I. Introduction
Channel state information (CSI)-based application development, including healthcare, security and Internet of Things (IoT), has received immense attention over the past years. In terms of activity recognition, many traditional approaches with carry-on sensors [1]–[4] or cameras [5] have achieved desirable performance. However, it is now considered as inconvenience to ask users to wear sensors all the time because of the battery charge issues. Besides, it also raises many privacy security concerns on camera-based systems. On the contrary, CSI can be extracted from commercial wireless devices instead of requiring extra costs of equipments as in traditional approaches. Therefore, it has attracted broad interests in recent years.