Chapter 1Characterization of Wireless Transmitter Distortions

1.1 Introduction

Wireless transmitters designed for modern communication systems are expected to handle wideband amplitude and phase modulated signals with three major performance metrics: linearity, bandwidth, and power efficiency. First, linearity requires the minimization of distortions mainly caused by the transmitter's radio frequency (RF) analog circuitry in order to preserve the quality of the transmitted signal and avoid any loss of information during the transmission process. Second, bandwidth is critical for multi-carrier and multi-band communication systems. Moreover, wider bandwidths are needed to accommodate higher data rates. Third, power efficiency is an important consideration that affects the deployment and operating costs of communication infrastructure as well as environmental impact.

In general, distortions refer to the alteration of the signal due to the imperfections of the transmitter's hardware. Distortions observed in wireless transmitters have various origins such as frequency response distortions, harmonic distortions, amplitude and phase distortions, and group delay distortions, in addition to modulator impairments (including direct current (DC) offset, gain, and phase imbalance), and so on. Among these distortions, the predominant ones are those due to the nonlinearity present in the transmitter's RF front end and mainly the RF power amplifier (PA). Indeed, wireless transmitters are made ...

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