Optimal Satellite Data Downloading To Multiple Ess By ISL Offloading In LEO Satellite Networks

With the rapid development of network globalization,terrestrial communication network has been unable to meet people's needs for extensive information acquisition and long-distance information dissemination.The emergence of satellites has made up for the shortage of terrestrial communication network and increased the way of information transmission.In recent years,major communication companies have proposed their own satellite network planning.More and more satellites have been launched into space for networking,widely used in information acquisition,target detection and navigation.Compared with MEO and GEO satellites,Low Earth Orbit(LEO)satellites have the advantages of low cost and launch costs,lower communication latency and lower signal attenuation,so it has become a research focuses in the industrial and academic fields.LEO satellite orbits the earth periodically and collects data.Because the communication time between the satellite and the ground station is very short and the storage capacity of the satellite is limited,it is necessary to download data to the ground station in time.The high-speed operation of satellite results in the dynamic change of the network topology,and the relationship between satellites is very complex.It is of great significance to design efficient satellite-to-ground data scheduling and downloading algorithms in complex scenarios.Earlier studies focused on collision-free data downloading scheduling between satellite and ground.The scheduling effect depends on the length of time window of satellite-ground communication.On this basis,we introduce the inter satellite link(ISL)to help data downloading.Under the condition that there is no conflict in inter-satellite data routing,the corresponding data is allocated according to the time window of satellite downloading to the ground station,so as to reduce the waste of satellite-ground communication time and improve the data downloading throughput of the whole system.We study the multiple satellite and multiple ground station scenario.The goal is to maximize the amount of data downloaded from LEO satellite networks to the ground station in one operation cycle.In the Manhattan topology,the time window of satelliteground communication is uniformized to avoid wasting.According to the characteristics of satellite-ground simplex communication,the integer programming method is used to schedule the satellite-ground data downloading.On this foundation,a Manhattan baseddata scheduling by using ISL(MBDS)algorithm is proposed to schedule the satellite data,which can improve the data downloading throughput of the satellite networks.Compared with the Manhattan topology,the space-time graph topology has more advantages,and the topological structure is more complex.In order to make full use of the advantages of space-time graph topology,the strategy based on inter-satellite data scheduling priority is used to maximize the communication time between satellites and ground stations,using particle swarm optimization improves the efficiency of searching the optimal solution.Routing tree structure is introduced into space-time graph.A space time graph based data scheduling by using ISL(SBDS)algorithm is proposed,which increases the choice of inter-satellite routing and further improves the data downloading throughput of the system.The simulation experiments are carried out in two classical systems,Globalstar and Iridium.The algorithm is validated by several indicators,such as the load variation of satellite networks,the number of ground stations,energy cost of ISL scheduling and data distribution.The simulation results show that our algorithm,MBDS and SBDS can significantly improve the data downloading throughput of the satellite networks,and has better performance in different scenarios.