Optimization of Active RIS Configurations in SIM Architectures With Mutual Coupling

This latter explores a novel multi-layer active reconfigurable intelligent surface (ARIS) system using a stacked intelligent metasurface (SIM) under the aware mutual coupling (MC) for enhanced beam manipulation and extended coverage by signal reflections across layers. Specifically, we aim to optimize the phase shifts of the multi-layer ARIS to maximize the received signal-to-noise ratio (SNR) subject to power constraints at both the base station (BS) and the multi-layer ARIS. In order to solve the formulated problem, a gradient ascent algorithm is used to optimize the ARIS for all layers. Numerical results verify the convergence and effectiveness of the proposed design. It also reveals the impact of key parameters, including the ARIS meta-atoms, the number of BS antennas, and the transmit power budget at BS and multi-layer ARIS. In particular, aware MC multi-layer ARIS outperforms as compared to the aware MC multi-layer passive RIS (PRIS).