Elimination of rogue Access Points (APs) is a challenging security goal of growing interest
and practical importance. However, even when network administrators suspect that
such devices are indeed present to attack their organization, physically locating their
whereabout is an intricate task. In this work a method is suggested for implementing
autonomous Direction Finding (DF), i.e., an apparatus for passively identifying the Angleof-
Arrival (AoA) of a received Wi-Fi signal, using a standard off-the-shelf Wi-Fi receiver.
Modern wireless communication standards, such as Wi-Fi (e.g. IEEE 802.11n), are based
on Orthogonal Frequency Division Multiplexing (OFDM) and Multiple-Input Multiple-
Output (MIMO) technologies. The key contribution of the current work is an approach of
employing the multiple receiving antennas jointly with OFDM Channel State Information
(CSI) as the basis for implementing an interferometry DF tool. This approach is theoretically
investigated via numeric analysis, and practically validated by a working prototype.
The performance of the prototype was evaluated both in the laboratory, in a sterile
environment, as well as in field trials. In realistic indoor setting the prototype was able
to acquire the AoA with a median error of 8–15 degrees.
© 2015 Elsevier B.V. All rights reserved.