A Geometry-based Non-stationary UAV-Ground Channel Model And Its Statistical Properties

Due to the ease operability,high maneuverability and low risk,unmanned aerial vehicles(UAVs)have attracted world-wide attention and found a wide range of applications,both military and civil.Considering the complex and changeable propagation environment,UAV channels show non-stationary characteristics,this means that the airborne communication system requires more reliable transmission of signals.Therefore,it is vital to establish accurate and reliable non-stationary UAV channel models for the UAV communication system design,optimization and performance evaluation.In this paper,a geometry-based non-stationary UAV-ground cylinder channel model and the corresponding time evolving algorithms of channel parameters are proposed.In addition,the theoretical statistical properties of the proposed channel model are derived and analyzed.It should be noticed that the proposed non-stationary UAV channel model considers not only the three-dimensional(3D)arbitrary trajectories,but also 3D antenna arrays of both terminals,and provides theoretical support for UAV communication system design and performance evaluation.The main work of this paper is as follows.(1)For the different scattering environments under the stationary scenario,regular-shaped geometry-based statistical channel models(GSCM)are analyzed.In order to show the non-stationary properties of UAV channels,the birth and death process of propagation paths and time variant characteristics of channel parameters are introduced,and then a cylinder non-stationary UAV channel model is proposed.Furthermore,to consider the 3D arbitrary trajectories and 3D antenna arrays of both terminals,an improved non-stationary UAV channel model is proposed.The improved model is more consistent with the real flight propagation and builds the theories foundation for the follow-up research.(2)For the improved non-stationary UAV channel model,the birth and death process of the propagation paths is simulated by the two-state Markov process,and the simulation method of the non-stationary UAV channel model is proposed based on the birth and death process.Meanwhile,the time evolving algorithms of non-stationary channel parameters are proposed,and modularization research on the key channel parameters,i.e.,path number,location vectors,path delays,path powers and angle parameters,is given.The channel parameters are simulated under the UAV propagation environment.Simulation results demonstrate that channel parameters can reproduce the non-stationary characteristics and are consistent with the real propagation.(3)For the improved non-stationary UAV channel model,the theoretical expressions of statistical properties,i.e.,auto-correlation function(ACF),cross-correlation function(CCF),doppler power spectral density(DPSD),level crossing rate(LCR),average fading duration(AFD)and stationary interval,are derived and analyzed.Time-variant statistical properties are simulated under urban line-of sight scenario and urban non-line-of-sight scenario,respectively,simulation results demonstrate that the proposed channel model can accurately reproduce the non-stationary characteristics of UAV channel model,and can be applied to the development and verification of UAV communication system.