Comment: Nonlinear SNR amplification of harmonic signal in noise

This comment relates to a recently published Letter, which computes the signal-to-noise ratio (SNR) of a harmonic signal in additive noise after transformation by an arbitrary memoryless nonlinearity. According to the authors, with a simple saturating nonlinearity having direct electronic implementation, an amplification of the SNR can be obtained. It is shown here that this computation and the resulting conclusion are not new.