FFT快速捕获算法在GPSC／A码与P（Y）码中的应用

一种快速、有效的GPS信号捕获方法是通过在整段数据上并行搜索伪码相位,对一段输入数字中频(IF)序列和一段本地复现伪码序列进行快速傅里叶变换(FFT)运算来实现。分析了用FFT实现循环相关及其在GPS C/A码捕获中的应用,采用整区间相关、扩展复现码折叠、叠加相加和叠加丢弃法实现P(Y)码快速直接捕获,用补零、线性内插、Sinc内插、平均相关和双倍长度补零法解决计算点数问题,用扩展计算点数方法解决由导航数据引起的相位反转、超长序列与短序列进行线形相关运算及用循环相关实现线形相关等应用中的具体问题。

Application of Fast FFT Acquisition Algorithm in GPS C/A and P(Y) Codes

FFT can be used to operate on a block of inputting intermediate frequency(IF) sequences and local replica pseudo code sequences through providing parallel search pseudo code phases.It is a fast and efficient acquisition approach for GPS signals.This paper analyzes the implementation of circular correlation using FFT and FFT application in fast acquisition of GPS C/A codes,realizes the fast direct P(Y) codes acquisition by using full interval correlation,extended replica code folding,overlap and adds,overlap and discard approaches.The problem of FFT operation points can be solved through zero padding,linear interpolation,Sinc interpolation,averaging correlation and double-length zero-padding.Moreover,such problems as the phase reversal caused by navigation data,linear correlation operation between extra long sequences and short sequences,linear correlation implementation using circular correlation in application can be solved by extending FFT operation points.