Research On User Association And Power Control Strategies In Ultra Dense Network

With the rapid development of the mobile networks,the demand of data services grows rapidly.Ultra dense network can achieve higher spectrum efficiency and hundreds of times capacity improvement by deploying much more base stations in the networks.Ultra dense network is one of the key technologies of the fifth generation mobile communication system to meet 1000 times capacity improvement goal.But as the the cell radius decreased,the coverage area of the small cell tends to be overlaped.One user can only belong to one base station in traditional user association,so other base stations become the source of severe intercell co-channel interference,which is the main factor to restrict the further improvement of system capacity.An efficient method to solve this problem is using multiple user association algorithm,which means that one user can be served by more than one base stations.It is worth noting that intercell interference is still a key challenge that limiting the system performance.Base stations can use the method of time domain?frequency domain?space domain?code domain and the power control to mitigate the intercell interference.And the power control method can improve the system throughput by adjusting the power of base stations.In this thesis,we focus on the spectrum efficiency and energy efficiency of system,and then we research on the user association and power control algorithm.The specific content is:First,we propose a method combining of user association and power control based on multiple user association in ultra dense network.In this thesis,we form a problem maximizing the sum of logarithmic rate of system based on the feature of ultra dense network and the feature of multiple user association.As the problem is difficult to solve,we propose an iterative algorithm,and solving the problem by solving the two sub-problems alternatively.The results show that the proposed algorithm can improve the system throughput and guarantee the fairness of users at the same time.Secendly,we propose a sleep algorithm of base stations based on user association and power control.We form a problem maximizing the energy efficiency of network based on the high density of base station.As the problem is difficult to solve,we propose a simplified algorithm.The results show that the proposed algorithm is efficient in spectrum efficiency and energy efficiency.