Research On The Clustering Method Based On CoMP In UDN

With the rise of the Internet of Things,the popularity of smart terminal devices and the rapid development of various applications have led to an explosive growth in the demand for mobile data.As an effective method to improve spectrum efficiency and network capacity,Ultra-Dense Networks(UDN)has become one of the key technologies of 5G.The base stations are close to each other due to intensive distribution of network,which leads to severely interference.Coordinated Multiple Point(CoMP)technology has the ability to improve system capacity and cell edge throughout through coordination among the cells.However,huge overhead is required for coordination amongs all cells,including precise synchronisation requirement within coordinated cells,complex beamforming design and scheduling among all base stations.To reduce this overhead,the small base stations needs to be clustered firstly,and the scope of cooperation is limited to each cluster.Designing the optimal CoMP cluster is one of the challenges for CoMP implementation for UDN,and it is also the key to obtain the potential CoMP gains.In order to mitigate the interference between small cells in UDN,CoMP clustering methods are studied separately for the uplink and downlink.The main works of this paper is as follows:(1)In order to mitigate the interference between small cells in ultra-dense network,a user-centric semi-dynamic clustering method is proposed for coordinated multiple point joint transmission scenario.Firstly,small stations are divided into non-overlapping clusters,and the small stations in the cluster and the small stations located outside the cluster but having large interference with the cluster are taken as the optional servicing stations of the user.Zero-forcing precoding is used to eliminate interference to users from non-serving base stations in the optional servicing stations.A number of candidate service stations are selected from the optional servicing stations.The serving station clusters are selected by cluster heads with the goal of maximizing sum of throughput of each user.A suboptimal method for selecting serving station clusters for users is given to reduce the complexity.Simulation results show that the proposed scheme improves the system throughput compared with the existing scheme in the same scenario.(2)For uplink interference problem in ultra-dense networks,a joint clustering and resource allocation scheme is proposed based on coordinated multiple point joint reception.Firstly,users and small base stations are divided into several clusters according to the uni-subband clustering.The multiple edge users in the same small cell are assigned to different user clusters.The users at the close edge of the adjacent small cell are assigned to the same cluster.The cell-center users are clustered according to the interference intensity of them to the existing base station clusters.Then,multi-sub band allocation is performed for user clusters.The user clusters containing the same small cell users are allocated different sub-bands,and the number of allocated sub-bands for each user clusters is as much as possible.Finally,the water-filling algorithm is used to allocate appropriate power to each user with the goal of maximizing the total transmission rate of the system.Simulation results show that spectral efficiency can be significantly improved by the proposed scheme.