Data Predistortion for Nonlinear Satellite Channels

Power amplifiers, an integral component to most wireless communication systems, are inherently nonlinear devices that introduce out-of-band spectral regrowth and constellation degradation to the amplifier output. One solution is to operate in a highly backed-off state to achieve quasi-linear performance. Operating in this region requires a higher-saturated power rating for a given output power and reduces DC-to-RF efficiency. A more effective solution is to apply digital predistortion which pre-compensates for the harmful nonlinear effects. Compensation can be done at the waveform level or operate at the symbol rate, known as data predistortion. In this work we study data predistortion for commonly adopted higher-order modulations, and study performance as a function of amplifier drive level relative to saturation, and as a function of the predistorter’s memory span. A math model for a nonlinear satellite with transponder filtering is employed.