Remote Vital Signal Detection Using Ambient Noise Cancellation Based on Beam-Switching Doppler Radar

The remote vital signal detection using the Doppler radar is proposed to reduce the measurement errors caused by environmental factors, including the subject’s body movements. The proposed method for remote detection is based on the radar with beam control, which allows for adjusting the antenna’s radiating direction through spatial synthesis of an antenna array. By altering the beam direction, the proposed radar distinguishes between vital signals (respiration and heartbeat) originating from the asymmetrical movements of the human lungs and heart and the noise signals introduced by environmental factors, such as stationary clutters and the subject’s body movements. The respiration and heartbeat are extracted from the raw radar data obtained from each direction with signal processing techniques, including dc offset removal and random movement cancellation, which are based on the relationship of Bessel functions. An additional algorithm for extracting the correlated data from the acquired vital signals and filtering sudden variations significantly enhances the detection accuracy in the proposed method. In a practical test scenario, the vital signs of a subject walking at 2 km/h on a treadmill were measured in the surroundings with stationary clutters using the proposed method with a beam-switching 5.8-GHz radar module at a distance of 1 m. The measurement results demonstrated error rates of less than 3 beats per minute (bpm) for respiration and 4.2 bpm for heartbeat, compared with reference values obtained from contact-type sensors.