Application of Beamforming in Wireless Location Estimation
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Application of Beamforming in Wireless Location Estimation Kamran Sayrafian-Pour1 and Dominik Kaspar2 1 National
Institute of Standard and Technology, Gaithersburg, MD 20899, USA of Computer Science, Swiss Federal Institute of Technology, Zurich, Switzerland
2 Department
Received 1 June 2005; Revised 27 November 2005; Accepted 1 December 2005 A simple technique to estimate the position of a given mobile source inside a building is based on the received signal strength. For this methodology to have a reasonable accuracy, radio visibility of the mobile by at least three access points is required. To reduce the number of the required access points and therefore simplify the underlying coverage design problem, we propose a novel scheme that takes into account the distribution of RF energy around the receiver. In other words, we assume that the receiver is equipped with a circular array antenna with beamforming capability. In this way, the spatial spectrum of the received power can be measured by electronically rotating the main lobe around the 360-degree field of view. This spatial spectrum can be used by a single receiver as a means for estimating the position of the mobile transmitter. In this paper, we investigate the feasibility of this methodology, and show the improvement achieved in the positioning accuracy. Copyright © 2006 K. Sayrafian-Pour and D. Kaspar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1.
INTRODUCTION
In recent years, technologies that find the location of mobile sources inside buildings are becoming an attractive area of research and development. A significant application of such technologies is in emergency situations where it is important to be able to locate or track the movements of the first responders inside closed environments. More commercial and public safety applications are also emerging every day. GPS provides this capability in the outdoor environment, where the line-of-sight propagation paths to GPS satellites exist. However, it cannot be used in the indoor environment where ceilings obstruct the view of the corresponding satellites. The problem of finding locations of mobile sources inside buildings presents special challenges. Obstacles such as walls, furniture, and other objects create a much harsher radio propagation environment. A variety of ranging and positioning techniques with different technologies such as RF, ultrasound, infrared, DC electromagnetic, and so forth, have been proposed to solve this problem [1]. Accordingly, various levels of localization accuracy, resolution, and complexity have been reported by such methodologies. A simple technique to estimate the position of a given source is based on the received signal strength (RSS). RSS is attractive because it is widely applicable to wireless sensor networks and does not require sophisticated localization hardware. The general philosophy in this
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