Research On Heterogeneous Resource Management And Performance Optimization In Wireless Caching Networks

With the proliferation of smart terminals(e.g.smartphones,tablets and laptops)and their applications,wireless multimedia data traffic is growing at an unprecedented rate,putting tremendous transmission pressure on the wireless communication network,resulting in the wasted bandwidth,energy and other resources,as well as greatly reducing the user’s quality of experience(QoE).To effectively address the challenges posed by the surge in multimedia data traffic and to improve network performance and user’s QoE,wireless caching technology has received great attention and development.The core idea of wireless caching technology is to utilize caching overhead in exchange for transmission benefits by pre-storing video data in the network edge nodes during off-peak hours,so as to relieve the service load of the wireless communication network by reducing the transmission distance between user and the requested video data,and to reduce the user content service latency and the energy consumption of the network.This thesis analyses the characteristics of multimedia data requests(content diversity,request grouping,and request heterogeneity of the same video),and studies the wireless caching network based on the three points:1)cache placement strategy,2)data transmission scheme,and 3)video coding technology.Combining wireless caching technology with multicast transmission,D2D transmission and SVC technology,the management of heterogeneous resources(storage,energy,transmission and other resources)and the performance optimization in wireless caching networks are explored to reduce redundant transmission of popular video data and improve the efficiency of resource utilization.Based on the hierarchical approach,this thesis focuses on the four scenarios:1)D2D-assisted collaborative caching network,2)Distributed heterogeneous collaborative caching network,3)D2D-assisted collaborative caching-multicast network,and 4)SVC-based collaborative caching-heterogeneous transmission network.This thesis also investigates both the optimization of caching placement strategy and the design of data transmission scheme,providing a theoretical basis and guidance for the design of cache-transmission scheme in wireless caching networks.The main works and contributions of the thesis are as follows:1)Research on the D2D-assisted collaborative caching network.In order to alleviate the transmission pressure of the wireless backhaul link,we study the D2D cooperative caching strategy and video acquisition scheme in the D2D-assisted collaborative caching network.First,the user’s caching resources are pooled through the caching resource virtualization process,and a D2D cooperative caching strategy is designed to allocate corresponding storage space for each video.The caching space of each user equipment is divided into two partitions,and popular videos are stored in the deterministic caching partition by the manner of deterministic caching while the remaining videos are stored in the probabilistic caching partition by the manner of probabilistic caching.Then,the user’s requested video can be obtained from the local cache,D2D collaborative cache,and core network.Finally,the D2D cooperative caching strategy is optimized by maximizing the cache hit probability.Since this optimization problem is non-convex,a Lagrange-based traversal algorithm is proposed.On this basis,the impact of power consumption expectation on network performance is analyzed.2)Research on the distribuuted heterogeneous collaborative caching network.Considering the content heterogeneity of video and the real environment of the caching network,we carefully design the caching placement strategy and data transmission scheme in the distributed heterogeneous collaborative caching network.First,based on the defined heterogeneous data model[popularity,user preference,file size],a local library of video blocks is constructed.The local popularity of video blocks is analyzed,proving that the local popularity is still a distribution with a long tail.Second,a distributed cooperative caching strategy is proposed,where users store the same most popular video blocks to alleviate the adverse impact of user mobility on the network performance while SmallBase Stations store the remaining video blocks in the probabilistic caching manner to enrich the diversity of stored contents and reduce the user’s caching pressure.Then,the successful transmission probability(STP)is derived by the Gauss-Legendre quadrature numerical integration,and the distributed cooperative caching strategy is optimized by maximizing the STP.According to the analysis of the optimization problem,a long tail distribution based heuristic caching placement method is proposed.Finally,based on the optimal caching strategy,the content service delay of users’random video requests is analyzed.3)Research on the D2D-assisted collaborative caching-multicast network.Considering the content diversity and request grouping characteristics of user video requests,we design a caching-transmission scheme in the D2D-assisted collaborative caching-multicast network.First,the probability distribution function of the multicast group scale is analyzed in the request accumulation time window,and a multicast-scale based caching resource allocation scheme is proposed,where videos whose corresponding multicast groups have larger probabilities to be non-empty are allocated more caching spaces,so that the frequently requested video blocks are physically closer to users.Then,a cooperative multicast-D2D transmission scheme is designed,where base station opportunistically multicasts the requested video blocks to users,and the failed receivers can obtain the missing video blocks from the successful receivers through the D2D joint transmission.Among them,the multicast and D2D transmission rates are derived by the Gauss-Legendre quadrature numerical integration.Finally,the closed-form expressions of the STP and average transmission delay of the network are derived,and the network performance of the proposed strategy is analyzed.Through the analysis,the average transmission delay is only related to the STP of the D2D transmission of the last video block.4)Research on the SVC-based collaborative cachingheterogeneous transmission network.Considering the heterogeneity of users’ requests for the same video,we provide users with heterogeneous video services by constructing a reasonable caching-transmission scheme in the SVC-based collaborative caching-heterogeneous transmission network.First,a SVC-based cooperative caching strategy is proposed,hierarchically storing different SVC-encoding layer files to provide video services with different perceptual qualities.Among them,a base layerbased multicast group aggregation process is presented,ignoring the quality difference of the videos requested by users.Users with the same video request can join the corresponding multicast group,using the limited frequency band to serve more users through one single multicast,and improving the resource utilization.Then,a hierarchical heterogeneous transmission scheme is proposed,where users obtain files of different layers of the requested video through cooperative multicast-D2D transmission and THz transmission.From the perspective of multicast,an efficient multicast transmission resource scheduling scheme is proposed,allocating more spectrum resources to multicast groups with higher nonnull probability,and making better use of the spatial reusability.Finally,the mathematical expressions of average offloading capacity gain and average energy consumption are derived,and an efficiency function optimization problem is constructed.The optimization problem can be effectively solved by the proposed greedy strategy-gradient descent based caching placement method and long tail distribution based heuristic caching placement method.