Design and implementation of digital predistorter with orthonormal polynomials

In many predistorter designs, polynomial model was used to describe the nonlinearity of power amplifiers (PAs). However, numerical instability can occur during model coefficients estimation. Orthogonal polynomial models presented in [1] [2] can help to alleviate the numerical instability problem in fixed-point implementation. In this paper, we propose a new orthonormal polynomial model to further improve the numerical stability of the polynomial model. Both simulation and experiment results show that the orthonormal polynomial model can achieve more spectrum regrowth suppression than the conventional polynomial model as well as the orthogonal polynomial model with the same finite word length.