Research On Vital Signs Detection Algorithm Based On 77GHz FMCW Radar

The article uses 77 GHz FMCW millimeter wave radar to detect human vital signs including respiration and heartbeat in a non-contact manner.Although there are many researches on vital signs detection based on FMCW radar,there are still some problems,such as respiratory harmonic processing,elimination of random body motion noise,suppression of dynamic clutter and static clutter in complex environment,accurate positioning and tracking of multiple targets,etc The development of radar vital signs system to high stability and high accuracy is limited by the existence of the problems in radar vital signs system.In view of the above problems,starting from the principle of FMCW radar,this article deduces the expression of IF signal of single cycle and multi cycle chirp signal in vital signs detection in detail,and then we samples the multi cycle IF signal in fast and slow time.From the perspective of power spectrum formula,we analyzes the principle of distance detection based on 1D-FFT and the principle of phase extraction in respiratory heartbeat signal detection based on 2D-FFT.In terms of respiratory harmonic processing,firstly,in the aspect of respiratory harmonic judgment,this article proposes two methods: the method of judging respiratory harmonic from 2D-FFT frequency domain combined with respiratory fundamental wave,and the method of judging respiratory fundamental wave according to the time domain peak mean square deviation of heartbeat signal;in terms of respiratory harmonic elimination,two methods are also proposed: The first method is to detect respiratory harmonics according to respiratory fundamental frequency and other spectral peak frequencies on 2D-FFT spectrum,and use notch filter to remove harmonics.The second method is to use the second-order difference of phase to reduce the influence of respiratory harmonics.In the multi-target location and tracking,this article mainly studies from range and azimuth detection those two aspects.In the aspect of range location,this article proposes a multi-target range tracking and locking algorithm,including target effective region locking for 1D-FFT spectrum data,extracting the first 3K largest peaks(K is the number of potential targets),peaks’ range bin mode statistics,selecting the peaks’ range bin according the number of occurrences,range bin de-duplication,K potential targets’ range bin selection,potential targets’ phase extraction,phase unwrapping,and so on This algorithm can effectively distinguish human targets from static clutter,and distinguish different human targets to achieve high-precision range detection.In the aspect of azimuth location,the target location method based on 1D-FFT and MVDR beamforming and the target location method based on 3D-FFT are proposed,which can suppress the dynamic clutter and reduce the amount of calculation.In the respiratory and heartbeat signal frequency estimation,this article uses three spectral estimation algorithms: 2D-FFT,MUSIC and MVDR algorithm.Hundreds of experiments were carried out on several different objects.According to the experimental data,the heartbeat detection errors of the three algorithms were 3.35%,4.37%,2.75%.The experimental results show that the performance of 2D FFT algorithm is the best among the three algorithms in terms of stability,accuracy of heartbeat detection and calculation complexity.Finally,this article uses Python to design the radar vital signs detection demonstration system,and realizes the UART communication between the upper computer and the lower computer.