Design And Implementation Of Air-ground BLOS Communication System

Under the background that the opening of domestic low-altitude airspace has been continuously promoted,The “can't conntect” problem of traditional ultra-short wave(V/UHF band)air-ground communication at low altitude is becoming increasingly prominent.In order to break through the blind area of traditional air-ground LOS(line-of-sight)communication,the troposcatter communication system is introduced into the field of air-ground communication to realize the air-ground ultra-short wave BLOS(beyond line-of-sight)communication at low cost,after comparing the advantages and disadvantages of existing and potential air-ground BLOS communication methods.To verify the feasibility of air-ground troposcatter communication,it is necessary to obtain the relevant data of air-ground troposcatter propagation characteristics.In the thesis,the parameters of air-ground troposcatter propagation characteristics are firstly modeled and analyzed,and the theoretical values of channel parameters such as median level,multipath delay,coherent bandwidth and frequency shift are obtained.Then the channel simulator and channel testing equipments are used to simulation test in the room.At last,in the field test,in the absence of the airborne environment,the airborne simulation environment is constructed to ensure the smooth progress of the test,and the conclusion that the actual propagation characteristics are basically consistent with the modeling analysis results is drawn.On the basis of channel research,the key technologies such as space diversity,modulation and demodulation,voice coding,and antenna of the ground station in the air-ground BLOS communication system are designed,and the ground station subsystem and the airborne station subsystem are further developed.On the premise of preserving the original hardware platform,the development of the airborne station subsystem is realized by changing the corresponding program of the transmission waveform and voice codec in the baseband processing unit of the airborne station,so that the BLOS communication ability between the airborne station and the ground station can be achieved.It not only speeds up the project schedule,but also reduces the technical riskThe test of the air-ground BLOS communication system is divided into two steps: firstly,the indoor simulator is used to test the system performance,function and threshold.Then the short-range test,the middle-range test and the in-motion test are carried out in the field.The experimental results further confirm that it is feasible to realize the air-ground ultra-short wave BLOS communication using the troposcatter channel.