Design Of Stable Routing For Near Space Dynamic Network

Near space network refers to the near-ground space approximately 20 km to 100 km from the ground.It is an interconnected information acquisition and distribution network composed of nearby space vehicles(such as airships,balloons,high-altitude drones,etc.)as communication carriers.Compared with satellite communication network and terrestrial communication network,near space network has advantages of flexible deployment,low cost,low latency,and large coverage.However,the topology of the network has the characteristic of high dynamic.The rapid movement of the network nodes leads to the severe on-off phenomenon of the link,so the stability of the network is poor,and the overhead is heavy,which result in a decrease in network performance.The high reliable transmission of the data is guaranteed,and the consumption of network resources is reduced by exploring analysis methods of link stability and designing high-stability routing protocols to select stable link.This can lay a theoretical and technical foundation for near space network.At present,link duration between two adjacent nodes which is widely used to measure link stability can directly reflect the stability of the link.The longer the link duration is,the higher the link stability is.Combining with the project of National Natural Science Foundation of China “Analysis and Optimization on Network Capacity of Near Space Communication Network with Dynamic Topology”,the main contributions of the thesis are as follows:(1)The research of link duration in most of the references only considers the traditional 2D plane,and it needs the support of GPS(Global Positioning System).The practical scope of application is limited.The existing achievements can no longer meet the complex airspace environment of the near space network.The theoretical expression of the 3D link duration is derived when the location information of nodes is available based on the 2D link duration model,and then the theoretical expressions of the 2D and the 3D link duration are derived when the location information is invalid.The existing 2D link duration expression is verified by using another different derivation method.The theoretical expression of the 3D link duration has a wider applicability when the location information is available,it can be equivalent to the 2D link duration through dimensionality reduction.When the location information is invalid,the obtained theoretical expressions of 2D and 3D link duration are only related to the communication radius,relative distance,relative speed,and Doppler shift,which simplifie the calculation of the link duration and improve the realizability of the project.(2)Aimed at the complex and highly dynamic near space network,existing routing protocols have fewer considerations for link stability factors.OLSR based on link duration(Optimized Link State Routing based on Link Duration,LD-OLSR)protocol is proposed.The link duration is used as the routing standard in the OLSR protocol.The more stable path is selected.The MPR(Multipoint Relay)node selection algorithm is improved.The algorithm does not increase the number of MPR set nodes of the original algorithm.The neighbor node with the longer link duration serves as an MPR node.Then the code implementation and simulation analysis of the design protocol are carried out based on the NS2 simulation platform.In the near space network environment,LD-OLSR protocol is compared with DIS-OLSR(OLSR based on Distance)and OLSR protocols.Simulation results show that: the network performance of the different protocols is affected by node density and network dynamics;Compared with DIS-OLSR and OLSR protocols,the LD-OLSR protocol has obvious advantages in terms of end-to-end average delay,packet loss rate,normalized throughput,TC(Topology Control)packet number and routing overhead at a certain node density;In the same dynamic scenario,LD-OLSR is superior to DIS-OLSR and OLSR protocol in TC packet number and routing overhead.