RIS-aided Cooperative FD-SWIPT-NOMA Performance Over Nakagami-m Channels

Abstract

In this work, we investigate Reconfigurable Intelligent Surface (RIS)-aided Full-Duplex (FD)-Simultaneous Wireless Information Power Transfer (SWIPT)-Cooperative non-Orthogonal Multiple Access (C-NOMA) consisting of two paired devices. The device with better channel conditions (\(D_1\)) is designated to act as a FD relay to assist the device with poor channel conditions (\(D_2\)). We assume that \(D_1\) does not use its own battery energy to cooperate but harvests energy by utilizing SWIPT. A practical non-linear Energy Harvesting (EH) model is considered. We first approximate the harvested power as a Gamma Random Variable (RV) via the Moment Matching (MM) technique. This allows us to derive analytical expressions for Outage Probability (OP) and ergodic rate (ER) that are simple to compute yet accurate for a wide range of system parameters, such as EH coefficients and residual Self-Interference (SI) levels, being extensively validated by numerical simulations. The OP and ER expressions reveal how important it is to mitigate the SI in the FD relay mode since, for reasonable values of residual SI coefficient, its detrimental effect on the system performance, is extremely noticeable. Also, numerical results reveal that increasing the number of RIS elements can benefit the cooperative system much more than the non-cooperative one.