Implementation of Vehicle Monitoring and Positioning System Based on GPRS

0 Introduction

 

　  With the development of society, the number of cars is increasing, and the car brings convenience and enjoyment to people, but it also brings many problems. For example, vehicles are stolen, and other unexpected troubles (underlock, lost, robbery, etc.). The emergence of wireless GPS positioning systems can be said to solve this problem to some extent. Nowadays, many car GPS devices are more commonly based on the transmission mode of the radio and based on the SMS transmission method. The former needs to purchase an expensive radio station, the mobile terminal is very cumbersome, and the signal is relatively susceptible to interference; while the latter receives a large amount of data at a time. Restricted ( 140B ), and its communication costs are higher.

  　 In view of these considerations, this paper proposes a GPRS- based vehicle monitoring and positioning system. GPRS has a wide coverage, low communication costs, " high speed " and " always on " features. The GPRS- based vehicle monitoring and positioning system has low service cost, light equipment and strong anti-interference ability, providing seamless connection with the INTERNET and eliminating the trouble of applying for wireless resources.

 

1 Introduction to GPRS

 

1.1   GPRS features

 

  　 After years of development, the GSM network has been very mature. GPRS is a new data transmission service developed on the basis of the existing GSM network . It is one of the contents to be implemented by the GSMPhase2.1 specification. GPRS is a packet-based overlay on the existing GSM wireless interface circuit, it aims to provide 115 k bit / s packet data service rate. Replenishing circuit-switched networks with packet switching is an important upgrade to GSM technology. One of the great advantages of packet switching is the flexibility to allocate network resources. Therefore, in addition to the advantages of GSM traditional network applications (wide coverage, large number of users, stable network), GPRS has many unique advantages:

(1)     Packet switching technology is used to efficiently transmit high-speed or low-speed data and signaling, optimizing the utilization of network resources and wireless resources.

(2)     Network access is fast and provides a seamless connection to existing data networks.

(3)     Supports applications based on standard data communication protocols, and can interoperate with IP networks and X.25 networks.

(4)     Charging functions based on data traffic, service type, and quality of service (QoS) can be implemented .

(5)     The core network layer adopts IP technology, and the bottom layer can use a variety of transmission technologies to easily realize seamless connection with a rapidly developing IP network.

(6)     GPRS can provide transmission rates up to 115kbit/s (maximum value is 171.2kbit/s , excluding FEC ).

 

  1.2 GPRS system composition method

  　 (1) Introducing 3 main components in the GSM system

• GPRS Service Support Node (SGSN, Serving GPRS Supporting Node)

• GPRS Gateway Support Node (GGSN, Gateway GPRS Support Node)

• Group Control Unit (PCU)

(2) Software upgrade of GSM related components The principle of GPRS system is shown in Figure 1 .

 　　　　　　　　　　　　　　　 

Figure 1 Schematic diagram of GPRS system

 

 

 

1.3 Overview of the progress of GPRS standardization work in China

China began tracking the relevant standards of GPRS in 1996 . In April 2000, it has completed the "900 / 1800MHz TDMA digital cellular mobile communication network GPRS Tunneling Protocol (GTP) specification" by the Ministry of Information Industry made telecommunications transmission "GPRS operational research" pre-preliminary research results. Since 1998 , Chinese operators have begun to work on the construction of GPRS test network in China , and the standardization work is extremely urgent. In 2000 and the first half of 2001 , a series of standards related to the general packet radio service of the 900/1800 MHz TDMA cellular mobile communication network has been promulgated .

 

2 GPRS-based vehicle positioning system monitoring overall design

　  Overall design block diagram Figure 2 shows

　　　 

Figure 2 Overall design of vehicle monitoring and positioning system based on GPRS

 

  　 The user can simply call the service center to realize the inquiry and control setting of the vehicle. The service center realizes the monitoring and management of the vehicle through the INTERNET according to the requirements of the user . Another way, users at home can be implemented to monitor the vehicle in the case of an authorized service center, the only equipment needed is a PC, INTERNET access, the service center the user's IP and port number to inform the mobile terminal, and It is stored in the NVM (no power loss) area, at which point the service center will completely hand over the monitoring rights of the vehicle to the user. If the user is driving out, the monitoring right can be returned to the service center in the same way, so that the service center can help according to the monitoring situation (such as emergency alarm, guiding, etc.). Because the GPRS module can only communicate with the set IP and port number, it can only be completely controlled by one party under any circumstances.

The data has experienced two parts of the GPRS wireless channel and the INTERNET wired transmission during the entire transmission process . The command data sent from the service center (or user PC ) is sent to the INTERNET through the specified IP address and port number , and is encapsulated into a GPRS packet data packet to the GPRS network through a seamless connection between GPRS and INTERNET , and is supported by GPRS. The mobile transceiver module receives the processing and implements the data transmission. When the mobile terminal feedback information data in a mobile terminal labeled as a GPRS packet, the GPRS wireless module transmits to the GPRS network through GPRS and seamless connection between the INTERNET data labeled as TCP / IP packets into the data sent to the specified INTERNET The IP and port enable uplink transmission of data.

Figure 3 mobile terminal

  　 In FIG 3, GR47 instruction received from the GPRS network, GPS positioning acquired (GPS time, latitude and longitude, speed, direction, etc.), according to the request command (or active on the hair), sends the data to a certain format through the GPRS network Service Center. Control of the vehicle is achieved through the I/O port on the GR47 .

 

3 GPRS-based vehicle positioning system monitoring embodied

3.1 Hardware implementation

The hardware required for this system is: wireless transceiver module supporting GPRS , GPS receiver board, system startup control chip, watchdog, serial level conversion chip, and network PC .

(1)     The wireless module used is Sony Ericsson 's new generation mobile communication GSM module GR47 . It supports dual-band 900/1800 MHz and 850/1900 MHz and is expected to be used in machine-to-machine and man-to-machine applications, suitable for sending and receiving data ( SMS, CSD, HSCSD, GPRS ), can also make voice calls through GSM network, which is convenient for us to expand applications in the future. The module has the ability to store and run code that the user writes when the processor is down, and is used by the underlying translator (the software part of the system is implemented this way, as described in more detail later). There are two script storage spaces equivalent to 44K available, and 25K operation RAM . The serial channel uses asynchronous communication to connect the application system or auxiliary unit to the module. They consist of three UARTs : UART 1 completely uses RS232 and closes the communication line. UART 2 can be connected to the GPS unit using an interface , and the download software accepts the recorded information. UART 3 can be embedded in the application. The board has a complete IP/TCP/UDP stack, which extends the working code software and does not require a client to implement it. The UDP/IP protocol is used in this system.

(2)     The system startup control chip uses MOTOROLA 's SN54/74LS123 .

Structure diagram Figure 4 shows:

Figure 4 SN54/74LS123 structure diagram

The function table is as follows:           

Table 1 SN54/74LS123 function table

The main hardware connection circuit diagram of the vehicle monitoring and positioning system based on GPRS is shown in Figure 5 :

FIG 5 GPRS-based vehicle positioning system monitoring hardware connection of FIG.

 

The module power is turned on / off by the ground ( pull low ) 14 pin (RST2) , releasing the pin and pulling it internally to the high state. When the system is powered up, 74LS123 pulls RST2 low to start GR47 . The watchdog monitor program runs. Once the program runs abnormally, the GR47 and the power chip are restarted by 74LS123 . The GPS receiver board is connected to the UART3 port of the GR47 . UART 3 consists of full-duplex communication system communication, including transmission and reception lines. It is the interface between application system and module data communication. It can be used to implement data reception and transmission.

3.2 software implementation

   　 The software implementation of the system consists of two parts: the mobile (vehicle) part and the service center (user) part. The service center software is implemented by C#.net . Using the functions provided by C#.net , it is very convenient to establish UDP connection and send and receive data. We focus on the development of mobile software.

There are two implementations of the mobile part, one is to use the AT command directly , " AT " Is an abbreviation for A Ttention , which is a line-oriented command language consisting of a string of alphanumeric characters. It is sent to the modem to instruct the execution of the command specified by the character. The user uses the AT command to communicate with the modem in the serial port and the transceiver module to control its action. The other is to use C code, the module has the ability to store and run the code that the user writes when the processor is down, and is used by the underlying translator. The GR47 module supports the C language, specifically a subset of the standard C , supporting two basic data types: cha r (8bit) and int (32bit) .

The language structure includes:

  If - then - else statement

  While loops

  For loops

And its integrated development environment M2mpower IDE comes with a rich library of functions, providing a number of function interfaces that can be directly called by the user. Great convenience for application development.

       This system is implemented in the second way. Because the GR47 only provides 44K of user program storage space, the design of the entire program must be carefully conceived. The specific functions of the software implementation are: point name return, timing / fixed point return, in / out area alarm, burglar alarm, black box function, continuous driving prompt, robbery alarm, etc. The flow chart is shown in Figure 6.

Figure 6 mobile terminal program flow chart

       After the program starts running, the variable initialization value and each status flag are read from the NVM (the area where the power is not lost) for initialization. After establishing a UDP connection, register with the service center. After the registration is successful, the service center will obtain the SIM card number and ID number of the mobile station . That is, the first connection is one-way (from the car station to the service center), after that In order to communicate in both directions. In the main loop, GPS data is read every cycle to ensure that the GPS information is always up to date. The following determines whether the service center has issued a command, and if so, analyzes the command to perform related actions, otherwise it continues to execute. Then determine each status flag bit (such as overspeed flag, time to flag, etc.), if the flag is set, action, otherwise continue. Monitor the external I/O port to see if there is any external input (such as robbery alarm, help alarm, etc.), and if so, send a command to notify the service center. In order to ensure the reliability of the system, we have integrated the software watchdog and hardware watchdog. Try to arrange the dog-feeding statement in the time-consuming part of the low-level function (such as the data read / send part) to reduce the number of dog-feeding statements and ensure storage space.

 

4 Conclusion

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