Optimization of an adaptive cubic predistorter for multilevel quadrature amplitude modulation

The performance of an optimized waveform predistorter to compensate for the nonlinear distortions in M-QAM (quadrature amplitude modulation) digital radio links is analyzed. 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 distorters 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 than not only the conventional cubic predistorter but also the baseband digital predistorter