A Discrete Newton's Method for Gain Based Predistorter

Xiaochen Lin,Aifei Liu,Minglu Jin

doi:10.4236/ijcns.2008.11003

Abstract

Gain based predistorter (PD) is a highly effective and simple digital baseband predistorter which compensates for the nonlinear distortion of PAs. Lookup table (LUT) is the core of the gain based PD. This paper presents a discrete Newton’s method based adaptive technique to modify LUT. We simplify and convert the hardship of adaptive updating LUT to the roots finding problem for a system of two element real equations on athematics. And we deduce discrete Newton’s method based adaptive iterative formula used for updating LUT. The iterative formula of the proposed method is in real number field, but secant method previously published is in complex number field. So the proposed method reduces the number of real multiplications and is implemented with ease by hardware. Furthermore, computer simulation results verify gain based PD using discrete Newton’s method could rectify nonlinear distortion and improve system performance. Also, the simulation results reveal the proposed method reaches to the stable statement in fewer iteration times and less runtime than secant method.

Highlights

Radio frequency (RF) power amplifiers (PAs) play an important role in wireless communication systems, but are inherently nonlinear
Among various linearization techniques, digital baseband predistortion is more attractive than others by virtue of its simplicity and ease of implementation with digital signal processor (DSP) equivalently in baseband
We take into account the gain based predistortion [1] which employs a lookup table (LUT) block using random access memory (RAM)

Summary

Introduction

Radio frequency (RF) power amplifiers (PAs) play an important role in wireless communication systems, but are inherently nonlinear. To compensate for nonlinear of PAs, linearization is an indispensable technique today. Based on above, [2] presents a broadcasting adaptive algorithm more efficient for updating PD. [3] proposes a modified broadcasting adaptive algorithm, which does not require special form of training sequence. K. Cavers generates an idea that the adaptation issue can be converted to the root finding problem on mathematics and presents secant method. K. Cavers, [4][5], and [6] present combining dichotomy with linear method, rapid secant method, and combing dichotomy with Newton’s method, respectively. In this paper, we propose discrete Newton’s method to adapt a PD which has the advantages of fast convergence and low computational load.

Gain Based Predistortion

Simulation Results

Conclusion