Research And Implementation Of Weak Signal Detection Of Vital Signs Based On Millimeter Wave Radar

The detection of vital signs parameters based on radar has great potential in continuously monitoring the health status of users.Compared with the traditional contact instruments such as wearing electrode pieces and sensing devices,it avoids the discomfort of wearing the equipment and is more suitable for health monitoring in daily life.The vital sign signal is extremely weak.How to extract the vital sign signal from the complex echo signal is the difficulty of research.This subject designs a realtime vital sign detection system based on 77 GHz linear frequency modulated continuous wave(FMCW)radar,which can realize human target positioning and vital sign parameter detection at the same time.The main work includes:(1)The modulation of frequency and phase of FMCW IF signal for small displacement is analyzed,the vital sign signal extraction scheme is determined,the advantages of radar hardware platform are analyzed,and the radar parameters are configured in combination with the resolution required for human target positioning and the characteristics of vital sign signal.(2)Aiming at the problem that it is impossible to accurately locate human targets in complex environment,which affects the acquisition of vital signs signals,a 2D human body positioning algorithm is designed.Firstly,in the range direction,the multi delay line weighted pulse canceller is used to suppress environmental clutter and improve the accuracy of human positioning in the range dimension.Secondly,in the azimuth direction,the beam scanning is used to obtain angle information,and the characteristics of multiple input and multiple output(MIMO)radar are used,Combined with the time division multiplexing mode of transmitting antenna,the virtual antenna is extended to improve the angular resolution.Finally,combined with human body positioning information and beamforming technology,spatial filtering is realized to strengthen the human body echo signal.The measured data show that the algorithm can accurately locate the human body in a complex environment within 5meters from the radar.(3)By tracking the target position of human body and combining the phase change of intermediate frequency signal to obtain vital signs signal,band-pass filters of different frequency bands are designed to separate respiratory and heartbeat signals.For respiratory frequency estimation,a frequency estimation method based on short time Fourier transform(STFT)and auto correlation(AC)is proposed to improve the detection accuracy under different respiratory states;For heartbeat frequency estimation,a frequency estimation method based on STFT and time domain peak spacing is proposed to improve the accuracy of single frequency domain detection,and Kalman filter is used to process the final detection results to improve the stability of detection data.(4)A real-time vital signs detection system based on millimeter wave radar is built.The upper computer is designed through QT software,and the UART communication between the upper computer and the lower computer is realized.A large number of experiments have been carried out on the proposed real-time detection algorithm of respiratory and heartbeat frequency for different detection scenarios.The experimental results show that the accuracy of respiratory and heartbeat detection within 3 meters is more than 95%,and the accuracy of respiratory within 5 meters is more than 90%.