A Study On The Extreme Performance And Degrees Of Freedom Of Massive MIMO Based On Electromagnetic Theory

With the development of fifth-generation(5G)wireless communication,more and more terminal devices are connected to the wireless network,and mobile data traffic is increasing exponentially.Traditional MIMO communication systems cannot provide the high spectrum efficiency required by 5G communication.Massive MIMO technology is able to improve the channel capacity and spectrum efficiency of wireless communication systems significantly and it is known as one of the key technologies of 5G.Compared with traditional MIMO systems,Massive MIMO provides a gain in degrees of freedom(DOF)in the spatial domain.This paper focuses on Massive MIMO and derives the upper bound of the average channel spatial DoF for continuous arrays with a limited array size under the more general non-isotropic scattering propagation environment.Based on the electromagnetic field source theory,this paper first proposes a system model for the study of spatial degrees of freedom,combined with the solution of the active wave equation,and obtains a physics-based mathematical model for the analysis of degrees of freedom containing array spatial information.Among them,we applied the dyadic Green’s function to solve the wave equation.When solving the mathematical expression of the Green’s function,Fourier integration was used to solve the problem,and a normalization method was proposed to process the integration result.The Green’s function was mapped to obtain the mathematical model of spatial DoF analysis.Then based on this model,we decompose the degrees of freedom in the spatial domain.For the degrees of freedom in each dimension after decomposition,we propose a novel spatial angle domain analysis method,which combines the array formation,size,and the range of the angular interval,through the definition of integral gives the expression of the spatial degrees of freedom.Finally,based on the aforementioned method,we obtain through mathematical derivation the upper bound expressions of the spatial DoFs for continuous linear arrays,continuous area arrays,and volumetric arrays,and verified our conclusions through numerical simulations under the CDL physical channel model.Based on electromagnetic theory,this thesis proposes a novel angular space domain method for calculating the upper bounds of the spatial degrees of freedom of the array.This method is suitable for regular antenna arrays in non-isotropic scattering environments,and it has a wider range of applications.Based on the method in this paper,the spatial DoF of a continuous array with a limited array size is derived,and the extreme communication performance of Massive MIMO can be analyzed.The optimal number of antennas of the size-constrained array can be given by the spatial degrees of freedom,which has practical value for the deployment of discrete antenna arrays in actual Massive MIMO communication systems.