ABSTRACT
Locations of devices or objects are important information in many applications. This is particularly true for wireless sensor networks, which usually need to determine devices’ context. For outdoor environments, the most well-known positioning system is the global positioning system (GPS) [5]. This positioning system uses 24 satellites set up by the U.S. Department of Defense to enable global threedimensional positioning services; it has two levels of accuracy: stand positioning service (SPS) and precise positioning service (PPS). The accuracy provided by GPS is around 20 to 50 m.
