Transmission Theory And Technology Of Cloud Radio Access Network With Edge Caching

With the rapid growth of wireless devices and data traffic in 5G wireless networks,Cloud Radio Access Network(C-RAN)is considered to be one of the candidates for meeting the increasing data rate requirements.It has been observed that mobile data traffic is generated by a large number of repeated downloads of popular content,of which mobile video traffic accounts for the majority.Caching popular content at the edge of the cellular network is able to offload data traffic from the core network,reduce access latency and backhaul costs,and increase network throughput.This thesis focuses on the energy efficiency and physical layer security of C-RAN based on edge caching.Aiming at the problem of the low energy efficiency(EE)of a downlink C-RAN with edge caching and fronthaul compression,we introduced the fronthaul compression transmission strategy and the data sharing transmission strategy respectively to solve the problem due to the fact that the capacity of the fronthaul links is limited,and the performance of the two transmission strategies is compared.Considering that the system ergodic sum rate is related to the rapidly changing small-scale fading factors,in order to reduce computational complexity,the large-dimensional random matrix theory is used to derive the approximate expression of the EE.Then,a closed-form expression of optimal cache capacity that maximizes the EE is derived.Simulation experiments show the correctness of the derived approximate expression of the EE,the trade-off between the EE and the transmit power,and the dependence between the EE and the cache capacity.Aiming at the problem of insufficient security caused by the broadcast feature of wireless transmission in cellular networks,edge caching is used to implement physical layer security transmission,thereby improving network security performance.To ensure the confidentiality of all messages,this physical layer security mechanism considers a worst-case scenario where all other non-target users in the network can cooperate to eavesdrop the data that the base station transmit to the target user.Then,in order to analyze the impact of caching on security performance,two different caching strategies are adopted and the performance of the two caching strategies is compared.Simulation results show the impact of the cache capacity on the security performance,which helps to design a proper caching strategy to effectively improve the security performance of the system,thus achieving physical layer security transmission.