Research On Caching Placement Algorithm In UAV-Assisted Cellular Networks

With flexible flight and good channel characteristics,unmanned aerial vehicles(UAV)can provide communication services as base stations.In addition,the introduction of UAVs into cellular networks to form UAV-assisted cellular networks can effectively expand the system capacity and ease the load on base stations,and is expected to play an important role in scenarios such as communication recovery and hotspot coverage.In UAV-assisted cellular networks,in response to traffic congestion caused by a large amount of repeated data transmission,positive caching can place some popular contents in advance on edge nodes closer to users,such as UAVs,and effectively alleviate network load pressure and improve user content acquisition performance.Therefore,UAV-assisted cellular networks combined with edge caching have been one of the hot research directions.The work is supported by the National Natural Science Foundation"Research on Multilevel Cooperative Caching in UAV-Assisted Cellular Networks".In order to ensure the effective placement of contents and improve caching performance,the caching placement algorithm is crucial.This thesis studies caching placement algorithms in UAV-assisted cellular networks,including the joint optimization algorithm of caching placement and radio resource allocation for cache-enabled UAVs,and the joint optimization algorithm of cooperative caching placement for cache-enabled UAVs and user equipments.The contributions of the thesis are:1)This thesis reviews the current researches on caching placement algorithm in UAV-assisted cellular networks.Firstly,the caching technology is summarized around the development history,strategy mechanism,and performance indicators.Then,the thesis analyzes the UAV-assisted cellular network,including the applications of UAV-assisted cellular communication and the main research concerns of UAV-assisted cellular networks.Based on the above analyses of caching technology and network scenario,the current classification and research progress of caching placement algorithms for UAV-assisted cellular networks are summarized,and the problems existing in the existing researches are sorted out.2)Aiming at the problem of limited energy and wireless backhaul bandwidth of UAVs in UAV-assisted cellular networks,this thesis proposes a joint optimization algorithm of caching placement and radio resource allocation for cache-enabled UAVs.The thesis establishes a joint optimization problem of user association,caching placement and backhaul bandwidth allocation with the goal of minimizing user content acquisition delay across the entire network and divides it into three stages to obtain a low-complexity suboptimal solution.First,user association is obtained through a many-to-one two-dimensional matching algorithm based on the exchange matching theory;then,caching placement is obtained through a many-to-many two-dimensional matching algorithm based on the delay matching theory;finally,the backhaul resource allocation is obtained based on the Lagrange multiplier method.The three phases iterate continuously to obtain the best user association,caching placement,and backhaul resource allocation.Simulation results show that the proposed joint optimization algorithm of caching placement and radio resource allocation for cache-enabled UAVs can effectively reduce user content acquisition delay,alleviate backhaul traffic congestion of UAVs,and reduce energy consumption of UAVs.3)Aiming at the problem of limited storage of cache-enabled UAVs in UAV-assisted cellular networks,this thesis proposes a joint optimization algorithm of cooperative caching placement for cache-enabled UAVs and user equipments.The proposed algorithm jointly optimizes the caching placement of UAVs and user equipments with the goal of minimizing average user content acquisition delay across the entire network.In the first step,each UAV updates its stored contents based on the alternating direction method of multipliers(ADMM).On that basis,the second step is to update the contents cached by all users based on the global greedy algorithm.Simulation results show that the proposed cooperative caching placement algorithm for cache-enabled UAVs and user equipments can effectively reduce user content acquisition delay and improve system performance.