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

Abstract

Abstract-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.