The User Scheduling Scheme For CoMP Tranmission Under Imperfect Backhual

To adapt to the ultra-dense and multi-tier deployment of network for the fifth generation(5G)wireless communication systems,the further cooperation and coordination among different entities will be a key requirement to mitigate interference in 5G network.Coordinated multipoint(CoMP)transmission and reception techniques,defined in Release 11 of the Third-Generation Partnership Project Long-Term Evolution Advanced(3GPP-LTE Advanced)specifications,are a family of techniques where multiple transmission points are coordinated to improve the performance of certain terminals especially for cell-edge user.However these CoMP schemes are supported by LTE-Advanced with almost ideal backhaul connections between transmission points,and the practical implements of CoMP still pose a number of challenges from backhaul conditions,such as limited capacity and finite delay.For improving the performance of certain terminals,this thesis studies the following four aspects:Firstly,we introduce the technical background of CoMP which can generally be categorized into two modes:coordinated beamforming(CB)and joint transmission(JT)and user selection strategies in detail.Secondly,we evaluate the optimal soft mode switching under limited-capacity backhaul.The designer evaluate a soft mode switching between these two modes by optimizing the amount of data sharing to maximize the sum rate under the backhaul capacity constraints,which leads to a superposition of CoMP-CB and CoMP-JP when the backhaul capacity lies in a certain region.By deriving the closed-form solution in a two-cell case,the designer analyzes the optimal division of the data of each user for CoMP-CB and CoMP-JP and analyzes the throughput scaling law with the backhaul capacity.The results of the considered three transmission strategies are all obtained from channel-orthogonal users[74].We can see that the soft mode switching performs better than the other two strategies.Thirdly,we evaluate sequential and incremental precoder design for joint transmission network MIMO systems with imperfect backhaul designed.The designer first optimizes the precoder at the serving base station(BS)and then sequentially optimizes the precoders of nonserving BSs in the JT set according to the descending order of their probabilities of participating in the JT[75].Simulations show that,under the practical backhaul link conditions,the scheme is much better than the autonomous global precoding scheme.Fourthly,we study MAX-ESINR scheme to solve the problem of backhaul delay.When the channel is time-correlated,MAX-ESINR scheme can improve the system performance.