| The fifth-generation mobile communications system(5G,also known as IMT-2020)has ultra-high spectral efficiency and transmission rate.As the leading technology of 5G,Massive MIMO systems greatly increase system capacity and energy efficiency by using a large number of antenna arrays.In the future 5G system,coexistence and simultaneous service of a large number of users become inevitable.Multi-user MIMO beamforming precoding and user selection algorithms are key technologies for solving user-to-user interference and improving system capacity.However,with the dramatic increase in the equivalent dimension of massive MIMO channels,problems such as difficulty in obtaining channel state information(CSI),severe pilot pollution,and high complexity are the bottlenecks that limit its development.This thesis studies multi-user transmission schemes that are applicable to massive MIMO systems.It aims to solve the problems such as large pilot overhead and large amount of computation in existing precoding and user selection algorithms.At present,the development of navigation and positioning technology at home and abroad is relatively mature,with high precision of positioning information and wide applicability,and it can meet the real-time requirements of communication.Based on the research and improvement of the linear precoding and user selection algorithm of the existing massive MIMO system,this thesis innovatively introduces navigation and positioning information assistance and uses a small amount of real-time positioning information data from users to design efficient beamforming.The user selection algorithm can not only guarantee the flexibility of the transmission end,but also avoid the complex channel estimation and CSI acquisition process.While solving the multi-user interference and improving the system capacity,the system complexity is greatly reduced.Based on the current research on massive MIMO technology and the development trend of 5G,the main research contents of this thesis are as follows:Firstly,research on the theoretical characteristics of massive MIMO technology.Analyzes and summarizes the main gain sources of massive MIMO technology a nd the technical chal enges they face,and elaborates on the key factors.Secondly,research on massive MIMO precoding.Based on the research of the existing precoding,aiming at the proble m of CSI acquisition overhead,the joint space-division multiplexing two-level precoding transmission scheme that is suitable for FDD system is researched,and its capacity performance and feedback overhead are simulated and analyzed.Thirdly,research on massive MIMO user selection algorithm.Based on the research of traditional user selection algorithms,a low-complexity user selection algorithm based on MRT beamforming is proposed.The simulation shows that when the base station obtains full CSI,the algorithm can improve the capacity of MRT precoding system while reducing the user chooses algorithm complexity.Finally,research on location-aided massive MIMO multi-user transmission scheme.By introducing location information assistance,combined with the ideas of space division multiple access and greedy algorithm,a Location-Aided Beam Division User Selection(LA-BDUS)algorithm and a Location-Aided Greedy User Selection(LA-GUS)algorithm are proposed respectively for different application scenarios.The simulation results show that the performance of the proposed algorithms is similar to that of the traditional optimal greedy user selection algorithm.It has good interference suppression and capacity performance,and greatly reduces the computational complexity. |
PDF Full Text Request