  Human behavior recognition has been considered as a core technology that can
facilitate variety of applications. However, accurate detection and recognition
of human behavior is still a big challenge that attracts a lot of research
efforts. Recent advances in the wireless technology (e.g., Wi-Fi Channel State
Information, i.e., CSI) enable a new behavior recognition paradigm, which is
able to recognize behaviors in a device-free and non-intrusive manner. In this
article, we first provide an overview of the basics of Wi-Fi CSI based behavior
recognition. Afterwards, we classify related applications into
three-granularity: signals, actions and activities, and then provide some
insights for designing new schemes. Finally, we conclude by discussing the
challenges, possible solutions to these challenges and some open issues
involved in CSI based behavior recognition.
