The Joint Power of NOMA and Reconfigurable Intelligent Surfaces in SWIPT Networks

Simultaneous Wireless Information and Power Transfer (SWIPT) offers a viable solution for facilitating efficient and sustainable communication networks that serve energy-limited communication devices, as in the forthcoming Internet of Things (IoT) era. Towards exploiting the benefits of SWIPT schemes at their full capacity, achieving both spectral and energy efficiency, Reconfigurable Intelligent Surface (RIS) and Non-Orthogonal Multiple Access (NOMA) technologies allow for effectively treating challenges associated with the low efficiency over long distance and the spectrum scarcity, respectively. In this article, the joint optimization of the RIS elements’ phase shifts, the IoT nodes’ downlink allocated powers, and their harvested energy, is used as the means to maximize the IoT nodes’ sum downlink rate and their weighted uplink data rate. The corresponding optimization problem is formulated as a single-leader multiple-followers Stackelberg game, and solved accordingly, via a distributed and iterative algorithm. The overall proposed optimization framework is evaluated via modeling and simulation, in terms of its spectral efficiency and harvested energy, allowing also to obtain some key insights about the gain provided by the assistance of RIS to a NOMA-operated SWIPT network of IoT nodes.