| Car driving safety is an eternal topic,and people have made great efforts to this end.Currently in the era of intelligence,the imagination of autonomous driving technology has gradually become a reality.The application of radar as an "eye" of smart cars is also ubiquitous,including speed-measuring ranging radar,adaptive cruise control radar,anti-collision radar,and other vehicle monitoring radars.In this paper,aiming at the help of automobile lane change,the triangular wave frequency modulated continuous wave(FMCW)ranging technology is used,and the 24 GHz radar is used as the radar front end.A low-cost radar ranging system is researched and implemented.The core of FMCW technology is to measure the time difference of echo signals.The measurement method is to add a time identification to the transmitted signal by frequency modulation technology.Finally,the difference frequency of the transmitted signal and the echo signal is used to measure the distance of the target.The speed of the target can be measured by Dopp.Le frequency.Based on the above principles,this paper analyzes and designs the hardware structure of the FMCW radar ranging system,including the radar front end and signal processing module.Under the premise of ensuring the system measurement parameters,this paper selects K-LC2 millimeter wave radar as the signal transceiver,and selects STM32F407VET6 as the main controller and digital signal processor.Through the analysis of the echo signal,the bandpass filter is designed to filter the signal.The automatic gain control amplifier is used to ensure the amplitude range of the signal.Then the data is sampled by the AD module to realize the distance and velocity measurement.In fact,when the vehicle speed is low,the external noise and the clutter are extremely disturbed,which makes the measurement of the distance difficult.At this time,the safety hazard is small.Therefore,the system adds a CAN communication module to complete the extraction of the vehicle speed.Only when the vehicle speed is high,the ranging function is enabled.In order to realize the alarm function to the driver,the system designed the alarm LED light control module and the turn signal output module.Experiments show that the above hardware structure can achieve the expected goals.Considering that external noise and interference will make it difficult to extract the target signal,the system must have certain noise processing and interference suppression capabilities.To this end,this paper analyzes the types of radar signal interference and signal detection algorithms.In the signal processing process,the noise cancellation is realized by parallel processing of the I and Q signals.On the basis of analyzing a large number of documents,it is proposed to use the unit average constant false alarm algorithm to complete the detection of radar signals.By adaptively adjusting the decision threshold,the detection probability of the system can be improved.In order to further suppress the clutter interference,the method of multiple accumulation of signals is used to reduce the false alarm probability.The key to ranging and speed measurement is to find the frequency of the IF signal.The Fourier transform can well extract the signal spectrum.The algorithm adopted is Fast Fourier Transform(FFT).By analyzing the spectrum leakage and the fence effect,it can be known that the algorithm will have certain error in the ranging accuracy.Aiming at the shortcomings of FFT algorithm,this paper studies the chirp Z-transform algorithm which improves the accuracy of ranging.This algorithm can significantly improve the spectral resolution and further reduce the effect of the fence effect.Finally,the paper completed the real vehicle test and spectrum analysis of the FMCW radar ranging system.In the process of real vehicle test,the signal spectrum is observed by the host computer software,and the state and cause of the signal are analyzed.Then the system’s lane change auxiliary function is verified.The overall experimental results show that the system is basically implemented and the test results are stable and reliable. |
