Research On Asynchronous Coded Caching In Fog Radio Access Network

With the rapid proliferation of smart devices and mobile application services,wireless networks have been suffering an unprecedented data traffic pressure in recent years.As a novel network architecture,fog radio access network(FRAN)is proposed to better meet the performance requirements of future mobile communication systems.At the same time,code caching,as a new technology,can effectively reduce network congestion by using edge caching and coding.However,user requests for contents are typically asynchronous,and coded caching with asynchronous requests has not been further studied,which will affect the practical application of coded caching in FRAN.Therefore,asynchronous coded caching in FRAN is studied in this thesis.Firstly,asynchronous coded caching with uniform popularity distribution in FRAN is studied.To minimize the fronthaul load,the encoding set collapsing rule and encoding set partition method are proposed to establish the relationship between the coded-multicasting contents in asynchronous and synchronous coded caching.And a decentralized asynchronous coded caching scheme is further proposed,which provides asynchronous and synchronous transmission methods for different delay requirements.The simulation results show that the proposed scheme creates considerable coded-multicasting opportunities in asynchronous request scenarios.Secondly,the performance of the above asynchronous coded caching scheme with uniform popularity distribution is analyzed.We first derive the expression of the fronthaul load of the proposed scheme for the special case,and then establish the upper and lower bound of the fronthaul load of the proposed scheme for the general case.Lastly,we analyze the influence of the system parameters on the performance,and show that the fronthaul load of our proposed scheme is at most a constant factor larger than that of the Maddah-AliNiesen's decentralized synchronous coded caching scheme.The simulation results show that the maximum request delay can be adjusted more flexibly while the same considerable coded-multicasting opportunities are created,when the number of F-APs increases with a large cache size.Finally,asynchronous coded caching with a nonuniform popularity distribution in FRAN is studied.First,a cache placement method is proposed for the nonuniform popularity distribution.Second,the problem of encoding the transmitted contents is transformed into a graph coloring problem,but it is difficult to approximate in general.Then,a greedy constraint coloring algorithm is further proposed.At last,a decentralized asynchronous coded caching scheme based on graph coloring algorithm is proposed.The simulation results show that our proposed scheme can achieve considerable fronthaul load gain when the delay requirement is relaxed in asynchronous request scenarios.