Abstract
The majority of the nonlinearity in a communication system is attributed to the power amplifier (PA) present at the final stage of the transmitter chain. In this paper, we consider Gaussian distributed input signals (such as OFDM), and PAs that can be modeled by memoryless or memory polynomials. We derive closed-form expressions of the PA output power spectral density, for an arbitrary nonlinear order, based on the so-called Leonov-Shiryaev formula. We then apply these results to answer practical questions such as the contribution of AM/PM conversion to spectral regrowth and the relationship between memory effects and spectral asymmetry.
Highlights
Power amplifiers (PAs) are important components of communications systems and are inherently nonlinear
When a nonconstant modulus signal goes through a nonlinear PA, spectral regrowth appears in the output, which in turn causes adjacent channel interference (ACI)
Stringent limits on ACI are imposed by the standard bodies and the extent of the PA nonlinearity must be controlled
Summary
Power amplifiers (PAs) are important components of communications systems and are inherently nonlinear. If the PA input is Gaussian, the PA output power spectral density (PSD) has been derived for a 5th-order nonlinear PA in [1, 2]. The objective of this paper is to derive closed-form expressions for the PA output PSD (or output autocovariance function) for an arbitrary nonlinear order, for both the memoryless and memory baseband polynomial PA models. The Gaussian assumption significantly reduces the complexity of the analysis Equipped with these formulas, we can answer practical questions, such as how important or necessary it is to correct for the AM/PM distortion in the PA and possible mechanisms for spectral asymmetry in the PA output spectrum. In order not to interrupt the flow of the paper, we defer the rather technical proofs of our theorems to Section 6
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