Research on Key Technologies of Spatial Information Network Based on DTN
|Course||Communication and Information System|
|Keywords||Spatial information networks Delay-tolerant networks (DTN) DTNgateway Routing Algorithm Transmission protocols|
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.