Research On Rain Attenuation Model For Near Space Communication System's Air-ground Channel

Near space communication system is often regarded as a hybrid communication system.It is associated with wireless access in terrestrial communication system,but in the aspects of network architecture and power control are very similar to satellite communication system.In the near space communication system,UAVs,airships and balloons are added to the traditional satellite communication system as the HAPS relay station.High altitude platform has wide coverage,rapid deployment,low power consumption and other advantages.In the military investigation,transatlantic communications,emergency communications and other fields,High altitude platform has shown unique advantages.High altitude platform will also be an important candidate technology of the civil communication in the future.It has proposed one of the potential solutions to solve the last mile problem by International Telecommunication Union(ITU).Because the altitude of high altitude platform relay station is usually above 20 km level,the air-ground link is affected by factors such as cloud,rain,fog,snow,air absorption and multipath effect.The environment of air-ground channel is very complex.And when the frequency is more than 10 GHz,rainfall is the main factor affecting the propagation of electromagnetic wave,which seriously affects the effectiveness and reliability of the communication system.Therefore,it is necessary to study the air-ground link channel model of the high altitude platform which can reflect the actual channel environment.In this thesis,the rain attenuation of the existing high altitude platform of 27-31 GHz is studied in conjunction with the National Natural Science Foundation Project " Analysis and Optimization on Network Capacity of Near Space Communication Network with Dynamic Topology".A rain attenuation prediction model based on the diameter of the equal effect rain cell is proposed in the scene of air-ground channel.Frequency of the predicted signal is set to 20 GHz and 30 GHz mainly,and the rainfall characteristic attenuation is calculated using the L-P raindrop distribution.The main research contents are as follows:(1)The modeling foundation,basic input parameters,parameter acquisition methods and calculation steps of models for rain attenuation prediction(ITU-R model,DAH model,SAM model,etc.)are summarized.(2)Based on the theory of raindrop,attenuation simulation of high altitude platform air-ground link's rain characteristics,analysis of the characteristics of attenuation,rain attenuation and raindrop size distribution,frequency,elevation,polarization,rainfall intensity,rain attenuation spectrum feature is used to calculate the appropriate link between high altitude platform air-ground link.(3)According to the existing rain attenuation model usually assumes the slant path completely through the rain,but in reality,the signal path is usually not totally covered by rain.This thesis proposes a rain attenuation prediction model based on equivalent rain cell diameter in near space communication system.According to ITU-R P 311-11,using the ITU-R line of sight link rain attenuation data in the database,compare the classic rain attenuation prediction model and prediction model in this thesis by simulation,found that this thesis' s model has better accuracy than the classical rain attenuation prediction model to predict the signal path is not completely through the rain.