Research On Millimeter Wave Beam Alignment Based On Conformal Antenna

With the rapid development of unmanned aerial vehicle(UAV)communication technology,UAVs are playing a key role in both military and civilian applications,such as fire fighting,disaster rescue,remote monitoring and military cruising.The application of millimeter wave communication technology to UAV networks can meet the requirements of high data transmission rate.The characteristic of millimeter wave is that it transmits signals in the form of narrow beams,so it has strong directivity.A UAV network has the characteristics of high mobility,which leads to the beam misalignment in UAV millimeter wave communications.Therefore,in UAV millimeter wave communication scenarios,the beam alignment accuracy is critical to the system performance.In order to solve this problem,we integrate the conformal antenna on the head surface of the UAV to obtain a larger beam spatial coverage,and for the UAV air-to-air communication scenario,research on the millimeter wave beam alignment method based on the conformal antenna is carried out.The main research contents and contributions are as follows:To establish a directional link for air-to-air UAV communications,we propose a hierarchical codebook design of millimeter wave based on cone conformal antenna(COA),and design a beam training method according to the codebook.Firstly,the array response of COA in millimeter-wave band is analyzed in detail.Secondly,inspired by the binary tree structure,the design standard of hierarchical codebook is given,i.e,the beam coverage of the codewords.To design the codebook,it is necessary to sample the beam elevation angle and azimuth angle.Since the elevation angle and azimuth angle are not independent,the design standard of hierarchical codebook cannot be achieved directly.To solve the problem,a joint beam-width factor is proposed to control the beam coverage of the codewords.The realization of the hierarchical codebook is by activating part of the antenna sub-arrays,then a method of joint subarray activation and beam-width control is proposed,and obtains a COA-based closed-form solution of the hierarchical codebook.According to the hierarchical codebook,the millimeter wave beam training method is designed.The simulation results prove the correctness of the codebook,and the designed beam training mechanism effectively reduces the training overhead.Compared with the traditional uniform planar array,the conformal antenna performs better for the system spectrum efficiencyIn order to maintain the directional link between UAVs,we design a millimeter wave beam tracking mechanism based on CO A.The general idea is to predict the AO A(Angle of Arrival)and AOD(Angle of Departure)directly through Gaussian process,which is a kind of machine learning method.First,a low-frequency feedback communication protocol is designed to match millimeter wave beam tracking.Secondly,in order to improve the prediction accuracy of the Gaussian process,combined with the motion model of UAVs,this paper designs a new kernel function based on the existing kernel function.Finally,combining the low-frequency feedback communication protocol and Gaussian process,the millimeter wave beam tracking algorithm is designed.According to the predicted AOA and AOD,UAVs realize beam tracking through beamforming technology.The simulation results prove that the kernel function design is reasonable and effective,and the prediction accuracy of AO A and AOD is high.Compared with position-based beam tracking,the proposed method has better system performance,and the achieved system spectrum efficiency is close to the optimal one.