| Abstract |
In the recent years in the area of networks a small revolution has taken place: the Wireless Local Area Networks. Initially they appeared in 1997 as IEEE standard 802.11 and the exponential fall in product prices has lead to a first seen prevalence, even in consumer devices. One important characteristic that reveals or increases the value of a network are the provided services. Position location in wireless networks is a unique service with many capabilities and extensions. The uses of this service originate exactly from the knowledge of the user's position, such as emergency tracking, user surveillance and paging, security, radio administration and design, navigation and information. The development of a positioning system has to encounter all the problems that show up in a wireless transmission environment and deal with the electromagnetic radiation propagation. The physical transmission medium fluctuates dynamically and is not deterministic describable, resulting in no constant measurements in time. Even more the compatibility with the corresponding products is needed for a system to be widely implemented. However the existing systems need a long preprocess in order to operate in a place, demand the active participation of the device being tracked, thus limiting the range of compatible products and don?t address effectively the environmental changes. In this thesis we have developed a novel position location technique that copes with the above problems, and may be used directly with present and future wireless network devices, without regard to the standard used. The positioning needs no information about the device or any user intervention. In addition it adapts dynamically to the environmental changes and self-adjusts in any condition of the wireless medium. We confirmed the capabilities of the technique with the use of simulation and proved the high accuracy in position location that can be achieved. Finally we developed a prototype system compatible with 802.11b, the dominant wireless networks standard today, and studied its performance under real conditions. In conclusion the developed technique succeeds in two important aspects, while it keeps the positioning accuracy: a. the low cost that originates from the fact that is totally compatible with all the present devices b. the convenience of deployment as it does not require any information about the user and the environment. The positioning system with these specifications can accomplish its goal, namely the direct and undisturbed provision of services that increases the value of the network and makes it useful for the user.
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Τεχνική Εντοπισμού Θέσης Χρήστη Ασυρμάτων Δικτύων
