Power Efficiency Improvements through Peak-to-Average Power Ratio Reduction and Power Amplifier Linearization
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Research Article Power Efficiency Improvements through Peak-to-Average Power Ratio Reduction and Power Amplifier Linearization Ning Chen,1 G. Tong Zhou,2 and Hua Qian3 1 Freescale
Semiconductor, Inc., Austin, TX 78729, USA of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA 3 Marvell Semiconductor, Inc., Santa Clara, CA 95054, USA 2 School
Received 9 June 2005; Revised 14 February 2006; Accepted 24 November 2006 Recommended by Enis Ahmet Cetin Many modern communication signal formats, such as orthogonal frequency-division multiplexing (OFDM) and code-division multiple access (CDMA), have high peak-to-average power ratios (PARs). A signal with a high PAR not only is vulnerable in the presence of nonlinear components such as power amplifiers (PAs), but also leads to low transmission power efficiency. Selected mapping (SLM) and clipping are well-known PAR reduction techniques. We propose to combine SLM with threshold clipping and digital baseband predistortion to improve the overall efficiency of the transmission system. Testbed experiments demonstrate the effectiveness of the proposed approach. Copyright © 2007 Ning Chen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1.
INTRODUCTION
Modern transmission formats, such as orthogonal frequency-division multiplexing (OFDM) and code-division multiple access (CDMA), have gained tremendous popularity thanks to their high spectral efficiency. However, a drawback is the low power efficiency of these systems. OFDM and CDMA signals suffer from high peak-to-average power ratios (PARs), making them susceptible to nonlinearities that are inherent in the RF/microwave power amplifiers (PAs). To avoid nonlinear distortions, the average operating power of the PA has to be backed-off significantly, giving rise to low DC to RF conversion efficiency. PA efficiency enhancement is a critical issue for wireless communication applications. In a typical cellular base station, the RF PA and its associated cooling equipment are responsible for approximately 50% of the overall DC power consumption and 60% of its physical size [1]. On the other hand, it is reported that in today’s cellular phones, over 90% of the power used to transmit the signal is wasted in the form of heat that stays inside the phone [2]. The topic of power efficiency has attracted much attention in recent years. There are two key factors that contribute to the low PA efficiency in these applications: (i) high PAR value of the signal, and (ii) nonlinearity of the PA. Many techniques have been proposed to reduce the PAR, such as deliberate clip-
ping, complementary coding, selected mapping (SLM), and so forth [3–5]. Among the many PA linearization techniques, adaptive digital baseband predistortion is the most costeffective [6]. To the best of our knowledge, few references except for [7, 8] have discussed joint PAR reduction an
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