Design of GPS Vehicle Satellite Positioning Simulation System
1. Introduction At present, the vehicle technology is very mature. It is widely used in the anti-theft tracking of private cars, the dispatch control of logistics vehicles, the security of taxis, the electronic stop signs of buses, and so on. It has become very cheap. A few hundred dollars in the market can be bought [1]. Its core technology is GPS, and the electronic ground is the soul of GPS. Only through it can the vehicle be positioned. After the vehicle position is determined, the data is sent to the third party through wireless transmission, so that the vehicle positioning can be realized. With this technology, we have established a model that can simulate the operation of the vehicle. It can determine the position of the vehicle through the GPS positioning system, send the position information of the vehicle to the control center through the wireless transmission system, and send control commands when there is a control center. To the vehicle, to get the vehicle to the designated location, that is, to establish a model of the GPS/GSM "unmanned" vehicle system, of course, this model is built on the highway, when the driver can drive on the highway The control button is used to send instructions to the workstation. After the workstation confirms, the driver is informed that the vehicle enters the “unmanned†state. The exercise of the vehicle is determined by the control center. When the highway exits, the control center will inform the driver that it will The driving right of the car is returned to the user, in order to prevent accidents, the user can also interrupt at any time.
This system simulates this model, using GSM as the medium for data transmission, using the PC as the control center, replacing the vehicle with a small car, simulating the operation of the vehicle on the campus, first sending the position information by GPS, and then sending the information by GSM. It is transmitted to the PC and processed by the PC to display the position of the car on the map. Then the PC sends a command to transmit the command to the car through GSM, and the car is executing the command. 
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Figure 1. Driverless control system model
2. Overview of system implementation theory
GPS currently has 24 satellites in the constellation of space satellites, including 21 working satellites and three in-orbit spare satellites. Each satellite is equipped with 4 high-precision electronic clocks to provide high-precision time standards for GPS positioning. User equipment is mainly composed of GPS receiving hardware and data processing software, as well as a microprocessor and its terminal equipment [3].
The GSM network is the wireless communication network with the widest coverage and the most common application in China. The transmission speed is fast, the price of a single data transmission is cheap, the voice is not occupied, and the performance of the two-way transmission can conveniently realize the information collection and remote control of the collection station equipment, realizing remote control, telemetry and the like. Therefore, the use of GSM for wireless communication is very reasonable [4].
3. System implementation scheme design Trimble's GPS module is used in the design for trolley positioning. Two Siemens GSM modules are used for wireless data transmission of trolleys and PCs, and the setting of the trolley part is completed by key input. The current information is displayed in the liquid crystal, and the serial port and the GSM module are communicated on the PC, and then displayed on the electronic map written based on the VB platform.
4. Hardware system design
4.1 Power supply voltage regulation part of the system power supply is 7.5V, and the operating voltage of the single-chip microcomputer is 5V, LM7805 is a 5V tributary power supply chip. 
Figure 2 system power supply
4.2 GPS interface circuit Because the level of 51 series MCU is TTL level, and the GPS module is 3.3V power supply, LM1117 is selected as the power supply of GPS module. The communication part selects MAX3232 to convert the logic level of 3.3V into 232 level. . 
Figure 3 GPS interface circuit diagram
4.3GSM interface circuit In the use of GSM module, its power supply range is 7.5~24V wide, and its output level is 232 level, which can lead to the serial communication data line.
4.4 GSM/GPS control part Since the MCU we use has only one serial port, we need to switch the serial port. We use the relay, but because the I/O port of the MCU has a small driving current, the relay can't work, so we use ULN2003 as the driver, it is the reverse drive open output Darlington, as shown in Figure 2, we use the single-chip tube current to drive the relay.
Figure 5 GSM / GPS control section
4.5 Motor Control Part of the motor control part We use the inherited motor drive chip L298, its performance is relatively stable, and the drive current is large. Its circuit diagram is as follows.
4.6 Display section In the display section, we use 12864 LCD. In order to make the hardware structure simple, we use the serial mode. 
Figure 6 shows the section
5. Software implementation [5] 
Figure 7 Flow chart of the car control part
6. Conclusion This system realizes the simulation operation of GPS vehicle positioning system. Using GSM as the data transmission medium, the experimental car replaces the actual vehicle, and the PC is used as the vehicle control center to process the car position information and direct the car movement. The software test system realizes the collection of the car position, and the command can also be received and executed by the car.
The author of this paper innovates: Integrate the three technologies of single chip microcomputer, GPS and GPRS, and apply it to the vehicle monitoring system reasonably and effectively, realizing the real-time monitoring and dispatching of the vehicle, improving the safety and working efficiency of the vehicle. The system has been run on our campus patrol car system, saving nearly 10,000 yuan for the school. Practice has proved that the communication function of this system is reliable and reasonable in design.
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