On Developing Dependable Positioning

Developing indoor positioning remains challenging, especially when we consider an emergency and disaster scenario wherein positioning infrastructures fail. In this case the objective consist in providing to first rescuers (firefighters) robust and reliable positioning under harsh conditions. Toward this goal, we present a navigation system, then, we survey the class of faults that threaten this system along with possible ways of handling it. I. POSITION AND NAVIGATION The proposed positioning system makes use of active and contact-less Radio-Frequency IDentification (RFID): firefighters are equipped with RFID readers while RFID tags are disseminated in the building so as to serve as anchors. The pair-wise distance separating the reader to an anchor, is estimated based-on the Received Signal Strength (RSS)[1][2]. The resulting distance is used to multilaterate the position of the reader. Given that the signal may be perturbated (§1), successive RSS measurements are sanitized, i.e., filtered: infrequent values and outliers are removed so as to ensure that the largest quorum of consistent values is selected. Then, based on the measurements provided by m tags, the position (xp, yp) is approximated by multilateration. Multi-laterating consists in determining the intersection of m circles; each circle C i being centered on an anchor and characterized by a radius corresponding to the measured RSS: (xp − xi) 2 + (yp − yi) 2 = RSS i (1) with (xi, yi) defining the anchor’s coordinates. Multilateration can be seen as resolving a least-squared problem, i.e., finding the