Throughput-Optimal RIS-Aided Uplink NOMA Transmissions with Downlink Simultaneous Wireless Information and Power Transfer

In this paper, we consider a reconfigurable intelligent surface (RIS)-aided network with simultaneous wireless information and power transfer (SWIPT) and investigate the maximization of the system uplink throughput with non-orthogonal multiple access (NOMA) transmissions. Within the SWIPT framework, the Internet of Things (IoT) devices are allowed to upload contents to the base station (BS) by using previously harvested energy. In this setting, considering the energy harvesting and the transmission model, we aim to maximize the global system uplink throughput under the IoT devices' minimum uplink data rate constraints. A two-step alternating optimization algorithm is devised to address the considered throughput maximization problem in which the RIS coefficients are optimally determined for both downlink (DL) and uplink (UL) phases. Simulation results demonstrate the effectiveness of our proposed approach in improving the system uplink throughput levels while satisfying the IoT devices' minimum uplink data rate constraints in the RIS-aided uplink NOMA transmissions with downlink SWIPT.