Indoor Positioning Using Wireless LAN Radio Signals

Bernd Eissfeller, Danilo Gänsch, Swen Müller and Andreas Teuber

Abstract:	In recent years a lot of work has been done to establish a wide spectrum of techniques which may serve for indoor positioning and navigation. At the same time the number of possible applications has increased continuously. Relevant taxonomies of indoor positioning techniques distinguish them in different ways, e. g. [4]. One major distinction is whether or not the installation of a hardware infrastructure is necessary in advance of the positioning procedure. Using Wireless LAN standards for indoor positioning requires a number of suitable distributed access points. However, since there is an increasing number of users of this standard in wireless communication one can benefit from the synergy between communication and locating by using the same hardware devices. Main subject of this paper is the evaluation of a wireless LAN for indoor positioning. The commercially available Ekahau Positioning Engine (EPE) was selected for evaluation. EPE provides a fully software-based approach for the positioning solution and is able to run with the majority of WLAN hardware devices (access points and PC cards) meeting the IEEE 802.11b standard. For performance evaluation of the EPE three different test environments have been selected which are particularly relevant for potential applications. First, a very large undivided rectangular room of 200 square meters is considered for the simulation of an open-plan office or a factory building. The second environment is a tunnel representing a two-dimensional structure simulating long hallways. The third environment is a typical office environment with offices connected to a central foyer. In all three environments a mobile device is located on various marked points. An accuracy analysis comprising an absolute accuracy and a sample standard deviation is carried out. Especially the office environment is used for a number of further considerations: Firstly, the increase of accuracy when adding a (redundant) access point is investigated. The analysis distinguishes between sample points on rails and aside rails and leads to the problem of systematic errors. Secondly, impacts of errors like failed or displaced access points on the position accuracy are investigated. Thirdly, noise behavior of the radio signals is investigated by long-term measurements. Fourthly, kinematic measurements are carried out. Based on these experiences a general assessment of the EPE is done. Main problems and uncertainties are summarized, and possible remedies are recommended. The latter ones particularly comprise two aspects. Firstly, an approach of removing the systematic errors is attempted to be applied. Secondly, an approach of a network of reference tags augmenting the signal strength database is proposed.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	1936 - 1947
Cite this article:	Eissfeller, Bernd, Gänsch, Danilo, Müller, Swen, Teuber, Andreas, "Indoor Positioning Using Wireless LAN Radio Signals," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 1936-1947.
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