中文说明：
由于卫星与用户接收机二者的连线方向上存在相对运动，因此引起了载波和伪码的多普勒效应，再加上接收机晶体震荡频率漂移和卫星时钟频漂等原因。接收机实际接收到的卫星载波中心频率一般不再等于信号被发射时的标称频率，这就需要接收机在载波频率一维对信号进行搜索。同时，由于卫星到接收机的距离时刻变化，加上接收机始终相对于GPS时间的偏差又并不固定，因而接收信号的伪码相位值也在改变，所以接收机也要在码相位一维对信号进行搜索。扩频信号的捕获是一个对目标信号频率域和相位域进行的二维搜索过程。
English Description：
Due to the relative motion between the satellite and the user receiver, the Doppler effect of carrier and pseudo code is caused. In addition, the frequency drift of the receiver crystal oscillation and the frequency drift of the satellite clock are also caused. The center frequency of satellite carrier received by the receiver is no longer equal to the nominal frequency when the signal is transmitted, which requires the receiver to search the signal in one dimension of carrier frequency. At the same time, because the distance from the satellite to the receiver changes at any time, and the deviation of the receiver from the GPS time is not fixed, the pseudo code phase value of the received signal is also changing, so the receiver also needs to search the signal in the code phase dimension. The acquisition of spread spectrum signal is a two-dimensional search process in frequency domain and phase domain of target signal.