Research Of Coordinated Multiple Points Transmission Technology In Ultra-Dense Networks

Ultra-Dense Networks(UDN)as one of the key technologies of 5G can bring considerable system capacity enhancement.There are some characteristics such as intensive deployment of small base stations,community radius reduction and base station location random,so it can bring serious challenge to the realization of UDN.The Coordinated Multiple Points(CoMP)transmission technology can share user information and jointly provide services for users by using the cooperation between base stations,and applying it to UDN can effectively mitigate serious interferences among users,and users can accept services of multiple collaborative small base stations,which can alleviate the problem of performance degradation caused by users frequently switching cells.However,the UDN will increase the system capacity and energy consumption,and the dense and random deployment method will increase the difficulty of deployment of backhaul networks.So wireless backhaul network is considered in UDN,CoMP transmission requires high backhaul capacity while the wireless backhaul capacity is limited.Considering the high energy consumption of UDN and high backhaul capacity demand of CoMP,this thesis further study the CoMP transmission technology in UDN.The main research work is as follows:Firstly,aiming at the model of CoMP Joint Transmission of UDN,this thesis study a user centric set of cooperative small base stations aggregate that form from dynamic clustering method of user centered.This thesis propose a method of resource allocation in CoMP based on the cost function.Establishment of transmission rate distribution function of small base station based on transmission energy consumption and data transmission delay of small base station,this thesis use convex optimization theory to solve the optimal allocation problem of the rate of small base station.The simulation results show that the proposed method can adjust the rate distribution of the small base station according to the constraints.Even in the situation of the number of cooperative small base stations reaches a certain value and in a certain range of user service request rates,the method proposed in this thesis has higher energy efficiency relative to the comparison algorithm.Secondly,considering about the wireless backhaul in CoMP transmission of UDN,which has been highly requested by CoMP.The two transmission modes of joint transmission and coordinated beamforming require different backhaul capacity.To take account of energy consumption,a hybrid CoMP transmission method based on two step optimization is proposed in this paper.The method can improve the performance of the system by two steps.The first step optimization of power distribution,second step optimization model selection.There are two modes of transmission in the system at the same time that can maximize system throughput under limited energy and backhaul capacity.The simulation results show that the method proposed in this thesis has the higher system throughput compared to the comparative method under a certain backhaul capacity.