Indoor Positioning Using Wireless LAN Signal Propagation Model and Reference Points

Jaywon Chey, Jae Woong Chun, Jang Gyu Lee and Gyu-In Jee

Abstract:	GPS is widely used for outdoor positioning in many applications. But it is not suitable for indoor positioning because of weak signal level. The accuracy of positioning error is up to the order of tens to hundreds meters when GPS is applied indoors. So new technology of indoor positioning with the accuracy of several meters is required to provide location-based services in ubiquitous environment. Indoors, the location of a mobile user can be determined through the wireless communication signals such as wireless local area network (WLAN), bluetooth and ultra wide-band (UWB) besides GPS. Recently WLAN has been installed in a number of indoor areas such as office building, terminal, campus, park and so on. This paper uses the received signal strength of WLAN to determine the location of a mobile user instantly. Conventional method for indoor positioning stores each sample point’s signal strength in a database beforehand and compares mobile user’s signal strength with stored signal strength in the database to find out the sample point nearest to a mobile user. However, this method needs many sample points and needs to build the database of received signal strength in each sample point and to update it since any modifications of indoor structure change the signal strength of sample point received from APs. To resolve these difficulties we install additional reference points with APs indoors and use the signal strength of reference points received from APs to determine the location of a mobile user without using the database of received signal strength. This paper uses wall attenuation factor model as WLAN signal propagation model instead of basic signal propagation model to increase location accuracy since wall is a dominant effecting structure for signal propagation indoors. Wall attenuation factor model is derived from adding wall attenuation factor that is multiplied by the number of walls between AP and reference point. Indoor positioning performance is presented by the test experiment for two signal propagation models that are basic signal propagation model and wall attenuation factor model. Experiment result shows the meter-level accuracy irrespective of any changes in indoor environment and proposes wall attenuation factor model using reference point after comparing two results of basic propagation model and wall attenuation model. Moreover this method using reference point need not build database of the signal strength received from many sample points and update it.
Published in:	Proceedings of the 2005 National Technical Meeting of The Institute of Navigation January 24 - 26, 2005 The Catamaran Resort Hotel San Diego, CA
Pages:	1107 - 1112
Cite this article:	Chey, Jaywon, Chun, Jae Woong, Lee, Jang Gyu, Jee, Gyu-In, "Indoor Positioning Using Wireless LAN Signal Propagation Model and Reference Points," Proceedings of the 2005 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2005, pp. 1107-1112.
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