Research And Implementation Of Signal Source Simulation In Dynamic Scenario For Satellite-Based ADS-B Receiver

In the ADS-B(Automatic Dependent Surveilance-Broadcast)aviation management monitoring system,for better information sharing,more efficient and economic traffic regulation,aircrafts automatically broadcast their current status,locations,speeds,etc.The receiver of satellite-based ADS-B system is mounted on the low-orbit satellite and takes advantage of the altitude of satellites to receive the ADS-B message of aircrafts.Hence,problems in deployment location and coverage limitation of the traditional ground-based station ADS-B system are solved.Great reasearch enthusiasm from both domestic and aborad of satellite-based ADS-B system receivers are shown due to above mentioned advantages.To complete the test of accuracy,sensitivity,de-overlapping capability,and realtime decoding performance of massive messages of recievers in laboratory,simulations of signal sources in dynamic scenario are of great significance.In the dynamic satellite-based ADS-B scenario,for every single message signal of an aircraft,transmission power,propagation delay,path loss,Doppler shift,and effecets on signal power of both transmitting and receiving antenna pattern should be considered.The simulated RF analog signal of multi-target and multi-message superimposed in time-domain received by the satellite in the dynamic scenario are obtained.This thesis designs a single channel outputing satellite-based ADS-B simulating signal source in dynamic scenario,specific works are as follows:(1)Cover range of the satellite to the ground and the number of aircrafts are determined according to the satellite orbit scenario.Initial position,altitude and speed of each aircraft are randomly generated according to the civil aviation operation criteria.Following the DO-260 B standard,the ICAO,flight number,transmission power,and message broadcasting time of each aircraft are generated randomly.Hence the aircraft message information groups received by the satellite in the dynamic scenario are obtained;(2)The aircraft message information are encoded according to the message type,and modulated with PPM digital intermediate frequency.The change of transmission attenuation and the Doppler frequency of each message signal are considered during modulation,to obtain digital intermidiate freqency signals of different carrier frequencies and power.The digital intermediate frequency signals of each aircraft are firstly superimposed in time domain.Then the superimposed intermediate frequency signals are amplified and quantized.Sequentially,the quantized digital intermediate frequency signals are fed into the TXDAC to output I and Q analog signals.A single-channel RF signal in set scenario is obtained with the further processing of I/Q signals by quadrature upconversion,filtering,and attenuation,.(3)The analog signal source is implemented using the evaluation boards KC705 and AD9361 and tested accordingly.With the receiver,the accuracy of each type of message generated by the signal source and the capability to generate multi-objective and multi-message complex signals in dynamic scenario are tested.The oscilloscope is used to test the ability of the signal source to output time-domain overlapping signals.