消除数据调制影响的FFT捕获方法

在利用快速傅里叶变换(FFT, Fast Fourier Transform)捕获扩频信号的过程中,为了提高捕获精度,会遇到基带数据调制影响捕获性能的问题.主要分析了基带数据符号跳变影响FFT捕获性能的原因:在频域内造成待检测信号的幅度衰减以及频点偏移.提出了一种解决此问题的方法:通过对I和Q两路信号的运算,构造一个不受数据调制影响的复信号,对此信号作FFT,完成捕获.给出了此方法的MATLAB仿真,以及基于现场可编程门阵列(FPGA, Field Programmable Gate Array)的实现方案.实验数据表明,此方法消除了基带数据调制对FFT捕获性能的影响,且在相等积分时间的条件下,比常用方法的捕获精度提高了一倍.

FFT-based acquisition method to eliminate influence caused by data modulation

To achieve higher acquisition accuracy while using FFT(fast Fourier transform)-based algorithm to acquire spread spectrum signal,integration across data bit transition boundaries is necessary.However,performance degradation due to data modulation must be eliminated.Two effects of baseband data shift on acquisition performance,amplitude attenuation and frequency offset of the detected signal in frequency domain,were analyzed.A method to solve this problem was given.This algorithm constructs a complex signal which is free from data modulation,and detects Doppler shift using this signal through FFT.Simulation in MATLAB and FPGA(field programmable gate array)-based implementation of this method was also described.The simulation and experiment results verify that,this method can overcome the problem caused by baseband data shift,and improve acquisition accuracy by one times compared with conventional method in the same predetection integration time.