Research On Millimeter Wave Beam Tracking Methods In Conformal Antenna UAV Networks

In recent years,with the development of unmanned aerial vehicle(UAV)technology,UAV communications have been widely used in various fields.As the millimeter wave band has abundant spectrum resources,UAVs can meet high date-rate requirements by using millimeter wave to transmit signals.For highly dynamic and long-range UAV network scenarios,fast and accurate millimeter wave beam tracking is the basis for the establishment and maintenance of mobile millimeter wave communication links.However,narrower millimeter-wave beams are needed to focus energy against fading in long-range scenarios,making beam tracking more difficult.In addition,a large number of antennas need to be carried in order to form narrow-beam.As the number of antennas increases,large-scale arrays incur higher hardware costs and energy consumption.The payload and energy supply on UAVs are limited and cannot afford the huge communication overhead.To solve the above problems,this paper considers the integration of conformal arrays on the surface of UAVs to significantly reduce UAV flight drag while obtaining larger beam space coverage,and investigates high-performance and low-cost millimeter wave beam tracking methods for the conformal arrays UAV network scenario.The main research contents and innovation points of the paper are as follows:Firstly,in order to achieve high-performance beam tracking for UAV networks,this paper proposes a millimeter-wave hierarchical codebook design based on conical conformal array(COA)and the corresponding beam training method.This paper firstly analyzes the array characteristics of the COA in detail,derives the relationship between the millimeter wave beam angle and the activation subarray of the CO A,and uses the maximum activation subarray to generate the bottommost codeword in the hierarchical codebook.Secondly,in order to find the activation subarray required to generate the upper codeword,this paper derives the constraint relationship between the hierarchical codebook and activation subarray applicable to COA in detail,and finds the activation subarray to generate the upper codeword by solving the optimization problem.Further,a corresponding millimeter wave beam training method is designed to achieve high performance beam tracking at both transceiver and transmitter sides by searching the code word based on the predefined hierarchical codebook and the optimal beam direction from the terminal feedback.The simulation results demonstrate the correctness of the layered codebook,which has a strict coverage relationship among the codewords in the codebook;the designed beam training mechanism achieves a higher system performance while effectively reducing the training overhead compared with the traditional exhaustive beam search.Secondly,in order to realize low-cost beam tracking for UAV networks,this paper adopts a dynamic subarray architecture and designs a corresponding array assignment method based on this architecture.Specifically,this paper firstly analyzes the system model of the conformal anrray unmanned network when the dynamic subarray architecture is adopted,and investigates the dynamic array assignment algorithm based on the greedy growth criterion.Further,this chapter proposes a dynamic array assignment algorithm based on bilateral matching theory.The proposed algorithm considers the selection between arrays and UAVs in both directions and accomplishes bilateral matching based on matching theory.The simulation results prove the effectiveness of the design method:the system spectrum efficiency of the conformal array is higher compared with the traditional planar array;the proposed method has better system performance compared with the array assignment algorithm based on the greedy growth criterion;the energy efficiency of the method in this paper is higher compared with the fully connected architecture,and the beam tracking is completed at a lower cost.