“…By analysing the patterns of its wireless signal, today's AP has evolved beyond a pure WiFi router, but is also widely used as a type of 'sensor device' to enable new services for human sensing. Particularly, recent studies have found that WiFi signals in the form of Channel State Information (CSI) [1], [2] are extremely promising for a variety of devicefree human sensing tasks, such as occupancy detection [3], activity recognition [4], [5], [6], [7], fall detection [8], gesture recognition [9], [10], human identification [11], [12], and people counting [13], [14]. Unlike the coarse-grained received signal strengths, WiFi CSI records more fine-grained information about how a signal propagates between WiFi J. Yang, X. Chen, D. Wang, H. Zou and L. Xie are with the School of Electrical and Electronics Engineering, Nanyang Technological University, Singapore (e-mail: {yang0478,dazhuo001,zouh0005,elhxie}@ntu.edu.sg).…”