Research On Non-uniform Frequency Offset In Reverse Link Of TDRSS

Tracking and data relay satellite system(TDRSS) is a system which provides service as control, telemetry and data relay for lower orbit spacecraft. As a new space-based system, TDRSS has the advantage of high rate and high coverage compared with ground-based system. TDRSS plays an important role when building a global network of space and earth.Combined with National Natural Science Fund Project ‘The study on the mechanism to worsen the DBF(Digital Beam-forming) performance and the technology to improve the DBF performance in the reverse link of the TDRSS', this thesis makes research on non-uniform frequency offset in channels, reveals the rules of frequency offset in 30 channels and analysis the influence to ground DBF. It also proposed a method to correct the frequency shift with frequency estimation and adaptive phase compensation technology.The main contents of this thesis are as follows:Due to the Doppler shift exists in satellite link, this thesis studies the method which obtaining the orbit parameters by satellite ephemeris file, realized the transformation of the satellite orbit parameters from the J2000.0 ECI(Earth Centered Inertial) the ECEF(Earth Centered Earth Fixed). And calculate the Doppler shift between TDRS(Tracking and Data Relay Satellite) and ground station with the relative motion model. Combined with the transmitting method of TDRSS reverse link, analyses the rule of frequency offset in 30 channels. Results shows that the Doppler shift between satellite and ground station can reach ±800Hz.In reverse link of TDRSS, TDRS transform the receive signals of phased array to ground station by FDM method, and complete the DBF in ground station. Doppler shift which comes from relative motion can destroy the uniform of amplitude and phase of array signals. In order to analyze the influence of non-uniform frequency offset to DBF performance derived the mathematic model how non-uniform frequency offset impact DOA(Direction of Arrival) estimation by study on classical MUSIC(Multiple Signal Classification) algorithm. And set up the simulation model of TDRSS reverse link. Simulation results show that non-uniform frequency offset can bring periodical changes to DOA estimation, reduce spectral peak, beam pattern point offset and broaden the main lobe.With the aim of improving the performance which deteriorated by non-uniform frequency offset, exploring channel frequency offset compensation method in on-ground DBF technology on the basis of classical frequency estimation algorithm. According to the characteristic of multi-channel transmission, designing channel frequency offset compensator with frequency estimation algorithm and adaptive phase compensation algorithm. Through simulation, the designed compensator can correct the non-uniform frequency offset, eliminate the periodical changes in DOA estimation, increase the height of spectrum peak, stabilize the beam pattern, narrow the main lobe, and improve the performance of DBF.