Recearch On Beamforming Technologies For UAV Millimeter Wave Communication Systems

With the emergence of emerging unmanned aerial vehicle(UAV)applications,the demand for UAV data transmission capabilities for many datadriven services has shown explosive growth,posing severe challenges to traditional UAV communication based on the Sub-6 GHz band.In response to the above problems,UAV millimeter wave(mmWave)communication came into being.The huge available bandwidth of mm Wave can provide UAV s with ultrahigh data transmission rate(gigabit per second)and ultra-low end-to-end delay(sub-milliseconds),effectively improving the UAV’s service capabilities in the field of perceptual information collection and auxiliary wireless access,and has broad application prospects and significant practical value.In recent years,the research community has carried out some preliminary research work in the field of UAV mm Wave communication.As a communication carrier,UAVs face problems such as limited energy,limited computing power and flight control,and mm Wave beamforming for UAV scenarios still have many problems in architecture design,alignment mechanism and application-oriented optimization.At present,the application of UAV mm Wave beamforming technology in practical scenarios still faces the following challenges:1)In view of the high sensitivity of UAV’s energy efficiency and computing power,how to design a beamforming scheme,including hardware architecture and alignment mechanism,so as to improve the reliability of UAV mm Wave communication;2)Aiming at the high mobility of UAVs,how to jointly optimize UAV three-dimensional deployment/trajectory and beamforming to obtain high-quality UAV mm Wave communication services.In view of the above challenges,this dissertation studies the key issues such as the design of beamforming architecture and alignment strategy for UAV and flying beamforming strategy for static and dynamic scenarios,aiming to achieve lowlatency,high-reliability and high-capacity UAV mm Wave communication.The specific research work and contributions of the dissertation are as follows:1.High-energy-efficient and low-complexity beamforming schemes for UAV communication.In order to achieve highly reliable UAV mm Wave communication,this dissertation first studies the beamforming hardware architecture design,and then designs the beamforming alignment mechanism based on this architecture.Aiming at the beamforming hardware architecture design,a theoretical analysis model based on stochastic geometry is proposed,and the energy-efficient UAV beamforming hardware architecture configuration scheme is obtained by comprehensively weighing the power consumption and capacity of the system.Aiming at the beamforming mechanism design,a beam pattern adaptive low-complexity fast beam alignment mechanism is proposed,which reduces the beam scanning space by predicting the communication beam angle range through geometric analysis,thereby significantly improving the spectral efficiency of the system.By combining the above two schemes,the power consumption and computing power requirements of the UAV can be optimized under the premise of meeting the diversified communication needs,and the balance of service capabilities and communication overhead can be achieved.2.Flying beamforming strategy for static communication scenarios.In order to achieve high-capacity UAV mm Wave communication,a joint design strategy for UAV 3D deployment,quantitative hybrid beamforming and power allocation is proposed for the communication scenario of UAV static deployment.This dissertation models a joint optimization problem to maximize the spectral efficiency of the system,and proposes a two-stage optimization strategy.Aiming at the problem of poor UAV deployment accuracy caused by environmental differences between regions in urban communication scenarios,a fine-grained line-of-sight(LoS)probability model based on 3D cities is constructed,and a UAV deployment algorithm based on particle swarm optimization(PSO)is designed.Aiming at the quantization distortion introduced by the digital-to-analog converter(DAC),a quantization hybrid coding algorithm based on alternate projection algorithm,zero-forcing(ZF)and minimum mean square error(MMSE)is designed,and the transmit power is allocated by the water-filling(WF)algorithm.In addition,this dissertation also proposes a beam angle change model for random fluctuations to explore the effect of random fluctuations of the UAV attitude on the system capacity.Simulation results show that the proposed fine-grained UAV deployment algorithm based on PSO can achieve a performance advantage of more than 13%in system spectral efficiency at low signal-to-noise ratio and high quantization resolution,and the proposed quantized hybrid beamforming algorithm based on MMSE can achieve about 14%improvement in system spectral efficiency compared with ZF-based algorithm at low signal-to-noise ratio.3.Flying beamforming strategy for dynamic communication scenarios.In order to further improve the system performance by utilizing the high mobility of UAVs,a joint design strategy of UAV 3D trajectory,beamwidth and power allocation is proposed for the communication scenario of UAV dynamic cruise.In this dissertation,a joint optimization problem is modeled by analyzing the effect of beamwidth on beam training time and beamforming gain,and an optimization architecture based on deep reinforcement learning(DRL)is proposed.The architecture consists of two progressive stages,first optimizing the 3D trajectory of the UAV,and then jointly optimizing the beamwidth and power allocation.For these two sub-problems,optimization algorithms based on deep deterministic policy gradient(DDPG)and proximal policy optimization(PPO)are proposed respectively.This strategy can effectively improve the normalized spectral efficiency of the system by balancing the beam training time and the beamforming gain while jointly optimizing 3D trajectory,beam width and power allocation.In addition,the proposed optimization algorithm based on PPO achieves an 18%normalized spectral efficiency improvement compared to the optimization algorithm based on DDPG.In summary,this dissertation is oriented to the UAV mm Wave communication system,and proposes a series of solutions to the design of beamforming architecture and alignment mechanism in practical scenarios and the flying beamforming strategy for static and dynamic communication scenarios,and verifies the effectiveness of the proposed scheme based on theoretical analysis and simulation experiments,laying an important technical and theoretical foundation for the wide application of UAV mm Wave communication system.