星载AIS信号的带通采样与恢复

针对卫星接收机对模拟器件性能要求较高的问题，提出直接对接收到的射频信号进行采样，将模拟信号转换成数字信号，后续处理用软件模块实现的方法。同时结合自动识别系统（AIS）本身两个载波频率接近以及带宽较窄的特点，根据Nyquist带通抽样定理实现以较低速率采样来获取船舶状态信息，研究了一种星载AIS信号全数字解调方法和信息检测恢复技术。首先介绍了带通采样原理，其次详细研究了多用户AIS信号采样频率的确定、两个频道信号分离方法以及单通道信号如何下变频为基带信号，其中基带信号检测采用简化的基于Viterbi的非相干检测方法，最后结合AIS协议进行信号的恢复，并通过示波器采集实际船台发送的AIS信号进行了实验，验证了该过程的正确性。

Bandpass sampling and recovery of satellite-based AIS signal

According to the high performance requirements of satellite receiver for analog devices, this paper puts forward a new method of directly sampling the RF signal to convert the analog signal to digital signal and the subsequent processing in software module implementation. At the same time, in order to obtain the status information of the ship at a lower sampling rate according to Nyquist band-pass sampling theory and take full advantage of the characteristics of AIS(Automatic Identification System) whose two carrier frequencies are close to each other and the bandwidth is narrow,a digital demodulation method of satellite-based AIS signal and the information detection recovery technology is studied. Firstly, band-pass sampling theory is introduced. Secondly,the determination of the sampling frequency of multi-user AIS signal, two-channel signal separation method and how single-channel signal is down-converted to a base band signal are discussed in detail. The base band signal is detected by the simplified Viterbi-based non-coherent detection method. Finally, the digital signal is recovered according to AIS protocol specifications, and the experiment of using oscilloscope to collect AIS signal transmitted by the practical berth verifies the correctness of the process.