| The mega constellation satellite network system composed of a huge number of satellites has the advantages of long communication distance,strong scalability and global coverage,and is increasingly used in national defense construction,military reconnaissance,scientific and technological research,and residential life.In the foreseeable future,the mega constellation system will participate in the overall construction of the 6G network as a supplement to terrestrial communication,and is one of the highest certainty technologies of 6G at present.Routing technology is the key technology of mega constellation networking.Excellent routing algorithm completes the constellation network satellite node topology maintenance,route calculation,QoS guarantee for different priority services and other functions,and is the exchange and forwarding hub of on-board data flow.The reasonableness and stability of on-board routing protocol design directly affect the communication status of the whole satellite network.The LEO satellite mega constellation is in a frequently changing topology,and most existing routing schemes suffer from efficiency and scalability issues,as well as limited resilience to link/node failures.For example,in snapshot routing,the network is divided into snapshots and routes are computed for each snapshot.If the topology changes more frequently,each snapshot will last for a shorter period of time,thus requiring more snapshots,which can lead to higher overhead.In addition,the global user distribution is uneven,and the satellite load is greatly affected by the time of the coverage area and the number of local users,which makes it easy for local traffic to exceed the network carrying capacity and lead to congestion.High orbit satellite network has the characteristics of stable network and strong bearing capacity,offloading traffic from congested areas of low orbit satellites to high orbit satellites can significantly improve network throughput,reduce packet loss rate,and improve user experience level.In this thesis,we propose a hierarchical routing algorithm for giant constellations and a traffic offloading routing algorithm for double-layer satellite constellations,and analyze the performance of the proposed algorithm through simulations for the above problems in the composite constellation scenarios of giant constellations of low-orbit satellites and high-orbit satellites and low-orbit satellites,respectively.The main research work of the thesis is as follows.(1)A hierarchical routing algorithm is proposed for mega constellations of low-orbiting satellites.The algorithm is based on the idea of hierarchical routing in terrestrial networks,and it implements the autonomous domain division of satellites in the whole satellite constellation,after which different routing algorithms are adopted for interdomain routing.The inter-domain routing adopts X-Y routing for 2D Mesh network to minimize the overhead and complexity of routing algorithm;the intra-domain routing adopts OSPF-based link state routing algorithm,which can ensure stable transmission and fast convergence within short distance.When the constellation size is in the thousands,the convergence time can be compared to similar algorithms,which can be reduced to 10%50%of similar algorithms,in the number of packets used to maintain the route is about 1%of the OSPF algorithm.(2)A multilayer constellation routing algorithm for congestion control is proposed for multilayer satellite mega constellations.Based on the user Qos demand for traffic diversion,when there is a system low-orbit satellite system traffic exceeds a certain threshold or the result of traffic prediction will exceed the system carrying capacity,the traffic with low delay requirements will be forwarded to high-throughput high-orbit satellites in priority to put to ensure the overall system throughput.Traffic monitoring is performed at each satellite node to realize the prediction of the upcoming huge network traffic and to start the dual-path routing mechanism in advance to avoid network congestion.Acknowledgement signals are sent at regular intervals during the time slice to avoid packet loss and network congestion due to node failure,and the second path is enabled to avoid network congestion when an approaching node failure is detected.Simulation results show that the traffic offload routing algorithm for a twotier satellite constellation can increase network throughput by more than 30%compared to a single-tier constellation.(3)Based on STK platform and OPNET network platform to build giant satellite constellation simulation platform,through STK to design the network topology of giant constellation,through the intelligent interface to open the barrier between OPNET network simulation software.Then the network traffic generation and routing algorithm design and implementation are carried out through OPNET to complete the protocol simulation function.Based on the above platform,the performance of the proposed algorithms is simulated under the respective application scenarios and compared with related algorithms to verify the effectiveness of the algorithms. |
