Study On The Nonlinear Distortion And Group Delay Distortion Of TDRSS Reverse Link Channel

Tracking and data Relay Satellite System, referred to as TDRSS, which provides data Relay, continuous Tracking and rail optimum control service between middle or low orbit spacecraft and spacecraft, the spacecraft and the ground station, which is also referred to as the Relay System. As a novel space-based tracking, telemeter and command system, Tracking and Data Relay Satellite System plays an important role in increasing its coverage rate of the mediate/low orbit aircraft and decreasing the amount of ground telemetry stations in the satellite communication system. Therefore, it has a wide application prospect.To relieve the complicated signal processing, the tracking and data relay satellite(TDRS) just completes the frequency division multiplexing(FDM) of 30 independent element signals and signal power's amplification. And each element signal will be transmitted to the Ground Terminal after being Frequency Division Multiplexing(FDM), and then the Ground Terminal make Digital Beaming Forming(DBF) on the basis of relative phase and amplitude difference of the 30 element signal. The nonlinearity of HPA and the group-delay caused by the 30-filter-group make the DBF performance to be deteriorated, whichrestricts the development and construction of the next generation TDRSS.As to this problem, the main research contents and contributions are as follows:(1)Channel characteristic of TDRSS reverse link was researched. nonlinear distortion and Group delay distortion of TDRSS was analyzed, and the mechanism how the nonlinear distortion and the inter-channel group delay mismatch comes was explored(2)The mechanism how nonlinear distortion and inter-channel group delay mismatch of TDRSS affect the performance of DBF was explored. Mathematical model was established, and the mathematical formula derivation was used to analyze the nonlinear distortion and the group delay distortion effect on the properties of DBF. The simulation model was set up in Matlab/Simulink platform as well. And influence of DBF due to nonlinear distortion and inter-channel group delay mismatch of TDRSS was analyzed by computer simulation.(3)The adaptive equalization was adopted to compensate nonlinear distortion and group delay distortion which affects DBF performance of TDRSS. The validity of the equalizer based on the improved LMS algorithm was verified through the comparison of simulation results before and after the equilibrium in the simulation platform. In combination with the power efficiency of HPA, the article also comes up with the viewpoint of dynamic equalization.By analyzing the affection of DBF performance due to inter-channel group delay mismatch and nonlinear distortion of TDRSS's reverse link, significant conclusions have been drawn, which can lay the theoretical and technical basis for promoting the construction and development of TDRSS.