14.4 LOCATION TRACKING AND PREDICTION
14.4.1 Location Tracking
For complete operation, the smart office system needs a service that provides the current positions of the users. This service should at least be able to determine the room a user is currently staying in. Therefore several location-tracking techniques exist. We will give an overview of some alternatives before explaining our own approach and experiences.
Pathbreaking work on positioning systems was done by Want et al.  with their Active Badges. They employed a room-accurate positioning system based on IR LEDs and sensors. A radio technique, wireless LAN, was employed in the RADAR system by Bahl et al. . Especially this work discusses a wide range of methods for analyzing the measurements. Other radio techniques were analyzed by Feldmann et al. (Bluetooth ) or Ni et al. (RFID ), among others. For all mentioned techniques, a medium error of about 2–5 m was reported. ARIADNE  promises to amend this, and also not to need large overhead for the recording of a reference map through the automatic construction of radio propagation maps. Here, the medium error reported drops to about 1 m.
Definitely better outcomes can be gained by the use of ultrasonic [13, 39]. Here, the error lies at 10 cm resp. 50 cm in 95% resp. 90% of all cases. However, these gains must be seen alongside with the high costs for the technical equipment and its installation.
Due to the high inaccuracy or the high costs for existing systems, ...