Research On Massive MIMO Antenna Technologies

Focusing on the Massive multiple-input multiple-out(MIMO)antenna technology,one of key technologies in the next generation cellular mobile communications,the research of this dissertation mainly contains the following aspects: Massive MIMO antenna selection technology and algorithm,approximate calculation of the half-power beam width(HPBW)of a circular array under the uniform cylindrical array antenna deployment for Massive MIMO and antenna design for sub-6 GHz band of the fifthgeneration(5G)of mobile communication systems.In this thesis,the antenna selection technology in Massive MIMO is studied in depth based on the criterion of channel capacity maximization.The antenna selection algorithm based on the traditional maximum-volume of a submatrix(also called square submatrix's maximum-volume,SMV)is a suboptimal algorithm that obtains a near-optimal capacity performance,while it only can solve the square submatrix problem,that is,the algorithm only can deal with antenna selection problem of the antenna selection number exactly same as the number of single-antenna terminals.By introducing the volume of a rectangular matrix,the submatrix's volume can be extended to calculate a rectangular submatrix's volume.Accordingly,we apply the rectangular submatrix's maximumvolume(RMV)into Massive MIMO antenna selection.As a result,a Massive MIMO antenna selection algorithm based on RMV is proposed.The RMV-based antenna selection algorithm not only overcomes the inherent defects of the SMV-based antenna selection algorithm,but maintains the near-optimal capacity performance of the SMVbased algorithm.In addition,its computational complexity is a little lower than that of the SMV-based antenna selection algorithm.Besides,a novel antenna selection based on global iterative swapping is proposed for Massive MIMO,including the cases of perfect channel estimation and imperfect channel estimation.Similar to the SMV-based algorithm,this kind of antenna selection also obtain a near-optimal capacity performance.According to the global iterative swapping antenna selection method,three algorithms are developed,i.e.global search local swapping antenna selection algorithm(GSL-swapping),global search global swapping antenna selection algorithm(GSG-swapping)and improved global search global swapping antenna selection algorithm(IGSG-swapping).GSL-swapping algorithm obtains a better capacity performance than the SMV-based algorithm,while they are same in computational complexity.Although GSG-swapping algorithm's capacity performance is a little lower than that of GSL-swapping algorithm,it achieves a significant reduction in computational cost.Moreover,when the antenna selection number is comparatively larger than the number of single-antenna terminals,the capacity loss is substantially negligible.IGSG-swapping algorithm obtains a further reduction in computational complexity at the cost of a small capacity performance loss,providing a balance between capacity performance and complexity performance.More importantly,the algorithms based on global iterative swapping can select any number of antennas,completely removing the limitation in the SMV-based algorithm.Furthermore,a modified global iterative swapping antenna selection with better capacity performance is proposed by means of a matrix transformation technique,which successfully avoids the approximation process in the derivation and completes the theory of global iterative swapping antenna selection.Based on the modified global iterative swapping method,a modified global-searching local-swapping(Modified-L)algorithm and a modified global-searching global-swapping(Modified-G)algorithm are proposed for Massive MIMO antenna selection.Both algorithms achieve a better capacity performance,especially at a low signal-to-noise ratio.To further reduce the computational cost,Modified-L algorithm is combined with the random selection algorithm,obtaining selection-selection Modified-L(SS-Modified-L)algorithm and group-selection Modified-L(GS-Modified-L)algorithm.The complexity of both algorithms greatly reduces at the expense of a small capacity performance loss.The capacity performance loss becomes very small for a large antenna selection number.Considering an airport scenario under the air-to-ground communications,we first discuss the deployment of the Massive MIMO antenna system for a ground base station briefly,and then the approximate calculation of HPBW for a uniform circular array(UCA)is studied under the configuration of uniform cylindrical array.Two very simple formulas are proposed to estimate the HPBW of UCA in horizontal and vertical planes.Their correctness,accuracy and calculation speed are evaluated by numerical calculations.Compared with the existing estimation formulas,the proposed approximate formulas have a simpler form,which can compute the HPBW of a main lobe with different directions within a certain angle range.Consequently,the approximate formulas proposed in this thesis is more applicable and meaningful in engineering.In the aspect of antenna design for the 5G sub-6 GHz band,two examples of broadband dual-polarized antenna design are presented in this dissertation.By designing the feeding connectors and parasitic structures specially and carefully,the properties,such as impedance,coupling between structures,of the antennas can be controlled and tuned,so that almost the same effective lengths of current paths on the crossed-dipoles can be attained and a symmetrical current distribution can be obtained on the inactive antenna.As a consequence,the proposed antennas attain good performances.Some properties the antennas attained are analyzed and explained in detail from the aspect of current distribution.In order to verify the proposed antennas,one of them is manufactured and measured.Generally,the measurement results are consistent with the simulation results,indicating that the antenna proposed in this thesis is well-designed and achievable.