What are the needs and requirements of the terrestrial digital TV transmission system?
From a macro perspective, terrestrial digital TV is mainly considered from the perspectives of standards, users, and industries. First of all, for terrestrial digital TV transmission standards, the first requirement is to meet the requirements of terrestrial digital TV transmission; the second is to truly have China's independent intellectual property rights; the third aspect is to be functionally scalable; the fourth aspect is also required to develop corresponding Test the system to verify the recommended transmission standard. Secondly, from the user's point of view, it is required to provide a payload code rate greater than 20Mbps for HDTV signal transmission and a payload code rate greater than 5Mbps for SDTV signal transmission, and to use a simple antenna to support indoor fixed reception and support under vehicle speed movement conditions Mobile reception; also must have a single frequency networking capability with a signal coverage radius of not less than 35 kilometers; in addition, the overall performance index should be better than or equivalent to the performance of the corresponding foreign existing standards. Functionally, it has the scalability to support the transmission of multi-priority multimedia data streams such as HDTV, SDTV, audio, data, and short messages. It can realize receiver positioning, timing reception, two-way interactive services and personalized information services for users in the future. Such system function expansion provides the necessary technical foundation. For the industry, the most important thing is to have autonomy, that is, to organically integrate its own basic invention patent into its own transmission standard system, form a relatively complete independent intellectual property rights, and build technical barriers to protect China's digital TV industry. Then it is required to have good economy: the technology is mature and has its own dedicated chip; strive to have the maximum product compatibility with the most common international standards, so as to expand the international development space of China's digital TV industry and share international technical equipment resources. Considering the wireless transmission system of terrestrial broadcasting itself, it is necessary to consider from the aspects of transmission information capacity, anti-dynamic multipath interference / frequency selective fading channel, and single frequency network signal coverage. Generally speaking, the height of DTTB's transmitting antenna is several hundred meters, and the transmitting power is several hundred to several kilowatts, covering tens of kilometers; DTTB should be able to work in single-frequency network mode for larger area coverage of the same frequency signal; China The transmission bandwidth of DTTB is 8 MHz, and the transmission technical measures should mainly aim at frequency selective fading. In terms of transmission information capacity, HDTV requires a payload code rate greater than 20Mbps; SDTV requires a payload code rate greater than 5Mbps; in addition, multimedia service data provides a payload code rate greater than 20Mbps.
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