Robustness of ISAC Waveforms to Power Amplifier Distortion

In this work, we consider an integrated sensing and communication system, where both functionalities happen in the same time and frequency resource. We study the effect of non-linear power amplifier (PA) distortion in the sensing performance of the Orthogonal Frequency Division MUltiplexing (OFDM), Single carrier (SC), and Orthogonal Chirp Division Multiplexing (OCDM) waveforms. We analytically characterize the PA-induced distortion in all three waveforms and obtain closed-form expressions for the distortion power. We show that PA distortion causes an increase of the sidelobes of the delay and Doppler ambiguity function. Our analysis reveals that, although SC experiences a lower PA distortion, it outperforms OFDM only in the very low noise power region, as it suffers from noise enhancement. Moreover, OCDM always gives an inferior sensing performance compared to OFDM and SC, as it suffers from both noise enhancement and high PA distortion.