Intelligent Reflecting Surface Assisted Full-Duplex Relay Systems: Deployment Design and Beamforming Optimization

Intelligent reflecting surface (IRS)-aided wireless relaying technology has aroused great interest recently as a promising new solution to enhance the system performance. However, most existing works only consider the decode-and-forward (DF) relay and ignore the base station (BS) to user direct link. In this paper, we focus on an IRS-aided full-duplex (FD) amplify-and-forward (AF) relay system and study the deployment design and beamforming optimization problem. Specifically, we first analyze the asymptotic rates achieved by three IRS deployment strategies (i.e., deploying the IRS near the BS, relay and user) when the number of reflecting elements becomes sufficiently large to obtain useful insights. Then, for the practical case with finite number of reflecting elements, we aim to maximize the transmission rate under different IRS deployment strategies by jointly optimizing the IRS reflection coefficients and transmit powers at the BS and relay. For the case of deploying the IRS near the user, a block coordinate decent (BCD)-based algorithm is proposed. For the cases of deploying the IRS near the relay and BS, we propose a virtual stochastic successive convex approximation (VSSCA) algorithm to solve our considered deterministic optimization problems efficiently. Finally, numerical results are provided to demonstrate the asymptotic performance analysis as well as the effectiveness of our proposed algorithms as compared to various benchmark schemes.