RF signals can be used not only for data transmission, but also for environment sensing. In the indoor environment, signal generated by the transmitter propagates through multiple paths, such as direct radiation, reflection and scattering, and superimposes at the receiver, carring the information of the characteristics of the environment. It is not unusual to use radio for environment sensing. Typical applications include radar systems for detecting spacecraft and indoor localization with UWB. Compared with dedicated radar and even UWB signals, Wi-Fi has great advantages in ubiquity. However, Wi-Fi signals have narrow bandwidth, low time resolution and imperfect signal processing devices. Thus, it is necessitated to develop theory and technology for Wi-Fi based environment sensing, and achieve highly accurate environment sensing on commercial Wi-Fi devices. While both Wi-Fi and radar are not new, but for the first time, the combination of the two hit a spark of innovation in the field of mobile computing.
Wi-Fi based environment sensing technology has been widely applied. In security-sensitive scenarios, such as surveillance of confidential areas, disaster response, protection of important objects, etc., it needs to promptly detect the presence and activities of persons (staff or intruders) that do not carry any wireless devices in sensitive areas. Apart from security, passive human detection can be widely used in a variety of ubiquitous computing applications. For example, In museums, introduction of exhibits can be automatically displayed when visitors approach them; In supermarkets, items of most interest recently can be counted; Or in elevators and carriages, the number of passengers can be evaluated. In addition, Wi-Fi based environment sensing technology can be applied to detect fine-grained pose, gesture and breath, or tiny motions of human.