In the existing industrial monitoring systems, commonly used information transmission methods are: digital microwave, digital radio, wired fiber, cable, etc. Digital microwave and digital radio will be limited by transmission distance and frequency, while wired fiber and The network cost of the cable is high, and it is not suitable for the case where the monitoring point is very dispersed and the transmission distance is long.
CDMA 1X provides a good means of information transmission for the dispersion of monitoring objects, lack of organic links between monitoring nodes, relatively small amount of monitoring information, and low real-time requirements.
CDMA 1X is willing to refer to the first phase of CDMA 2000 (rate is higher than IS-95, less than 2MB/s), can support 308kb / s data transmission, the network part introduces packet switching, can support mobile IP services, is now There is a new bearer service developed on the CDMA IS-95 system to provide CDMA users with data services in packet form.
Because CDMA 1X adopts reverse coherent demodulation, fast forward power control, transmit diversity, Turbo coding and other new technologies, its capacity is much higher than that of IS-95. From the theoretical analysis results, if it is used to transmit voice services, The total capacity of the CDMA 1X system is twice that of the IS-95 system. If used for transmitting data services, the total capacity of the CDMA 1X system is 3.2 times that of the IS-95 system, and the theoretical bandwidth of the CDMA 1X is 300 kb/s. The application bandwidth is about 100kb/s (bidirectional symmetric transmission), and TCP/IP connection is provided on this channel, which can be used for applications such as Internet connection and data transmission.
2 CDMA 1X based wireless communication
2.1 Networking Solution
The wireless data transmission system generally consists of a data service center, a communication network, and a data terminal. Considering factors such as the amount of service data, security, reliability, network status, and cost, the following networking methods are adopted: the communication server fixes the IP on the public network. Or a fixed domain name is connected to the Internet. After the CDMA data terminal unit (DTU) is powered on, the connection is established with the communication server. If the communication server does not have a fixed IP address, the fixed domain name can be obtained by installing the peanut shell software. The solution has low cost. The communication quality is stable, the security is moderate, and the operation is reliable.
2.2 Principle of wireless data transmission
According to the above networking scheme, the principle of uplink transmission of data is as follows:
(1) The lower computer transmits data to the DTU through the RS232 serial port;
(2) The DTU sends the data into a TCP/IP packet and sends it to the wireless network;
(3) The TCP/IP data packet is transmitted to the Internet via the system packet data service node and is searched for a designated data service center (communication server) on the Internet;
(4) The communication server transmits the data to the host computer and stores it in the history database.
3 system design3.1 PC design
The upper computer includes two parts: real-time monitoring system and historical database.
The real-time monitoring system uses Wonderware's InTouch system, which mainly realizes the following functions: system management function; data processing function: including data query function, data storage function, data timing report function; alarm function: including real-time response function, alarm linkage processing function, Alarm setting function, alarm confirmation function, alarm storage function, operation control function, historical database select Wonderware's Industrial SQL Server, mainly realize the following functions: data statistics, report function, historical data query function, historical data graph, printing function.
3.2 lower position machine design
The lower computer selects ABB AC31 series PLC, including CPU module and I/O module. The CPU receives one or more operation control commands of the specified monitoring center to the device, and performs corresponding operation control actions on the related devices through the I/O module. The monitoring center returns the operation result, and the lower computer mainly implements the following functions:
Data acquisition function, data query function, timed reporting function, operation control function.
3.3 CDMA data transmission interruption
The CDMA data transmission interruption uses the CDMA H7710 DTU of Shenzhen Hongdian Technology Development Co., Ltd. The terminal has the following characteristics:
(1) H7710 DTU provides RS232/422/485 interface directly, providing transparent, full-duplex, and peer-to-peer data transmission channels for users' data devices.
(2) Ordinary GPRS/CDMA Modem usually needs to be attached to a virtual dial-up Internet access on a PC. The data of the PC is used for data transmission and reception and protocol conversion. The H7710 DTU has built-in automatic network connection and protocol processing module, which does not require background computer support.
(3) H7710 DTU can realize point-to-point, point-multipoint, and center-multipoint peer-to-peer data transmission, and the transmission delay is generally less than 1 s.
(4) The H7710 DTU can automatically attach to the GPRS or CDMA network from the beginning, and establish a communication link with your data center to send and receive data of user data devices at any time.
(5) H7000 mobile data communication can build a virtual mobile data communication private network covering all of China through the Internet network without relying on the data interface equipment of the operator switching center.
The CDMA H7710 DTU must set the event parameters before use: CDMA 1X network login user name and password, communication interface parameters, fixed IP address and port of the communication server or communication server domain name, DTU online working mode, and so on.
3.4 Design and Implementation of Communication Server
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