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A Novel Predistorter Design for Nonlinear Power Amplifier with Memory Effects in OFDM Communication Systems Using Orthogonal Polynomials
Yitao ZHANG Kiyomichi ARAKI
Publication
IEICE TRANSACTIONS on Electronics
Vol.E93C
No.7
pp.983990 Publication Date: 2010/07/01 Online ISSN: 17451353
DOI: 10.1587/transele.E93.C.983 Print ISSN: 09168516 Type of Manuscript: Special Section PAPER (Special Section on Recent Progress in Microwave and MillimeterWave Technologies) Category: Keyword: power amplifier, nonlinear distortions, memory effects, predistorter, orthogonal polynomials, complex Gaussian distributed, orthogonal frequency division multiplexing (OFDM),
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Summary:
Orthogonal frequency division multiplexing (OFDM) signals have high peaktoaverage power ratio (PAPR) and cause large nonlinear distortions in power amplifiers (PAs). Memory effects in PAs also become no longer ignorable for the wide bandwidth of OFDM signals. Digital baseband predistorter is a highly efficient technique to compensate the nonlinear distortions. But it usually has many parameters and takes long time to converge. This paper presents a novel predistorter design using a set of orthogonal polynomials to increase the convergence speed and the compensation quality. Because OFDM signals are approximately complex Gaussian distributed, the complex Hermite polynomials which have a closedform expression can be used as a set of orthogonal polynomials for OFDM signals. A differential envelope model is adopted in the predistorter design to compensate nonlinear PAs with memory effects. This model is superior to other predistorter models in parameter number to calculate. We inspect the proposed predistorter performance by using an OFDM signal referred to the IEEE 802.11a WLAN standard. Simulation results show that the proposed predistorter is efficient in compensating memory PAs. It is also demonstrated that the proposal acquires a faster convergence speed and a better compensation effect than conventional predistorters.

