Spatial Sparsity-Based Pilot Attack Detection and Transmission Countermeasure for Cell-Free Massive MIMO System

In this article, we investigate the security performance of a cell-free (CF) massive multiple-input-multiple-output (MIMO) system that is composed of a large number of randomly distributed access points (APs) and multiple users. There may be an eavesdropper who launches an active pilot attack during uplink channel estimation stage to eavesdrop on information in data transmission stage, which threaten the security of the system. A spatial sparsity-based pilot attack detection (SS-based-PAD) method is proposed in this study to determine whether there is an active eavesdropper. Different data transmission schemes were developed according to the detection results. In the presence of an eavesdropper, rate maximization power allocation (SRM-PA) algorithm is proposed to maximize the security of the eavesdropped user. On the contrary, achievable rate equalization power allocation (ARE-PA) algorithm is proposed to provide fair services for all legitimate users. Moreover, an AP selection scheme and corresponding conjugate beamforming are used to enhance the security performance of the system and mitigate the impact of a pilot spoofing attack.