The Rain-induced Fading Effects On Millimeter Waves Terrestrial Link Of 5G Mobile Communication System

Millimeter wave is an important part of 5G spectrum strategy for its rich spectrum resources.The application of millimeter wave technology to 5G mobile communication networks is a research hotspot in domestic and overseas.For the application scenario of multi-path propagation of complex topographic features in the 5G mobile communication technology,a combination method of the theory and experiment is adopted in this thesis.The effects of the topographic features multipath propagation environment on the attenuation and signal fluctuation effects caused by rainfall are studied,and whether the existing model can properly evaluate the transmission effects.The main research contents of this thesis are as follows:The relationship between channel fading coefficient and transmission scattering effect is discussed.Therefore,the research aspects of this thesis are mainly introduced: attenuation effect and signal fluctuation effect.The size distribution feature and dielectric property of particles in rainfall environment are simulated and discussed.The research lays the theoretical foundation for subsequent theory and experimental analysis.The rainfall attenuation and signal fluctuation of millimeter wave in the line-of-sight environment are studied,and a “comparative standard” is provided to analyze the influence of multipath environment on rain attenuation and rain-induced signal fluctuation effects.Based on the scatter-absorption theory of particles,the mechanism of rain attenuation is described briefly.The limitations of existing rain attenuation engineering models are analyzed through simulation.Then,a method for modifying the parameters of attenuation model is proposed.The aforementioned modified method is verified by the parameters at 35 GHz given by ITU-R.On the basis of the random media wave propagation theory,the signal fluctuation effect caused by scattering of rain particles is studied.Based on the self-built experiment systems for measuring the channel fading characteristic at Ka-band and rainfall physical characteristic,and the experiments on rain attenuation and rain-induced signal fluctuation effect are carried out in the line-of-sight and multipath environments,respectively.On the basis of the measurement principle of instrument,the extraction method for measuring raindrop spectrum is optimized.A method for modifying the parameters of weibull model based on measured raindrop spectrum is proposed,and the accurate raindrop size distribution model for Xi'an is established.Then,combing with the equivalent permittivity theory,the parameters of exponential rain attenuation model is modified.The calculated rain attenuation results and experimental measurement results under line-of-sight environment are compared,which verifying the feasibility of the proposed modified method.However,when substituting the rainfall characteristic in multi-path into the modified model,the calculated and experimental results show that the multi-path environment will “amplify” the rainfall attenuation and the depth of signal fluctuation.Based on the wave propagation theory and equivalent uniform medium theory,a model of wave propagation in complex environment is established.On the basis of the model,the rainfall attenuation model and signal fluctuation statistical model under the multipath propagation environment of terrain features are deduced.The rainfall attenuation and signal fluctuation characteristic under the multi-path influence of typical topographic features are simulated and discussed,which revealing the mechanism of “amplifying” atmospheric transmission effects in multipath environment.Compared with the measured results in typical rainfall time series,the validity of the model is verified.The research method in this thesis has important significance for studying the propagation characteristics of millimeter-wave under combined effects of snowfall,sand storm and other adverse weather conditions and multi-path propagation environment of topographic features.The research results is greatly significant to model of the millimeter wave channel in 5G usage scenario,and it has important application value to further improve the performance of 5G millimeter wave mobile communication system.