Research On RSSI-based Passive WiFi Positioning

In recent years, with the rapid development of wireless communication technology, the importance of location based service(LBS) has become increasingly prominent in practical application. Due to obstacle blocking in dense-constructed areas and indoors, the commonly used satellite positioning system has been greatly influenced in terms of its positioning performance. Therefore, adopting the widely existed Wi Fi network for indoor positioning has become a hotspot in current researches.The thesis first designs a RSSI-based passive WiFi positioning system mainly composed of front-end AP module, socket communication module, service module and positioning algorithm module, and adopting the method of router “passive” positioning. The advantages of this system lie in that:(1) it supports any WiFi device without pre-installed APP or positioning chip;(2) no hardware modification is needed for the positioning router;(3) the background system can directly obtain the positioning data without waiting for the positioning target to actively report its position information. Through the design of the software and hardware, this thesis has realized the preset functions of the modules, thus providing a actual test platform for the following verification of positioning algorithm.Secondly, the thesis studies a number of new methods to improve the precision of the positioning system from the following three respects:(1) adopting the Gaussian filter method to screen the collected RSSI data so as to filter out the dots with relatively great error;(2) studying commonly-used indoor propagation models and conducting tests on indoor environment attenuation factors to further acquire a propagation loss model that conforms to the actual measurement environment;(3) carrying out a comparative analysis on the existing positioning algorithms and proposing an improved hybrid location algorithm based on maximum likelihood and weighted centroid algorithms combining with centroid algorithm and maximum likelihood algorithm.Finally, the new method studied above is applied to the passive WiFi positioning platform of this topic, and hence a complete set of positioning demonstration system is constructed. Experimental results show that compared with original positioning systems, the proposed system can preferably meet the demands for design performance, realizing the effective improvement in positioning precision.