Non-Line-of-Sight Vital Sign Detection Using Multipath Propagation of UWB Radar

Noncontact detection of vital signs, such as respiration and heartbeat, can be implemented with high accuracy using commercial radar sensors. However, the task is more challenging for non-line-of-sight (NLOS) scenarios, wherein the direct path between the radar and target is blocked. In this letter, we propose a method for detecting the vital signs of an NLOS target using the multipath propagation characteristics of the ultrawideband (UWB) radar. The UWB radar is suitable for the NLOS target detection because the multipath-rich channel information can be estimated using an extremely narrow pulse with a wide bandwidth. By analyzing the multiple propagation paths of the NLOS scenario, we demonstrate that the second-order path is the most appropriate for vital sign detection. The experimental results showed that the proposed NLOS vital sign detection method can estimate respiration and heartbeat frequencies within the frequency resolution.