Understanding Normalized Mean Squared Error in Power Amplifier Linearization

This letter provides a detailed analysis of the normalized mean squared error (NMSE) of an ideal orthogonal frequency-division multiplexing (OFDM) system, subject to soft clipping of the power amplifier (PA) output. Based on the central limit theorem, the OFDM baseband input is modeled as white Gaussian noise, and based on the Bussgang theorem, the NMSE is studied in some detail. Asymptotes describing the NMSE for the considered system are derived, when the system is working in the linear operation mode and when working under compression, respectively. Detailed yet simple expressions between the NMSE, average output power, saturation voltage of the PA, and the noise level of the additive channel or thermal noise are derived, which are believed to provide insight into the system's behavior.