Optimal data downloading by using inter-satellite offloading in LEO satellite networks

In recent years a large number of LEO (Low Earth Orbit) satellites have been launched into space for various applications, such as weather forecast, environment monitoring and military surveillance. One important task of these satellites is to collect data and download them to Earth Stations (ESs) for further processing. Since LEO satellites fly at high speeds and have very limited contact time with ESs, they may not have sufficient time to download data to the ground. Existing work focused on scheduling data downloading from satellites to the ES such that the throughput of the downloading is maximized. However, what the scheduling algorithms can do is very limited in this scenario due to the disparity of the contact time a satellite has and the amount of data it carries for downloading. In this paper, we propose a novel scheme that uses inter-satellite links (ISLs) to offload data among satellites before they contact with the ES. A satellite with large amount of data but little contact time can offload data to other satellites that have surplus contact time. By offloading data among satellites on-the-fly in space, each satellite can carry the right amount of data when it comes to download its data to the ES, such that its contact time can be fully utilized. Extensive simulations have been conducted to evaluate the effectiveness of our proposed method. The simulation results show that the data downloading throughput by using ISL data offloading can be increased significantly.