Unmanned Aerial Vehicle Channel Modeling For B5G/6G Wireless Network

In recent years,the standards of the fifth generation(5th Generation,5G)mobile communication have been gradually determined,and the second stage of 5G has also been determined recently.Thus,the key technologies of beyond 5G(B5G)and 6th generation(6G)mobile communications also need to be further studied.Due to its low price,flexible deployment,and high mobility,unmanned aerial vehicle(UAV)is regarded as an important enabling technology for supporting B5G/6G networks and is widely used in many fields.The development of any wireless technology depends on an accurate understanding of the characteristics of the wireless channel.Different from traditional terrestrial wireless communications,UAV communications usually have its unique characteristics,such as attitude variations(i.e.pitch,roll and yaw,etc)and three-dimensional(3D)space arbitrary motion trajectory,that motivates our research of UAV channel modeling.In addition,the combination of key B5G/6G technologies such as millimeter-wave(mm Wave)and intelligent reflecting surface(IRS)with UAV will also introduce new features to the wireless channels.To sum up,for the research of channel modeling in UAV,we should not only fully consider the specificity of UAV itself,but also focus on the technical difficulties brought by B5G/6G.Based on the above requirements,this dissertation studies the radio wave propagation characteristics of UAV wireless channels from various aspects.The main contributions and novelties of this dissertation are as follows:1)For air-to-ground(A2G)scenarios with UAV attitude variations,a wideband nonstationary multiple input multiple output(MIMO)geometric channel model is proposed,which uses a 3D hemisphere composed of circles of different radii to describe the scattering environments and further characterize the clustering effects.Considering the complexity of the UAV attitude variations,it is characterized by a sinusoidal process.The expressions of space-time-frequency correlation function,Doppler power spectral density and quasi-stationary interval are derived.Finally,the influence of attitude variations on the above channel characteristics when UAV is equipped with omnidirectional and directional antennas is studied respectively.2)For the air-to-air(A2A)scenarios,a wideband non-stationary MIMO geometric channel model is proposed,which describes the ground and roadside scattering environments by a 3D single cylinder.In order to make the trajectory of UAV more realistic,a 3D Gaussian Markov process is used to describe the motion state of UAV.The expressions of space-time-frequency correlation function and Doppler power spectral density are derived,and the effects of different UAV trajectories on the above channel characteristics is analyzed.3)For mm Wave A2 A scenarios,a wideband non-stationary MIMO geometric channel model is proposed,which describes the scattering environments of mm Wave UAVs through a 3D multiple-layer cylinder and heterogeneous scattering sources(i.e.,local and far clusters).Based on the geometric relationship between the transceiver and the scattering cluster,time-varying parameters in the channel model are derived.The two-state continuous-time Markov process is used to mimic the dynamic properties of scattering source(i.e.,clusters appear/disappear with time),and the smooth time evolution of scattering source is achieved.The expressions of space-time-frequency correlation function,Doppler power spectral density,and quasi-stationary interval are derived,and the impact of carrier frequency and scattering source on the above channel characteristics is investigated.4)For IRS-assisted A2 G scenarios,a narrowband stationary MIMO geometric channel model is proposed,which describes the scattering environments through a 3D single cylinder.Further,IRS is placed below UAV to extend the signal reflection range.From the perspective of radio wave propagation,some novel methods are proposed to design the reflection phase of IRS.The expressions of channel impulse response(CIR),spreading function,space-time correlation function and channel capacity are derived,and the influence of the proposed IRS phase on the above expressions is analyzed.Finally,the problems encountered in the actual deployment of IRS are also explored.Therefore,this dissertation focuses on the wireless channels in the UAV scenario.Based on the geometric modeling theory,a variety of UAV channel models for B5G/6G applications are established,and the effects of mobility,mm Wave,and IRS on UAV channel characteristics are also discussed separately.These studies will make up for the lack of channel modeling in the current UAV scenarios,and offer technical support for the design,theoretical analysis,performance evaluation,and network optimization of future UAV communication systems.