Content Caching Strategy In Integrated Satellite-Ground Network

In recent years,with the rapid development of satellite networks,Integrated Satellite-Ground Networks(ISGN)has been proposed as a promising future network architecture.Caching popular content on satellites can improve content distribution efficiency and relief the burden of traffic on ground network.Existing satellite caching researches focus on optimizing the caching performance of satellite networks without considering the impact of packet loss caused by the instability of satellite communication links on satellite caching performance.In addition,most existing researches on satellite caching consider a single-layer satellite network model,since the cache space on satellites is limited,satellites need to frequently connect to the ground network to retrieve content,resulting in huge download delay for users.Therefore,this paper proposes a network coding-based satellite caching strategy to reduce download delay and improve the reliability of satellite transmission.Then,considering the limited cache space of each individual satellite and in order to improve user experience,this article proposes a collaborative caching strategy for multi-layer satellite network to achieve collaboration between satellites,aiming to improve cache hit rate.The main research contents of this paper are as follows:1)A satellite caching strategy based on network coding technology is studied.First,the upper limit of the number of coded blocks to be cached for each content is calculated according to the packet loss rate.Then,the satellite caching decision problem is transformed into a multiple knapsack problem,and the optimal satellite caching strategy is obtained by solving the knapsack problem.Experimental results show that,compared with other caching algorithms,the proposed algorithm can improve the cache hit rate and reduce content download delay.2)A multi-layer satellite network inter-satellite collaborative caching strategy based on Lyapunov optimization is studied to improve the benefits of satellite caching.This paper divides the ground area according to the coverage range of low-earth orbit satellites,and the cache content of each low-earth orbit satellite is determined based on the popularity of content in the respective regions,the topology graph,and the caching situation of adjacent satellites.Experimental results show that,compared with other caching strategies,the proposed algorithm can improve the cache hit rate and reduce content download delay.