On the Robustness of AoA as an Authentication Feature Under Spoofing: Fundamental Limits from Misspecified Cramer Rao Theory

The robustness of angle of arrival (AoA) as a physical layer authentication (PLA) feature under spoofing attacks is studied, assuming a digital uniform linear array verifier. The verifier estimates the AoA assuming a legitimate user's single source model, whereas the received signal is generated by a multi antenna adversary at a different angle, leading to a model mismatch. Closed form expressions are derived for the misspecified Cramer Rao bound, the PLA decision threshold, the spoofing detection, false alarm and misdetection probabilities. Simulation results validate the theoretical findings and highlight the impact of the signal to noise ratio, array geometries, spoofing precoding and number of snapshots on authentication robustness.