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Design of CMA's Broadcast System for Meteorological Data—CMACast
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摘要: CMACast是中国气象局基于DVB-S2标准的新一代卫星数据广播系统，使用亚洲卫星4号星一个完整的C波段转发器对中国及亚太地区进行气象资料、卫星遥感资料及流媒体视频的广播。该文详细介绍了CMACast的系统结构、主要功能和关键技术，并与中国气象局现有的3个广播系统PCVSAT，DVB-S和FENGYUNCast以及EUMETCast，GEONETCastAmericas进行了比较。比较结果表明：CMACast覆盖面广，技术领先，功能强大，是目前世界领先的卫星数字广播系统。预计2012年初CMACast全面建成并投入使用，CMACast系统建成后，将全面整合PCVSAT，DVB-S和FENGYUNCast 3个系统的业务和用户，成为中国气象局唯一的广播系统，并作为GEONETCast的亚洲区域中心，向亚太地区进行GEOSS数据的广播。
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关键词:
- 卫星数据广播;
- DVB;
- CMACast;
- GEONETCast
Abstract: Due to broad coverage, low-cost user equipment and easy installation, data broadcast system based on commercial communication satellite has been considered to be the most effective way for data dissemination worldwide. CMA has implemented three satellite broadcast systems, PCVSAT, DVB-S and FENGYUNCast since 1998. PCVSAT and DVB-S, which are Ku band systems covering China and surrounding area, are primarily used to distribute land and air based observation data and products. FENGYUNCast, which is a C-band system covering Asia and part of the south-western Pacific area, is primarily used to distribute space-based observation data and derived products from Fengyun series satellites of China. FENGYUNCast becomes part of GEONETCast Centre of GENONETCast Network in Asia-Pacific region in 2008. Currently PCVSAT, DVB-S and FENGYUNCast have 2400, 700 and 200 users respectively.The coexistence of three broadcast system causes inefficiency and inconvenience to both CMA and users. In 2008, CMA started to build a new system, CMACast, to consolidate the services and users of the three systems together. CMACast is a multimedia dissemination system based on the second-generation Digital Video Broadcast (DVB-S2) technology with both file and multimedia transmission capability, employing a whole 36 MHz C-band transponder of AsiaSat-4 and the transmission capacity can reach up to 70 Mbps. Besides high data rate, CMACast is expected to enhance user management and data exchange cooperation with other regional GEONETCast Network Centres (GNC), including EUMETCast and GEONETCast Americas.CMACast is not only the main component of CMA national and international communication system, but also the main component of WMO IGDDS and GEONETCast. The infrastructural, main function and key technology of CMACast and its comparison between PCVSAT, DVB-S, FENGYUNCast, EUMETCast and GEONETCast Americas are introduced. Infrastructural introduction includes system architecture, coverage and capacity. Main function includes file broadcast, multimedia broadcast, data exchange, user management and data reception. Key technology includes DVB-S2 standard, bandwidth sharing mechanism and dynamic data encryption mechanism. The comparison result indicates that CMACast is a leading satellite data broadcast system in the world with broad coverage, advanced technology and multiple functions.CMACast is on trail operation in the middle of 2011 and will operate simultaneously together with PCVSAT, FENGYUNCast and DVB-S from June to October in 2011, when all the users of the current three systems will transit to CMACast. After that, the current three systems will be closed and CMACast will be the only operating data broadcast system of CMA.-
Key words:
- satellite data broadcast;
- DVB;
- CMACast;
- GEONETCast
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图 5 CMACast接收通道目录设置界面
Fig. 5 Channel and directory configuration for CMACast data reception
表 1 DVB-S与DVB-S2标准主要技术比较
Table 1 Main technical comparison between DVB-S and DVB-S2 standard
指标 DVB-S DVB-S2 调制解调 QPSK QPSK, 8PSK, 16APSK 信道编码 Viterbi, Reed-Solomon LDPC, BCH 基带滤波 α=0.35 α=0.2~0.25 
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表 2 CMACast速率统计复用策略
Table 2 Bandwidth sharing mechanism of CMACast
级别 约束条件 功能描述 特别要求 应用目标 通道组 最大速率 通道组内所有广播通道实际播发速率和的最大值 通道组内所有广播通道实际播发速率和在任何时候都不能超过通道组的最大速率 通道组最大速率的限制是为了满足文献[18]中，当有一组通道的广播需要在另一颗卫星上进行转发，以扩大系统覆盖范围时，最大速率的限制可保证转发信号的带宽不超过在第2颗卫星上的租用带宽 通道 最小速率 通道有数据广播时，需达到的最小速率 系统中各通道最小速率的和小于系统总速率 通道的最小速率指系统最拥挤的情况下，仍可保证的速率。对于流媒体业务，最小速率就是保证流媒体传输质量的速率 最大速率 通道数据广播可占用的最大速率 通道数据广播的最大速率不能超过系统总速率 通道最大速率的限制是为了避免某通道速率过高，而且小文件过多时，对小站文件接收系统造成的冲击 优先级 通道获取系统剩余速率的先后顺序 优先级高的通道，优先获取剩余速率 0级优先级最高，为流媒体广播的优先级，1~9为文件广播的优先级 1级目录 优先级 1级目录文件广播的先后顺序 对于通道下的多个1级目录，高优先级目录中的文件先于低优先级目录中的文件发送 1级目录的优先级可分为4级
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表 3 CMACast的动态加密机制
Table 3 Dynamic encryption mechanism of CMACast
层次 名称 密鈅产生 加密 解密 备注 1 用户密钥 (UK) 内置在加密狗中 固定不变 不可复制 UK即小站ID号 2 业务密钥 (SK) 动态生成SK，
周期可设置主站使用UK对
SK进行加密小站使用UK对
SK解密SK更新周期
为15~30 d3 加扰控制字 (CW) 动态生成CW，
周期可设置主站使用SK对
CW进行加密小站使用SK
对CW解密CW更新周期为30 s 4 实际数据 文件和流媒体 主站使用CW对
实际数据加扰小站使用CW对
实际数据解密
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表 4 卫星数据广播系统能力比较
Table 4 Capacity comparison between satellite data broadcast systems
类别 指标 PCVSAT DVB-S FENGYUNCast EUMETCast GEONETCast Americs CMACast 系统构成 工作频段 Ku Ku C Ku, C C C 覆盖范围 中国及
周边地区中国及
周边地区中国及亚太
绝大部分地区欧洲、非
洲、美洲北美、中
美、南美中国及亚太
绝大部分地区调制方式 QPSK1/2 QPSK3/4 QPSK 3/4 QPSK 3/4 QPSK 3/4 8PSK 5/6 信息速率 2 Mbps 8.5 Mbps 8.8 Mbps 16 Mbps 2 Mbps 70 Mbps 主站操作系统 Windows Windows Windows Windows Windows Linux 小站操作系统 Windows Windows Windows Windows Linux Windows Linux 系统功能 文件广播 有 有 有 有 有 有 流媒体广播 MPEG1 MPEG4 MPEG2，MPEG4，
H264，VGA用户管理 接收机地址 接收机地址 接收机地址 加密狗 加密狗 加密狗 子网管理 有 有 数据交换 有 有 有 关键技术 传输标准 HDLC DVB-S DVB-S DVB-S DVB-S DVB-S2 统计复用 通道 通道、1级目录 通道组、通道 通道组、通道 通道组、通道、
1级目录动态加密 有 有
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