Analysis and Identification of Wiener-Hammerstein System in Frequency Domain Using Two-Tone Measurements for Nonlinear RF Transmitters

Hyunchul KU  

Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E91-A   No.9   pp.2435-2441
Publication Date: 2008/09/01
Online ISSN: 1745-1337
DOI: 10.1093/ietfec/e91-a.9.2435
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Nonlinear Theory and its Applications)
Category: Analysis, Modelng and Simulation
Keyword: 
memory effects,  nonlinear,  RF power amplifier,  transmitter,  two-tone,  WiBro,  Wiener-Hammerstein,  

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Summary: 
This paper presents analysis and identification method of Wiener-Hammerstein system to characterize a nonlinear RF transmitter in fundamental frequency zone. A two-tone signal is used to analyze and identify a Wiener-Hammerstein model. A RF signal is converted to baseband-equivalent complex signal, and Wiener-Hammerstein model is considered to have a baseband equivalent complex polynomial and linear filters. For a two-tone input signal, closed form descriptions of the output signal in the time domain and frequency domain are developed using a newly suggested nonlinearly modulated two-tone phasors (NMTP). The relationship between frequency terms of input and output signals in RF transmitters are represented with linear matrix-vector equation based on NMTP analysis. An advantage of the proposed method is its simplicity using closed form analysis and linear approximation. In addition, we can model a wideband system with relatively narrowband measurements by sweeping two-tone signal. The prediction of spectral regrowth and the predistortion performance for WiBro 1FA signal demonstrate the validity of the proposed approach in identifying the nonlinear RF transmitters.