ABSTRACT
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The development of localization technologies and the growing importance of ubiquitous and context-aware computing have led to a growing business interest in location-based applications and services. Most applications need to locate or track physical assets inside buildings accurately, thus the availability of advanced indoor positioning has become a key requirement in some markets. Unfortunately, this requirement cannot be met by the global positioning system (GPS), which is unable to provide valid location information in most existing indoor environments-especially far indoorsbecause the signals transmitted from the GPS satellites are blocked by walls. In addition, the GPS often fails in urban canyons due to buildings obstructing the path between the receiver and the satellites. Possible alternatives include wide area cellular-based positioning systems such as global system for mobile communications (GSM), general packet radio service (GPRS), and universal mobile telecommunications system (UMTS), but they are not accurate enough for some stringent location-based applications. Hence, localization techniques specifi cally designed for use indoors are currently being researched and developed in order to complement the GPS so that the continuous tracking of mobile targets, regardless of their environments, becomes feasible.
