| In recent years, frequent meteorological disasters have caused the heavy losses of lives and properties. Most of those losses, spring from warning information not transmitted in time which caused by their release platforms having problems of transmission aging, limited coverage of information and other constraints. Therefore, the selection of warning information release platform is significant to disaster prevention and reduction. As the DAB (Digital Audio Broadcasting) technology has advantages such as large coverage area, high reliability of work, low transmission power and reliable delivery to mobile receivers, it has been a reliable mean of early warning information transmission in disaster prevention and reduction in china. However, DAB can only transfer audio and text information, and can not transfer video information. DMB (Digital Multimedia Broadcasting) is expanded based on DAB, and compared with DAB system it strengthens the ability of error protection and the efficiency of coding method. The information of audio, text and video can be transmitted simultaneously in DMB system, which solves the singleness of audio broadcasting of the early warning information.On the basis of DMB research, a warning information synthesis pre-processing system based on DMB is designed. The functions of this system include:compression and synthesis of early warning information, channel coding and rate control. In the aspect of theory, based on the codec algorithms of MPEG-4AAC and H.264, it realizes compression of video and audio information real time and efficiently. When dealing with the synthesis for video and audio warning information, the synchronization mechanism of video and audio warning information is used to guarantee the information be played synchronically in decoder. Moreover, to improve the reliability and correction capability, Reed-Solomon coding and convolutional interleaving coding are used to realize channel coding for synthesized transport stream. Finally, to solve the technical difficulties of transmission rate instability and the high precision of the coding parameters which makes it difficult for software to realize, a method of inserting null packages is proposed to achieve constant bit rate controlling.In the aspect of realizing, based on the above-mentioned theoretical research results, the software for the warning information synthesis pre-processing system based on DMB has been designed, which includes the functions of warning information compression, warning information synthesis, channel coding and intelligent stream rate controlling. During the test stage of the system, a DMB radio station has been built by combining the software with the hardware in our lab for verifying the functions of this pre-processing system: Firstly, DMB sending system is used to code and send out the TS (Transport Stream) packets, which have been processed by the system. Meanwhile, a DMB receiving system is used to receive and decode them. We judge whether the system is designed successfully or not by verifying the playback of the decoded warning information. The results show that, the transport stream coded by this system can be transmitted by DMB sending system, and also can be decoded and played smoothly and synchronously in DMB receiver without obvious distortion from original audio/video information. From the above testing results we can conclude that all modules of the pre-processing system are working properly and stably.The pre-processing system has been tested in our lab and been successfully applied to the multichannel disaster warning information receiving platform which the China Meteorological Administration specified R&D. The platform has been tried out in more than a dozen provinces, autonomous regions in china, and is spreading the industrialization of relative products. |
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