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The China Meteorological Administration Satellite Broadcasting System (CMACast system), owing to its extensive coverage and the significant advantage of being intercontinental and end-to-end, unaffected by ground communication conditions, becomes one of the crucial communication means for global meteorological data distribution services. As the China Meteorological Administration continuously enhances its global monitoring, global forecasting, and global service capabilities, the requirements for providing meteorological data distribution services to international users, especially those along the Belt and Road lnitiative, become increasingly demanding. However, the CMACast system has an obvious service shortcoming in that its broadcast signal coverage is limited to the Asia-Pacific region. To meet the global meteorological service demands, the satellite broadcasting system of the meteorological informatisation system project is comprehensively upgraded. Among these upgrades, the expansion of the broadcast coverage area is one of the most significant. The selection of transponders for the new broadcast communication satellites and the design of broadcast parameters are key issues that need to be addressed with priority. Through a survey of all communication satellite resources over China, based on the coverage area of satellite C transponders, four communication satellites are initially selected as the research objects from 20 on-orbit communication satellites of CITIC Satcom and China Satcom. Through a comprehensive comparison and analysis of the coverage area, signal strength, transponder frequency, and the coverage of existing users of these four satellites, the results show that the AsiaSat 7 is the optimal choice. Therefore, based on the AsiaSat 7, the broadcast links to the Belt and Road lnitiative regions and countries are calculated and analysed respectively. The results indicate that using the AsiaSat 7 can meet the requirements of the broadcast service, verifying the correctness of choosing the AsiaSat 7 as the broadcast transmission design. At the same time, to make the new broadcast system compatible with all existing users, actual tests are carried out on various modulation methods, coding rates, roll-off factors, and broadcasting rates under the condition of antennas with different receiving apertures. Through actual tests, 8PSK modulation, 3/4 coding rate, and 0.1 roll-off factor are optimally selected as the operation parameters for the broadcast service. This not only meets the needs of the expanded and upgraded broadcast coverage but also is compatible with all existing users. The achievements are applied to the upgrade and construction of the CMACast system in the meteorological informatisation system project. As a result, the coverage of the new-generation CMACast system is expanded from the Asia-Pacific region to the Belt and Road lnitiative regions such as the Middle East and Africa, enhancing the information network support for meteorological services in these regions.