| In recent years,the research of auto-driving systems and advanced driving assistant systems(ADAS)has been widely concerned.As an important part of the two systems,the millimeter-wave automotive radar can measure distance,speed and angle information of targets around the vehicle,and reduce the probability of traffic accidents effectively.However,the performance of detecting weak moving targets degrades in the actual traffic environment,due to the short wavelength and low transmitting power of millimeter-wave automotive radar signal.Compared with 24 GHz automotive radar,77 GHz automotive radar has the advantages of larger signal bandwidth,larger equivalent isotropically radiated power(EIRP)and higher integration,so the application of 77 GHz millimeter-wave automotive radar has vaster prospects.This thesis takes 77 GHz millimeter-wave linear frequency modulated continuous wave(LFMCW)automotive radar as the research object,and studies the key signal processing technology of automotive radar.The main research contents and innovations are illustrated as follows:Firstly,different transmission signals of automotive radar are studied,and the advantages and disadvantages between the slow-ramp triangular LFMCW signal and the fast-ramp sawtooth LFMCW signal are compared.The theoretical basis of the beat signal processing of fast-ramp sawtooth LFMCW automotive radar is studied in detail,including the theory of range and velocity measurement based on two-dimensional fast fourier transform(2D-FFT),and angle measurement theory based on angle FFT.Secondly,this thesis studies the preprocessing method before the beat signal are subjected to FFT,in order to reduce the influence of continuous wave radar internal interference on the beat signal.A moving target indicator scheme based on coherent accumulation and coherent subtraction in slow-time dimension is proposed,aiming at the problem that weak moving targets are masked by stationary clutter in Doppler dimension.Three commonly used mean-level constant false alarm rate algorithms are analyzed and compared to increase the detection probability of automotive radar finding targets in complex environments.According to the characteristics of 2D-FFT spectrum broadening of radar common targets,a peak grouping algorithm for determining the center position of targets is proposed.Subsequently,aming at the problem that the insufficient performance of angle measurment using angle FFT,the principle of expanding aperture of the receiving array antenna based on multiple-input multiple-output(MIMO)radar is studied,and the angle measurement principle of multiple signal classification(MUSIC)algorithm is further studied.For the angle measurement of related sources,this thesis employs the MUSIC algorithm based on forward-backward spatial smoothing.Finally,experiments of the stationary target scene and the real road scene are conducted by using the AWR1642 millimeter-wave radar.The correctness of the signal processing algorithm proposed in this thesis is verified by comparing the processing result of the beat signal with the experimental scene. |
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