Leveraging Power Amplifier Distortion for Physical Layer Security

This paper introduces a new approach to physical layer security (PLS) by leveraging power amplifier (PA) nonlinear distortion through distortion-aware precoding. While some conventional PLS techniques inject artificial noise orthogonal to legitimate channels, we demonstrate that inherent PA nonlinearities typically considered undesirable can be exploited to enhance security. The zero 3rd order (Z3RO) precoder applies a negative polarity to several antennas to cancel the PA distortion at the user location, resulting in distortion being transmitted in non-user locations. Redirecting the distortion to non-user locations creates interference for potential eavesdroppers, lowering their signal-to-noise-and-distortion ratio (SNDR). Numerical simulations reveal that the Z3RO precoder achieves up to a $2.5\times$ improvement in secrecy rate compared to conventional maximum ratio transmission (MRT) precoding under a $10\%$ outage probability, SNR of $32$ dB and $-5$ dB input back-off (IBO) where the PAs enter the saturation regime.