Study And Implementation On Key Technologies Of Ground-air Communication System

Ground-Air communication refers to the process of mutual information transmission between a ground base station and an air vehicle.In recent years,with the rapid development of the aviation industry,aviation demand has become increasingly strong,and air traffic control has become increasingly complex.UAVs have developed rapidly,not only in the military field,but also in academic and civilian applications.The communication between the aircraft and the ground base station,the communication between the UAV and the IoT node,and the wireless sensor have considerable research significance,which means that the ground-to-air communication is becoming the focus of research.This paper designs the ground-to-air communication system based on the OFDM modulation method.And the main tasks as follows: 1.From the perspective of time domain and frequency domain,the fading characteristics of ground-air communication are studied respectively.The ground-space channel is two-path,and the time-selective fading channel with Doppler spread of about 300 Hz is concluded.The fading channel is modeled by statistical modeling method.The validity of the model is verified by experimental simulation analysis.The influence of the fading characteristics of the ground-to-air channel is visually demonstrated,which provides an application scenario for subsequent system practice research.2.Through the detailed research on key technologies such as time synchronization and frequency synchronization,the optimal solution suitable for engineering implementation is found to solve several key problems existing in the system using OFDM modulation.The details are as follows: First,time synchronization,the solution is carried out in two steps: a,frame synchronization is responsible for identifying the arrival time of the signal frame,and after analyzing the probability of missed and wrong capture,the multi-segment comb-like capture method is the optimal solution;b.Timing synchronization is responsible for judging the starting position of the FFT.After comparing the timing offset and complexity,the system uses a local sequence to calculate the cross-correlation method.Then there is frequency synchronization.The ground-air communication system needs to estimate and compensate for the large frequency offset due to its own characteristics.The solution is to perform rough and exact frequency offset estimation,so that the residual frequency offset after compensation is small,and it can be balanced.Finally,some other key technologies are studied,including PAPR suppression,soft demodulation,channel estimation and equalization.3.The development of hardware baseband system for key technologies of ground-air communication has been realized.Based on the vivado design environment and FPGA platform,the baseband system design,development and preliminary verification were completed.This paper highlights the implementation details of several key modules including port definition,main process and key state machine,and verifies the feasibility of the scheme through simulation waveforms.