Adding indoor location capabilities to an IEEE 802.11 WLAN using real-time RTT measurements

An accurate real-time application which locates mobile users in an indoor environment is highly demanded in hospitals, warehouses, etc., provided that minor changes in their infrastructure are required. Most present-day location techniques require a great calibration effort, or special devices which are not cost-effective. Avoiding these needs, this paper implements an autonomous positioning technique based on IEEE 802.11 RTS/CTS two-frame exchange in a real scenario. Two estimators of the delay profile measured are analyzed and a linear regression of them at each distance is performed from which the distance between a mobile user and an access point is estimated. Experimental results, without any tracking information nor nonline-of-sight mitigation, reveal the effectiveness of the proposed method.