Multilayer Irregular RIS-Assisted Wireless Communication System Performance Optimization

Reconfigurable intelligent surfaces (RISs) are expected to play crucial roles in enhancing energy and spectral efficiencies, as well as the security of 6G networks. However, regular RIS, where elements are arranged regularly over RIS grids, is not spectral efficient in dynamic channels due to the high overhead, especially in the case of a large number of RIS elements. In this article, we introduce a new multilayered irregular RIS (MLI-RIS) architecture with a corresponding design optimization framework to reduce the required overhead, in addition to optimizing the spectral and energy efficiency of the wireless network. The proposed MLI-RIS design strategically disperses elements irregularly across multiple layers, harnessing additional spatial degrees of freedom to amplify signal power and optimize system capacity. To simplify the optimization problem and reduce required overhead, the proposed framework decouples the optimization problem into the MLI-RIS topology design problem, which is based on channel state information, and the elements’ phase and precoding optimization problem. Advanced optimization techniques, such as modified tabu-hybrid sophisticated neighbor search-simulated annealing and neighborhood exploration and refinement-cross entropy are utilized to optimize these two problems. Results of extensive simulations demonstrate that the proposed MLI-RIS exhibits significant superiority over both irregular RIS setups and conventional multilayer regular RIS architectures. These findings highlight MLI-RIS as a transformative solution, positioning it as a cornerstone in the evolution toward future wireless communication paradigms.