Research On Hybrid Beamforming For Millimeter Wave Massive Multiuser MIMO Systems

With the increasing communication demands in recent years,the spectrum resources of low frequency bands have been gradually exhausted.As one of the key technologies of the 5th generation mobile networks(5G),millimeter-wave communication is considered to bring several orders of magnitude improvement in spectral efficiency and energy efficiency.Thanks to the short wavelength of millimeter waves,large numbers of antenna elements can be integrated within a small space in millimeter-wave multiple-input multiple-output(MIMO)systems,in order to obtain large array gains and overcome path loss.However,due to the limitation of hardware cost and energy consumption,conventional fully-digital beamforming methods that require a radio frequency(RF)link for each antenna element are no longer applicable.To address this challenge,hybrid digital and analog beamforming architectures are proposed.In this dissertation,we mainly study the hybrid beamforming technology in millimeter-wave massive multiuser MIMO systems.We consider a millimeter-wave massive multiuser MIMO system with a practical partially-connected hybrid structure and propose to jointly design the hybrid beamformers of both the base station(BS)and the users.For the purpose of achieving a high array gain,a sparse principal component analysis(PCA)based algorithm is utilized to obtain the corresponding analog precoding and combining matrices.Then we develop an iterative algorithm to jointly design the digital precoding and combining matrices under a weighted minimum mean square error criteria.Simulation results demonstrate that our scheme can approach the performance of those with fully-connected structures,with rather high energy efficiency.Multi-panel antenna array is a promising hardware solution for massive MIMO,due to its easy implementation and low cost.We consider a millimeter-wave massive multiuser MIMO system with the BS employing multi-panel array,and propose an efficient hybrid beamforming scheme.The analog beamformer is derived by maximizing the effective array gain.The digital part designing includes decoupling different panels and Geometric Mean Decomposition(GMD)based Tomlinson-Harashima Precoding(THP).Since the use of phase shifters introduces a constant modulus constraint,which in turn causes some performance loss,we propose a compensation method in baseband.Simulation results show that the proposed scheme can achieve a better throughput performance than a full-panel MIMO system of the same size,and it's verified that the baseband compensation matrix plays a significant role in maintaining the system performance.When the users are overcrowded,the proposed scheme can still maintain a good performance.