China Mobile Multimedia Broadcasting (CMMB) is a mobile multimedia broadcasting standard independently developed by China and with completely independent intellectual property rights. At present, CMMB networks in major cities across the country are under construction and improvement, and the coverage test of CMMB signals provides an important data basis for network optimization and adjustment. The construction of digital TV broadcasting network is a long-term and complicated process, and it needs constant 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 network.
This design is based on the high-performance single-chip STM32 and GPRS wireless communication solution to achieve real-time monitoring of the CMMB network coverage of the test point, and use 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 power supply method of the terminal board adopts a solar power supply system to ensure its long-term stable work without power and personnel guarding. Finally, through comprehensive testing, all the required functions can be achieved, fully meeting the requirements of this design.
1 Test requirements analysis
In order to monitor the test points in real time and accurately, the following points need to be made. The geographic location of the test site, including longitude and latitude, is counted at least once per second; the battery power of the terminal board power supply is updated in real time; the average power within the 8 M signal bandwidth, in dBm, is counted once per second, and the measurement accuracy reaches ± 1 dBm ; CMMB signal decoding LDPC packet error rate, RS packet error rate, statistics every second; the server can change the information reporting interval at any time, and can change the terminal tuner and demodulator configuration parameters to adapt to different regions of demodulation The parameters are different.
2 Overall design
The system is divided into a test terminal and a server. The server only needs a personal computer with good performance, and the test terminal is mainly composed of the following modules: RF front-end module 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 set the tuning channel and demodulation parameters for the tuner and demodulator of the RF front end, and read the 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 an intermediate frequency signal; the CMMB tuning demodulation module mainly demodulates and channel decodes the signal; the power measurement and storage module is responsible for converting the signal power to a level The signal is sent to the ADC of STM32 and the system setting parameters are stored. The GPS receiver is used to obtain the geographic position information of the monitoring point. Finally, the processor sends the information to the server through the GPRS wireless module and receives control commands from the server. The overall structure of the system is shown in Figure 1.
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