Partial Non-Orthogonal Multiple Access: A New Perspective for RIS-Aided Downlink

In this letter, a novel reconfigurable intelligent surface (RIS) aided partial non-orthogonal multiple access (P-NOMA) downlink is investigated, where the passive beamforming on the RIS is designed for serving paired user equipments (UEs), with their signal frequencies partially overlapped. We consider the general case that all UEs have both direct and reflection links undergoing Rayleigh and Nakagami- {m} fadings. By approximating the effective channel gains of the P-NOMA UEs as Gamma random variables, we derive the closed-form expressions of the lower and upper bounds on the achievable rates. The accuracy of the derived close-form expressions are verified through simulation and numerical results, where the proposed RIS-aided P-NOMA downlink considerably outperforms the conventional NOMA and orthogonal counterparts.