synchronization cannot be achieved when the signal-to-noise ratio is lower than 6 dB.In order to solve the problem, a FFT frequency offset estimation algorithm based on interpolation is proposed.The unbiased estimation of frequency offset can be obtained by onetime interpolation, which is followed by binary search to improve the estimation accuracy of frequency points near spectral line.The estimation accuracy of the algorithm are simulated and the implementation and verification of the algorithm in a deep space probe transponder are given.The results show that the estimation accuracy of the proposed algorithm is better than interpolation algorithm such as parabola and Rife.When the number of binary search iterations is equal to 5, reliable carrier recovery can be achieved within the whole frequency offset estimation range.The carrier synchronization threshold of the deep space probe transponder based on the algorithm design can reach 2 dB, which is 4 dB lower than traditional transponder.