On the combined response of clipper-amplifier cascade for PAPR reduction of OFDM signals

Abstract

Orthogonal frequency division multiplexed (OFDM) signals have high peakto-average power ratio (PAPR) which results in excessive nonlinear distortion when amplified by power amplifiers (PA) and hence, reduction in system signal-to-noise (SNR) and spectral efficiency. Clipping has been one of the most popular and low-cost technique for reducing the PAPR of OFDM signals. The overall spectral efficiency of an OFDM system that involves clipping depends on the combined response of the cascade of clipper-amplifier and not only on the response of the clipper. In this article, the performance of clipped and nonlinearly amplified OFDM signals is studied. The combined response of a clipperamplifier cascade is obtained using an orthogonalized behavioral model which enables in-band and out-of-band nonlinear distortions to be accurately predicted without using the Gaussian assumption of signal statistics. Furthermore, different clipping characteristics are studied where it is shown that the overall nonlinear distortion, and hence the overall SNR, is highly dependent on the type of clipping characteristics and the clipping ratio. Simulation results are verified by Simulink measurement model which uses measured amplifier characteristics in a "General Amplifier" block.