Research On Beam Width In Millimeter Wave Channel

With the rapid development of fifth-generation mobile communication technology,the lowfrequency band of radio spectrum tends to be saturated,while millimeter-wave with its abundant spectrum resources attracts wide attention.However,millimeter-wave has disadvantages such as short wavelength,poor penetration and serious path loss.In order to solve these defects,millimeterwave communication usually adopts large antenna array and beamforming vector technology.Beamforming technology can concentrate the energy sent to a specified area,thus improving system performance.It is one of the core technologies of 5G.But precisely because of this characteristic of energy concentration,any change in the channel may cause the receiver to deviate from this specific area,thus reducing the robustness performance of the system.Therefore,high gain and strong robustness are a tradeoff,and beam width is one of the indicators to measure this tradeoff.Traditional antenna beamwidth definitions are based on the antenna itself,for example,the commonly used Half-power Beamwidth(HPBW)and First-null Beamwidth(FNBW)are defined independently of the beamforming and are only related to the antenna itself,which cannot consider the impact of the number of antennas and the characteristics of the millimeter-wave channel in the actual transmission process.Aiming at these problems,the main research contents and achievements of this thesis are as follows:Firstly,the definition of beamwidth is proposed and studied for beamforming under linear arrays with the help of concepts in Grassmannian manifolds,and on this basis,the construction method of beamforming with broadened beamwidth is discussed.This definition takes into account the effects of beamforming and the characteristics of the millimeter-wave channel,and allows the calculation of the beamwidth according to the channel utilization,making this definition more flexible than the traditional beamwidth definition.Simulations show that the beamwidth of the newly constructed beam is wider than that of the traditional array response vector form.It is also found that the higher the number of antennas,the more energy can be concentrated,but the beamwidth is limited and thus the robustness is weaker.Secondly,the definition of beamwidth in linear arrays is extended to planar arrays under planar arrays for beamforming,and three two-parameter beams are proposed to investigate the nature of their beamwidths.Simulations show that such beams take into account the planar array channel vector characteristics and are more suitable for planar arrays as compared to beams with a single parameter,which can modulate the direction of the beam in both horizontal and vertical dimensions.It is also found that the shape of the antenna array has an effect on the coverage of the beam,with the side with the higher number of antennas having a smaller beam coverage.In summary,firstly,a new definition of beamwidth is proposed in this paper for the beamforming vector.Secondly,beams with wider beamwidths are constructed.Finally,the new definition of beamwidth is discussed and analyzed under a uniform linear array and a uniform planar array,respectively.