Enhanced Phase Realignment Techniques for the PAPR Reduction in OFDM Systems

Abstract

This paper presents a simple and effective solution for the peak-to-average power ratio (PAPR) problem in orthogonal frequency-division multiplexing (OFDM) systems. Since the OFDM signal has a high PAPR, it generates inevitable nonlinear distortions at the output of a high-power amplifier. A new technique of PAPR reduction called phase realignment (PR) and its modified version called modified PR (MPR) are proposed, which require neither side information nor do they impose any modification of the receiver. Furthermore, four possible variations of the MPR constellation structure are proposed and evaluated in terms of PAPR reduction and bit-error-rate (BER) performance. The proposed PR and MPR provide considerable reductions in PAPR. MPR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> gives a comparatively high PAPR reduction, followed by MPR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , PR, MPR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and MPR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> in descending order. The PAPR reductions of MPR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and MPR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> tend to converge to that of the PR as the modulation order increases, whereas MPR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> gives a low PAPR reduction. These techniques are designed to allow a certain level of BER degradation, which is defined by a transmit error vector magnitude (EVM) limited to a specified threshold, to reduce the PAPR and the average power (equally important in terms of power efficiency). The proposed techniques produce the reduced out-of-band radiation compared with the original OFDM signal and have moderate computational complexity. The EVM threshold is imposed to design optimum amplitude and phase margins for the PR and MPRs. Furthermore, we present the analytic upper bound BER expressions of the proposed techniques.