Research And Implementation Of A AP Side Indoor Positioning System Based On WLAN

Outdoor positioning technology, especially GPS, in recent years has been widely used, high-precision positioning services played an important role in the military and civilian aspects, which has brought great convenience in people’s daily lives, but due to construction stoppers, GPS signal is quite weak in the room, and the satellite signals even can’t be searched in a considerable part of this case, so the GPS seems too powerless at this situation, but it is in urgent need of a reliable way to solve indoor positioning and navigation problems, for example, the large shopping mall and large warehouse. This paper designs a positioning algorithm which based on differential received signal strength(RSS) in multi-antenna AP side, this simple positioning system is low cost and don’t need to add too many additional devices, but the positioning accuracy is also guaranteed, the experiment proved that this system can effectively improve the accuracy and stability than other Wi-Fi positioning method, so it is a viable and reliable indoor positioning methods.Firstly, we propose multi-antenna differential positioning ideas based on the statistical properties of the received signal strength, it can effectively reduce the instability of received signal strength during transmission, because the two antennas are separated by a close distance, and the Wi-Fi signals they received can be considered roughly passing the same transmission environment, the difference of RSS between the two antennas only comes from the distance of them, we can calculate the track of the target through this distance and differential RSS of antennas, and then achieve the position through multiple AP. At last, we also design a simple and effective algorithm to determine the coordinates of the target.Secondly, After analyse the received signal strength, we discover that many outliers often appear in the samples which could influence the positioning accuracy, therefore we take the median filter method to reduce the interference of external factors on the RSS, and also reduce the reflection, refraction and diffraction effects of Wi-Fi signals to some extent.Finally, we realize a positioning system based on the designed positioning algorithm by using three Wi-Fi routers, and the datagram like protocol is used in positioning system which is designed for this system. All the routers are devided into master router and slave routers in the program, and the program has four modules which is designed by the need of the system, the control package and the RSS data is transported by using the postioning protocol designed before, and finally obtain the location information of positioning target by calculating module running on master router.