Performance Analysis In Fog Radio Access Networks Based On The Stochastic Geometry

With the rapid proliferation of smart mobile devices and social networking services,wireless networks are under increased data traffic pressure.Fog radio access networks(F-RAN)can effectively alleviate network congestion by placing popular contents closer to users at off-peak hours.Consequently,the fronthaul data traffic can be greatly reduced since there is no need to retrieve these cached contents from the cloud server.In the F-RAN,fog access points(F-APs)are equipped with limited storage space.Due to storage constraints,performance analysis and caching design are becoming ever more important in order to achieve a better network performance.Firstly,Based on the user-center cluster strategy,the successful transmission probability is analysed in the paper.Depending on whether the file is partitioned or not,two cooperation strategies are proposed.Firstly,by using tools of stochastic geometry,we first derive the expression of successful transmission probability with different transmission strategies.Then,by maximizing the successful transmission probability,we formulate the optimization problem.Further,we proposed a lower computation complexity caching placement algorithm based on the fruit fly optimization algorithm.The simulation results showed that our proposed algorithm can achieve a superior performance.We obtain the impacts of caching size of F-AP,file popularity distribution and target SIR on successful transmission probability.The simulation results showed that our proposed caching design is more effective.Secondly,we make a analysis on the fronthaul offloaded traffic.Firstly,we assume that the user equipments are configured with a limited successive interference cancellation.When the requested file is partitioned,if the subfiles cached in the closer F-APs can be decoded successfully,the interference from the closer F-APs can be cancelled and the performance of the network can be further improved.When the file is not partitioned,all the F-AP in the cluster jointly transmit the same whole file,then the transmission stability is improved and the offloaded traffic is more than the scenario that when the user is served by only one F-AP.The simulation results showed that our proposed cluster model can achieve a larger fronthaul offloaded traffic.Finally,we make a analysis on the transmission delay.Firstly,by using tools of stochastic geometry,we first derive the expression of delay when the file is wholly cached,partitioned and uncached and then we obtain the closed expression in the special case.Then,based on these theoretical results,we discussed the impacts of caching size of F-AP,file popularity distribution,SIC capability and the number of cooperative F-APs on the delay.The simulation results showed that,in the F-RAN that considers the SIC and cooperative caching,the transmission delay can be effectively reduced.The performance including successful transmission probability,fronthaul offloaded traffic and delay is more superior than the traditional strategies like MPC and LCD strategy.