A Loss-Aware Element Selection Framework for Unit-Cell Splitting in Energy Harvesting Reconfigurable Intelligent Surfaces

Reconfigurable Intelligent Surfaces (RISs) offer a low-cost, energy-efficient alternative to conventional repeaters and relays, enhancing wireless coverage and spectral efficiency through dynamic electromagnetic wave manipulation. The potential of a self-powered RIS is explored in the literature by employing element splitting (ES) on the RIS surface. This approach allocates some elements for beam steering, while the remaining elements are used for RF energy harvesting (EH) to meet RIS energy needs, aiming to create self-sustainable communication systems. The heuristic algorithms existing in the literature for such element allocation are valid only for ideal EH circuits, therefore, the proposed work incorporates combiner losses into the analysis to identify the most effective algorithm for maintaining system performance in terms of maximizing signal-to-noise ratio (SNR) and meeting the energy requirements of the RIS. Subsequently, the analysis reveals the necessity for a new loss-aware element selection algorithm (LA-ESA), which is proposed in this work. The results finally underscore the need for an innovative architectural paradigm shift in developing self-powered RIS, particularly in light of combiner losses. This shift is anticipated to enable a more robust software solution for self-powered RIS that meets hardware needs, thereby advancing the concept of self-sustainability and supporting environmentally friendly innovations in wireless communication.