Security Performance Analysis of Cell-Free Massive MIMO over Spatially Correlated Rayleigh Fading Channels with Active Spoofing Attack

The authors investigate the security performance of the cell-free massive multiple-input multiple-output (MIMO) system over spatially correlated Rayleigh fading channels in the presence of an active pilot spoofing attack. There are a large number of distributed access points (APs) simultaneously serving a smaller number of users under the cell-free massive MIMO system, which is a promising technology in the future wireless communication. We focus on the downlink secure transmission employing the minimum mean square error (MMSE) estimator and performing the distributed conjugate beamforming technique. Generalized closed-form expressions of per-user achievable rate are derived. Also, we carry out the analytical results of the upper bound on the information rate leaked into the active eavesdropper. Numerical results reveal the ergodic secrecy rate (ESR) is influenced significantly by the active eavesdropper and the condition of channel fading correlation.