【作者】 周建国；

【导师】 晏蒲柳；

【作者基本信息】 武汉大学 ， 通信与信息系统， 2013， 博士

【摘要】 当前我国航天事业进入飞速发展期,以往传统的空间信息传输方式已不能满足复杂空间操作的需求,因特网服务的全球拓展和向地球外层空间的延伸是网络技术发展的必然趋势。我国的空间信息传输网络建设发展滞后,主要表现在星上、星地和地面三部分传输协议尚未进行一体化设计,不同卫星与地面之间采用的传输协议各不相同,且大多都是专用协议,在开展空间任务时需要进行星地之间的协议转换,协议之间的互操作效率较低；造成系统的兼容性和可靠性较差,浪费了许多不必要的人力、物力资源。与此同时,由于缺少符合国际标准的空间信息传输协议,更不利于将来与国际航天机构进行合作交流。针对我国航天测控网的实际发展情况,研究建立一个空天地一体化的互联互通网络,可以为航天信息的获取、存储和分发提供统一的平台,促进航天信息的统一管理、高效共享和综合利用,对国防信息化建设将起到不可估量的促进作用,因此,空间信息网络已成为近年来网络领域的重要研究热点之一。空间信息网具有航天器节点高速运动、网络拓扑不断变化、信息传输的延时大、误码率高、链路频繁断开等不同于陆地网络的特点,给网络建设带来了新的挑战。为加快我国空间信息传输网络体系架构的建设,需要研究当前国际航天大国的空间信息系统的先进理论。容延迟网络(Delay-tolerant networks, DTN)是提供跨越间歇、中断、动态网络的可靠消息传递的网络协议,在受限网络条件下应用时具备良好的自然属性。为此,本论文研究基于DTN的空间综合信息网络的网络体系结构,研究符合我国实际情况的空间信息传输网络协议体系结构及其关键技术,为我国空间网络建设提供一定的技术支持。本文所做主要工作和贡献如下：1.提出了适于我国实际的基于DTN的空间信息网络协议体系结构。并利用规范说明与描述语言SDL对Bundle协议进行了详细描述与设计,给出了协议设计的系统图、模块图、进程图及过程图。然后在Telelogic Tau平台下使用SDL Suit对所实现的Bundle协议系统进行了仿真验证。最后使用TTCN Suite对协议系统进行了一致性测试,测试表明用SDL语言设计的Bundle协议系统与Bundle协议规范RFC5050是一致的。协议的实现与仿真验证结果证明,用SDL描述语言进行通信协议设计可以保证协议的逻辑正确性,有效地缩短协议开发周期。2.设计了DTN网关。在OPNET仿真平台下对空间DTN网关进行了建模,并对基于DTN网关的空间卫星网络进行仿真。仿真结果表明,DTN网关能够显著降低由于网络链路频繁中断导致的丢包率,增强通信的可靠性,表现出良好的适用性。为进一步验证星DTN网关对星地间信息传输的有效性,设计了半物理仿真方案,实验表明在极端的链路情况下(即不存在通信链路时),DTN网关可以对通信数据进行保管,并在通信链路出现时再将这些数据发送出去,从而大大降低了丢包率,提高了通信的可靠性,进一步证明了DTN网络在我国空间信息网络中应用的可行性与必要性。3.提出了多拷贝混合型最大吞吐量HMMT接触路由算法。CGR路由非常适合在链路可预测的空间DTN网络场景进行部署。但是,CGR路由中消息是按照单副本路由转发,同一时间网络中只有一个节点携带同一消息,算法降低了网络开销,但可靠性相对较低。同时,CGR中路由算法是逐跳路由,而且在路由中仅仅考虑本地节点的状态知识,搜索最小代价路由,未考虑链路的连通时序与吞吐量的关系。HMMT路由算法结合洪泛式路由策略与计算转发路由策略的思想,根据卫星运行规律可预知的特征建立时间图模型,由建立的时间图模型产生具有顶点和边的拓扑图,依据链路的连通时序与吞吐量,以增加消息转发的可靠性和最大化路径吞吐量为目标计算消息转发路由,并通过基于OPNET的多星组网仿真验证了算法的有效性。4.提出了空间信息系统传输控制协议初步配置建议。本文深入分析研究了目前各种主要的空间信息传输协议,比较检验这些传输协议在空间链路中的有效性。选取部分代表性协议Vegas、Cubic、Hybla、SCPS-TP和LTP,采用网络仿真器模拟星地链路、PC模拟飞行器和地面站终端,对这些传输协议的性能进行了分析,在此基础上提出了我国空间信息网传输层协议的初步配置建议,为后续协议的优化提供指导。更多还原

【Abstract】 The traditional spatial information transmission cannot meet the needs of complex spatial operations due to the current rapid development of China’s aerospace industry.Global expansion and extension of Internet services to the outer space is the inevitable trend of development of network technology. China’s space information transmission network construction and development lags behind, owing to the lack of the integrated design of satellite, satellite-ground and ground transmission protocols. Transport protocols vary differently between different satellites and ground, and most of them are proprietary protocols,protocol conversion between the satellite and the ground are required in carrying out space missions. The interoperability between protocols shows low efficiency, resulting in the poor system compatibility and reliability and waste of unnecessary human and material resources.At the same time, the lack of spatial information transfer protocol in compliance with international standards impedes the future cooperation with international space agencies.In view of the actual development of Telemetry, Tracking&Command network, the establishment of an Space-Air-Ground interconnection network is necessary for providing a unified platform for aerospace information acquisition, storage and distribution and facilitating unified management of space information, efficient sharing and utilization, and playing an invaluable role in national defense information construction. Therefore, spatial information network has become an important field of research in recent years.Spatial Information Network is characterized by high speed motion of spacecraft, constantly changing network topology, long information transmission delay, large error rate and link frequent disconnection,which is different from terrestrial networks and has brought new challenges to network construction. To speed up the construction of space information transmission network architecture, it is necessary to study the current international space powers’ advanced theory of spatial information systems.DTN is a new network architecture which can provide reliable messaging cross intermittent, interruption, dynamic network and have good natural attributes under challenged network conditions. To offer some technical support for the construction of China’s space network, integrated information network architecture based on DTN and spatial information transmission network protocol architecture and key technologies that are in line with China’s actual situation is studied in this paper. The primary work and contributions are as follows:1. Spatial information network protocol architecture based on DTN is proposed. Bundle protocol is described and designed in detail using specification and description language (SDL), and system diagram, block diagram, process diagram and process diagram of protocol design are provided.Then the accomplished bundle protocol is simulated and verified using the SDL Suit based on Telelogic Tau platform. Finally, consistency testing for the accomplished bundle protocol is conducted with the TTCN Suite and results have shown that the Bundle protocol system realized is consistent with the bundle protocol specification, RFC5050.Protocol implementation and simulation results have shown that using the SDL description language for communication protocol design can guarantee logical correctness of protocol and effectively shorten the protocol development cycle.2. DTN gateway is designed. Modeling of space DTN gateway and the simulation of space satellite network based on DTN gateway is done under the OPNET simulation platform. Simulation results have shown that DTN can significantly reduce packet loss rate due to the frequent interruption of network link, enhancing the reliability of communication and showing a good applicability. In order to verify the applicability of DTN gateway for the information transmission between the satellite and the ground, a semi-physical simulation program is implemented and experimental results have shown that the DTN gateway can keep the communication data the link in extreme circumstances (i.e. there is no communication link), and resend the data when the communication link appears, thus greatly reducing the dropout rate and improving the reliability of communication. Thus, feasibility and necessity of the DTN network in China’s space information network are further validated.3.A hybrid multiple copies maximum throughput contact based routing algorithm-HMMT is presented. CGR routing is ideal for deployment DTN network scenarios where the links are predictable. However, messages are forwarded with a single copy in the CGR routing, at one time only one node in the network will carry the message. This algorithm reduces network overhead, but the reliability is relatively low. Meanwhile, CGR routing algorithm is a hop by hop route, and only considers the knowledge state in the local node, and searches least cost routing without considering the relationship between timing and throughput.HMMT routing algorithm integrates the idea of flooding routing and computing forwarding routing policy, and establishes a predictable time graph model based on the satellite operation rules, and generates a topology map of vertices and edges, calculates routes for the sake of promoting the reliability and maximizes path message forwarding throughput based on the time series and throughput, and validates the effectiveness of the algorithm based on multi-satellite network simulation using OPNET.4.Preliminary configuration recommendations for transport layer protocol of spatial information systems are presented. This paper deeply analyzed the current major spatial information transport protocols and compared their effectiveness in space links. Some representative transport protocols such as Vegas, Cubic, Hybla, SCPS-TP and LTP are analyzed using network simulator to simulate satellite link, PCs to simulate aircraft and ground station terminals. Preliminary configuration recommendations for spatial information network are proposed on this basis, providing guidance for the subsequent protocol optimization.更多还原