A Coarse-to-Fine Robust Estimation of FMCW Radar Signal for Vital Sign Detection

This paper presents a robust vital sign detection system, which uses 77GHz mmWave radar sensor. Two essential signals breathing and heart beat rate are estimated by measuring the change in phase of FMCW signal with time. Breathing harmonics have significant impact on the heart beat spectrum. In order to extract heart beat signal, a coarse-to-fine estimation approach is developed. The first contribution of this approach is to predicts the heart beat rate in the time domain of the unwrapped phase signal, where an adaptive threshold is calculated to filter invalid wave peak-valley pairs. Furthermore, observation window size selection for the vital sign detection is optimized by two criteria: peak difference and local SNR. The second contribution is to estimate heart beat rate in spectral domain based on the predicted rate. Experiments show that this coarse-to-fine approach gives a robust estimate of heart rate as well as breathing rate.