“…For example, time-of-arrival (ToA) [3], [6], [31], [32], [33] and direction-of-arrival (DoA) [34], [7], [35], [36] methods require a strong enough line-of-sight (LOS) signal component between the access point (AP) and the user, which is often not the case in indoor environments that contain a lot of obstacles and partitions. Fingerprint schemes [4], [5], [8], [37], [38], [39], [40], [41] don't require LOS, but require measurements from many different APs to get accurate results. Since the main reason of having a WLAN is for data transmission, there is no incentive to cover locations with multiple APs.…”