Research On Caching And Distribution Mechanism In Satellite-Terrestrial Cooperative Networks With Edge Computing

In recent years,with the rapid growth of the number of mobile devices and the continuous emergence of business scenarios,such as Industrial Internet and high-definition video,data traffic in the network was soared.These above-mentioned development statuses not only require the mobile communication network to have higher carrying capacity,but also put forward higher requirements for robustness and ubiquity of the network.Faced with these challenges,it is difficult to solve the problem fundamentally only by increasing access equipments and improving bandwidth.Currently the development of satellite communication network provides a new direction to solve the above contradictions.With the help of satellites,the seamless global coverage and the efficient content distribution using broadcast and multicast technology can make up for the deficiencies of terrestrial communication network to a certain extent.Exploring the cooperative mode of satellite communication network and terrestrial communication network is an important direction of the next generation of mobile communication technology.Satellite communication network and terrestrial communication network have different characteristics in coverage,propagation delay and network capabilities.To achieve efficient cooperation,on the one hand,the two networks are required to give full play of their advantages to improve the effect of resource utilization.On the other hand,the impact of inherent disadvantages should be minimized,such as the satellite movement will causes content distribution interruption.With the above objectives,it is of great significance to design adaptive network resource management and control schemes as well as content caching and distribution mechanisms.In this thesis,the capabilities of satellite-terrestrial cooperative networks are enhanced with the help of multi-access edge computing and network virtualization.On this basis,the research and innovation of content distribution mechanisms in satellite-terrestrial cooperative networks are focused:Firstly,an architecture of satellite-terrestrial cooperative networks is proposed with edge caching and computing capabilities,and the video business scenarios where there are multiple versions and can be transcoded between versions is considered.According to the two ways of satellite serving users defined in the 3GPP standard documents:directly or with the help of base station,two kinds of content distribution strategies are designed:Satellite Transcode and Distribute Directly(ST-DD)and Base Station Transcoding to Assist Satellite Distribution(BST-ASD).Both of these two strategies include process of transcoding and distribution,but focus on the use of resource at the satellite or base station respectively.The simulation results show that in terms of computing and downlink resource consumption,ST-DD is 53.6%and 71.3%lower than BST-ASD,respectively,which shows ST-DD has better resource utilization effect.Secondly,considering the capability of satellite is still weak to efficiently complete all the distribution tasks by ST-DD strategy at this stage,so the design of the combination of ST-DD and BST-ASD is carried out,which requires coordination under a deeper intergration architecture.A vitual satellite-terrestrial cooperative networks is proposed to break the gap between heterogeneous networks and achieve deeper integration between satellite network and terrestrial network.The virtual resources of the network are controlled by the Mobile Virtual Network Operator(MVNO).Then,the optimization problem is constructed with the goal of MVNO's revenue,and the BPSO-based selection algorithm(BPSO-SA)is designed to make distribution schemes.The algorithm solves the problem that wireless virtual network resources are difficult to estimate,and compared with the Random-based selection algorithm(RSA)and the Popularity-based selection algorithm(PSA),BPSO-SA can increase the revenue of MVNO by 28.9%and 12.3%,respectively.Thirdly,to solve the problem of interruption in the multicast distribution process caused by the high-speed movement of low-orbit satellites,a satellite-terrestrial cooperative distribution strategy based on the predictive satellite service time information is proposed.The strategy is judged on the condition that the service time of the satellite can complete the content distribution.If there is a qualified satellite within the longest waiting time,the user will obtain the content through satellite multicast,otherwise the content is obtained by terrestrial network.In this strategy,the calculation formula of the satellite service time is given based on the network model,and the expressions of network resource consumption and average waiting time of users are further derived.To adjust the conflict between network and users,the optimization objective is constructed by the method of coefficient weighting,and the network parameter,the longest waiting time of users,is decided by the pattern search algorithm.Simulation results show that network resource consumption or user waiting time can be adjusting the weight coefficient.