Research On Coded Caching In Hierarchical Networks

With the development of wireless communication networks and 5G technology,caching technology has gradually entered the public’s view.Caching technology originated from Content Delivery Networks(CDNs),which reduce network communication congestion by pre-placing some data content within network nodes close to users or storing data content directly in users’ memory.Traditional caching schemes can only achieve local gains.To further improve the efficiency of caching,coded caching technology has been proposed.Coded caching designs coded multicast signals based on the cache content of multiple nodes,achieving not only local gains but also global gains,which greatly enhances network transmission efficiency.The coded caching scheme can be applied to multiple network models,with the hierarchical network model being the most realistic topology model.However,due to its large number of users and complex network structure,there are few coded caching schemes designed for hierarchical networks,and the design difficulty is high.The existing coded caching schemes also have problems such as high transmission load in the first layer(backbone link)and a high subpacketization level.In addition,network transmission security and privacy have not been considered.In response to the limitations of the above work,this paper proposes two types of coded caching schemes by using combinatorial design theory,which achieve the goals of low transmission load and low file subpacketization level.At the same time,this paper also provides a hierarchical coded caching scheme for security and privacy issues.The main research content and achievements are as follows:1.This paper proposes a combination structure based on the theory of combinatorial design,namely the Hierarchical Placement Delivery Array(HPDA),from which one can obtain a coded caching scheme under a hierarchical network model.Therefore,designing a hierarchical coded caching scheme is simplified to designing an HPDA.2.This paper proposes the first type of construction method for HPDA,called the grouping construction method.The basic idea is to group the existing PDA(a matrix composed of symbols “*” and integers according to certain rules)and redesign the elements of the sub-matrix after grouping.The coded caching scheme obtained by the grouping construction method can greatly reduce the transmission load of the first layer because this scheme maximizes the use of cache content of each layer to design the transmission strategy.3.As the grouping construction method is only applicable to hierarchical network models with some parameters,to construct HPDA with arbitrary parameters,this paper proposes the second type of construction method,called the composite construction method.The basic idea is to nest two existing PDAs.The coded caching scheme obtained by the composite construction method can flexibly achieve a tradeoff between the transmission load of two layers or a tradeoff between transmission load and subpacketization level.This is because when PDAs with low subpacketization level or low transmission loads are selected,HPDA with low subpacketization level or low transmission loads can be obtained,respectively.4.To ensure the security and privacy of wireless communication network transmission,this paper designs a coded caching scheme for security and privacy issues based on HPDA.The scheme effectively prevents external malicious users from obtaining any file data from monitoring signals by adding security and privacy keys during the caching and transmission phases,while ensuring that the user’s request information is not known by other nodes.