Predicting spectral regrowth of nonlinear power amplifiers

• Published in: IEEE transactions on communications Vol. 50; no. 5; pp. 718 - 722
• Main Authors: Zhou, G.T., Kenney, J.S.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.05.2002; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Analytical models; Channels; Closed-form solution; Communication systems; Density; Digital modulation; Exact solutions; Fourier transforms; Interchannel interference; Mathematical analysis; Narrowband; Nonlinearity; Power amplifiers; Power generation; Signal generators; Spectra; Time domain analysis
• ISSN: 0090-6778; 1558-0857
• DOI: 10.1109/TCOMM.2002.1006553

Power amplifiers (PAs) are important elements in communications systems and they are inherently nonlinear. Nonlinearity generates spectral regrowth (i.e., spectral broadening) in digitally modulated signals which causes adjacent channel interference. In this paper, we present a closed-form expression for the auto-covariance function of the PA output, whose Fourier transform yields the output power spectral density (PSD). The PA input does not need to be Gaussian and the PSD calculation can be carried out using common PA descriptions such as the AM/AM and AM/PM characteristics. We assume that the input is narrow-band, thus PA memory effects, on the order of a symbol period, are not present. The analytical results allow us to predict spectral regrowth without running expensive or time-consuming time-domain simulations; they also lead to a variety of optimization possibilities in transmitter design that includes the PAs.