A Novel Frequency-Tracking Algorithm for Noncontact Vital Sign Monitoring

Noncontact vital sign monitoring, based on mm-wave frequency-modulated continuous wave (FMCW) radar, can be widely applied in elderly care, clinical diagnoses, and in-vehicle occupant detection. The radar can monitor the Doppler signal reflected by the chest displacement and then analyze the phase change of echo to get the respiration and heartbeat signals. This article proposes a frequency-tracking method based on an improved birth–death strategy to calculate vital sign rate in real-time. There are two main steps to estimate the vital sign rate from frames within a second. First, the M-Rife algorithm is employed to interpolate the frequency of each frame. Second, find the matching frequency points between the adjacent frames in a second by using an improved birth–death strategy and calculate the frequency ratio for each matching point link. Then, choose the longest link whose initial frequency is closer to the frequency at the last second. The value of the link tail will be a vital sign rate at the current second. The proposed method is simulated in a public noncontact vital dataset to verify its feasibility and accuracy. To further demonstrate the method, this article carried out a series of experiments. The experimental results show that the method has an accuracy rate of 98% for the heartbeat rate in real-time and reduces the effect of clutter and respiratory harmonics on the heartbeat rate.