Nonlinearity effect of high power amplifiers in communication systems

Abstract

Power Amplifier (PA) is a very important component in communication systems which consume a significant fraction of the total energy and is mostly nonlinear. There is an inverse relationship between the PA efficiency and its linearity. Nonlinear PAs are desirable from an efficiency point of view. The price paid for higher efficiency is that it causes growth in spectrum and causes adjacent channel interference. It also causes in-band distortion, which degrades the bit error rate (BER) performance. Transmission systems, like orthogonal frequency-division multiplexing (OFDM), has tolerance to inter-symbol interference and good spectral efficiency but are subjected to nonlinearities of power amplifiers, due to their high peak-to-average power ratio (PAPR), which occurs because of large fluctuations in their signal envelopes. To reduce the spectral regrowth and to reduce BER, PA linearization is necessary. In this paper, Peak clipping, random phase shifting, selected mapping (SLM) and dummy sequence insertion (DSI) methods have been presented to reduce the PAPR and consequently the effect of nonlinearity and to improve the spectral and energy efficiency of PA.