Novel digital platform for deep space transponders: the transmitter side

Aim of the paper is to present a novel digital platform for the transmitting side (NDP-Tx) of a deep space transponder which has been developed by Alenia Spazio in the frame of the ESA study on "Digital Techniques for TT&C Transponder". The proposed design has unique features in terms of flexibility and interfacing with the spacecraft command data sub-system (CDS). The NDP-Tx supports standard telemetry modulation formats based on residual carrier and more advanced schemes aiming to improve the space-to-earth link performance. In fact, in case of limited available power, as for satellite transmitters, the power efficiency is maximised driving the power amplifier in saturation, i.e. in the non-linear region of its transfer characteristic. Using constant (i.e. GMSK) or quasi-constant (i.e. Square-Root Raised Cosine SRRC-Filtered OQPSK) envelope modulation allows the transmitter stage to operate in saturation without the drawback of the non-linear distortion (i.e. adjacent channel interference due to sidelobes spreading and regeneration).