Random Edge Caching For Cooperative Transmission In Heterogeneous Networks

With the arrival of the fifth generation mobile communications system(5G),5G commercial is about to become a reality.As a large number of mobile terminal devices are connected to the wireless network,not only the mobile data traffic increases exponentially,but also the traditional macro cellular network structure faces great challenges.Moreover,the demands for wireless communication services has been shifting from the connection-oriented services such as traditional voice telephony and messaging to kinds of content-oriented services such as social networks and multimedia.Heterogeneous networks are one of the important candidate technologies in 5G communication systems.However,backhaul availability and capacity along with the incell interference caused by dense base station become a hindrance to the performance in heterogeneous networks.Edge caching is an effective solution to alleviate the burden of backhaul and base stations cooperation can mitigate the inter-cell interference.Therefore,this thesis will study random edge caching strategies on oriented cooperative transmission in heterogeneous networks.Stochastic geometry theory is a method that can effectively model heterogeneous network and analyze the performance of networks.This thesis first uses the Poisson point process to establish the location distribution of base stations model.In order to improve the spatial file diversity,this thesis adopts a random caching scheme.Aiming to manage intra-cell interference in heterogeneous networks,this thesis proposes a cooperative transmission scheme based on cooperation radius.Using tools from stochastic geometry,this thesis theoretically derives a tractable successful transmission probability expression based on the proposed cooperative transmission scheme.Compared with the result from the Monte Carlo simulation,it is shown that the expression is convincing.In fact that there is always some errors when predicting files popularity,this thesis considers two sorts of errors and models them.By maximizing the successful transmission probability,the cache distribution is optimized and an optimal caching is obtained.Compared with the existing two cache designs,the optimal caching can achieves a promising successful transmission probability gain.With simulating the influence of errors on the successful transmission probability,it is demonstrated that the optimal caching under the proposed scheme can make better robustness in the presence of errors.Considering a more realistic scenario,this thesis makes some improvements in the original cooperative radius based cooperative transmission scheme,by limiting the number of base stations that participate joint transmission and adopting the random discontinuous transmission.This thesis proposes a flexible cooperative transmission scheme based on random caching and realistic conditions.According to the improved scheme,this thesis derives the successful transmission probability expression and then makes some analysis.The phenomenon that there is a trade-off between the number of active small base stations and the intra-cell interference in the region of cooperation radius is pointed out.The simulation results show the impact of key network parameters on the successful transmission probability for a specific file.Furthermore,we make some analysis of optimal active probability.For a given active probability,the successful transmission probability is maximized to obtain the optimal cache distribution.The simulation results prove the existence of the optimal active probability.It is found that the optimal active probability does not achieve a huge successful transmission probability performance improvement,but may reduce the energy consumption of entire networks.