Research On The Performance Of Massive MU-MIMO System In Presence Of Mutual Coupling

In recent years,massive multiple-input multiple-output(MIMO)technology plays a huge role in the modern communication network system.The technology has two characteristics of massive information transformation / storage and high-speed data transmission,which can fully meet the requirements of high spectral efficiency and high system capacity.However,in a highly densely arranged antenna array,the current/voltage signal on the antenna will be directly or indirectly affected by the adjacent antenna.That is,the voltage signal received on each antenna element will induce current on its own antenna element and excite the corresponding electromagnetic field,which will affect the adjacent antenna element,which is a potential source of performance degradation of the MIMO system.Considering the existence of electromagnetic mutual coupling between array elements,it is a necessary research topic to design a better transmission scheme to improve the transmission performance of a large-scale multi-user multiple-input multiple-output(MUMIMO)system.This topic mainly starts with the description of the advantages of the Massive MIMO system,and briefly describes several 3D channel models based on the fulldimensional MIMO technology,such as the pure LOS channel model,the Ricean channel model,the Saleh-Valenzuela channel model and the Kronecker channel model.The generation mechanism of mutual coupling between elements on the transmitting and receiving antenna arrays in the system is described,and the advantages of beamforming are explained in detail with examples.This thesis studies the massive MIMO system from the perspectives of precoding and power allocation in the electromagnetic mutual coupling system,selecting the appropriate precoding algorithm and designing the corresponding power allocation algorithm to optimize the performance of the transmission system:(1)Based on the millimeter wave channel model of Saleh-Valenzuela,the linear precoding algorithm of the massive MU-MIMO multiple-transmit multiple-receive communication system is studied.Firstly,when the Channel State Information(CSI)is known,the precoding algorithm is used to verify the performance of the system,and the advantages and disadvantages of the three precoding algorithms are compared in detail.Secondly,considering the electromagnetic mutual coupling between the array elements,the induced electromotive force(EMF)method is used for deriving the channel capacity expression,then the thesis simulates and discusses the performance loss caused by the electromagnetic mutual coupling effect between the array elements.Finally,different linear precoding algorithms are applied to the channel considering electromagnetic mutual coupling.Simulation results show that the block diagonalization(BD)precoding algorithm of the three linear precoding algorithms can completely eliminate the inter-user interference and achieve the optimal system performance.(2)Based on BD precoding algorithm,power allocation algorithm is studied.In order to maximize the total channel capacity of the system,a two-stage power allocation algorithm based on greedy algorithm is proposed.The algorithm is divided into two stages.In the first stage,the power optimization problem is considered from the user level.The power allocated to each user's data stream needs to be calculated.The second stage considers from the antenna level,and allocates the power of each data stream sent to each user on the basis of user-level power.It successfully decomposes the optimization problem established in the first stage into multiple sub-level problems and calculate the power that should be allocated to each data stream for each user on each sub-level problem.Finally,the simulation is carried out on the MATLAB platform,and the superiority of the two-stage power allocation is verified.