“…Several studies have already shown the possibility of extracting physical space information from radio waves using wireless sensing. This has been applied for various purposes, including device localization [3]- [7], [22]- [29], device-free user localization [8], [9], [23], [30]- [32], gesture recognition [10], [11], [33], [34], device-free motion tracking [12], [35], [36], RF imaging [37]- [39], crowdedness estimation [40], activity recognition [13], [14], respiratory monitoring [15], [41], heart rate monitoring [41], material sensing [16], [42], soil sensing [17], keystroke recognition [18], emotion recognition [19], in-body device localization [43], object state change detection [20], touch sensing [44], device proximity detection [45], device orientation tracking [46], and human detection through walls [38], [47], [48]. While these studies have explored new possibilities using an application-specific approach, the present work is unique in that it attempts to construct a general-purpose wireless sensing technique.…”