低信噪比高动态条件下基于FFT的二维平移累加PN码捕获算法

Two-dimensional Shift Accumulation Algorithm Based on FFT for PN Code Acquisition in High Dynamic and Low SNR Environment

针对低信噪比高动态条件下直接序列扩频(DSSS)系统中PN码捕获的问题,提出了基于FFT二维平移累加的PN码捕获算法。首先对现有的PN码捕获技术进行了分析,然后研究了时变的载波频偏与码频频偏对PN码捕获的影响,在此基础上,提出了基于FFT二维平移累加的PN码捕获算法。算法的基本思想是对相关器输出的相关值在载波频偏不确定度与码相位不确定度同时进行平移,从而消除相关峰"漂移"现象,增大非相干累加的有效性。给出了采用此算法的捕获系统结构图,并对关键参数进行了分析。最后,通过仿真表明了该算法对捕获系统有6 dB的改善。

This paper provides two-dimensional shift accumulation algorithm based on FFr for acquisition of high dynamic DSSS（Direct Sequence Spread Spectrum） signal with low signal-to-noise ratio（SNR）. Firstly, current PN code acquisition technologies are analysed. Secondly, PN code acquisition affected by changing carrier fre- quency offset and code frequency offset is researched. On this base, two-dimensional shift accumulation algo- rithm based on FFr for acquisition of PN code is provided, and the fundamental idea of the algorithm is that cor- relation results from correlators will be shifted simultaneously in carrier frequency offset and cede phase uncer- tainty region, and this can eliminate the phenomenon of correlation peaks drift and makes non - coherent accu- mulation more effective. Structure diagram and working principle of acquisition system which uses this algorithm are given, and choice for important parameters is analysed. Simulation shows that performance of acquisition system is improved by 6 dB with this algorithm.