The Research Of Cooperative Caching And Transmission Strategies For 5G Ultra-Dense Networks

With the rapid deployment of smart terminals and the increasing demand of service quality in emerging applications,the network traffic volume have grown exponentially.The Fifth Generation Mobile Communication(5G)has gained huge popularity in both academia and industry.Among them,Ultra-dense network(UDN)is considered as one of the key techniques to meet the users requirements and improve capacity.UDN generally consists of a large number of low power small base stations(SBSs).This can provide high data transfer rate for a large number of users at the same time.Meanwhile,the network edge caching technology makes popular files stored closer to the user,so as to decrease download delay.How to deal with the characteristics of the UDN to combine file caching and transmission strategy worth studying.Nevertheless,the storage capacity of a single SBS in UDN is very limited,so the cooperative cache between multiple SBS is particularly important.How to decide whether or not to store a file in a SBS may depend on the file's popularity,hit ratio,transmission delay and etc.We study the above problems with the main contributions in this paper as follows:A clustered-based caching strategy(CBCS)with limited storage in UDN considering user static is proposed.A novel clustering scheme based on SBSs' load capacity and location is proposed.The files are sorted by popularity,and according to the number of clusters inside SBSs,file is split into different pieces.Then,the corresponding file fragment cache in different SBSs until the cache space is used up.Finally,we target the minimum average download delay under the constraint of the number of SBSs in a cluster.The simulation results demonstrate that the proposed algorithm has a lower average download delay and could achieve a better hit ratio.Secondly,a graph-coloring based caching(GCC)algorithm in UDN is proposed for moving user under limited SBS storage capacities.Considering the possible downloading interruption or even failure due to the random moving of users and small coverage of SBSs,we employ random ant coloring algorithm for grouping the SBS to cache fragments of several files.Then,the problem is formulated of how to conduct caching placement on SBSs aiming to maximize the amount of data downloaded from SBSs.Next,we decompose optimization problem into independent of each sub-problem.We use the greedy algorithm for each sub-problem and combining the heuristic algorithm to obtain the results.Simulation results show that the algorithm can reduce user download delay.