Research On Estimation And Separation Of Chirp Signals Based On Fractional Fourier Transform

Linear frequency modulation(LFM)signal is widely used in radar and communication system.Because of the complicated electromagnetic environment,signal sorting and recognition become more difficult.Especially under the low signal to noise ratio,LFM signal parameter estimation has great significance.Meanwhile,receiver may receive more than one signals at one time,so how to detect and separate signals become an important research topic in the field of electronic countermeasure.The main research of this paper is how to detect and separate LFM signals by Fractional Fourier Transform(FrFT).The traditional time-frequency analysis method such as Short Time Fourier Transform(STFT)and Wigner-Ville distribution have problem with low-resolution or cross term interference while estimating the parameter of LFM signals.Compared to traditional time-frequency analysis method,FrFT does not have these problems.But two dimensional search is involved in FrFT,which have a huge amount of computation.This will affect real-time performance of signal detection.Two kinds of Improved algorithm are mentioned in this paper:One is LFM signal parameter estimation based on FrFT-interpolation method;another is LFM signal parameter estimation based on Nuttall window Energy Barycenter Correction Method(EBCM).Algorithm based on FrFT-Interpolation method using spectrum interpolation to enlarge the search step size r and reduce computation.Algorithm based on Nuttall window is using the good performance of Nuttall window to improve the accuracy of EBCM,and then,estimate the Order number of FrFT by the corresponding relation between frequency modulation rate and the Order number of FrFT.By this Order number,we can have accurate estimation of frequency modulation rate and initial frequency by small range search.At last,We use MATLAB to simulate the two Algorithm.Multi-component signal separation method based on CLEAN using the method by masking known signals.This method can separate multi-component signals and complete the parameters estimation.But the method doesn't fit to the idea of dimensionality reduction involved in two kinds of Improved algorithm.Paper introduce a improved multi-component signal separation method based on CLEAN,which can be used in two kinds of Improved algorithm.We also use MATLAB to simulate the performance.Finally,a hardware system with DSP is used to test the algorithm.The experimental results are consistent with the MATLAB simulation results,which proves the practical value of the method.