Mitigation of Pilot Spoofing Attack in Frequency Selective Channels

In a time-division duplex (TDD) multiple antenna system, the channel state information (CSI) can be estimated using reverse training. A pilot contamination (spoofing) attack occurs when during the training phase, an adversary also sends identical training (pilot) signal as that of the legitimate receiver. This contaminates channel estimation and alters the legitimate beamforming design, facilitating eavesdropping. Most of past approaches to pilot spoofing detection are limited to flat fading channels. A recent approach proposed superimposing a random sequence on the training sequence at the legitimate receiver for detection of pilot spoofing attack over frequency selective channels, with unknown channels and channel lengths, except that an upper bound on the number of channel taps is assumed to be known. In this paper we augment this approach with joint estimation of both legitimate receiver and eavesdropper channels, and secure time-reversal precoding, to mitigate the effects of pilot spoofing. The proposed mitigation approach is illustrated via simulations.