SBAS电文时序动态编排算法

星基增强系统（SBAS）通过GEO卫星转发SBAS电文实现对GNSS服务性能的提升，以满足民航用户不同飞行阶段的导航需求，因此，合理有效的电文内容及播发时序设计是系统实现高质量服务的重要保证。为提高电文编排的灵活性，避免固定时序填补空余电文引起的播发资源浪费，提出了一种SBAS电文时序动态编排算法，在满足国际标准要求的前提下，综合利用SBAS电文龄期和最大播发间隔实现待播发电文的自动选择。利用NTMF实测数据对当前各主要SBAS的电文进行了特性分析，对所提方法的单双频SBAS电文编排效果进行了评估。结果表明:所提算法可保证电文时序符合国际标准要求，实现了重要电文的优先播发，将空余时隙进行动态分配实现了各类型电文播发间隔的近等比例缩短。与固定时序相比，单频SBAS完好性电文播发间隔缩短约15.0%，首次定位时间缩短约8%，双频SBAS电文首次定位时间缩短约6.5%；与固定时序的BDSBAS B1C电文相比，完好性服务能力提升约14.7%，首次定位时间缩短约16.7%。所提算法有效提升了SBAS电文播发的播发效率，实现了SBAS播发资源的100%有效利用。 

Dynamic SBAS message scheduler algorithm

Satellite Based Augmentation Systems (SBAS) provide SBAS messages through GEO satellites to improve the performance of GNSS in order to meet the navigation needs of civil aviation users, and reasonable and effective message content and broadcast schedule design are important for SBAS to achieve high-quality services. In order to improve the flexibility of message scheduler and avoid the waste of broadcast resources caused by filling the null messages, this paper proposes an automatic scheduler of SBAS message. Under the premise of meeting the requirements of international standards, this scheduler comprehensively uses the age of SBAS message and the maximum broadcast period to realize the automatic selection of the message type to be broadcast. At the same time, this paper uses NTMF data to analyze the characteristics of the current SBAS message, and evaluates the application effect of the proposed scheduler in single- and dual-frequency SBAS message. The results show that this scheduler can ensure that the message schedule meets the requirements of international standards, can achieve the priority broadcast of important messages, and can realize the nearly equal proportion shortening of the broadcast interval of each message type by dynamic allocation of spare time slot. Compared with rigid scheduler, the integrity message broadcast interval is shortened by about 15.0% and the first positioning time is shortened by about 8% for the single-frequency SBAS, and the first positioning time is shortened by about 6.5% for the dual-frequency SBAS message. Compared with BDSBAS B1C rigid scheduler, the integrity message broadcast interval is shortened by about 14.7% and the first positioning time is shortened by about 16.7%. The scheduler can effectively improve the efficiency of SBAS message broadcasting and realize 100% effective use of SBAS broadcast resource.