Design and implementation of GPS/GPRS vehicle monitoring terminal

In recent years, with the popularization of automobiles and the construction of roads, economic exchanges between cities have become more frequent, and the areas of activities have become larger and larger, resulting in serious problems such as traffic congestion, increased traffic accidents, and increased exhaust emissions. The emergence of intelligent transportation systems has effectively improved the above traffic problems. Intelligent transportation systems are a comprehensive transportation and management system that effectively integrates advanced information technology, communication technology, sensor technology, control technology, and computer technology and applies them to the entire transportation management system, and establishes a comprehensive transportation and management system that works in a wide range and in all directions, in real time, accurately, and efficiently. It improves transportation efficiency, alleviates traffic congestion, improves road network capacity, reduces traffic accidents, reduces energy consumption, and reduces environmental pollution through the harmony and close cooperation of people, vehicles, and roads.

The vehicle monitoring system is a branch of the intelligent transportation system. It integrates advanced wireless positioning technology, geographic information system and modern mobile communication technology. It not only plays a major role in the intelligent transportation system, but also provides anti-theft and anti-robbery alarms, emergency medical assistance, entertainment and other services. This article selects the vehicle terminal module in the entire system for design and implementation, and introduces the GPS vehicle terminal.

1. About GPS Vehicle Terminal

The GPS vehicle terminal is also called the GPS vehicle management system or GPS vehicle monitoring system. It is a comprehensive system of software and hardware that relies on satellite positioning, geographic information, wireless communication and other technical means to grasp the vehicle's location and status in real time and provide scheduling management information.

1 Overall structure of vehicle monitoring system

The vehicle monitoring system consists of four parts: GPS satellite, vehicle terminal, communication network (GPRS and Internet) and monitoring center. During the operation of the vehicle, the GPS receiver of the vehicle terminal receives the positioning data, calculates the current longitude, latitude, speed, heading and other information (time, status), etc. of the vehicle, and then transmits it to the monitoring center with a static IP address through the GPRS network and stores it in the central database. After receiving the information uploaded by the vehicle, the monitoring center scientifically dispatches and manages the vehicle according to its current status, thereby improving operational efficiency. Customers can also inquire about the current status of a specific vehicle through the Internet or telephone.

The overall structure of the system is shown in Figure 1.

2 Characteristics of vehicle-mounted terminals

1) Compact appearance and stable performance. The main unit is as big as a cigarette box and can be installed in a very hidden place. The GPS antenna does not need to be placed outside because it uses the fourth-generation module with super-strong reception, so it can be placed in a relatively hidden place in the car. The internal components of the main unit are all imported industrial-grade materials. The core GSM module is the German Siemens brand, the GPS module is the HOLUX SIRF III, the core microcontroller is the most stable P IC, and other IC components are from the German TI company.
2) Simple installation. You only need to connect the two power cords of the original car. The oil cut-off device can be connected or not. If you need to install the oil cut-off device, just cut off the power supply line of the original car oil pump and connect it in series to this machine.
3) Low false alarm rate. This product focuses on humanized design to minimize the false alarm rate.
4) Multiple precautions to ensure that there will be an alarm. [page]

3 Functions of the vehicle terminal

The satellite receiving module of the vehicle-mounted GPS/GPRS terminal collects GPS satellite data and obtains the vehicle's geographic coordinate information after data processing. After the information is processed by the vehicle-mounted terminal, it is sent to the GPRS wireless communication network by the GPRS wireless communication module. The GPRS network establishes a data channel supporting TCP/IP between the vehicle-mounted terminal and the monitoring center connected to the Internet according to the corresponding protocol. The vehicle-mounted GPS/GPRS terminal relies on this data channel to exchange information with the monitoring center. The monitoring center can also send control commands and service information downward through this channel.

In addition to vehicle positioning, the system can also provide a variety of services such as anti-theft and anti-robbery, cutting off fuel and power for moving vehicles, displaying dispatch information, medical assistance, mobile phones, etc.

2. Vehicle Terminal Hardware Design

The vehicle terminal hardware system is based on ATMEGA64(L) microcontroller and GPS+GPRS module, and its structure is shown in Figure 2.

1 Information processing and control module

This article uses the AVR series of single-chip microcomputer systems, which are mainly used for information processing and controlling the various components of the vehicle-mounted station to perform corresponding operations according to the requirements of the communication protocol. The module consists of a CPU, an external memory, an I/O interface, and a control logic circuit. The CPU is implemented using an ATMEGA64 (L) single-chip microcomputer, which has two serial ports, used to communicate with the GPS and GPRS modules respectively. It is a low-power 8-bit CMOS microcontroller based on an enhanced AVRRISO structure. Due to its advanced instruction set and single-clock cycle instruction execution time, the data throughput of ATMEGA64 (L) is as high as 1MIPS/MHz, which can alleviate the contradiction between power consumption and processing speed in the system.

2 GSM/GPRS+GPS module

The GSM/GPRS+GPS module uses the SIM508 module from SIMCOM. The SIM508 module is a product that fully integrates tri-band GSM/GPRS and GPS with 20-channel capabilities into one module (34mm×55mm×3mm). The design of this product fully meets the requirements of the vehicle application environment (temperature, humidity, shockproof, etc.). In particular, the SIM508 with integrated additional components can save a lot of time and cost. The vehicle terminal obtains the specific location of the vehicle through the GPS part of the module, and after CPU processing, it is displayed to the user and sent to the monitoring center through the GPRS part to achieve real-time positioning and tracking of the vehicle, while also realizing voice and short message communication functions.

3 Input and output modules

The input of the vehicle terminal mainly includes two ways: remote control input (main input device) and handle input. Considering the limitations of handle input in emergency situations, this paper uses the remote control as the main input device, which can be used to complete functions such as voice dialing, sending and receiving short messages, medical assistance, maintenance assistance, and opening and closing equipment.

The output is realized through the 12232F LCD module, which can display graphics or 7.5×2 (16×16 dot matrix) Chinese characters. The interface with the external CPU can be parallel or serial. Considering the simplicity of programming, this vehicle terminal uses a serial interface connection. [page]

3. Vehicle terminal software design

This software system adopts a modular design method. Each module implements a function or a protocol. Each functional module appears in the form of a sub-function, which shortens the software development time and facilitates program modification and transplantation. At the same time, when writing the software, some software application interfaces are reserved to facilitate software upgrades, such as adding new protocols.

The software system functional modules are shown in Figure 3.

1. Workflow of the software system

The main functions of the vehicle terminal software system are completed by the main program. The main program adopts the system structure of the state machine, and its workflow is shown in Figure 4.

When the program is working, it first initializes the GPS and GPRS serial ports, and then enters the main control loop. In the main control loop, it first identifies whether the GPS data is valid, that is, whether the positioning is successful. If the positioning is successful, the system will go to the next state and establish a GPRS connection, otherwise it will re-position. After the GPRS connection is established, the processed positioning data can be sent to the monitoring center. At the same time, during the operation of the main program, it can also respond to the interrupt request input by the remote control to realize other functions.

2 Software System Protocol Stack

Based on the OSI model and the standard TCP/IP protocol stack, this system adopts a four-layer network transmission protocol: transport layer, network layer, data link layer and physical layer. The system protocol stack structure is shown in Figure 5.

Considering the situation of dozens, hundreds or even thousands of vehicle terminals in the vehicle monitoring system, for such applications with small data volume, multi-point dispersion, high real-time requirements and large number of terminals, it is better to use UDP rather than TCP at the transport layer. As a network layer protocol, the IP protocol mainly cuts the data stream into appropriate sizes, and then transmits these data packets to the destination IP by selecting routes and using different routes. Above the physical layer, the PPP protocol, as the only designated data link layer protocol of GPRS above the physical layer, transforms the original physical layer connection into an error-free data link through CRC verification and confirmation. After the PPP negotiation is successful, the system will successfully log in to the Internet remotely and obtain the IP assigned to it by the gateway. The physical layer channel between the terminal and the network is the GPRS connection. The specific GPRS protocol has been built into the GPRS modem. After the data end sets the correct AT command for the GPRS modem, the AT dial-up command can be used to dial up the connection. After receiving the dial-up feedback response from the GPRS modem, a physical channel, namely the GPRS channel, is established between the terminal and the network.

3 Future Development Trends of Urban Intelligent Transportation

With the increasing development of urban traffic problems, urban traffic integrated information platforms, global positioning and vehicle navigation systems, urban public transportation vehicles and taxi vehicle command and dispatch systems, and urban integrated emergency systems will all usher in great development opportunities.

In general, the development trend of urban intelligent transportation system will be a comprehensive, multi-department driven development model. Since the urban intelligent transportation system will involve the work of relevant citizens, public security traffic management, transportation department vehicle management, urban construction, communications and other related departments, the development process of urban intelligent transportation in the future will inevitably be a multi-department driven development process involving transportation and public security.

Conclusion

This article introduces the implementation of vehicle monitoring system terminal based on GPS/GPRS, and gives detailed software and hardware composition and design implementation. After multiple tests, the system is stable and the effect is good. The system can be applied to the fields of hand command monitoring system, urban rental car management system, logistics transportation system, medical rescue system, etc., and the market prospect is extremely broad.