Adaptive Digital Predistortion for The Power Amplifiers Based on Look-up Table with Tanh as a Nonlinear Indexing Function

摘要

Today's radio frequency power amplifiers represent the most important component in the wireless systems which are characterized by linearity and efficiency. Various techniques for enhancing linearity have been suggested by many research groups. However, digital predistortion (DPD) is spotlighted among these. Adaptive DPD is mainly realized by using look-up table (LUT) or polynomial method. [1] shows the improvement using polynomial method, [2] shows the LUT method of different path using RLS algorithm, and [3] reports the LUT method using Cartesian feedback for linearization. Different from these, [4]-[5] show the nonlinear index scheme using not uniform spacing for LUT. [5] suppresses IM power using a non-uniform spacing for LUT based on the μ-law companding method. Moreover, the computation load is reduced by nonlinear indexing. In this paper, we employ the hyperbolic tangent (tanh) instead of equal spacing for LUT which uses the normalized least-mean square (NLMS) for the system estimation, eventually improving linearity and computation speed.