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Abstract-On-board processing (OBP), a paradigm that allows for manipulation of the signal at the satellite transponder, is being embraced by a large section of the satellite community. Exploiting OBP can lead to efficient implementation, bandwidth saving, lower redundancy, and better performance. Enabling processing aboard a satellite necessitates re-assessing the implementation of a number of signal processing techniques which, so far, have been ground-centric. In this work, we investigate the possibility of implementing signal predistortion (SPD) aboard a satellite having digital transparent processor (DTP). Such satellites employ transponders that allow for the implementation of limited functionalities in the digital domain. On-board predistortion can then be performed on the digitized data and can provide better performance compared to on-ground techniques. However, the conversion to the digital domain performed by an analogto-digital converter (ADC) introduces different types of noise. Among these, the clock jitter requires the implementation of estimation and compensation algorithms. In this paper we propose a reduced-complexity on-board signal predistortion algorithm capable of post-compensating the jitter introduced by the ADC, and pre-compensating the distortion generated by the amplifier.

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Beamforming with large-scale antenna arrays (LSAA) is one of the predominant operations in designing wireless communication systems. However, the implementation of a fully digital system significantly increases the number of required radio-frequency (RF) chains, which may be prohibitive. Thus, analog beamforming based on a phase-shifting network driven by a variable gain amplifier (VGA) is a potential alternative technology. In this paper, we cast the beamforming vector design problem as a beampattern matching problem, with an unknown power gain. This is formulated as a unit-modulus leastsquares (ULS) problem where the optimal gain of the VGA is also designed in addition to the beamforming vector. We also consider a scenario where the receivers have the additional processing capability to adjust the phases of the incoming signals to mitigate specular multipath components. We propose efficient majorization-minimization (MM) based algorithms with convergence guarantees to a stationary point for solving both variants of the proposed ULS problem. Numerical results verify the effectiveness of the proposed solution in comparison with the existing state-of-the-art techniques.