IQ Signal Demodulation for Noncontact Vital Sign Monitoring Using a CW Doppler Radar: A Review

Using a Doppler radar for noncontact detection is a promising way to monitor vital signs of a subject more conveniently than other common contact medical devices, but has many challenges including null-point issue, dc offset, and nonlinear distortion. The wireless property of a radar system easily affects the Doppler signals, so it needs a demodulation method to obtain the vital sign information. Furthermore, detecting precise information for respiration rate (RR) and heart rate (HR) of the subject needs further signal processing to extract the target signals from the demodulated signals at various interference levels. Hence, this study reviews research on continuous-wave (CW) Doppler radar, signal demodulation and subsequent signal processing to address the problems for noncontact vital sign monitoring.