Optimal Data Downloading From Satellites To Multiple Ess By Using Isl Offloading In Leo Satellite Networks

In order to meet more needs from military and civilian,recently,a large number of small satellites supporting different applications have been launched into space.With the start of Space X,Boeing and One WEB satellite networking plans,the leading position of satellite network in next generation mobile internet is further stabilized.Since Low Earth Orbit(LEO)satellite is showing its superiority with short propagation delay,low cost and low energy consumption,it is gaining more attention from universities and enterprises.For LEO satellite system,an important task is to transfer the collected data to earth station(ES).Although LEO satellite has many advantages,there are still challenges in the research of data downloading.On the one hand,LEO satellites have the characteristics of higher speed relative to the earth,limited coverage area,large number of satellites,dynamic of constellation topology.On the other hand,the geographical locations of ESs are unevenly distributed,the contact time between an ES and a high-speed mobile satellite is very limited.Even if the contact time between satellites and ESs is predictable,the throughput bottleneck of data downloading from satellites to ESs is still difficult to break through.In this paper,we propose a dynamic topology routing strategy based on time division,using Inter-Satellite Link(ISL)to schedule the data carried in satellites and make the data downloading throughput optimization.At the same time,our strategy will ensure the non-blocking and conflict-free of ISL data routing during any time window.In fixed data scenario,the algorithm allocates download time based on perfect match,and offload data from satellites with surplus data to satellites with surplus download time in Manhattan topology.To avoid routing conflicts or link congestion,only one-hop routing is permitted for each link in a time slot.In dynamic data scenario,the algorithm assigns multi-hop ISL path for the data generated in each time slot and route them to ESs.A large number of simulations have shown that our algorithm has broken through the bottleneck of traditional methods.The optimality of our method depends on the routing capacity of constellation: when constellation load is low,the throughput is almost optimal;otherwise the throughput is still better than the method without ISL data scheduling.