A distributed positioning system based on real-time RSSI enabling decimetric precision in unmodified IEEE 802.11 networks

In this paper we present a distributed positioning system for indoor environments based on a network of compact independent anchor nodes operating as specialized WiFi access points. Each node is built with component-off-the-shelves and it is capable of standard IEEE 802.11 connectivity at 2.45 GHz. The enabling technology for the localization is the Switched Beam Antenna (SBA) equipped in each node, which permits a space division multiple access at network-level. The positional information is the result of a maximum likelihood estimation driven by the expected signal space partition of the constellation, and it is tolerant to noisy power measurements, such as Received Signal Strength Indicator, thanks to angular filtering capability of the SBA, which in addition operates in circular polarization. Experimental validations demonstrate the performance of a 3-anchors network, operating within the IEEE 802.11 protocol, monitoring a single nomadic node inside a 7 m2 indoor square area. It results that 68% of the square area is covered with a localization error below 50 cm, with a mean error of 47 cm. Inside the triangular mesh defined by the three anchors, the mean error drops to 39cm, with 88% of the area being below 50 cm. In addition, the maximum error is always below 77 cm.