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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. INDEX TERMS Physical layer security, cell-free massive MIMO, multigroup multicasting, pilot spoofing attack. * Strictly speaking, the derived results are spectral efficiency (bits/s/Hz) as bandwidth hasn't been considered at the expressions of R n k and R nE .

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The authors investigate the secure communication in multigroup multicasting cell-free massive MIMO systems in the presence of an active pilot spoofing attack. With the imperfect estimated local channels at access points, a distributed conjugate beamforming with normalised power constraint policy is exploited for downlink multicasting transmission. Closed-form expressions for the per-user achievable rate and information leakage to eavesdropper are derived, respectively. Numerical results are presented to verify the correctness of their analytical results and quantitatively analyse the impacts of eavesdropper's spoofing pilot power and a number of groups on the secrecy performance of the considered systems.

This paper considers the secure transmission in a cell-free massive MIMO system with imperfect radio frequency (RF) chains and low-resolution analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) at both access points (APs) and legitimate users, where an active eavesdropper attempts to wiretap the confidential data. The Gaussian RF impairment model (GRFIM) and additive quantization noise model (AQNM) are used to evaluate the impacts of the RF impairments and low resolution ADCs/DACs, respectively. The analytical results of the linear minimum mean square error (MMSE) channel estimation show that there is nonzero floor on the estimation error with respect to the RF impairments, ADC/DAC precision and the pilot power of the eavesdropper which is different from the conventional case with perfect transceiver. Then, a tractable closed-form expression for the ergodic secrecy rate is obtained with respect to key system parameters, such as the antenna number per AP, the AP number, user number, quality factors of the ADC/DAC and the RF chain, pilot signal power of the eavesdropper, etc. Moreover, a compensation algorithm between the imperfect RF components and the inexpensive coarse ADCs/DACs is also presented. Finally, numerical results are provided to illustrate the efficiency of the achieved expressions and the devised algorithm, and show the effects of RF impairments and low resolution ADC/DAC on the secrecy performance.