Random Caching Based Cooperative Transmission In Heterogeneous Wireless Networks

In recent years,with the rapid development of mobile Internet,various mobile terminal devices such as smart phones and tablet computers have been widely penetrated into people's lives.Due to the access of massive mobile terminal devices,the volume of communication data increases exponentially every year,so network operators have to significantly increase network capacity.One solution to improve network capacity and coverage is to deploy a heterogeneous network(Het Net).The heterogeneous network deploys short-distance,low-power small base stations(SBS)within the coverage of the macro base station(MBS)to provide closer and higher-quality communications for user equipment(UE).Small base stations include pico base stations,pico base stations,home base stations,wireless WIFI access points,and relay stations.Base station cooperation is regarded as one of the solutions to effectively reduce the extra inter-cell interference caused by dense small cells,which can improve the network performance of heterogeneous networks,but it also poses a major challenge to the backhaul,and the small cell cache is considered to be An effective method to reduce backhaul load in heterogeneous networks.This paper considers small cell cooperation and small cell caching in a large-scale downlink heterogeneous network.The main research contents and contributions are as follows.We propose two base station(BS)cooperation schemes to enhance the performance of random caching.We derive a tractable expression for the successful transmission probability(that is,the probability that a user can successfully receive the requested file)under each scheme.We consider the successful transmission probability maximization by optimizing the caching distribution to obtain an optimal random caching strategy.However,the optimization problems in both schemes are non-convex.To solve these problems,by exploring optimality properties and using optimization techniques,under each scheme,we obtain a locally optimal solution in the general case and a globally optimal solution in some special cases.The experimental results show that compared with the BS cooperation scheme based on other caching strategies,our schemes can effectively relieve the backhaul load and provide the a better service of quality for mobile users.To capture the impact of user mobility on the design of random caching,two special mobility scenarios,namely high mobility and static scenarios,are considered.Specifically,we derive a closed-form expression for the successful transmission probability under a given transmission delay.In each scenario,we consider the maximization of the successful transmission probability,which is a challenging non-convex optimization problem.In the high mobility scenario,we obtain a global optimal solution.In the static scenario,we develop a low-complexity iterative algorithm to obtain a stationary point.