  We discuss the use of angle of arrival (AoA) as an authentication measure in
analog array multiple-input multiple-output (MIMO) systems. A base station
equipped with an analog array authenticates users based on the AoA estimated
from certified pilot transmissions, while active attackers manipulate their
transmitted signals to mount impersonation attacks. We study several attacks of
increasing intensity (captured through the availability of side information at
the attackers) and assess the performance of AoA-based authentication using
one-class classifiers. Our results show that some attack techniques with
knowledge of the combiners at the verifier are effective in falsifying the AoA
and compromising the security of the considered type of physical layer
authentication.
