Research On Wireless Transmission Technology In Millimeter Wave Band Of 5G Systems

5G systems can support 1000 times of traffic growth,and theoretically the peak transmission rate can reach 10 Gb/s.The existing licensed bands are no longer sufficient to meet above requirements,so researchers turned their attention to the millimeter wave(mmWave)band.The 5G mmWave communication systems can effectively combat pathloss of mmWave signal in the free space by utilizing the large unlicensed bandwidth in mmWave band and combining the directional beamforming gain which provided by the massive MIMO.Conventional massive MIMO systems use full precoding scheme which requires each radio-frequency(RF)to be connected each antenna.However,the deployment of RF hardware increases the system complexity and power consumption,duing to the large number of antennas in mmWave massive MIMO systems.Analog and digital hybrid precoding is a good choice.This thesis studies on wireless transmission technology in the mmWave band of 5G systems.The main work can be summarized as follows:Firstly,this thesis introduces mmWave communication technology and massive MIMO technology of 5G systems.And then,the mmWave massive MIMO systems and precoding technology are introduced in detail,meanwhile,three hybrid beamforming structures are also classified.Secondly,this thesis proposes a novel hybrid precoding algorithm for single-user mmWave massive MIMO systems.Hierarchical idea is adopted,the first level is about the analog precoding matrix design.This thesis proposes a new analog precoding algorithm.After that,the digital precoding matrix is designed at the second level.Lastly,the original optimization problem can be formulated to be each transmit antenna sub-array optimization problem with the constraint of each antenna power allocation,then we can obtain optimal hybrid precoder by using iterative method.Simulation results show that the proposed optimal hybrid precoder can achieve performance close to the full digital precoder.Finally,this thesis proposes a hybrid precoding algorithm for multiuser mmWave massive MIMO systems.First of all,the algorithm uses EGT methods and DFT basis to reconstruct analog precoding and combining matrices.Then,the extended matrix BD algorithm is used to eliminate the inter-user interference.Lastly,after analog precoding and combining matrices are determined,according to the singular value decomposition(SVD),we can further design the digital precoding and combining matrices.Simulation results show that the proposed algorithm can achieve better performance than the EGT and traditional BD hybrid precoding algorithm.