Design and implementation of China Mobile Multimedia Broadcasting Intelligent Network Monitoring System

　　China Mobile Multimedia Broadcasting (CMMB) is a mobile multimedia broadcasting standard independently developed by my country with completely independent intellectual property rights. At present, CMMB networks in major cities across the country are being built and improved, and the coverage test of CMMB signals provides important data basis for network optimization and adjustment. The construction of digital TV broadcasting networks is a long and complex process that requires continuous adjustment and optimization to achieve an ideal effect. Only effective and accurate network coverage testing can provide a reliable basis for adjustment and optimization. A mature and stable CMMB network coverage test system is of great significance to the development of CMMB. Therefore, it is necessary to design a coverage test system for CMMB networks.

　　This design realizes real-time monitoring of CMMB network coverage at the test point based on the high-performance single-chip microcomputer STM32 and GPRS wireless communication solution, and uses the GPS receiver to upload the geographic location information of the test terminal to the server, completing the precise positioning of the monitoring terminal.

　　The terminal board adopts a solar power supply system to ensure long-term stable operation without power supply and personnel supervision. Finally, through comprehensive testing, it can realize all the required functions and fully meet the requirements of this design.

　　1. Test Requirements Analysis

　　In order to monitor the test point in real time and accurately, the following points need to be done. The geographical location of the test site, including longitude and latitude, is counted at least once a second; the battery power of the terminal board is updated in real time; the average power within the 8M signal bandwidth, in dBm, is counted once a second, and the measurement accuracy reaches ±1 dBm; the LDPC packet error rate and RS packet error rate of CMMB signal decoding are counted once a second; the server can change the information reporting time interval at any time, and can change the terminal tuner and demodulator configuration parameters to adapt to the different demodulation parameters in different regions.

　　2 Overall design

　　This system is divided into a test terminal and a server. The server only needs a personal computer with good performance, while the test terminal is mainly composed of the following modules: RF front-end module, power measurement and storage module, GPS receiver, solar power supply module, processor module and GPRS wireless communication module. Each module is mainly connected and communicated through the GPIO port of the STM32 microprocessor. The processor needs to tune the channel and set the demodulation parameters of the tuner and demodulator of the RF front end, and read information such as RS packet error rate and LDPC packet error rate. The CMMB signal tuner mainly tunes the high-frequency signal received from the antenna to output the intermediate frequency signal; the CMMB tuning and demodulation module mainly demodulates and decodes the signal; the power measurement and storage module is responsible for converting the signal power into a level signal and sending it to the ADC of the STM32 and storing the system setting parameters. The GPS receiver is used to obtain the geographical location information of the monitoring point. Finally, the processor sends the information to the server through the GPRS wireless module and receives the control command from the server. The overall structure of the system is shown in Figure 1.

　　3 System Hardware Design

　　3.1 RF front-end module

　　The RF front-end module includes a tuning unit and a demodulation unit.

　　The RF signal tuning module in this system uses MXL5007. The chip can receive continuous frequency signals from 44 to 885 MHz through antenna or wire, and tune the input RF signal to output 4 to 44 MHz intermediate frequency signal. This chip also has the function of lossless loop-out of the original RF signal, which allows the chip to output the intermediate frequency signal to the power measurement module while also losslessly looping out a CMMB signal to the subsequent demodulation module, making it an ideal choice for the tuner of this system.

　　The tuning and demodulation module uses the IF206 chip from Innofidei Video, which supports the CMMB broadcast channel standard and multiplexing standard; can receive satellite signals and terrestrial signals at the same time; has low power consumption, low cost, and no special requirements for front-end and back-end equipment.

　　3.2 GPRS wireless communication module

　　This system uses GPRS wireless communication solution, using Fibocom's G600 module, supporting Dual 900/1800 or 850/1900 dual frequency. The G600 module has a compact appearance, low power consumption, reliable GPRS data connection, built-in TCP/IP protocol stack, and uses serial port communication.

　　3.3 GPS Receiver

　　The monitoring terminal collects the geographical information of the monitoring point through the GPS receiver, including: longitude and latitude, altitude, etc. The test system displays the test data at the corresponding position on the map according to the obtained GPS information. The GTS-4E-00 module is selected in this system, which is packaged in stamp patch and can adapt to harsh working environments such as high temperature, high humidity, and electromagnetic interference. Its simplified circuit diagram is shown in Figure 2. TXD is connected to STM32 serial port 1, the module wake-up end is connected to PA9, and J1 is the receiving antenna.

　　3.4 Processor Module

　　The processor is the core of the entire monitoring terminal, responsible for collecting data from the RF front end and communicating with the server. The processor uses the STM32F103RCT6 microcontroller, which is a new 32-bit embedded microprocessor based on the Cortex-M3 core. It combines high performance, real-time, low power consumption, high integration, etc. The system clock is as high as 72 M, the development is simple, and a variety of peripherals are integrated in the chip. The circuit diagram of the microcontroller is shown in Figure 2.

　　Among them, the PB6 and PB7 ports of the microcontroller are its IIC interfaces, responsible for communicating with MXL5007 and the storage chip AT24C1024; the PA5-PA7 ports are its SPI interfaces, used to communicate with IF206; the PA10 port is the serial port 1 receiving end, used to receive GPS module data, and the PA9 port is used to enable the GPS module; PA2 and PA3 are serial port 3, used to communicate with the GPRS module G600; PC2 and PC3 are respectively used as the enable and reset terminals of MXL5007; there are also two 12-bit ADCs inside the STM32, and PC4 is the internal ADC1 analog input port, used to measure the average power of CMMB signals.

　　3.5 Solar power supply module

　　The test terminal adopts solar power supply, which enables the terminal to work stably for a long time in the absence of power and unattended conditions. The power interface of the monitoring terminal board adopts DC-12 V, and adopts solar power supply. The controller is designed to manage the charging and discharging of the battery. This controller is designed for solar DC power supply system and uses an intelligent controller with a dedicated computer chip. The functional block diagram of the controller is shown in Figure 3.

　　4 System Software Design

　　The software programming of STM32 processor adopts C language programming, and the development environment is MDK-4.0. The basic principle of the software is shown in Figure 4.

　　After the system is turned on, it is initialized, including initializing the various peripherals of STM32, reading the parameter values ​​previously set by the system from EEPROM, and initializing MXL5007 and IF206. After the system is initialized, it reads the remaining power of the solar battery, GPS information, RS packet error rate, LDPC bit error rate, signal average and other information, and then determines whether to establish a connection with the server. After the connection is successfully established, it uploads these data to the server at the set time interval; at the same time, it always checks the command information from the server, such as setting the time interval for changing information upload, the threshold values ​​of various parameters, the frequency of the tuning and demodulation chip, etc. After the parameters are modified, they are immediately stored in the EEPROM to prevent the information from being lost during power failure. These parameters will be read out again after the next startup. [page]

　　5 Equipment prototype and system joint debugging

　　After the test terminal equipment prototype and server software were completed, the project team used the equipment prototype and server software to conduct system joint debugging. The project team selected three monitoring points in Beijing. The monitoring point information is shown in Table 1. A CMMB monitoring terminal was placed at each of the three monitoring points, as shown in Figure 5.

　　Each monitoring point transmits monitoring parameters to the server in real time. The server obtains monitoring data through the IP network and performs analysis and alarm processing according to the software settings. The monitoring interface of the server software is shown in Figure 6.

　　Through equipment joint debugging, the project team optimized the system performance and improved the system stability. After several days of experiments, it was proved that the monitoring system can respond to the signal status of the CMMB network in a timely and effective manner.

　　6 Conclusion

　　The monitoring system uses the STM32 processor development platform and GPRS wireless communication solution, successfully realizing real-time monitoring of the user-side CMMB network coverage, providing a highly efficient and convenient means of supervision for the majority of engineering and technical personnel, and meeting the design requirements.