Low Complexity Predistortion and Equalization in Nonlinear Multicarrier Satellite Communications

Aiming to reduce the power/mass requirements in satellite transponders and to reduce mission costs, joint
amplification of multiple carriers using a single high-power amplifier (HPA) is being considered. In this scenario, a
careful investigation of the resulting power efficiency is essential as amplification is nonlinear, and multicarrier signals
exhibit enlarged peak-to-average power ratio. Thus, operating the amplifier close to saturation vastly increases signal
distortion resulting in a severe degradation of performance, especially for higher order modulations. This paper
proposes a reduced-complexity digital predistortion (DPD) scheme at the transmitter and a corresponding equalizer
(EQ) at the receiver to mitigate these nonlinear effects. Scenarios include both the forward as well as the return links.
In particular, the paper exploits the MIMO Volterra representation and builds on a basis pursuit approach using a
LASSO (least absolute shrinkage and selection operator) algorithm to achieve an efficient basis representation,
avoiding large computational complexity, to describe the selection of predistorter/equalizer model. The work further
compares and contrasts the two mitigation techniques taking various system aspects into consideration. The gains in
performance and amplification efficiency demonstrated by the use of DPD/ EQ motivate their inclusion in
next-generation satellite systems.