Design and implementation of a WLAN based location positioning system

Pao Yue-kong Library Electronic Theses Database

Design and implementation of a WLAN based location positioning system


Author: Lam, Chung-chi
Title: Design and implementation of a WLAN based location positioning system
Degree: M.Sc.
Year: 2008
Subject: Hong Kong Polytechnic University -- Dissertations.
Wireless LANs.
Wireless communication systems -- Location.
Department: Dept. of Computing
Pages: viii, 156 p. : ill. ; 30 cm.
Language: English
InnoPac Record:
Abstract: The objectives of this project are to propose a WLAN based location positioning model for the indoor environment and to develop a prototype to demonstrate how the proposed model works. At the beginning of the project, we studied the WLAN RF signal characteristics in both indoor and outdoor environments. Through the study, we have identified some RF signal characteristics and their relationships with the indoor environment. Subsequently, we reviewed several research studies on WLAN based location positioning systems. We observed some common challenges faced by these systems. Through the literature review, we also observed that most of the systems were based on the empirical data measurement approach. One reason being that the RF signal strengths and RF signal patterns have complicated relationships with the environment especially when operating in an indoor environment. On the other hand, the empirical data measurement approach faces two challenges. Firstly, dedicated effort is required to collect sufficient training data in the offline phase. The more accurate the system requires, the more data is required to be collected in the offline phase. Another challenge is that the environment may change from time to time, either a major shift or a transient change. As a result, the radio map will become outdated after a period of time. These systems have proposed some mechanisms to overcome such challenges. Regarding the above findings, we have proposed a model to address most of the issues that have been identified. Our proposed model aimed to be a software-based, easy to be implemented, accurate and robust one. Basically, we considered RF signals collected in both the offline and online phases as clusters of values rather than single values. We tried to measure the degree of similarity between two RF signal patterns so as to determine if they were collected at nearby locations. Additionally, to cater for the transient change of the environment, the signal attenuation effect of the mobile user and the orientation variation of the mobile device, we developed a simple user tracking mechanism to reduce wrong location estimates. To demonstrate how the proposed model worked, we have developed a Java based prototype, which consisted of several system components. Data collection and location positioning were handled by separate system components, which could run on different computers. The reason behind is that the mobile device often does not have sufficient processing power to perform complex calculation in a short period time. During the prototype evaluation, we found that the performance of our pattern matching algorithm was acceptable and comparably better than a common location positioning algorithm. In conclusion, our proposed model could be easily implemented in any indoor environment. Importantly, the accuracy of the model was acceptable, which could achieve a mean distance error of less than one meter.

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