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In existing industrial monitoring systems, common information transmission methods include digital microwave, digital radio, wired fiber, and cable. However, digital microwave and radio are limited by transmission distance and frequency, while wired fiber and cable networks are costly and not ideal for scenarios with widely dispersed monitoring points and long transmission distances.
CDMA 1X offers an effective solution for situations where monitoring objects are spread out, there is a lack of direct links between nodes, the volume of data is relatively small, and real-time requirements are not high. CDMA 1X is based on the first phase of CDMA 2000, offering higher data rates than IS-95 but below 2MB/s. It supports data transmission at up to 308kb/s, introduces packet switching in the network, and enables mobile IP services. Additionally, new bearer services have been developed on the CDMA IS-95 system to provide users with packet-based data services.
Thanks to advanced technologies such as reverse coherent demodulation, fast forward power control, transmit diversity, and Turbo coding, CDMA 1X has significantly higher capacity compared to IS-95. Theoretical analysis shows that when used for voice services, CDMA 1X can support twice the capacity of IS-95. For data services, it can support 3.2 times the capacity. The theoretical bandwidth of CDMA 1X is 300kb/s, with an application bandwidth of around 100kb/s (symmetrical bidirectional transmission), and it supports TCP/IP connections for Internet access and data transfer.
Wireless communication based on CDMA 1X includes networking solutions and principles of wireless data transmission. The wireless data transmission system typically consists of a data service center, a communication network, and a data terminal. Considering factors like data volume, security, reliability, network status, and cost, a networking approach is adopted where the communication server connects to the public network via a fixed IP or domain name. After the CDMA data terminal unit (DTU) is powered on, it establishes a connection with the communication server. If no fixed IP is available, a fixed domain name can be obtained using software like Peanut Shell. This solution is cost-effective, stable, secure, and reliable.
The principle of uplink data transmission involves several steps: the lower computer sends data to the DTU through an RS232 serial port; the DTU packages the data into a TCP/IP packet and transmits it over the wireless network; the packet travels through the system's packet data service node and is directed to the designated data service center on the Internet; finally, the communication server forwards the data to the host computer and stores it in the historical database.
In system design, the upper computer includes a real-time monitoring system and a historical database. The real-time monitoring system uses Wonderware’s InTouch, which provides functions like system management, data processing, alarm handling, and operation control. The historical database uses Wonderware’s Industrial SQL Server for data statistics, reporting, and historical data retrieval. The lower computer uses ABB AC31 series PLCs, including CPU and I/O modules, to perform data acquisition, query, timing reports, and control operations.
For CDMA data transmission, the H7710 DTU from Shenzhen Hongdian Technology Development Co., Ltd. is used. It features direct RS232/422/485 interfaces, built-in automatic network connection and protocol processing, and supports point-to-point, point-to-multipoint, and center-to-multipoint data transmission with low latency. It can automatically connect to GPRS or CDMA networks and communicate with the data center at any time. It also allows building a virtual private mobile data network across China without relying on operator equipment.
Before use, the H7710 DTU must be configured with parameters such as login credentials, communication interface settings, the server’s fixed IP or domain name, and the working mode. The communication server is designed and implemented to ensure seamless data exchange between the DTU and the host system.