基于时变图模型的空天DTN星座网络传输协议优化

With the trends of the globe developments on the scientific aerospace techniques and space communications, this project develops an elaborated Store-and-Forward space Disruption-Tolerant Networks via distributed constellations of orbited spacecrafts, which could achieve the rapid return of scientific data by multi-hop delivery. In the project, we attempt to explore the influential aspects of the channel dynamic of each hop on the end-to-end bundle delivery, and find the best route to transport the bundle constantly, by building a time-driven graph of network topology. Using the Extreme Value Theory, we estimate the delivery performance of each section of entire route and deriving the suitable criterions of end-to-end performance. Then, using the Linear/Nonlinear programming algorithms, we could obtain the optimal parameters for the system settings of the bundle delivery, which would efficiently expedite the return of the scientific data from the constellation-based DTN networks. By exploring the collaborated supporting capabilities of the constellation-base network in the high dynamic scenarios, as in this work, we could make systematic theoretical and technical breakthroughs on the real-time applications, such as disaster monitor system, fast-response micro-satellite team. As a hopeful result, the project expects to make the following improvements: obtaining significant gains with the respect of the bundle delivery delay and system throughput. Besides, we will build an experimental platform for the space network with the networked computers and necessary wireless hardware, which could effectively simulate the dynamic of the real space environment and develop the technical experiments.

本课题面向国家航天科技和空天科学的发展趋势，结合空天网络的实时性应用和应急需求，以解决空天任务数据的可靠和快速返回问题为切入点，深入探索在高动态链路条件下DTN网络的匹配传输机理，构造空天图像数据的连续传输路径，实现空天网络星座分布、数据的转发策略和链路特性之间的匹配。主要目标是基于时变图模型建立网络传输性能的评估体系，优化设计与星座分布和链路特性相匹配的传输策略，在保障可靠性条件下加快数据在网络中的传递，为空天网络传输资源的准确评估、快速聚合和高效利用奠定理论基础，也为空间信息和应急快速响应的时空连续支撑能力提供界定和分析工具。本课题搭建能够模拟高动态链路特性的空天DTN网络实验平台（5个物理节点以上），以低轨卫星星座+天链一号星座系统为例，开展地面网络仿真实验。

本项目围绕着的总体科学目标，针对自然科学基金重大研究计划《空间信息网络基础理论与关键技术》的“空间信息网络模型与高效组网机理”核心科学问题开展研究。以分布式星座的空天DTN网络体系结构作为研究对象，以面向空天图像数据实时传输应用的分布式星座设计为切入点，基于时变图模型准确刻画网络拓扑的动态特性和演变规律，深入探索在高动态链路条件下DTN网络的匹配传输机理。本课题经过三年多的深入探索，获得下列研究结果：.1、本课题围绕着网络传输能力的评估和优化，研究高动态下空间DTN网络的匹配传输理论与方法，解决科学数据的可靠传输和快速返回问题。重点解决合适的动态拓扑描述与分析模型，在此基础上对数据业务的传输路径和传输参数进行优化，减小端到端的传输时延，提高网络的传输性能；.2、本课题围绕着分布式卫星星座网络的拓扑控制问题，通过建立骨干网进行数据的传输，确保任意卫星节点通过所提出的骨干网来建立端到端路径，并保证路径的整体性能有所提升；.3、本课题围绕着卫星网络连接中断、流量拥塞等突发情况下的传输策略问题开展研究。基于时空图和卫星业务的ON/OFF概率模型，提出了可以有效避免拥塞的最小开销路由算法，解决卫星网络在突发条件下的数据传输难题；.4、针对分布式星座的高动态拓扑带来的数据分发难题，本课题通过引入网内缓存机制设计基于沿路缓存的数据分发策略，减少数据分发过程中的冗余链路，减少数据分发时延，提高分发性能。