Attack Detection for Massive MIMO Relay System

This article focuses on a two-hop relay system, where a potential malicious single-antenna relay may forward altered symbols to a base station (BS) equipped with massive antennas, while the BS also receives signals from direct channel between itself and the source. The main challenge is that the malicious relay may not only alter symbols, but also transmit misleading pilot symbols to impair the channel estimation at the BS. With this regard, we investigate attack detection without reliable channel estimation. During each channel coherence interval, the BS receives pilot signal, namely, reference vector (RV), and immediately examines reliability of the RV by utilizing its massive antennas. If it is reliable, the received information signals, namely, information vectors, will be projected into the RV. The projection gives compressed signal with one dimension. After
$n$
intervals, the BS could obtain an
$n$
-length sequence of compressed signals across
$n$
different channel coherence intervals and an
$n$
-length sequence of direct signals from the direct channel. We prove that arbitrary attacks are detectable by comparing empirical distribution of these two sequences with its
a priori
stochastic distribution. Furthermore, simulation confirms that our proposed schemes outperform other existing attack detection methods.