A common approach to estimating node positions is direct mea- surement or triangulation against landmarks in the immediate one- hop vicinity. Active Badge [24] relies on the closest infrared re- ceiver to locate specialized beacons carried by tracked assets. RADAR [19] relies on a centralized database of signal fingerprints from land- marks obtained at all locations and orientations to localize a node. Lorincz andWelsh [14] propose a similar RF fingerprint-based node localization technique that relies on strength signatures and a dis- tributed database. Cricket [25] relies on time difference of arrival between radio and ultrasound signals to measure distances to ded- icated beacons. VORBA [26] uses angle of arrival measurements from.
