Signal Preprocessing for Heartbeat Detection Using Continuous-Wave Doppler Radar

A signal preprocessing method is proposed for effectively monitoring heartbeats from signals obtained using a continuous-wave (CW) Doppler radar. The proposed method consists of windowing with a size optimized for heartbeat detection, detrending to minimize the effect of dc drift, and data reconstruction to increase the fast Fourier transform (FFT) resolution. A window size of 3 s effectively extracts the heartbeat alone from the received signals of the CW radar, which comprised respiration, motion, and heartbeat signals. The effect of the low-frequency noise caused by the internal heat generation of hardware components is reduced by the detrending technique, and the low resolution of the FFT, due to a small number of samples, is improved through reconstruction by combining data from three windows. The signal-to-noise ratio of the measured waveform was improved to 5.83 dB using the proposed method in a 5.8-GHz CW radar. For the data acquired for 60 s, the proposed method showed a heartbeat detection accuracy of 95.8% by using a signal processing time 13% lower than that of the conventional method.