Secrecy Analysis and Active Pilot Spoofing Attack Detection for Multigroup Multicasting Cell-Free Massive MIMO Systems

In this paper, we investigate the secure transmission in multigroup multicasting cell-free massive MIMO system in the presence of pilot spoofing attack. With the imperfect uplink and downlink channel estimation, a distributed conjugate beamforming processing with normalized power constraint policy is exploited at access points (APs) for downlink multicasting data transmission. Closed-form expressions for the per-user achievable rate are derived with and without downlink training, respectively. Also, the analytical results of the upper bound on the information leakage to eavesdropper are carried out. Moreover, a mechanism based on the minimum description length (MDL) is presented to detect pilot spoofing attack. Consequently, the achievable ergodic secrecy rate is obtained to evaluate the system's secrecy performance. The numerical results are presented to quantitatively analyze the impacts of eavesdropper's spoofing pilot power and the number of groups on the secrecy performance of the considered systems.