Study Of Highway Tunnel Vehicle Positioning System Based On ZigBee Technology

With rapid development of highway construction, our country has the most complicated tunnels with the fastest developing speed in the world. However, the traffic safety situation of tunnel is not optimistic, tunnel has become a major distribution point of traffic accidents and accident black spots. Among various types of tunnel accidents, accidents particularly caused by vehicles stowed with dangerous or potentially dangerous goods have the most serious consequences, which will result in large economic losses, lead to the longest traffic disruption and have the most adverse social impact. However, the present tunnel video surveillance system and alarm system show deficiencies during the rescue and disposal of accidents:such as cameras near accident spot cannot obtain detail information of the accident due to the dense smoke; pre-alarm time of temperature sensing optical fiber and infrared alarm system is too long, therefore missing alarm and false alarm my happen; GPS system will lose positioning function in the tunnel as a result of shielding effect, thus position of the vehicle and state of dangerous goods cannot be transmitted in real time. On this background and situation, this paper focuses on the goal of integrated vehicle surveillance system in the tunnel, conducts research on vehicle location system in tunnel, and proposes vehicle location system based on ZigBee technology.Transmission mechanism and characteristics of radio waves in the tunnel were analyzed, conclusion indicating that electromagnetic transmission near the tunnel comply with free space model were gained according to Fresnel regional theory; RSSI-d logarithmic model in terms of strength and distance of electromagnetic signal was derived on the basis of T-R field strength prediction function, and the RSSI-d model was employed as fitting function to fit ranging function in tunnel environments. Then several classic positioning algorithms based on ranging were summarized, defects of trilateration algorithm were emphatically analyzed, and a corresponding improved algorithm--optimal node centroid weighted algorithm was proposed.Framework and node deployment of ZigBee positioning system were designed in an integrative manner, according to the actual situation of mechanical and electronic systems of highway tunnels. Hardware platform of the system was built based on ZigBee module, and main software modules of the mobile nodes and reference nodes were designed on the basis of ZigBee stack.The ZigBee positioning system can serve as a subsystem of integrated vehicles surveillance system in the tunnel, in order to implement vehicle positioning and tracking, thus can conduct real-time positioning on vehicles with dangerous goods, make up for the defects of existing surveillance and alarm system during the process of the accidents warning and rescue, and realize remote management by positioning and tracking of construction workers and rescue personnel. The proposed ZigBee positioning system has certain application value in location and tracking of vehicles, personnel and equipment.