Research On Beamforming Technology In Millimeter Wave System Of UAV

This thesis comes from the key research and development project of Shaanxi Province,which is to study the beamforming technology in the UAV millimeter wave(mm Wave)system.The UAV mm Wave communication system has attracted wide attention from scholars at home and abroad due to its high flexibility,large bandwidth,fast transmission rate,and rapid deployment.Compared with crowded low-frequency electromagnetic waves,mm Wave has a large number of free frequency bands to provide large bandwidth support for the system.The beamforming technology can use the antenna array to generate a narrow beam with high gain,which can be applied to the millimeter wave system to overcome the problem of large transmission loss.UAV platforms have many advantages,but the energy of UAV platforms is limited.To use beamforming technology in UAV mm Wave systems,the implementation complexity of beamforming algorithms should be reduced.At the same time,the UAV platform will jitter due to the influence of wind during the flight,which will lead to beam mismatch and system performance degradation.Based on these problems,this thesis studies the beamforming technology in the UAV mm Wave system to provide a reference for the design of the UAV wireless communication system.The main tasks of the thesis are as follows:Firstly,the principles of Digital Beamforming(DBF),Analog Beamforming(ABF),and Hybrid Beamforming(HBF)are introduced.Then the transmission characteristics of millimeter wave and its channel model are described.Finally,the impact of UAV platform jitter on system performance is analyzed.Aiming at the problem of limited UAV energy,high energy consumption of digital beamforming algorithms,and high complexity of existing hybrid beamforming algorithms,a low-complexity hybrid beamforming algorithm based on improved Gradient Pursuit(GP)is proposed.The algorithm first uses a low-precision codebook for the first search.After the first search location is found,a small high-precision codebook is used for the second search near the location to complete the solution of the hybrid beamforming matrix.Compared with the traditional hybrid beamforming algorithm based on Orthogonal Match Pursuit(OMP)and the hybrid beamforming algorithm based on GP,the proposed algorithm can greatly reduce the implementation complexity without affecting the spectrum efficiency of the system.Aiming at the problem of beam mismatch caused by UAV platform jitter,an adaptive beamforming algorithm that can deal with different jitter intensities is proposed.The algorithm uses the distribution of multiple Direction of Arrival(DOA)estimation results to adaptively adjust the range of the beam domain,so that the target is always within the beam alignment range.Under different jitter intensities,the simulation results show that the average spectral efficiency of the proposed adaptive beamforming algorithm is better than or equal to that of the beamforming algorithm that uses a fixed wide/narrow beam,which reduces the impact of beam mismatching on system performance.