摘要
在星载AIS系统中,针对AIS接收机在近地卫星轨道上高速运行而造成的接收信号具有较大的多普勒频偏和传输延时的问题,提出了一种星载AIS信号两步求精的频偏估计算法。通过对Fitz算法的估计误差进行分析,发现其估计精度和估计范围都与求和项数有关,因此可以在利用AIS信号特征序列构造辅助函数消除调制信息后,通过较小的求和项数对星载AIS信号进行频偏粗估计,然后对接收信号进行频偏补偿,再通过一个较大的求和项数对补偿后的信号进行频偏精细估计,得到高精度的频偏估计值。仿真结果表明,算法的频偏估计精度比较高,十分接近其克拉美劳界,而且简单易于实现,能适用于较低的信噪比和较大的时延的情况,为星载AIS信号的频率估计提供了新的方法。
In the satellite- based AIS system, the AIS receiver moves at the speed of 7.5km/s in low- earth orbit, which results in large Doppler frequency offset and transmission time dely. In response to these problems, a novel estimation algorithm to refine the frequency offset for the satellite - based AIS signals is proposed. It turns out that the summation terms of Fitz estimator has a bearing on its estimation accuracy and range. Thus, the proposed algorithm utilizes the character sequence to construct an auxiliary function to remove the information phase, and a coarse frequency offset value is gotten by using the auxiliary function with the help of a small summation term, which is com- pensated to the received signal, then a large summation term is selected to obtain a fine frequency offset value by pro- cessing the compensated signal eventually. Simulation results show that the proposed method has high estimation accuracy, which is very close to the Cramer - Rao bound, and it is easy to implement. Additionally, this method can be applied to the lager Doppler frequency offset and time delay situation, and it provides a novel frequency estimation method for the satellite - based AIS signals.
出处
《计算机仿真》
CSCD
北大核心
2016年第4期136-139,共4页
Computer Simulation
基金
国家自然科学基金(61371108)
天津市高等学校科技发展基金计划项目(20140706
20140707)
关键词
特征序列
频偏估计
克拉美劳界
Character sequence
Frequency offset estimation
Cramer - Rao bound
作者简介
刘琛（1989-），男（汉族），河南省信阳市人，硕士研究生，主要研究领域为海事卫星信号同步。
马社祥（1962-），男（汉族），甘肃人，教授，硕士研究生导师，主要研究领域为海事卫星通信、移动通信。
