A WSN-based, RSS-driven, Real-time Location Tracking System for Independent Living Facilities

We present an indoor, real-time location tracking system (RTLS) based on a wireless sensor network (WSN) where the received signal strength (RSS) readings collected by immobile nodes (Pegs) from mobile (tracked) nodes (Tags) are translated into location estimates for the Tags. The process employs a database of samples previously collected from known locations; thus, the scheme falls into the category of profile-based solutions, with RSS readings being the only kind of input to the estimator. Compared to other schemes hinged on the same general idea, the novelty of our approach consists in systematically taking advantage of multiple transmit power levels at the Tags. This allows us to effectively emulate RFID-type of operation, when a nearby Peg can authoritatively identify the location by perceiving a weak signal from the Tag (indicative of the Tag’s immediate proximity), while otherwise falling back to elaborate fitting of multiple readings (collected by several Pegs) to produce a (possibly approximate) location estimate. The location service of our network is an add on to its other duties which consist in providing connectivity within an independent living (IL) facility for the purpose of inconspicuously monitoring the patients, detecting anomalies, signaling alarms, and so on.