Research And Implementation Of WLAN Location System Based On RSSI

The application of wireless network becomes more and more popular as the internet is developing rapidly, and many kinds of value-added service based on WLAN are appearing. Wireless location service is a more promising one among these services. Wireless local area network (WLAN) location based on received signal strength indication (RSSI) is becoming a hot research topic of wireless location technology gradually because it does not require extra hardware device.There are two main classes of RSSI based WLAN positioning techniques : fingerprinting technique and radio propagation modeling technique. The former one utilizes the signal strength distribution map to determine the user's position. The latter one makes use of signal propagation theory in indoor environment, then sets up a mathematic model to estimate the user's position. The RADAR system, proposed by Microsoft, realizes the function of indoor positioning technology by employing the two kinds of techniques respectively.This thesis introduces the WLAN location system based on radio propagation modeling technique, the one making use of signal strength to localize the user's position. The thesis proposes a location technique, which firstly determines the zone using signal strength, and then calculates the mobile devices' location, on the base of investigating WLAN location techniques at home and abroad. This kind of location technique could decrease the positioning error efficiently causing by signal fluctuation, when it is applied to the actual engineering.The location system works in two phases: the offline phase and the online phase. In the offline phase, the experiment environment is divided into several zones. In each zone, the RSSI range of each access point (AP) and the distance range to each zone are set, and then corresponding propagation model parameters are computed. In the online phase, the zone number is determinated by using the real time RSSI and the RSSI range. Then we calculate the mobile device's coordinate in geometric plane combing the real time SS and the parameters corresponding the zone and each AP.At the end of the thesis, test on the location system is implemented in a field setting. Experimental results show that the 25th, 50th, and 75th percentile values of the location distance error are 1.15 m, 1.75 m and 3.05 m respectively and it meets the engineering requirement.