Research Of Transmission Strategy Optimization For High Dynamic Links In Space DTN

In the 21 st century,in order to deal with the earthly environmental crises,timely,accurate and complete acquisition of space resource is increasingly important for earth sciences and production activities,such as environmental monitoring,disaster forecast and resource exploration.For another,information which represents the resource within the scope of space is vital for the strategic interests of national development.Supremacies of the air,seas,sapce and even information,which maintain the security of national borders,all need to have sheer ability of space information's acquisition,transfer and comprehensive utilization.Therefore,in recent years,the USA and European countries have launched the project of space information network.China also plans to give priority to developing aerospace technologies and build a space information network in the next fifteen years.Space information network is Space-Air-Ground integrated communication network,which consists of air and land users,space-based and air-based communication facilities,such as satellites orbiting at different altitudes,aircrafts and space platforms,etc.Space information network has wide-area continuous communication and monitoring ability.It is an indispensable way for real-time access to space information and also is a important means of interconnection between equipment-to-equipment.However,due to the high dynamic characteristics of bearing platforms,performance of data transfer in space information network is largely subject to time-varying topology.The main issues are reflected in the follows.On one hand,the on-off state of links evolves over time.Consequently,the network topology is frequently separated resulting in that TCP/IP is incompetent enough to transfer data over such environment due to lack of end-to-end paths.On the other hand,due to absent of network model to represent dynamic topology,the common-used strategy to address such topology is distributed routing which is capable to capture the latest status of network and accordingly select the optimal forwarding link hop-by-hop.However,its routing decision lacks of global network information and only ensures local optimality.Therefore,it is hard to meet the Qo S requirements of whole transfer.Finally,the link-state nature is time-varying(e.g.,the deterioration of bit error rate)due to the high-speed movements of nodes.It is likely to form a fading channel leading to the occurrence of abrupt disruption events and thereby introducing additional delay to data transfers.Aim at the first issue,in this paper,we adopt delay/disruption-tolerant networking(DTN)architecture to the communication scenario that we consider about.Accordingly,bundle/licklider transmission protocol(BP/LTP)is used to transfer data in our analysis.Aim at the other issues posed by dynamic network topology,we have designed a data transfer strategy based on time-varying graph and also proposed a disruption handling mechanism.The contributions of the paper are summarized as follows.(1)This paper analyzes the adverse effects to data transfers which result from time-varying network topology and discusses the disadvantages of existing solution i.e.distributed routing policy,and then presents a time-varying graph based analysis framework accordingly.The comparisons to common-used time-varying graphs are made in this paper,through which the space-time graph is selected as modeling approach.According to the characteristics of space-time graph,this paper proposes a specific graph construction algorithm for the first time.To improve the graph,edge's weights i.e.link's capacity and transfer cost are defined and the corresponding mathematical models are established through combining with DTN data transfer process.On this basis,aim at the issue of efficient remote sensing image data returns in space information network,we propose a so-called "min-cost multipath routing" policy.By comparing with contact graph based "earliest arrival multipath routing” strategy designed in this paper,we verify the feasibility of space-time graph based routing methodology.This work offers certain reference effect to time-evolving graph based analytical framework.(2)This paper considers the potential disruptions occurring in time-varying network as research object and redefines the notation,which is more conform to DTN data transfers.According to different origins,we define two types of disruptions and establish the corresponding mathematical models.To alleviate the negative impacts resulting from transfer interruption,this paper proposes a “bundle expedited transfer mechanism”.To achieve this scheme,we emphatically analyze the influences of disruption to bundle forwarding from the perspective of DTN transfer mechanism and protocol format,and accordingly present packet format's modification scheme and algorithms.We use bundle end-to-end delivery time,wasted transmission effort and buffer space release rate as performance metrics and establish the corresponding mathematical models.The comparisons with the traditional scheme in our simulations show that the proposed scheme can effectively reduce delay time as disruption occurs with no intensification of node's buffer space and additional overheads.