A Novel Peer-to-Peer Instant Messaging And Positioning System Based On The Fit AP Architecture

In the process of subway construction,there are following issues related to communication networks: 1) Ground management team cannot monitor and track the operating points without any wireless communications. 2) The communication efficiency of interphones is low. 3) Rescues cannot be launched in case of emergency due to the lack of a perfect positioning system.The aims of this work are improving the efficiency and reducing the cost of communication, tracking the construction personnel in real-time, and promoting the WLAN applications in the meantime. Our system provides a combination of a wireless network based on the Fit AP architecture, an indoor positioning system based on RSSI and IEEE 802.11 protocol stack, and an instant messaging system based on Peer-to-Peer technology and implemented on top of Android Studio. In the end, we applied the WLAN into tunnel, integrated the positioning module and communication module on Android platform, realized a novel P2 P instant messaging and positioning system based on Fit AP architechture. Overall, this paper is divided into the following four parts.Firstly, the realization of network system based on Fit AP architechture. It consists of ACs, AP group and STA group. AC takes full responsibility of IP address designation as the index server. AC and APs are interconnected successfully via the 5GHz frequency band or a wired line for serving the STA group.Secondly, the realization of positioning system based on WLAN. It combines one coarse grained sub positioning system and a fine grained one. The former is based on RSSI statistical model. APs divides the tunnel into serveral positioning sections based on APs' positions, then STA estimates the section it lies based on RSSI. The latter is made up of positioning server(PS), positioning anchors(PAs) and positioning targets(PTs). Under the schedule of PS, PA packages and sends the positioning frames, counts positioning response frames and estimates the distance between PA and PT, and then transmits the distance data to PS. Finally, PS will delivere all positioning data to the ground management system.Thirdly, an instant messaging system based on Android Studio. It consists of user interface(UI), data transmission, data storage and multimedia application sub modules. This Android application provides text, picture and voice message interaction platform. Furthermore, it displays all online users' positioning results by integrating positioning module.Finally, a series of tests and analysis of performance on our system has been made in this paper. Experimental results show that the instant messaging and indoor positioning system is successfully designed and implemented with good robustness and scalability.