Spectral analysis for bandpass nonlinearity with cyclostationary input

When a non-constant envelope signal goes through a nonlinear power amplifier, spectral regrowth (broadening) appears at the output of the power amplifier. To satisfy regulatory requirements on out-of-band emissions, spectral regrowth must be contained. We derive a novel closed-form expression for the output power spectral density when the power amplifier is quasi-memoryless and cyclostationarity of the digitally modulated input is taken into account. We compare our results with the conventional analysis where stationary input is assumed. We emphasize the importance of paying attention to the cyclostationary nature of the input when excess bandwidth is present.