Joint Optimization Of Cache Placement And Centent Delivery In UAV-assisted Cellular Networks

With the rapid development of mobile Internet and intelligent user terminals,data traffic in mobile Internet has been growing exponentially.Mobile edge cache technology can place popular contents in edge nodes closer to users,so as to avoid a large number of repeated transmission of popular contents,alleviate network congestion,reduce the load of base station and backhaul overhead.Meanwhile,with the rapid development of unmanned aerial vehicles(UAVs)supporting wireless communications,UAV-assisted cellular networks for hot spots area coverage has been widely concerned.Since the characteristics of flexible deployment and mobility,UAV can establish a good line of sight(LoS)link and provide high-speed data transmission service for users in the hot spots area when compared with traditional ground base station.Therefore,cache-enabling UAV-assisted cellular networks has been one of the hot research directions.This work is supported by the National Natural Science Foundation"Research on Multilevel Cooperative Caching in UAV-Assisted Cellular Networks".In order to improve the efficiency of content delivery and cache space utilization,we consider the joint optimization of cache placement and content delivery to improve system performance.In this paper,two scenarios of UAV-assisted macro cellular networks and UAV-assisted D2D(Device-to-Device)cellular networks are considered respectively,and the corresponding joint optimization algorithm of cache placement and content delivery is proposed.The main work of this paper is as follows1)This paper summarizes the current research about cache-enabling UAV-assisted cellular networks.Firstly,work on UAV-assisted cellular network communication is summarized,including UAV-assisted cellular networks application scenarios and main research classification.Then it summarizes the research of edge cache in cellular networks from five aspects:cache location,performance index,cache placement strategy,content delivery strategy and joint optimization of cache placement and content delivery.Finally,the research of cache-enabling UAV-assisted cellular networks is summarized,and problems in existing work are pointed out.2)In the UAV-assisted macro cellular network,aiming at the problem that limited UAV communication resource and cache resource affect the quality of experience(QoE)of users,this paper proposes a joint optimization algorithm of cache placement and content delivery to maximize the QoE of users.This paper establishes an joint optimization of UAV location deployment,UAV cache placement and user association to maximize the sum QoE of users in system.The optimization problem is divided into three subproblems to be solved,namely,UAV location deployment based on one-to-one swap matching,UAV cache placement based on greedy algorithm and user association based on Lagrange duality.Then three sub-algorithms iterate to obtain the suboptimal solution with low complexity.Finally,the simulation results verify the convergence,feasibility and effectiveness of the proposed algorithm.Simulation results show that the proposed algorithm can effectively reduce the content access delay,improve QoE and backhaul traffic offloading ratio.3)In UAV-assisted D2D cellular networks,aiming at the problem of limited UAV cache space,this paper proposes a joint optimization algorithm of cooperative cache placement and content delivery between UAV and D2D users.Firstly,a cooperative cache framework between UAV and D2D user terminals is proposed,in which D2D user treminals cache space can be used to alleviate the pressure of UAV cache space and improve system performance.This paper establishes an optimization problem with the goal of maximizing cache utility,and jointly optimizes D2D user terminal cache placement strategy,UAV flight trajectory and UAV cache placement strategy.The optimization problem is divided into three subproblems to solve,that is,D2D user terminal cache placement strategy based on many-to-many swap matching,UAV flight trajectory based on approximate convex optimization and UAV cache placement strategy based on dynamic programming.Then three sub-algorithms iterate continuously to obtain the suboptimal solution.Finally,the convergence,feasibility and effectiveness of the proposed algorithm are verified by simulation results.The simulation results show that the proposed algorithm can effectively improve the cache utility and backhaul traffic offloading ratio,provide high-speed content delivery for users.