Device-Free Motion Detection via On-the-Air LTE Signals

Wireless signals not only carry the information of data but also encode the information of propagation environments. The motion of an object can be sensed by analyzing the variation of channel-state information. Combining the function of wireless sensing and communication will further enhance the capability of smartphones. LTE signal, which is always on the air and is seamlessly covered, is a perfect external illuminator for wireless sensing. In this letter, we study the device-free moving object detection via LTE signals. We build a prototype to receive on-the-air LTE signal and extract the real-time channel response. The existence of a moving object is recognized by the amplitude of the interfered multipath, and the moving speed is derived by the phase of the dynamic reflection. The detection probability and discovery region are investigated, and field experiments are conducted to validate the analyses.