Adaptive polynomial pre-distortion for linearization of power amplifiers in wireless communications and WLAN

Abstract

This paper presents a new adaptive pre-distortion algorithm for linearization of power amplifiers and its application to non-constant envelope modulations such as QAM or OFDM. The pre-distortion system is polynomial. The criterion is minimization of a mean square error criterion between the baseband-equivalent of the output of the real amplifier and the ideally amplified signal. The analytic expression of the gradient of the criterion has been calculated. A stochastic gradient algorithm is applied using this analytic expression. A special normalization of the coefficients of the polynomial predistortion has been proposed to improve the speed of convergence. The method has been tested on a class AB power amplifier with a baseband signal corresponding to filtered QPSK and OFDM modulations.