Beamforming Design for Hybrid Active-Passive RIS-Aided WPCNs with NOMA

In this paper, we investigate hybrid active-passive reconfigurable intelligent surface (RIS) assisted wireless powered communication networks (WPCNs) with non-orthogonal multiple access (NOMA) to address severe path loss and energy ineffi-ciency in Internet of things (IoT) scenarios. Unlike conventional passive RIS schemes limited by multiplicative fading or fully active RIS designs with excessive power consumption, our hybrid RIS architecture combines a subset of active elements for signal amplification and passive elements for phase-shift optimization, effectively mitigating double-fading effects. We jointly optimize time allocation for downlink and uplink transfer, along with RIS coefficients under power constraints to maximize the sum rate while ensuring user fairness. Simulations show the framework greatly enhances the sum rate, enabling link connectivity.