Cooperative Cross-Layer Content Caching For Software-defined Radio Access Networks

With the development of communication and network technologies,video-based multimedia services have led to the growth spurt of moving data,which brings great challenges to wireless mobile communication network.On the one hand,a variety of technologies that improve the radio spectrum can enhance communication system capacity to a certain extent,but the expansion is far less than the growing speed of multimedia business.On the other hand,current studies have found that the popularity of Internet contents follow the Zipf distribution,i.e.,the user preference will lead to the small number of popular contents contribute to the most of traffic load.In the traditional centralized communication network architecture,the user's traffic have to traverse repeatedly the access network-core network(switch)-remote content server,which thus lead to backhaul link congestion,delay,low resource utilization and other issues.Considering the content reuse characteristic,network edge caching strategy that brings the contents closer to user has been widely studied in order to alleviate the contradiction between the massive business demand and backhaul link capacity of cellular mobile network.This paper proposes a cooperative content caching system architecture for Software-Defined Radio Access Networks(SD-RAN),where Macro-cell Base Station(MBS)provides control coverage and Small-cell Base Stations(SBSs)provide data coverage.By deploying storage units in the MBS and SBS located at the network edge,which can alleviate effectively the bottleneck of the backhaul capacity,reduce the network energy consumption and signal transmission delay.Specially,in order to optimize the allocation of storage resource with a sum storage constraint for more efficient contents caching,this paper proposes a cooperative cross-layer caching strategy and algorithm by establishing collaboration between SBS and MBS.In the paper,the average content provisioning cost is taken as optimization target.The optimal storage allocation factor at which the average content provisioning cost of the SD-RAN is minimized is analytically obtained in a closed form.The simulation results show that the average content provisioning cost of the proposed cross-layer algorithm using the optimal storage allocation factor will be significantly reduced.This paper also studied the baseline cross-layer non-cooperative content caching strategies.Simulation and comparison analysis results demonstrate that the performance of the cross-layer cooperative caching algorithm always outperforms the non-cooperative content caching algorithm under different parameters.In addition,there existing trade-off between SBS-SBS cooperative caching and SBS-MBS cooperative caching strategy which can be further optimized for lower content provisioning cost.