Research On Interference Coordination Based On Precoding Technology In Ultra Dense Network

With the development of Interenet technologies,the number of smart equipments is increasing and the traffic types become diversified,which leads to a higher demand of user's speed provided by the wireless communication system.The densification of small base stations is an efficient way to solve this problem.It can shorter the distance between users and the base stations and a higher frequency reuse freedom can be obtained so that it can meet the requirement of one of the 5G scenarios,the Enhance Mobile Broadband to improve the capacity of the whole system.However,as the number of users increasing and the shorter distance between users and base stations,the intererence among cells becomes more severe,which could degrade the performance of system.So,how to mitigate the strong interference in the ultra dense network is an important issue.In traditional cellular networks,precoding has become a major way to mitigate interference.In UDN,combining the precoding technology and the clustering of the virtual cells can be a useful method.This thesis firstly creates the system model of UDN,generating users and base stations based on Poisson Point Process,building channel model with large-fading and small-fading factors.To mitigate the effect of cell-edge users,this thesis adopts user-centric virtual cell for users to choose serving base stations.Meanwhile,it introduces some common precoding methods and analyzes their performance to use efficiently in UDN.Secondly,the thesis jointly considers clustering method of virtual cell and precoding technology.To balance the complexity of the system and the inter-cell interference,the thesis introduces a virtual cell clustering method based on RSRP and potential interference strength.Thus it could convert the intra-cell interference into inter-cell interference in clusters and then use the ZF and MMSE precoding method to mitigate interference.Lastly,based on the real scenario,the thesis takes the mobility of users into consideration by allocating different speed and directions to them.According to the directions of users and the time-varying feature of wireless channel,this chapter introduces a refreshing method of forming virtual cell clusters.For each user,small base stations can always provide better service for users in terms of their locations and speed.Aftering using the ZF and MMSE precoding technologies,the proposed algorithm can mitigate ping-pong effect and lower the handover failure ratio.