Simultaneous Transmission and Reception Transponder for Nano-satellite

Abstract

The feasibility of simultaneous transmission and reception (STAR) in the same frequency for space transponder in nano-satellite is discussed. The demand of the self-interference cancellation for the transponder is analysed by space-ground link budget, and a STAR superheterodyne architecturebased transponder is also presented. Based on the conventional space TT&C frequency scheme, a feasible frequency scheme and digital signal processing process for the STAR transponder are expatiated. A FFT based carrier acquisition method is modified to adapt to such STAR transponder.The implementation of the STAR transponder is simulated. The simulation results show that with properly deployingthe passive and active self-interference cancellation modules, the self-interference can be cancelled to meet with the demand of demodulation which also implies that the STAR transponder presented in this paper is feasible.The simulation results also show that the radio frequency self-interference cancellation(RFSIC) does matter in such STAR transponder by realizing 29dB self-interference cancellation, and a total self-interference cancellation of about 68dB can be realized by the combination of passive suppression and RFSIC. The numerical results show that the digital self-interference cancellation is not necessary for the transponder when the transmission power of ground-satellite uplink is high enough, and the phase noise power is increased by the digital self-interference module.