Joint User Association And Content Caching Algorithm In Cellular Heterogeneous Networks

With the explosive growth of demand for mobile network applications and high-speed multimedia services,single radio access technologies of traditional cellular networks are unable to satisfy the diverse traffic requirements of users.In order to tackle the above challenges,cellular heterogeneous network architecture was proposed.However,the dense deployment of cellular heterogeneous networks will put tremendous pressure on the backhaul network.Caching popular content at the edge network can significantly alleviates network backhaul pressure and improve network performance.In this thesis,the joint user association and content caching algorithms of cellular heterogeneous networks is studied.The main contents of this thesis can be summarized as follows:Firstly,an overview of the architecture and features of cellular heterogeneous network is given,and the key technologies in cellular heterogeneous networks are introduced.Then,user association,content caching,joint user association and content caching algorithms proposed for cellular heterogeneous networks are summarized.Finally,the importance of joint user association and content caching algorithms is emphasized.For a cache-enabled cellular heterogeneous network offering device-to-device(D2D)communication ability,a joint small base stations(SBS)cache partitioning,user association,and content caching algorithms are proposed.Firstly,in order to improve the utilization of cache space resources,this thesis proposes a backruptcy game-based algorithm of SBS cache space to obtain the optimal cache space allocation strategy.Based on this strategy,a joint user association and content caching algorithm is then proposed to minimize the service delay of all the users.By applying McCormick envelopes and Lagrangian partial relaxation method,the original optimization problem is transformed equivalently,and an iterative algorithm is then proposed to obtain joint user association and content caching optimization strategy.For cellular heterogeneous networks supporting content caching and base station collaboration,this thesis proposes a joint user association and content caching algorithm based on the minimization of the network cost.The network cost is modeled as the weighted sum of total service delay of all the users,the energy consumption of backhaul links and the cache energy consumption of the SBS,which is defined as the energy consumption generated by the cache when the users fetch contents from the cache.Based on different user service requirements and network resource status,a joint user association and content caching problem is formulated as a network cost minimization problem.In order to solve the problem,the Lagrange partial relaxation are firstly applied.Then the optimization problem is firstly decomposed into two sub-problems and a cooperative-hierarchical algorithm is proposed,and finally an iterative algorithm is proposed to obtain the joint user association and content caching optimization strategy.