Research And Implementation Of Demodulation Algorithms In Digital Radio Monitoring System

Digital radios, featured with high spectrum utilization, good voice quality and rich additional services, gradually take place of analog radios, and are used in public service and other industries. Because the traditional radio monitoring equipment cannot demodulate and decode the digital radio signal, and cannot meet the demand of monitoring tasks of digital radios, a monitoring equipment for digital radios must be developed. The demodulation algorithm, which achieve the demodulating and capturing of the digital radio signal, is one of the key technologies in the physical layer of the digital radio monitoring system. Therefore, the research and implementation of the demodulation algorithms for the digital radio monitoring system are of great significance.Based on the research situation of domestic and foreign CPFSK demodulation algorithms, first of all, the overall architecture of the digital radio monitoring system is analyzed in this paper, and the structure and function of the radio frequency front-end and the digital intermediate frequency signal process circuit board are analyzed in detail. Then, the principle of modulation and the burst structure of DMR/dPMR digital radios are detailed stated, and the best coherent detection algorithm, the 1-bit differential Viterbi algorithm and the differential frequency discrimination algorithm are analyzed and compared, and a demodulation algorithm which can be easily implemented in the digital radio monitoring system is given, and the digital down-conversion algorithm, the synchronization algorithm, the differential frequency discrimination algorithm and the frequency offset estimation algorithm are designed, and the demodulation algorithm is simulated and verified by the Matlab software. Next, the interface module, the digital down-conversion module, the frequency discrimination module and the synchronization module of the demodulation algorithm are developed by the VHDL programming language on the XC7K325T hardware platform, and the functions such as digital down-conversion, synchronization and frequency discrimination for the DMR/dPMR signal are implemented. Finally, the function test and performance test for the demodulation algorithm are performed by the Chipscope logical analyzer, and the test results show that the functions of the digital down-conversion module, the synchronization module and the frequency discrimination module are operating well, and the maximum usable sensitivity is -120dBm, which satisfies the requirement of engineering design.