Research On Performance Analysis And Joint Optimization Of Cache And Wireless Transmission

With the rapid development of wireless communication technology,the demands of users for data and multimedia services through the wireless network have a sharp increase.If we still adopt the traditional network optimization and management methods,it has been far unable to meet the explosive growth needs of current wireless traffic.Although technologies such as cooperative communication,smart antenna technology,interference management and radio resource management are of some benefit to improve the user's quality-of service(QoS),QoS of multimedia service is still inadequate.To address these challenges,a promising technique to solve these problems is caching.Small base stations and the user equipments can download data and cache these data during a period of low network traffic.When the user requires a file,the small base station or user with the required file can service the user directly.In this way,it can offer robust user's QoS,reduce burden of backhaul link and improve system capacity.This thesis focuses on the performance analysis and joint optimization of cache and wireless transmission,including three aspects as fellow:Firstly,in heterogeneous cellular network,small base stations have caching abilities,and can serve the user directly.The coverage probability of cache-enabled small base station(SBS)is studied by using stochastic geometry method.Moreover,simulation results show that cooperative multipoint(CoMP)transmission achieves a higher coverage probability than that of single-point transmission.Furthermore,Zipf distribution-based caching is more preferable than uniform distribution-based caching in terms of coverage probability.Secondly,thesis considers the performance analysis of cache-enabled mobile users in cellular network.The successful transmission probability is analyzed by using stochastic geometry method.Meanwhile,in order to optimize the successful transmission probability,two methods are considered,i.e.,file segmentation transmission and retransmission mechanism.Simulation results show that the successful transmission probability can be improved by several network parameters,e.g.,user density,transmission zone radius and caching probability,but exhibits a decline with increasing velocity or downloading time.Thirdly,by considering the backhaul delay and wireless channel quality,we jointly optimize the base station cache refreshment and handover.Moreover,we minimize the long term average delay in mobile network while maintain the stability of network.Lyapunov optimization technique is used to transform the stochastic optimization problem and maintain the stability of the system.The simulation results show that the proposed strategy achieves low long term average delay and good system stability.