Massive MIMO Antenna Array Topology And Structure-research And Design

As a key physical-layer technology of the fifth-generation(5G)mobile communications,massive MIMO,by equipping a largely increased number of antennas and RF chains at base stations compared to conventional MIMO,theoretically has high spatial resoultion and thus greatly impoves radio spectrum efficiency.However,in pratical system developments and deployments,engineers often meet the problem of low performanceprice ratio.That is to say,the significant increase in hardware complexity and cost does not lead to correspondingly significant improvement in performance,especially in the”difficult” propagation scenario where users are densely distributed.In view of this problem,most of the current researches focus on antenna selection,user scheduling and signal processing.There are few in-depth studies on the morphology and structure of massive MIMO antenna arrays.To solve the problem of low performance-price ratio,we propose an antenna array design idea and method that matches the electromagnetic wave propagation environment.It can fully explore the high degrees of freedom of the massive MIMO antenna array,and improve the system performance and reduce the system complexity by optimizing the shape and structure of the antenna array.Based on the idea that the antenna array design matches the electromagnetic wave propagation characteristics of the environment in which the base station is located,we optimize the structure of the massive MIMO antenna array by maximizing the upper bound of the statistical channel capacity.Taking the rectangular array as an example,this paper optimizes the number of horizontal and vertical antennas and the spacing between adjacent elements when the antenna and aperture resources are limited.At the same time,based on the 3GPP 3D channel model,the channel environment in a variety of typical5 G scenarios is obtained,and the electromagnetic wave propagation characteristics are characterized by the angular power spectrum as the basis for the antenna array design.Specifically,we optimized the design of rectangular dual-polarized antenna arrays in the scenes of urban macro areas and urban high-rise macro areas where users are densely distributed or dispersed on the ground or in high-rise buildings,and evaluated the system performance gains brought by the designed antenna array.Our research found that the optimized massive MIMO antenna array can bring greater performance gains compared with the currently commonly used massive MIMO arrays.Only in the ”difficult” propagation scenario where users are densely distributed in the urban macro area,the gain obtained is relatively small.The simulation results show that under the condition of 10 d B signal-to-noise ratio,the design array with ZF and MF beamforming will bring at least 32% and 24% increase in system rate improvement respectively,while the number of antennas and RF chains is much lower than the current commonly used arrays.It is to be noted that the low-complexity MF beamforming can reach 44%-72% of the channel capacity.Therefore,by designing a massive MIMO antenna array structure to match the electromagnetic wave propagation characteristics of a specific environment,we can not only greatly improve the system performance,but also deploy a smaller number of RF chains at the base station and use low-complexity MF beamforming.The research results in this paper provide a new idea for the implementation and performance enhancement of 5G massive MIMO systems.In view of the ”difficult” propagation scenario where users are densely distributed,since the system rate of the design array using ZF and MF is only 27% and 19% of the channel capacity respectively,in order to improve the system performance,we have introduced a new degree of freedom on the basis of antenna array design,i.e.,transmission electromagnetic metasurface design.We theoretically assume that the electromagnetic metasurface has the freedom to affect the phase of the incident wave and combining it with the antenna array is equivalent to changing the electromagnetic wave propagation or changing the response of the antenna array.By optimizing the parameters of the transmission metasurface,we can make the above two system rate indicators reach 61% and 51%of the channel capacity respectively.Research has shown that the introduction of electromagnetic metasurface can not only greatly improve the system performance of massive MIMO in ”difficult” propagation scenarios,but also provide the possibility to save antenna and aperture resources,which provides a potential new direction for antenna array design.