Research On Anti-interference Method Of Millimeter Wave Biological Radar

Millimeter-wave biological radar can detect respiration and heartbeat signals from a long distance.Compared with the traditional way,it can bring more comfortable and convenient experience to the human body,therefore it has gradually become a research hotspot in the field of radar.Millimeter wave radar is not only used in vital signs detection,but also widely used in weather forecasting,security,military,and intelligent driving assistance system.As the number of millimeter wave radars increases,the interference between radars may occur.Interference between radars will increase the noise floor of the signal,while respiratory and heartbeat signals are relatively weak,therefore vital signs will be drowned out.In addition,because the second,third and fourth harmonic frequencies of respiratory signal may be in the range of heartbeat frequency,it is difficult to correctly extract heartbeat signal.Therefore,this paper focuses on the above two problems,and the main work is as follows:(1)The interference in the detection of vital signs by millimeter wave biological radar is analyzed.Firstly,the influence of environmental clutter and mutual interference between millimeter wave radars is analyzed.For environmental clutter interference,the mathematical model and frequency domain characteristics of clutter interference are analyzed,and it is proved by simulation experiment.For the mutual interference between millimeter wave radars,the mathematical model and time-frequency domain characteristics of the interference are analyzed,and the influence of the mutual interference between millimeter wave radars on vital signs detection is theoretically analyzed.Then,the theoretical analysis is verified by the simulation of the mutual interference of vital signs by radar.For the interference of respiratory harmonics,the frequency range of respiratory harmonics may be within the frequency range of heartbeat signal,thus affecting the extraction of heartbeat signal.The effect of third harmonic of respiration signal on heartbeat signal is verified by simulation experiment.(2)The detection of vital signs under the mutual interference of millimeter wave radar is studied.An improved morphological component analysis algorithm is proposed to suppress the interference,and the adaptive parameters variational mode decomposition algorithm is proposed to extract the respiratory and heartbeat signals.Firstly,the interference signal is determined by the proposed detection algorithm,then the interference signal and the expected signal are separated by using the different sparsity of the expected signal and the interference signal in different sparse domains to suppress the interference.Although the interference is effectively suppressed,the sparse domain is not absolutely sparse,leading to the existence of residual noise.Therefore,the adaptive parameters variational mode decomposition algorithm is proposed to extract the respiratory and heartbeat signals from the signals with residual noise.The energy loss rate as the index to optimize the parameters,and adaptively adjusts the step size of the penalty value according to the center frequency of the mode.The experimental results show that the improved morphological component analysis algorithm can effectively suppress the interference,and the adaptive parameters variational mode decomposition algorithm can effectively extract the respiratory and heartbeat signals.(3)The heartbeat signal detection under respiratory harmonic interference is studied.The wavelet separation algorithm is proposed to separate respiratory harmonic and heartbeat signal.Firstly,the principle of wavelet technology is analyzed,and the multiresolution characteristic of wavelet is explained.Then,the correlation method is used to select the mother wavelet and the energy method is used to select the decomposition layers.Finally,the heartbeat signal is selected according to the method of energy proportion.Experimental results show that the wavelet separation algorithm can effectively separate respiratory harmonics from heartbeat signals,and the energy ratio method can correctly select heartbeat signals.