The indoor localization and positioning has been studied in a long history. The early indoor positioning system was Active Badge System [1]. It has used inside an office building. It transmits a unique infra red signal in interval 10 seconds. The detector was placed inside a building and set up as known position. It's detected the unique identifier and send the information into the location manager software. Although the system is successfully detecting the office staff, it suffers from several limitations. There are :
1) The scale is not well caused by limited range of infra-red ;
2) It suffer significant installation and cost of maintenance;
3) It works not very well with the sunlight.
Another system in indoor localization and positioning have been proposed in wide-area cellular network systems [2]. The measurement methods used were signal attenuation measurement, angle of arrival (AOA) and Time Difference of Arrival (TDOA). This system has been found effectively work in outdoor environment. In indoor environment, the system can't work properly because of the presence of multiple reflections by radio frequency (RF) signal.
In year 2000, Bahl and Padmabhan [3], have proposed RADAR system. It is known as RF-based localization system inside building. This system used the information of signal strength that collected at multiple receiver locations to do triangulation of the user coordinates. The system shows the ability of the system in user location estimation within a few meters of the actual position. The system also has potential to track user in a high degree of accuracy.
References
[1] R.Want ,A.Hopper, V.FalcaoJ. Gibbons., “The Active
Badge Location System,” ACM Transactions on Information
Systems, Vol. 40, No. 1, pp. 91-102, January 1992.
[2] S. Tekinay, “Wireless Geolocation Systems and Services,”
Special Issue of the IEEE Communications Magazine, April
1998.
[3] P. Bahl and V. Padmanabhan. RADAR: An In-Building RFbased
User Location and Tracking System. In Proccedings of
IEEE International Conference on Computer
Communications (INFOCOM 2000). Tel-Aviv, Israel, March
2000.
