Secrecy Analysis of RIS-Aided mmWave Systems over Independent Fluctuating Two-Ray Fading Channels

In this paper, we examine a millimeter-wave (mmWave) wiretap scenario where a multiple-antenna base station (Alice) communicates with a legitimate user (Bob) via a reconfigurable intelligent surface, while multiple colluding eavesdroppers (Eves) attempt to passively intercept the communications using the maximal-ratio combining scheme. We develop a framework for achieving the maximum effective secrecy throughput (EST) that meets both reliability and secrecy constraints. Firstly, we derive a generalized and tractable form of the independent fluctuating two-ray (IFTR) distribution for accurately modeling mmWave fading channels. Secondly, we propose a novel approximation method to statistically characterize the end-to-end channels, considering the phase-shift estimation errors at both Bob and the colluding Eves over the IFTR channels. Finally, we derive a new closed-form EST metric and its asymptotic expression.