Non-contact Vital Signs Detection in Dynamic Environments

Accurate phase demodulation is essential for vital sign detection using millimeter wave radar. The time-varying DC offsets and phase imbalance in complex scenarios can seriously interfere with the performance of demodulation. This letter proposes a novel DC offset calibration algorithm as well as a Hilbert and differential cross-multiply (HADCM) demodulation algorithm to solve the time-varying imbalance terms. It works by estimating the time-varying DC offsets from neighboring peaks and valleys, and uses the differential form as well as the Hilbert transform of the I/Q channel signals to obtain the vital sign signal. Simulations and experiments have verified the effectiveness of the novel algorithm under low signal-to-noise ratio. Compared with the existing demodulation algorithms, the proposed algorithm can not only recover the original signal in complex environments more accurately, but also reduce the interference of noise on the signal.