Distributed RIS SWIPT-IoT Systems: Optimizing Spectral Efficiency and Energy Harvesting

Distributed Reconfigurable Intelligent Surfaces (D-RIS) in a Simultaneous Wireless Information and Power Transfer (SWIPT) framework is investigated in this paper to enhance spectral efficiency (SE) and energy harvesting (EH) for an Internet-of-Things (IoT) node utilizing a power-splitting (PS) protocol with non-linear EH model. Two types of RIS selection strategies, namely Exhaustive RIS Approach (ERA) and Optimal RIS Approach (ORA) are analyzed and compared. Algorithmic solutions based on divide-and-conquer strategy are developed to optimize the PS ratio and transmission power, ensuring improvements in distinct objective of SE and EH. The analysis is performed through a comprehensive case study of five different scenarios, focusing on various factors such as RIS surface placement, node-to-RIS distance, RIS size, and their combined impact on system performance. Numerical simulations provide insights into the system's behavior under different configurations, revealing that the ERA strategy consistently outperforms the ORA in achieving better SE and EH outcomes. These results are viable in designing IoT systems using distributed RISs in data and energy domains.