The vehicle positioning system using GSM communication technology is generally composed of three parts: ①vehicle unit; ②monitoring center; ③GSM communication service system

　　(1) On-board unit

　　Vehicle terminal equipment includes: control unit (CPU), display unit (optional), GPS receiver, GSM mobile phone (or other communication modules: such as Siemens TC35 or MC35, but the peripheral circuit should be redesigned based on the mobile phone module interface), anti-theft alarm device (optional).

　　The main functions are:

　　(1) Anti-theft alarm function: When an emergency occurs, the user can trigger the hidden alarm button, and the vehicle-mounted unit will automatically transmit the location data in the GPS receiver to the monitoring center through the short message function of the GSM mobile phone. Anti-theft activation function, automatically send alarm information to the control center when the vehicle encounters illegal intrusion;

　　(2) Navigation function: GPS provides accurate position, speed and direction data of moving targets. The positioning accuracy without differential is about 10m, and the differential accuracy is 3-5m. The system can navigate through the dispatch center or store electronic maps on the terminal.

　　(3) Call function: The car GSM mobile phone can make a call, and when the user leaves the car, the mobile phone can be removed for normal use.

　　(4) Service: Provide a set of service buttons, when the owner needs to press the corresponding button, the service center will provide the service.

　　(2) Monitoring Center

　　The GPS differential reference module in the monitoring center is used to generate differential correction information and send it to the central processing unit; the central processing unit will manage the database, and send various scheduling, instruction information, and differential correction information to each vehicle-mounted unit through the GSM communication module. Send the received information from each vehicle-mounted unit to the electronic map or database for storage; the electronic map of the GIS module of the geographic information system will accurately display the real-time position of all the vehicles monitored; the function of the GSM communication module is to store the central processing unit. The sent command and differential correction signal are sent to each on-board unit, and the GPS information and sensor information of the vehicle sent by each on-board unit are received at the same time.

　　(3) GSM communication service system

　　The GSM communication service system consists of a GSM communication module and a GSM communication network. Its function is mainly to transmit data between the on-board unit and the monitoring center to ensure that the vehicle GPS information, sensor information and the instructions sent by the central processing unit are sent by each on-board unit. The differential correction signal is stably transmitted between the on-board unit and the monitoring center. The communication software adopts VC++ to realize: the communication between COMM_SEVER and COMM_CLIENT adopts WINSOCK components.

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