Research On Edge Content Caching Strategy In Heterogeneous Cellular Networks

With the rapid growth of the number of mobile users and the increasing variety of multimedia services,the channel capacity of wireless network and the bandwidth resources of return link are facing great challenges.Heterogeneous Cellular Networks(HCN),as an emerging heterogeneous expansion network architecture,can solve the macro-cell coverage blind spots and excessive network load pressure by flexibly deploying various small base stations.Content edge caching technology is one of the technologies with great development potential in the fifth generation mobile communication system.By caching popular data content to devices closer to the user,it can effectively reduce system energy consumption,decrease transmission costs and transmission delays of backhaul links,and improve system performance.This thesis focuses on content edge caching strategies in HCN,and improves system performance by setting reasonable caching strategies and algorithms.First of all,for the problem of less research on the combination of content cache technology and base station sleep technology in heterogeneous cellular networks,and the inefficient channel resource allocation of users in the overlapped small-cell base station(SBS),this thesis starts from the joint content caching and base station Sleeping technologies.In view of the optimal association between the user and the base station,with the goal of minimizing system energy consumption,the Joint Optimization strategy of Content Caching and base station Sleeping(JOCCS)is proposed in this thesis.This strategy determines the content caching status of the base station based on the condition of the base station sleeping and the content request from the base station associated user.At the same time,Discrete Quantum Particle Swarm Optimization(DQPSO)is introduced to solve the problem.In order to prevent the solution from falling into a local optimum,this thesis introduces the hybrid probability to optimize DQPSO,then this algorithm is called the hybrid DQPSO algorithm.Simulation results show that JOCCS can reduce system energy consumption effectively,and the DQPSO algorithm can quickly converge and perform better in global search ability.Secondly,for improving users' Quality of Experience(Qo E),and reducing the redundant data and increasing the diversity of content caching,in this thesis,the Delay based Optimal Cooperative Partition Caching and Delivery algorithm(DOCPCD)is proposed from the perspective of base station Cooperative Caching and transmission,aiming at optimizing the Delay of users' downloading contents.Based on the idea of partition caching,this algorithm divides the caching space into two parts: one part is to cache the relatively popular contents;the other part caches the new contents according to the user's request behavior so as to improve the diversity of the cache contents.A partitioned cache strategy enables resource complementarity.Simulations show that DOCPCD algorithm can effectively reduce the average download latency of users and guarantee a high content cache hit rate.