OPTIMIZATION OF AN ADAPTIVE CUBIC PREDISTORTER FOR MULTILEVEL QUADRATURE AMPLITUDE MODULATION

摘要

A compensation technique for nonlinearities is usually necessary in QAM digital radio link.The analog waveform compensator has the advantage of removing clustering and reducing out of band spectral emissions with respect to mcmoryless digital predistortion,besides its ease ealization.In this paper an optimization technique for cubic predistorters is proposed.The optimization is carried out by varying the predistorter characteristic against the working point of the power amplifier,whereas conventional cubic predistorters are aimed at approximating the HPA(High Power Amplifier)characteristic only in a fixed point(the origin or the saturation point).The receiver is supposed to provide amplitude and phase control.Simulation results show that the proposed solution performs much better if compared not only to the conventional cubic predistorters,but also to the base band digital predistorter.