Pick   To: Introduce a method of implementing a centralized control system for civil air defense and disaster warning based on GPRS . The system uses GPRS wireless data communication technology to achieve remote centralized playback and monitoring of civil air defense and disaster alarms, with the characteristics of fast control response and low construction and maintenance costs.
GPRS (General Packet Radio Service — General Packet Radio Service ) , which is a set of wireless transmission methods developed using the concept of “packet switchingâ€. GPRS is a new type of packet data transmission service opened on the existing GSM network. With the help of GPRS wireless access technology, people can easily access the Internet no matter when and where.
The use of GPRS wireless access technology to form a wireless data transmission system has a wide range of applications. At present, almost all low- and medium-rate data transmission services can be applied, including: industrial remote signaling, telemetry, remote control, and POS machine networking in the financial and retail industries , ATM networking, mobile banking, etc., as well as vehicle mobility data transmission, mobile vehicle scheduling and monitoring, etc. Application of GPRS technology in the mobile phone has been very extensive, and in industrial remote, telemetry, remote control aspect has just started, this is the use of GPRS wireless access technology to design and implement a civil defense and disaster warning centralized control system, is the GPRS technology Typical applications in industrial remote signaling, telemetry, and remote control.
system structure
The system is mainly composed of a central control center and an alarm remote control terminal. The other parts are provided by China Mobile Communications Corporation. Its structure is shown in Figure 1 .
The alarm issuing instruction is issued by the computer of the central control center (the central control center can be mobile or fixed ) . The alarm instruction issued by the central control center is transmitted to the alarm remote control terminal via the Internet network and GSM / GPRS network. After the terminal receives the command, it will start the alarm ( electric alarm, electro-acoustic alarm ) to sound, and the alarm sound information will be automatically sent back to the central control center, and it will be displayed on the electronic map of the computer one by one.
Picture 1 Â System block diagram
Picture 2 Â GPRS data communication module structure block diagram
Picture 3 Â Block diagram of alarm remote control terminal
GPRS wireless data communication
In the implementation of this system, the realization of GPRS wireless data communication is a very critical issue. GPRS is a new bearer service developed on the existing GSM system, the purpose is to provide data services in the form of packets for GSM users. GPRS uses the same wireless modulation standard, the same frequency band, the same burst structure, the same frequency hopping rule and the same TDMA frame structure as GSM . This new packet data channel is very similar to the current circuit-switched voice traffic channel. . Therefore, the existing base station subsystem (BSS) can provide comprehensive GPRS coverage from the beginning . GPRS allows users to send and receive data in an end-to-end packet transfer mode without using network resources in circuit-switched mode. Thus, an efficient and low-cost wireless packet data service is provided. Especially suitable for intermittent, sudden and frequent, small amount of data transmission, also suitable for occasional large data transmission. Using GPRS technology to realize data packet sending and receiving, users are always online and charged according to the flow rate, which greatly reduces the operating cost of the system.
The theoretical bandwidth of GPRS wireless data transmission can reach 171.2Kbps , the actual application bandwidth is about 40 ~ 100Kbps , and it provides TCP / IP connection on its channel ( connects GPRS / GSM network and Internet network through GGSN ) , which can be used for Internet connection , Data transmission and other applications. Then, to realize the GPRS data communication between the central control center and the remote control terminal of the alarm , it is only necessary for both to follow the TCP / IP protocol and work on the same network level. In the implementation of the system, we designed a GPRS data communication module for the remote control terminal of the alarm . The embedded TCP / IP protocol stack parses the TCP / IP data to realize the transparent transmission of data, and then builds an alarm system on the basis of it. Communication protocol. Considering that the GPRS data communication module uses a single-chip microcomputer to implement TCP / IP protocol parsing, the UDP protocol with less system overhead is adopted at the TCP network layer instead of the TCP protocol.
The GPRS data communication module is mainly composed of CPU , GPRS transceiver module, SIM card holder, configuration / diagnostic module, TTL serial communication interface, and extended data storage. Its structural block diagram is shown in Figure 2 .
GPRS transceiver module adopts MC35 GPRS wireless communication module of SIEMENS company . MC35 module embedded in the PAP (Password AuthenTIcaTIon Protocol) and CHAP (Challenge Handshake AuthenTIcaTIon Protocol) protocol stack for the two kinds of PPP (Point-to-Point Protocol ) connection to the GPRS data switching center, when the call connection is established, it MC35 It can send and receive GPRS packet data according to the GPRS network protocol and parse it, and output IP datagrams.
MC35 provides a standard AT command interface and an RS-232 interface for connection with external application systems; in addition, it also provides a SIM card interface for connecting a SIM card holder to connect to different GPRS operating networks.
The CPU uses Winbond 's 77E58 microcontroller chip, which has 32K of program memory inside , enough to embed IP and UDP protocol stack programs. At the same time, 77E58 has two serial ports, one is used to connect the GPRS transceiver module, and the other is used to output the data after UDP analysis.
Alarm remote control terminal
The alarm remote control terminal is an alarm actuator. It can be both an electric alarm control terminal and an electro-acoustic alarm control terminal. Its working principle is: when the alarm controller receives a legal command ( remote remote control ) or receives a valid keyboard operation ( manual operation, password protection ) , the controller controls the electric or electro-acoustic alarm drive circuit to complete the electric or electric Audible alarm. Its structural block diagram is shown as in Fig. 3 .
In the alarm remote control terminal, it is composed of Atmel 's AT89C52 single-chip microcomputer, GPRS communication module, voice circuit, sound intensity detection module, human-machine interface, alarm driver and other functional modules to complete communication, playback, status detection, manual operation and other functions.
Conclusion
The application of GPRS wireless access technology in industrial remote signaling, telemetry and remote control will have broad prospects. Using GPRS wireless access technologies to achieve centralized control of air defense and disaster alerts, it is only one aspect of technology GPRS. The alarm remote control system has been applied in many cities.
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