songhee-cho/paper-review

Remote Heart Rate Sensing with mm-wave Radar

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Abstract🍐

There are so many patients who need a continuous vital sign monitoring. Monitoring a patient with a wearable device such as using electrode-based electrocardiograhpy(ECG) signal recording device for a long time is very inconvenient. One possible solution is using contactless sensors such as radars to find vital signs of the subjects. In this paper, we demonstrate the use of frequency-modulated continuous wave(FMCW) radar operating at 77 GHz for monitoring a patient's heart rate in a retirement environment. Several experiments were conducted to validate the reliability of the radar responses. Finally, the whole system is tested in a bedroom with the radar above a bed and a patient lying on it.

Keywords: FMCW radar, health monitoring, wireless sensors, heart rate, vital monitoring.

내용 정리🧙🏻

  • FMCW radar를 통해 heart beating/breathing으로 인한 chest motion 측정
  • vital sign detection에서
    • 필요한 것: higher Doppler resolution → sensor operation frequency ∝ Doppler resolution
    • 필요하지 않은 것: UWB radar
  • FMCW radar의 원리
    • generator: chirp signal 생성, 시간에 따라 linear하게 증가하는 frequency
    • transmitter
    • receiver: correlation을 통해 object의 location과 velocity 정보가 담긴 IF(intermediate frequency) signal
  • estimation 종류
    • spectral algorithm: desired range phase의 Doppler FFT(Fast Fourier Transform) sample을 처리
    • temporal algorithm: time domain heart waveform 처리, # of peak를 셈
    • autocorrelation-based algorithm: heart wave waveform의 autocorrelation을 통해 first two peaks의 time difference를 고려할 수 있음
  • heart rate detection algorithm 순서
    • range FFT
    • unwrap phase
    • Doppler FFT
    • BPF(bandpass filter)
    • average of (1), (2), (3) estimations
  • 실험을 위한 set 구성
    1. range와 Doppler 관점에서 sensor accuracy 측정
    2. heart rate detection algorithm을 위한 actual step
  • 실험 결과
    • algorithm 처리 결과 waveform의 shape이 ECG signal과 유사한 behavior를 보임
    • behavior of ECG signal: a high peak followed by a lower and wider peak corresponding to the R and T waves respectively

알게 된 내용🧠

FMCW radar를 통해 얻은 heart rate 그래프를 통해 ECG signal 정보를 추출해 낼 수 있는 알고리즘 존재

질문 🤔

  1. 왜 77GHz에서 radar operation을 진행하는가?
  2. 해당 algorithm을 처리했을 때 heart rate로부터 ECG signal 정보가 추출되는 것이 단지 결과론적 우연이 아니라 두 데이터 간에 실제로 유의미한 관계가 존재하는가?