Distributed real-time hydrological monitoring system with wireless data communication

    Abstract: This article introduces a distributed real-time hydrological monitoring system based on wireless data communication. The system has functions such as real-time monitoring and alarming, local remote query of historical data, and hydrological trend prediction and analysis. At the same time, wireless spread spectrum technology and anti-interference measures for wireless data communications are elaborated.

    Keywords: wireless data communication spread spectrum anti-interference hardware/software design

The frequency of floods in the Yangtze River Basin is increasing year by year, and flood control has become the primary task of managing the Yangtze River. How can we better grasp the hydrological characteristics of rivers, predict the coming of floods, and prepare for flood control? Real-time hydrological monitoring has become an important part of waterproofing and water control. In order to avoid the disadvantages of manual monitoring, a distributed remote real-time hydrological real-time monitoring system with wireless data communication was developed. The system has functions such as real-time monitoring and alarming, local and remote query of historical data, and hydrological trend prediction and analysis.

1 Design and implementation plan of distributed hydrological monitoring system

The entire system consists of three parts: telemetry station, monitoring master station, and Intranet/Internet. Its structural composition is shown in Figure 1. There are a total of 13 telemetry stations, with the same structure as telemetry station #1.

1.1 Spread spectrum technology of digital transmission MODEM [1, 2]

WY9678E wireless data transmission MODEM is a new type of direct sequence spread spectrum wireless modem. Its working principle is: at the transmitting end, the spreading code with high code rate is directly used to spread the spectrum of the signal, and at the receiving end, the same spreading code is used. The frequency coding is despread to restore it to the original signal. Specifically: the signal D at the transmitting end is modulated by the modulo 2 adder and then generated by a pseudo-random code generator to generate a spread spectrum signal. The carrier signal is then modulated by the carrier modulator in QPSK mode. The bandwidth spread spectrum signal obtained after modulation is amplified by a wideband amplifier and then transmitted. out; and at the receiving end, the received signal is amplified and processed by a radio frequency broadband filter to improve the signal-to-noise ratio and extract the required signal to align the phase. The synchronization circuit picks up the accurate phase of the spread spectrum code sent and uses it as synchronization signal, so that the phase difference between the spread spectrum signal generated by its PN code generator and the transmitted spread spectrum code is as small as possible, so as to obtain information data D.

The system uses spread spectrum communication technology to bring design benefits: ① It improves the anti-interference performance of the system and has a higher signal-to-noise ratio; ② Since the spread spectrum signal is submerged in white noise, it is not easy to be discovered, so the signal is concealed It has strong performance and low interference; ③ it is easy to implement code division multiple access; ④ it improves the anti-multipath interference performance of communication. WY9678E works on the globally accepted, license-free 2.4GHz ISM band. It has a built-in 16-bit 80188 CPU, signal modem and RS422A/485 standard communication interface. The use of PLL synthesis technology makes it have high-frequency stability, and the use of time-division pulse code modulation PCM mode makes it have strong anti-multipath interference capabilities. Industrial control computers with PC104 bus mode have better communication compatibility. Used together, the communication performance has been greatly improved. The communication protocol between WY9678E and industrial computers (PC014 and monitoring industrial computers) is as follows:

·Communication interface: standard asynchronous RS-422A five-wire full-duplex mode;

·Communication word format: 1 stop bit, 7 data bits, even parity;

·Baud rate: 9600bps.

1.2 Antenna

The height and gain of the radio antenna directly affect the quality and distance of communication. In order to eliminate the influence of the high mountains in the Yangtze River Basin, an omnidirectional antenna that is resistant to lightning strikes, radio waves, and multipath interference is specially designed. It is installed on the shore, and the relative height to the ground is maintained between 20 and 50m, with a gain of 6dB~ 11dB, effectively improving the communication performance of the system.

2 Key technology research

2.1 Long-distance antenna electrical communication technology under strong interference

Because the banks of the Yangtze River are equipped with navigation radars, television transmitters and other strong electromagnetic field transmitting devices, radio communication channels are easily interfered with. Wireless data communication is the only channel for transmitting hydrological monitoring information, so wireless communication under strong electromagnetic interference is one of the key technologies of this system.

The way to solve this key technology is to use two sets of data transmission stations with different frequency points as a redundant design, and to avoid the main interference frequency bands in the selection of frequency points. At the same time, advanced and efficient coding technology and error correction technology are used to protect Correctness of transmitted instructions and data.

2.2 Multipath interference solution technology

The special physical environment of the Yangtze River Basin can easily cause multipath interference in wireless data communications. In this system, the correlation characteristics between spreading codes are used to add the same code sequence from the path signal at the receiving end to strengthen the useful signal, and then extract the strongest signal among them, thereby achieving effective anti-multipath interference .

3 System Programming

For data services, Windows NT is used as the server operating system, SQL Server is used as the database management system, and Power Builder is used as the development tool to develop Client/Server-based programs. The software design of the monitoring industrial computer part uses Windows 9X as the operating environment. The application software adopts Windows window technology and has a brand-new browser interface. The operation interface is graphical, making the operation more intuitive, convenient and flexible, and the window interface is more friendly. .

3.1 Monitoring part

The real-time monitoring system software mainly completes the following tasks: real-time monitoring of hydrological information and water regimes, equipment failure alarms, real-time centralized display and storage of measurement parameters, data management, analysis, statistics and query, regular and random printing of reports, etc. The functions of the software are shown in Figure 2. The software design of the monitoring part adopts the mixed programming method of Visual Basic and Visual C++. The communication program between the main station and the telemetry station uses Microsoft's MSCOMM ActiverX control and drives the database through ODBC to connect to the Access database in Office97/2000. The entire application is programmed in a modular manner, including the main control module, initialization and self-test module, communication control module, real-time monitoring module, data processing, monitoring and alarm module, data management module, report timing, random printing, etc.

3.2 Communication process solutions

In the entire programming process, real-time communication and monitoring modules are the most important. Once there is a problem with the communication program, the entire system will be paralyzed. Therefore, in the communication program, error control and fault tolerance technology are adopted. The communication control process is:

(1) Send commands and receive return data. First, the command and data are formed into strings Mark$ and Space$ respectively, and the time required to receive the returned data is set according to the communication rules. Start the RTS signal, use the query method to send the corresponding Mark$ and pace$ of P=Mark and P=Space respectively at single-byte intervals, and then cancel the RTS signal. The OnComm event is triggered when the first data of the returned data is received, and the timer is started at the set time interval. When a timer event occurs, read back all received return bytes during the timer event, then set the time interval corresponding to the lower computer reporting data directly and close the timer.

(2) The lower computer reports data directly. Since the time interval corresponding to the data directly reported by the lower computer is preset, when the first data of the reported data arrives, the corresponding situation is the same as receiving the returned data.

(3) Interference processing. When pure interference data arrives, the corresponding time interval is similar to that of the slave computer directly reporting data, and the timer event is also started. After the timer event is generated, the data is read in, and the interference data can be discarded after analysis by the control program. When interference data arrives along with normal data, the time interval for generating timer events can be appropriately lengthened to ensure that all data is read and analyzed.

The communication control adopts the above method to effectively solve the problems of bus contention, under-reception and mis-reception when receiving/transmitting data signals, data transmission errors, etc., which greatly improves the effectiveness and real-time performance of network communication control, and can improve equipment utilization rate.

Wireless remote real-time hydrological monitoring provides a relatively advanced analysis method for water regime prediction and forecasting in the Yangtze River Basin. This system uses the more advanced spread spectrum technology in the field of wireless communication and more effective anti-interference measures to ensure the safety and reliability of the system. It has certain promotion value and is suitable for monitoring and forecasting water conditions in reservoirs, Yangtze River tributaries, etc.