Research On Beam Searching And Scheduling Technology In Millimeter-wave Communication

Millimeter-wave is one kind of electromagnetic waves,whose frequency range is between 30 GHz and 300 GHz.Because of the short wavelength,high frequency,the narrow beam and good directional characteristics,the millimeter-wave system is usually combined with the large-scale antenna array technology and becomes a hotspot of 5G communication systems.Compared with the microwave,the signal’s attenuation increases dramatically in the atmospheric propagation environment.To make up for path loss and ensure the reliability of communication,a high gain directionally narrow beam is formed using large-scale antenna array.The traditional digital beamforming structure cannot be directly applied to the millimeter-wave systems due to its high hardware complexity.Therefore,the digital and analog hybrid beamforming is adopted in this thesis,in which the realization of analog beamforming at the radio frequency domain is focused.Analog beamforming based on beam codebook is widely used owing to its simplicity.The problem of multi-link beam searching is also gradually concerned.A fast and efficient searching algorithm is required to solve the problem of beam alignment at both ends of the transceiver in millimeter-wave systems.Meanwhile,how to utilize the space resources effectively becomes hot issues at the stage of study.In this thesis,the combinatorial beam searching problem of multi-radio frequency links in single-user scenario and the multi-beam scheduling problem in multi-user scenario are studied.Firstly,the key technology of beamforming and the system structure of millimeter-wave are expounded.Aiming at the beam searching of multi-radio frequency links about the hybird beamforming structure in millimeter-wave systems,the principle of generating a beam with the uniform linear array is studied.And the algorithm based on SVD decomposition,the ergodic algorithm and the criteria of beam selection are also discussed.For the multi-stream data transmission,combined with the theoretical analysis of the millimeter wave channel model,the way of ergodic search and iteration via a single link is proposed.The simulation results show that the heuristic searching algorithm with low complexity can greatly reduce the time complexity and obtain the good performance of spectral efficiency under the premise of guaranteeing the accuracy.For the problem of multi-beam scheduling in millimeter-wave communication system,the selection of beams and users is implemented using the maximum SINR and beam number fed back in user side.When the number of beams in base station and the number of service users are significantly larger than the RF chains,an improved multi-beam grouping strategy based on adjacent beam is proposed through the analysis of the beam grouping strategy based on equal space and the influence of inter-beam interference on system performance.It can increase the combinatorial possibility of different beams under the condition that the interference between them is small.At the same time,existing RF links are fully utilized,which can avoid the waste of hardware resources and improve the spectral efficiency performance.The simulation results show that the improved multi-beam scheduling strategy has better performance compared with the existing algorithms in different SNR,the number of multipath and users.