Research On Vital Signs Detection Technology Based On Millimeter-wave Radar

Respiration and heartbeat are important vital signs of human.Compared with the traditional contact methods,that using the non-contact detection technology based on radar to measure respiration and heartbeat has been widely concerned in some application scenarios,such as home monitoring,earthquake relief and epidemic prevention and control and so on.Compared with continuous wave radar and ultra-wideband radar,frequency modulated continuous wave radar plays an important role in the field of vital signs due to its characteristics of low power consumption,simple structure,strong antiinterference ability and high resolution.The 77 GHz millimeter-wave radar is studied in this paper to measure respiration and heartbeat from the single-receiver antenna system and multi-receiver antenna system.The main research work is as follows:(1)The signal model of vital signs based on millimeter-wave radar is presented in detail.Aiming at reducing the interference of I/Q data,we provide a detailed analysis of the geometric relations of DC offset,gain and phase imbalance in the frequency domain and in the complex plane respectively,then the corresponding compensation is derived.(2)For multi-target scenarios in complex indoor environment at different radial range,a method of range bin selection for vital signs targets is proposed by combining the motion model of respiratory with constant false alarm rate(CFAR)detection automatically.In order to reduce misjudgment by noise,the traditional smallest of CFAR detector is improved and an adjustment factor is introduced to make it suitable for the extraction of vital signs in multi-target scenarios.(3)In order to reduce low-frequency interference,the signal model of the vital signs is modified and a polynomial regression-based fitting method for the slight body displacement is proposed.By comparing the effect of different body displacement models through simulations and processing with the measured data,the results show that the method can restore the signal of vital signs effectively.To address the problem that respiratory harmonics tend to interfere with the estimation of heartbeat frequency,a recursive least squares adaptive notch is proposed to suppress respiratory harmonics,and simulations are conducted to compare with the method of respiratory harmonics signal reconstruction,and it is verified that the method in this paper can reduce the interference of respiratory harmonics on the estimation of heartbeat frequency.The analysis of the measured data is performed and the extracted vital signs are compared with the results of the electrocardiogram(ECG)monitor,the results of respiration rate and heart rate in this paper are close to those obtained by the ECG monitor,which verifies the effectiveness of the algorithm in this paper.(4)Aiming at distinguishing between multi-target at the same radial range,the signal model of multi-input multi-output(MIMO)radar is derived based on single-receiver antenna,a method of multi-target vital signs detection based on space-time-frequency combination are given,and a three-dimensional range-angle-doppler energy accumulation plane detection is proposed to obtain localization of vital signs targets,and it can reduce the interference of clutter and dynamic targets.Then,the digital beamforming is used to obtain the vital signs of the corresponding targets one after another.Finally,through the experimental analysis of different scenarios in this paper,the results show that the vital signs of different targets are extracted and distinguished better.