User Scheduling And Beamforming Design In MIMO-NOMA System

With the massive expansion of mobile communication services,the amount of mobile data of the fifth generation(5G)mobile communication systems will exponentially increase.In the face of the growing communications services,it will be major challenges to achieve high communication speeds,low latency,large-scale connectivity,and high spectrum efficiency for future 5G communication systems.In the case of limited spectrum resources,the traditional orthogonal multiple access(OMA)method has been difficult to support a huge number of connections.Therefore,in this context,Non-Orthogonal Multiple Access(NOMA)technology,which can support simultaneous transmission of multiple users,has attracted people's attention and is currently considered to be a very promising multiple access technology in 5G.At the same time,Multiple Input Multiple Output(MIMO)technology can double the spectrum utilization without increasing bandwidth and antenna transmit power.Therefore,the combination of MIMO and NOMA technologies,namely MIMO-NOMA technology,will provide a strong guarantee to achieve extremely high spectral efficiency in 5G.In this paper,for the 5G application scenario,the techniques of the user scheduling and beamforming design of MIMO-NOMA system are deeply studied.The content of the specific research can be summarized as follows.1.User scheduling and beamforming design for downlink single-cell MIMO-NOMA systems.Firstly,during the course of the user scheduling,in order to simultaneously take intra-cluster user interference and inter-cluster user interference into account,all user grouping were initially sparsely processed by the L1-norm regularization method according to the channel difference among the users.In the respect of user channel correlation,two users with large channel correlation were then divided into a cluster;Secondly,the fractional transmit power control(FTPC)is used to implement the power allocation of the intra-cluster users.Finally,an objective optimization function based on the sum rate maximization criterion was constructed,which was solved by successive convex approximation(SCA)method to obtain the BF matrix.Theoretical analysis and simulation results show that the proposed downlink beamforming design scheme with the user scheduling is superior to the classical user scheduling method,beamforming method and OMA in terms of system capacity and user fairness.2.User scheduling and beamforming design for multi-basestation MIMO-NOMA systems.Before the user scheduling,based on the K-Nearest Neighbor(KNN)algorithm,all basestations(BSs)in the area are firstly selected to provide communication services,which constitute virtual cells.And all users are classified into the initial strong and weak users in the virtual cell,which is recorded as the candidate strong user group and the candidate weak user group.Secondly,considering the weak users in the cell suffered from the large inter-cell interference,the improved cosine similarity is used to form the final weak users by selecting from the weak user group to communicate with the BS.Finally,in order to simultaneously consider the user interference in the cluster and the inter-cluster user interference,the final strong users are selected from the candidate strong user group according to the KNN algorithm and the channel difference between users.All strong users communicating with the BS are matched with weak users.Based on this,according to the maximization system and rate criterion,the majorize minimization(MM)algorithm is used to solve the beamforming matrix.Theoretical analysis and link simulation show that the performance of the proposed scheme is better than the random BF design,the traditional BF design and OMA.