Secure Transmission in Cell-free Massive MIMO System against Active Pilot Attack

Abstract

In this paper, we investigate the security of massive MIMO networks with cell-free (CF) massive multiple-input multiple-output (MIMO) systems with active eavesdroppers who obtains useful information by sending the same pilot as the legal user in the channel estimation stage. On the basis of conjugate beamforming, the closed-form expression of the security rate is deduced, and an optimal power allocation (PA) algorithm is designed to improve the safety of the system. According to the contribution to the user's security rate, a user-centric (UC) access points (APs) selection scheme is developed. Simulation analysis shows that the method proposed in this paper not only greatly improves the security rate of the system, but also reduces the system delay while ensuring the normal transmission of legal users.