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Abstract To improve the security and reliability of communication transmissions, this study proposes a novel hybrid secure scheme that combines a decode‐and‐forward (DF) relay and an intelligent reflecting surface (IRS) for downlinking multiple‐input single‐output systems. The proposal maximizes the minimum achievable secrecy rate by utilizing alternating optimization algorithms to derive the closed‐form solution of the beamforming vector, obtain the optimal power allocation factor with the successive convex approximation method, and obtain the optimal phase‐shift matrix with the semi‐definite relaxation method. The simulation results demonstrate that our approach outperforms state‐of‐the‐art solutions using only the IRS or DF relay. Moreover, performance improves at a high signal‐to‐noise when increasing the number of IRSs. Notably, a proper power allocation is important to achieve optimal performance.
Shi et al. (Sat,) studied this question.