Robust Device-Free Proximity Detection Using Wifi

Motion detection based on WiFi signals has gained much attention recently. However, most of the existing approaches can only detect motion in a large coverage area without knowing how far the target motion happens. In this paper, we propose two robust and responsive features in the frequency dimension, which are sensitive to the distance of motion, and establish the connection between the underlying radio propagation properties and the features. Extensive experiments in various environments demonstrate that the proposed proximity detection scheme can achieve true positive rates greater than 90% and 98% in corridor and room scenarios, respectively, while maintaining the corresponding false positive rates less than 5% and 1%. The responsiveness of the proposed scheme is verified by measured detection delays within 1.5 s for a detection distance of 2 m.