Research On Coded Caching Scheme In Dynamic User Network And Multi-access Network

With the development of 5G and microprocessor technology,base stations(BSs)as edge servers in edge computing networks can be used to obtain more storage and more efficient computing.The BS is close to the terminals of users,such that the edge computing network significantly improves the data processing speed and reduces transmission load.However,BSs in edge computing network will still bear great pressure during the peak time.Coded caching is an effective technology to reduce the transmission load.Without knowing the user's request,the server fills some packets to the user terminals in the off-peak time,and broadcasts the coded packets to meet the demands of users in the peak time.Thus,the network transmission efficiency is greatly improved and the network congestion is reduced.This thesis is mainly based on the research of centralized coded caching schemes in two kinds of edge computing network application scenarios.The main work is as follows:Firstly,in the edge computing network with dynamic number of users,this thesis designs a coded caching scheme with fixed subpacketization and dynamic number of users by constructing an appropriate placement delivery array(PDA).Based on the Maddah-Ali and Niesen(MN)scheme corresponding to the PDA,we remove some columns from the right side of the known conjugate PDA to obtain a new PDA with a flexible number of dynamic columns.It is worth noting that when the number of removed columns is within a certain range,the transmission load of PDA is order optimal.In addition,when the number of removed columns meets certain conditions,an improved scheme can be obtained by the combination method to reduce the transmission load.Theoretical proof and numerical results show that the scheme proposed in this thesis is close to the theoretical minimum result under the fixed subpacketization in terms of transmission load.Secondly,in the scenario of multi-access network,users can retrieve and access cachenodes with certain cache size in networks,such as content distribution network servers,small cell base stations,etc.In this thesis,we propose a new coded caching scheme based on a multi-access network with users and cache-nodes both have caches.Using the idea of PDA to describe a coded caching scheme,a cycle multi-access placement delivery array(CMPDA)can be defined,and then two methods to constructing CMPDA are proposed.According to these two construction methods,the coded caching scheme of multi-access network with both users and cache-nodes is designed,that is,the placement phase of users and cachenodes,the user-retrieval phase and the delivery phase.Firstly,CMPDA is ensure that there is no overlap of cached content between users and cache-nodes or between cache-nodes in the placement phase.Next,users can make full use of the cache size of cache-nodes in the user-retrieval phase to improve the hit rate of requested files.Furthermore,the multicast gain is generated between users as much as possible to effectively reduce the transmission load between the server and users in the delivery phase.