Keynote: From WiFi Sensing to Quantum Sensing: Toward a Wireless Sensing Theory.

WiFi/4G/5G based wireless sensing has attracted a lot of attention from both academia and industry in the last decade. However, most of the work focused on developing effective techniques for a certain application, very few work attempted to explore the fundamental sensing theory and answer fundamental questions such as the sensing limit, sensing boundary and sensing quality of WiFi/4G/5G signals. In this talk, I will first introduce the Fresnel zone model as a generic theoretic basis for device-free and contactless human sensing with WiFi/4G/5G signals, revealing the relationship among the received CSI signal, the distance between the two transceivers, the location and heading of the sensing target with respect to the transceivers, and the environment. Then we propose to define the Sensing Signal to Noise Ratio (SSNR) as a new metric to inform the sensing limit, sensing boundary and sensing signal quality of WiFi/4G/5G-based human sensing systems. In order to further increase SSNR and push the wireless sensing limit, we explore the Rydberg theory about how the Rydberg atom interacts with RF signals and develop the world first Rydberg quantum sensing system which senses tiny variations of RF signals caused by human activities, showing significant performance increase compared to WiFi or Radar based sensing systems.