Research On Method Of Caching Scheme And Wireless Resource Allocation In C-RAN

At present,the rapid development of 5G and Io T technology has promoted the explosive growth of the number of smart devices and the amount of data communicated.Cloud Radio Access Network(C-RAN)framework has significant advantages in suppressing interference,reducing energy consumption,and improving spectrum utilization,so it has been widely used.However,C-RAN will bring additional signaling overhead when cooperating with processing,and face the problem of limited fronthaul capacity.To effectively solve the bottleneck of fronthaul capacity limitation,some researchers have proposed distributed edge caching technology.It can not only alleviate the pressure caused by limited fronthaul capacity,but also significantly reduce the delay and energy loss of information interaction.Compared with traditional C-RAN,C-RAN based on distributed edge caching has obvious differences,and its resource allocation mechanism needs to be re-examined.This paper does the following research on the caching strategy and resource allocation mechanism in C-RAN based on distributed edge caching:First,the characteristics of C-RAN,Heterogeneous Cloud Radio Access Network,and Fog Radio Access Network are introduced,and the caching technology in C-RAN is summarized,including the problem of caching deployment location and caching strategy.It then explains the importance of caching to the C-RAN architecture.Then,the resource allocation technology in C-RAN is summarized,including the problems of task offload and user association and the problem of computing resource allocation.Secondly,aiming at the C-RAN scenario with layered virtual controller and distributed edge caching,under the constraint of total power,the problem of edge caching,user association,and computing resource allocation based on minimizing the average delay of the system is studied.By considering the downlink C-RAN system based on fronthaul compression,the expressions of system transmission delay and computing delay are deduced,and a system optimization problem based on edge caching,user association,and computing resource allocation based on minimizing the average system delay is established.Aiming at this optimization problem,a caching strategy based on user preference and user mobility is proposed to improve the caching hit probability of the system;a user association strategy based on the nearest distance and the limited number of access users per Remote Radio Head(RRH)is proposed;the sub-modularity of the computational resource allocation problem in the local server is proved,and it is transformed into a sub-modular function maximization problem with a matroid constraint.A heuristic computing resource allocation algorithm was proposed,and an approximate solution with an error within 0.5 of the optimal solution was found.Simulation results show that compared with the existing methods,the proposed method has significant advantages in reducing the average system delay.Finally,for the C-RAN scenario with layered virtual controller and distributed edge caching,the problem of edge caching and user association based on minimizing the average system delay and the total power loss of the system is studied.By considering the downlink C-RAN system based on fronthaul compression,the expressions of the average system delay and the total system power loss are respectively derived,and the system optimization problem is based on the product of t the average system delay and the total system power loss as the objective function of the system optimization.Based on the value of the objective function,the system optimization problem of edge cache and the user association is established.Aiming at this optimization problem,a file caching strategy based on file popularity and polling is proposed,so that three adjacent RRHs caching different files;a low-complexity heuristic user association algorithm is proposed based on the distance between each user and each RRH,the file application situation of each user and the file cache situation of each RRH.In order to reduce the total power loss of the system,the algorithm proposed in the system closes some inefficient RRHs and reassociates users associated with inefficient RRHs to other RRHs.Simulation results show that compared with the existing methods,the proposed method has significant advantages in reducing the average system delay and the total system power loss.