基于PMF—FFT的PN码捕获方法及性能

在高动态通信系统中，由于载体的相对运动，使载波附加了较大的多普勒频移。使用一组部分相关器结合快速傅里叶变换进行伪码捕获，可以将码相位-多普勒频率的二维搜索降为一维搜索，大大减少了捕获时间。文中讨论了该方法部分相关器长度和FFT点数对捕获性能的影响，推导相关损失与最大多普勒频移和相关器长度的关系，为分析捕获系统的捕获范围和选取相关器参数提供依据，给出两种确定分段相关器长度X的方法。最后仿真证明在PN捕获的同时该方法能够准确估计多普勒频移。

Analysis on PMF-FFT Based Acquisition of PN Code

In high dynamic communication systems, there exists a larger Doppler shift of the carrier because of the relative movement of satellites, and the Doppler frequency would seriously decay the correlated peak which identifies the alignment of the pseudo codes. In view of the environment with large Doppler frequency shift, the paper proposes the use of a set of Partial Matched Filters combined with Fast Fourier Transform to acquire pseudo code while estimate Doppler frequency shift. This method can reduce two dimensional search of code phase -Doppler frequency to one dimensional. In this paper, the effects of partial correlatiors＇ length and FFT points on the performance of PN code acquisition based on PMF-FFT are discussed. The relationship between coherent combining loss, PMF size and Doppler frequency shift is derived, which provides theoretical basis for selecting partial correlators＇ length. The method for selecting segmental length of a correlator is presented. Simulation results show that the method could estimate the Doppler frequency shift while acquire the PN code.