Research On Ultra-dense Network Technology In 5G System

The explosive growth of mobile data traffic in the future,the massive connection of devices,and the emergence of new types of new services and application scenarios have placed new demands on 5G systems.Ultra-dense network(UDN)technology is one of the key technologies to meet these challenges.Ultra-dense network refers to a network formed by widely deploying heterogeneous small cells on the existing macro cell cellular network.It can improve network coverage and increase system capacity,and has become a key network architecture in 5G wireless networks.However,while network densification brings system capacity increase,the interference problem in ultra-dense networks becomes more complicated due to the dense deployment of small cells.In this thesis,we propose an optimal power allocation scheme based on virtual cell local information for downlink interference of ultra-dense networks.Firstly,we analyze the system model and establish the interference matrix by applying graph theory knowledge.Then we design a noncooperative game model by designing the utility function with penalty factor.The small cell is usercentered to form a virtual cell to participate in the game and only optimize.It is then proved that the Nash equilibrium point of the model exists and is the point where the system total rate is the largest.Finally,after solving the convex optimization problem of utility function,a distributed optimal power allocation algorithm is proposed.The simulation results show that the average area throughput of the proposed algorithm is improved compared with the average power allocation algorithm.In this thesis,we also jointly implement multi-domain interference management technology to mitigate the same layer interference in ultra-dense networks,namely joint implementation of OFDMA scheduling,interference alignment,TDMA scheduling,and power optimization.First,the problem of interference coordination in small cells is formulated as an overlapping coalition formation game(OCFG),and OCFG can help to effectively perform IA.Based on this model,we propose a distributed joint interference management(JIM)scheme.By using the proposed algorithm,each small cell base station can cooperate and organize itself into a stable overlapping coalition structure and reduce interference from different alliances.The simulation results show that the proposed algorithm has improved performance in terms of system throughput.