Research On FMCW Lidar Ranging And Velocity Signal Processing Algorithm

Lidar is one of the most important systems for high-precision imaging in short range.Compared with traditional microwave radar,lidar uses shorter wavelength optical signal,which has the advantages of good directivity,high spatial resolution,strong anti-jamming ability,small volume and light weight.LFMCW radar can satisfy large time and bandwidth at the same time,and has high range resolution and operating range.By chirping continuous wave,the radial velocity of moving target can be accurately extracted,and the high-precision range and velocity measurement can be achieved.FFT is a fast algorithm for DFT operation,but DFT operation has fence effect,and there is a gap between adjacent spectral lines,which will make the maximum spectral line in the spectrum deviate from the actual position.Therefore,this paper uses Zoom FFT spectrum estimation algorithm to estimate the frequency spectrum of IF signal,which further improves the measurement accuracy of FMCW radar.The moving target will produce Doppler frequency shift,which results in rangeDoppler coupling and range error.This paper mainly studies the 2-D FFT algorithm of LFMCW signal to eliminate the range-velocity coupling phenomenon of moving target,and solve the range and velocity of moving target at the same time.CFAR is an effective method to detect signals from noise and clutter.In this paper,2-D CFAR detection is used to process the results of 2-D FFT.The range and velocity measurement of multi-target FMCW lidar is realized,and the clutter and noise are effectively suppressed.The following is the main research content of this paper:Firstly,according to the structure and measurement principle of LFMCW triangular wave lidar,the LFM signal,FMCW transmitting signal,echo signal and IF signal are modeled,and the characteristics of FMCW signal are analyzed.Then,aiming at the fence effect of DFT operation,several frequency correction algorithms are compared,and Zoom-FFT algorithm is proposed for spectrum estimation,which improves the ranging accuracy of stationary target.In addition,the ambiguity function of symmetrical triangular LFM signal is studied,and the range resolution and velocity resolution of LFMCW lidar are obtained.Aiming at the range-velocity coupling phenomenon caused by Doppler frequency shift of moving target,a 2-D FFT algorithm is proposed to decouple the range velocity,and the range and velocity of moving target are obtained.Finally,the method of 2-D CFAR combined with two-dimensional FFT is proposed to measure the range and velocity of moving target.On the basis of accurate measurement of range dimension and Doppler dimension,CFAR detection is carried out in range dimension and Doppler dimension respectively,and a new highdimensional signal processing method of FMCW lidar is proposed,which provides for the hardware realization of the ranging speed measurement algorithm for lidar.