Rate Maximization for Active-IRS-Aided Secure Communication Networks

We develop a secure communication scheme for an active intelligent reflecting surface (IRS) aided wireless network to maximize the mobile users' (MUs') transmission rate, where a multiple antenna base station (BS) transmits confidential information to MUs with the assistance of an active IRS. First, we formulate a rate maximization problem by jointly optimizing the transmission beamforming vectors, the IRS's phase-shifts and amplification-coefficients, and the system channel bandwidth allocation coefficients. Since the formulated optimization problem is non-convex with multiple coupled variables, we first adopt the block coordinate descending (BCD) method to decompose the formulated non-convex optimization problem into several subproblems, and then use the sequential convex approximation (SCA) method to transform the non-convex subproblems into the convex problems. Then, we can use CVX to solve them. Finally, the proposed scheme is verified by numerical analysis, which show that compared with the baseline scheme with passive IRS, when the noise power at the active IRS is much smaller than that at the MUs, our proposed scheme can achieve much larger transmission rates by using the active IRS even with a small number of reflecting elements.