Through-Wall Human Sensing with WiFi Passive Radar

Through-wall human sensing is of high interest for both military and nonmilitary applications, including counter-terrorism and law enforcement purposes, particularly in the modern, highly urbanized environment. Conventional active radar sensors possess good performance, however, at the expense of high cost and complexity of the transmitter/receiver design. This article demonstrates the effectiveness of a passive through-wall human sensing technique using opportunistic WiFi signals. With a simple software-defined radio receiver and advanced signal processing techniques, the position of indoor WiFi access point can be accurately localized, and its signal can be exploited to clearly detect the Doppler/micro-Doppler of human motions inside the room. Compared to the results in the current literature, this article demonstrates better detection sensitivity and capability to sense not only major motions such as walking and waving hand, but also very small human motions such as keyboard typing and breathing. In addition, an iterative adaptive approach is applied to effectively improve the Doppler resolution of WiFi passive radar. These enhanced sensitivities greatly expand the potential of WiFi passive radar for through-wall sensing applications.