Feasibility Study of Adaptive LUT-based Predistorter for OFDM in Non-Linear Satellite Downlink Channel

A very significant obstacle in employing orthogonal frequency division multiplexing (OFDM) in wideband satellite systems is its sensitivity to the non-linear response of the on-board traveling wave tube amplifier (TWTA). Since satellite systems are power limited, backing-off the TWTA by a significant amount is not a realistic option. Therefore amplifier linearization techniques need to be employed in order to limit the impact of the non-linear signal distortions. This paper, studies the feasibility of introducing a look-up table (LUT) based pre-distorter at the baseband of the gateway modem for linearizing the on-board TWTA. The LUT pre-distorter uses an adaptation algorithm for up-dating the table parameters according to the drifts in the amplifier´s response over time and frequency. The study concentrates on evaluating the performance improvements that can be offered by the LUT pre-distorter, by making realistic assumptions regarding the training process, which in the satellite system needs to be based on the transmission of training sequences that propagate via an imperfect channel