Research On Key Technology Of FMCW Lidar Ranging And Velocity Measurement

LiDAR(Laser detection and ranging)is an extension of the radar concept.LiDAR is used for target detection using laser as transmitted signals.Information such as target range,speed and azimuth can be obtained through receiving return signals reflected by targets.Compared with microwave radar,LiDAR uses a laser with a shorter wavelength as the transmitting signal,so the laser beam emitted by LiDAR has the advantages of smaller divergence angle and better directivity,and can achieve higher range resolution and angular resolution.In modern measurement techniques,frequency-modulated continuous waves(FMCW)LiDAR combines the advantages of conventional radar and laser coherent detection.It is widely used in various fields such as military reconnaissance,automatic driving,and terrain reconnaissance due to its characteristics of wide measuring range,synchronous ranging and velocity measurement,high resolution,and strong anti-interference.It has a very broad application and development prospect.But in practice,the resolution,accuracy,and sensitivity of FMCW LiDAR are seriously affected by the frequency modulation nonlinearity and random noise of laser source.Therefore,how to suppress the influence of frequency modulation nonlinear and random noise has become one of the important research problems of FMCW LiDAR.At the same time,the decoupling of ranging and velocity measurement and large field of view high-resolution imaging are also one of the research hotspots in the field of FMCW LiDAR.The main contents of this thesis are as follows:(1)This thesis introduces the principle of ranging and velocity measurement of FMCW LiDAR studies the factors that affect the resolution and accuracy of FMCW LiDAR,and then analyzes the influence of frequency modulation nonlinear and random noise.(2)A high repetition frequency,high bandwidth and narrow linewidth FMCW LiDAR based on external modulation sideband filtering is designed,including system scheme,technical index and test scheme.(3)Aiming at the problem that there are mirror peaks in the spectrum of FMCW LiDAR system beat signal after Fast Fourier Transform(FFT),a mirror peak suppression algorithm,including ellipse fitting algorithm and non-orthogonal correction algorithm,is proposed to achieve effective suppression of mirror peaks in the spectrum.(4)In view of the large number of noise points in the generated point cloud image,two point cloud filtering algorithms are proposed,including amplitude threshold filtering algorithm and velocity clustering filtering algorithm.The amplitude and velocity characteristics of the point cloud are used to filter out most of the invalid noise points and retain the effective point cloud,and the FMCW LiDAR point cloud image is optimized.(5)For the problem of expanding field of view angle and improving angle resolution at the same time,a coaxial multi-field fusion FMCW LiDAR ranging velocity measurement design scheme is proposed,which can realize the coaxial multifield fusion detection at different distances,solve the problem of expanding field of view angle and improving angle resolution at the same time,and effectively suppress the crosstalk generated in the detection process,and a specific design scheme is given.(6)In order to realize the decoupling of range and speed,a dual-channel dualchirped FMCW LiDAR design scheme is proposed,which can realize the measurement of range and speed at the same time.At the same time,it has the advantages of high repetition frequency,high detection accuracy,high sensitivity and strong antiinterference ability.(7)The FMCW LiDAR system has been designed with frequency modulation signal repetition frequency rate up to 100 k Hz,frequency modulation bandwidth up to2 GHz,and signal linewidth less than 10 k Hz.The key technical parameters of the system,including frequency modulation nonlinearity,ranging/velocity measurement resolution,ranging/velocity measurement accuracy,have been measured,and the results have been obtained and analyzed.The outdoor vehicle test is carried out and the result of point cloud is given.(8)The main research results in the process of writing this thesis and the shortcomings of the current work are summarized,and the improvement direction of the future research work is prospected.