Research On Millimeter Wave Beam Management Techniques In Mobile Scenarios

Millimeter wave spectrum resources are abundant,narrow beam,directional and faster transmission rate.However,its drawbacks such as severe path loss and poor penetration capability greatly limit the practical applications.Beamforming technology can compensate the high path loss of millimeter wave,but in mobile scenarios,the fast movement of the receiver leads to frequent beam switching by the transmitter and receiver,and the beam is more easily obscured.Therefore,high-performance beam management algorithms are of great importance in millimeter-wave communication systems.Beam management requires processing and analysis of the acquired signals to determine the appropriate beam shape and pointing.However,the conventional algorithms used in current millimeter-wave beam management generally require estimation of channels with relatively high system overhead,which makes beam management applications challenging for communication scenarios with high real-time performance.Thanks to the use of location-aware technology,it becomes easier to obtain the relative position between the base station and the target user based on binocular cameras,so this thesis proposes a series of location information-assisted improvement algorithms for millimeter-wave beam management,which include.(1)frequent beam switching is required in complex mobile scenarios,which increases excessive system overhead and delay.To address this problem,this thesis proposes a locationaided grid-based beam switching method,which takes advantage of the fact that the best beam pairs remain constant when they exist in the visual path,divides the grid beam one-to-one correspondence and coverage distribution structure,establishes a "location-beam" mapping table,and calculates the next moment based on the user’s location Based on the user’s position information and motion state,the next switching point is calculated.The simulation and analysis results show that the proposed method significantly improves the spectral efficiency of the system compared with the non-grid switching method,and the proposed hexagonal grid switching performance is better than the square grid,and the beam switching probability is reduced by 50%,which ensures the communication quality and verifies the rationality of the grid-based beam switching method.(2)In the scenario where the line-of-sight propagation beam is obscured,the RIS is used to establish a cascade channel for auxiliary communication,and in order to solve the nonconvex problem of maximizing and rate under the base station transmit power constraint,a joint grid phase-based transmit beam and RIS phase optimization algorithm is proposed to solve the problem.Specifically,the "position-phase" mapping table is first established by a gridded beam switching method,and the base station transmit beamforming is obtained by a closed-form solution based on the quadratic transformation algorithm criterion,while the RIS reflection phase is obtained by solving a series of sequential convex approximation problems with the Riemann conjugate gradient(RCG),and the obtained grid phase values are used as the initial points for the flow shape optimization.It is experimentally verified that the proposed joint optimization scheme can significantly outperform other benchmark methods.In particular,the alternating optimization scheme with the initial values of the lattice phase achieves a gain of about 3 d B compared to the alternating optimization with random initialization,achieving good performance.