Research Of Energy Efficiency Based Cooperative Caching Strategy In UDN

With the rapid development of communication technologies and the widespread popularity of intelligent terminals,mobile data traffic shows explosive growth.At the same time,various rising applications and services are increasingly urgent for high-speed low-latency networks as well.Ultra-Dense Networks(UDN)can provide rapid and stable services for end users by densely deploying accessing points(APs)so as to close the distance between APs and users.However,there are still kinds of obstacles in the UDN deploying process such as the shortage of backhaul link r-esource,the huge energy consumption of base stations and so on.Caching at the edge of wireless network can effectively avoid downloading duplicate contents,ease the burden of backhaul link,reduce the data transmission cost and delay and ensure the stability of service,so the quality of service and user experiment can be ensured.Therefore,caching is one of the key solutions to the problems of UDN.While for a single caching unit,the storage capacity is limited.It is difficult to provide effective caching service.Cooperative caching can coordinate several caching units to caching different contents so that the kinds and quantity of contents and caching hit ratio can be improved.So caching attracts many attentions these years.Base on the above background,this paper focus on the problem of cooperative caching in UDN.The aim of this paper is to optimize network energy efficiency.Two cooperative caching strategies are proposed and the main contributions of this paper are as follows.First,this paper proposes a coalition formation game based cooperative caching strategy.According to the energy consumption coefficient between small base stations(SBSs)and user equipments(UEs),an SBS grouping rule is defined.The SBSs in the same SBS group(SBSG)serve their UE cooperatively.The request probability of contents subjects to the Zipf s distribution and the contents with higher request probability need to be cached.The contents are cached in the SBSs in fragmentations.Iin order to find the optimal contents distribution to improve the energy efficiency,coalition formation game is introduced.The numerical results demonstrate that the caching scheme can improving the energy efficiency of the network effectively.Second,this paper proposes an online cooperative caching scheme according to the features of social network contents.The network is a two-tier heterogeneous network consisting of cache-enabled macro base stations(MBSs)and SBSs.Considering the random updating time of social netwoirk contents,an online reactive cooperative caching scheme is proposed.Then a multi-dimension decision function is defined according to the historical behaviors of local users and current heat of the content in order to decide whether caching a content or not.Besides,a caching allocation algorithm is designed based on the users' request probabilities and SBSs' coverages.Simulation results shows the online cooperative caching scheme san saving much transmission energy consumption of both backhaul link and MBSs.