Cellular mobile communication network base station parameter collection system implemented with PLC

    Abstract: This paper introduces a cellular mobile communication network base station parameter collection system implemented using the small programmable controller (PLC) product FP1-C24 of Panasonic Electric Company of Japan. Because PLC is used as the data collector, the system has the advantages of high reliability and low cost.

    Keywords: Programmable Controller (PLC) Data Acquisition Cellular Mobile Communication Network    

    Modern mobile communication networks adopt a cellular structure cell system and implement frequency reuse to improve frequency utilization. In order to meet coverage requirements and increase communication user capacity, a large number of mobile communication base stations must be established. Due to the large number and wide distribution of base stations, it is difficult to inspect base stations manually. Therefore, it is necessary to establish an automatic monitoring system for the status of base stations to facilitate the maintenance and management of base stations.

    As a new generation of industrial control device, programmable controller (PLC) has a simple structure, excellent performance, high reliability, strong anti-interference ability, easy to learn and use, and can be modified online. It has been widely used in metallurgy, Industrial control fields such as mining, machinery, and light industry provide powerful tools for industrial automation. At present, the functions of PLC are increasing day by day, especially when equipped with certain modules (such as A/D, D/A, etc.), which can collect and control analog quantities and have the function of remote communication, which makes the application fields of PLC greatly expanded. Based on the advantages of PLC, we apply PLC to the parameter collection of cellular mobile communication network base stations. It can conduct real-time monitoring of the base station’s transmit power, standing wave ratio, AC and DC power supply voltage, etc., and can also collect fire alarms and burglary alarms in the base station. Wait for the information, and then use the remote communication function of the PLC to send the information back to the monitoring room to achieve unattended base stations.

   1. Composition of base station parameter collection system

    According to the requirements for base station monitoring, this system must conduct real-time monitoring of the transmit power and reflected power of each channel transmitter of the base station, the 24V and 12V power supply voltages used by the base station equipment, the voltage of the AC power supply, rectification alarms and fuse alarms, etc. , and can monitor the room temperature, fire prevention, anti-theft and other safety information of the base station.

    The composition of the system is shown in Figure 1 . The core of the system is the data collector. The transmit power and reflected power of each channel are converted into 0~5V analog voltage by the transmitter and then sent to the data collector; AC voltage, 12V DC voltage, and 24V DC voltage also pass through the transmitter. It changes to a voltage of 0~5V and sends it to the data collector; the room temperature is detected by the temperature sensor and then converted to a voltage of 0~5V and sends it to the data collector; the rectifier alarm and fuse alarm information are switch values, smoke detectors and temperature detectors. The output of the fire alarm system is a switching value, and the infrared anti-theft alarm also outputs a switching value. These switching values ​​are sent to the data collector for collection.

    The data collector in the picture is implemented by the small PLC product FP1 produced by Panasonic Electric Company of Japan. Although FP1 is a small computer, it has high performance-price ratio and complete hardware configuration. It can be expanded by adding I/O modules, up to several hundred points; by expanding the A/D module, the input of analog quantities can be realized; the machine is equipped with an RS232 interface, which can realize the communication between the PLC and the PC. communication. Therefore, it is relatively easy to configure as a data acquisition system.

    2 Data collector implemented with FP1

The data collector is composed of an FP1-C24 main control unit and an expanded A/D unit, as shown in Figure 2 . The A/D unit is responsible for the input of analog quantities, while the main control unit is responsible for the input of switching quantities and the multiplexing switch for analog quantities.

    The A/D unit of FP1 has four analog input channels (CH0~CH3), and the occupied I/O channels are:

    CH0——WX9 (X90-X9F)

    CH1——WX10 (X100-X10F)

    CH2——WX11 (X110-X11F)

    CH3——WX12 (X120-X12F)

    Each channel can be input as voltage or current, with a resolution of 1% of full scale. When inputting voltage, the input range is 0~5V or 0~10V. This system uses 0~5V voltage input. Since each main control unit can only have one A/D unit, and each A/D unit only has 4 input channels, in order to measure more analog quantities, it is necessary to use a multi-channel selection switch to select the analog quantity and then input A /D module. In this system, the CH2 channel is used for 12V voltage measurement, the CH3 channel is used for 24V voltage measurement, and the CH0 and CH1 channels are expanded through the multi-select switch to measure the transmit power and reflected power, as well as the indoor temperature and AC voltage of the base station.

    The C24 main control unit has 16 input ports (X0~XF) and 8 output ports (Y0~Y7). Input ports X0~XF are used for switching inputs. X0~XF are divided into two groups, among which X0~ For the input of anti-theft alarm, fire alarm and other signals, the signal system must latch the situations that have occurred until the monitoring room issues a command to reset. The ladder diagram used for the X8 input latch is shown in Figure 3, and the ladder diagram used for the X9~XF latch is similar to Figure 3. The PLC internal general registers R148~R14F are used for the latches of X8~XF respectively. R15D is used as a reset register. The PC sends commands through the RS232 port to set or reset. When it is turned on, R148~R14F is reset. When R15D is set to open circuit, X8~XF monitor the input signal.

    Output relays Y2~Y7 are used as multi-way selection switches, and their connections are shown in Figure 2. Among them, Y2, Y4, and Y6 are used as a group. The signals sent to Y2, Y4, and Y6 are selected and sent to the CH1 channel of the A/D unit for transmitting power and AC voltage measurement; Y3, Y5, and Y7 are used as another group. , the selected signal is sent to the CH0 channel of the A/D unit for measurement of reflected power and indoor temperature. The PLC is programmed to turn on Y2, Y4, Y6 and Y3, Y5 and Y7 in turn, as shown in Figure 4. When the corresponding output relay is turned on, the corresponding signal is connected to the CH0 or CH1 channel of the A/D unit, and the A/D converted values ​​(WX9, WX10) of the CH0 and CH1 channels at this time are read and stored in the corresponding storage unit. Realize the collection of multiple analog signals. In order to avoid uncertainty in the data read when switching inputs, the A/D value (WX9, WX10) must be stopped reading before switching, as shown in Figure 4. Since the transmit power and reflected power of each channel of the base station must be read at the same time to obtain the standing wave ratio, it must be divided into two sets of multi-way selection switches. Y2 and Y3 are turned on at the same time and collected at the same time. The same is true for Y4, Y5, Y6, and Y7. . If you want to collect more analog inputs, you can use a main control unit with more output relays (such as C40) and add expansion I/O modules (such as E8, E40, etc.).

    Y0 output relay is used to reset the smoke alarm.

    3 Communication between PLC and PC

    FP1 can communicate with the PC through the RS232 port or RS422 port. The PC can set up the PLC, program the PLC, and read or set the status of the PLC's relays and registers through the communication port. FP1 adopts the MEWTOCOL-COM standard protocol, a dedicated communication protocol of Panasonic Electric Company of Japan. Its format is as follows:

    Among them, BCC is the block check code, which is generated from the previous characters according to certain rules. Panasonic Electric Co., Ltd. has given the BCC generation program; CR is the end code, and the value is 0DH.

    The FP1-C24 main control unit has both RS232 and RS422 ports. This system uses the RS422 port for programming the PLC, and uses the RS232 port as the remote communication port with the computer. The PLC preprocesses the collected base station information and stores it in the internal general data register units DT100~DT145. Use VB to program the PC and send the data block read command RD to the PLC through the COM2 port. After receiving the command, the PLC stores the data in DT100~DT145. The data is sent to the computer through the RS232 port, and the data is displayed on the display after being processed by the computer, thereby realizing the monitoring of the base station. At the same time, the PC can reset the latched X8~XF signals and the smoke alarm by sending the write contact command WCS to the PLC to set R15D and Y0. The program flow is shown in Figure 5.

    To sum up, this system uses PLC for data acquisition. After expanding the A/D module, the output relay of the PLC is used to form a multi-channel selection switch, thereby realizing the collection of multiple analog signals. Due to the advantages of PLC, the data acquisition system composed of PLC has the advantages of high reliability, strong anti-interference ability, and convenient construction. Experiments show that the data collector implemented with PLC can work reliably.