Chapter 9Processing of Nonlinearities1
The amplifier is a key element in a telecommunications system. In this chapter, we focus on the “high-power amplifier” (HPA) at the transmitter side. The efficiency of these amplifiers is very low (less than 50% in the best case for Class A amplifiers), and also they have nonlinear characteristics. Therefore, a part of terminal's power is consumed by power amplifier. Thus, the use of constant-envelope modulation schemes, such as Gaussian minimum shift keying (GMSK), for a global system for mobile communication (GSM) is justified where amplification efficiency is optimized by operating the amplifier near-saturation point. However, most of the standardized modulation schemes, whether single-carrier or multicarrier, are not constant-envelope schemes, and the consequences of nonlinear power amplification of radio frequency (RF) signal must be treated with greater concern.
The factor PR power ratio (PR) [PAL 05a], which is defined as the ratio between the instantaneous power and the average power of a signal, is used for measuring the envelope fluctuations of the signals to be amplified. This parameter appears in the literature under several acronyms such as peak-average power ratio (PAPR), peak-mean envelope power ratio (PMEPR), or crest factor (CF).
In this chapter, we will analyze the PR in various contexts (single-carrier, multicarrier, software radio (SR), and cognitive radio (CR)) and then present some methods for ...