Research On The Nonlinear Distortion And Equalization Technology Of TDRSS Return Link Channel

Since the 20 th century,the development of the Tracking and Data Relay Satellite System(TDRSS)has revolutionized the aerospace measurement and control communication technology.It plays an important role in building a global network of globalization.In the TDRSS return link,the relay satellite amplifies the received signals of the phased array antennas to the ground station through a high-power amplifier,and the digital beam forming(DBF)is performed by the ground station.The nonlinear distortion characteristics of the high-power amplifier destroy the amplitude and phase consistency of the signal of each channel element,which leads to the degradation of the direction of arrival(DOA)estimation and DBF performance.This thesis is based on the National Natural Science Foundation project“Research on the on-ground DBF Performance Deterioration Mechanism and Enhancement Technology of TDRSS Return Link”,and the nonlinear distortion problem of high-power amplifier is deeply studied.The GDM-SVSLMS equalization algorithm is proposed to effectively compensate nonlinear distortion.The research contents of this thesis are summarized as the following three aspects:Firstly,the nonlinear characteristics of the power amplifier is analyzed,and the mathematical model for the influence of the nonlinear characteristics of the power amplifier on the amplitude and phase of the 30-channel array signals is derived,the effectiveness of the model is verified through Matlab simulation results.Secondly,in order to analyze the effect of nonlinear distortion on the performance of TDRSS,the mathematical model of the influence of AM/AM and AM/PM transform distortion on the direction of arrival estimation and digital beamforming performance is derived.Then,based on the Matlab software,a TDRSS return link simulation system based on the DBF system under the satellite is built.The simulation results show that the nonlinear distortion will lead to the decrease of DOA pointing accuracy,which will affect the beam direction pointing angle,side lobe gain,and the deterioration of system error performance.Thirdly,in order to alleviate the degradation of DBF performance under the satellite caused by nonlinear distortion,a linear transversal adaptive equalizer is adopted.Based on the classical variable step size LMS equalization algorithm and Gradient Descent with Momentum algorithm,a variable step size Gradient Descent with Momentum(GDM-SVSLMS)algorithm is proposed and a channel equalization compensator is designed.Both theoretical and simulation experimental results show that the equalization compensator is feasible to correct the nonlinear distortion of the 30-channel array element signals,besides,the convergence speed and stability of the algorithm are improved.The channel equalization compensator designed in this thesis can eliminate the deviation of the DOA estimated angle,and correct the beam map pointing and reduce the side lobe.Therefore,it is able to improve the DBF performance under the satellite.The research results of this thesis can provide a certain reference value for the construction of China's second-generation relay satellite system-"Tian Chain No.2".