User Pairing Strategies for Downlink Reconfigurable Intelligent Surfaces-assisted Hybrid NOMA

Massive connection and high data rates are the main requirements for next-generation networks. The next-generation networks can meet their primary requirements by using a combination of reconfigurable intelligent surfaces (RIS) and non-orthogonal multiple access (NOMA) techniques. However, the conventional NOMA’s successive interference cancellation (SIC) complexity increases significantly with the number of users. Hybrid NOMA can resolve this problem by implementing user pairing strategies. This paper analyzes the sum rate of downlink RIS-assisted hybrid NOMA. Hybrid NOMA enables multiple users to share a time slot using pairing schemes, including time division multiple access (TDMA) and NOMA features. This reduces the complexity of the SIC and improves system performance overall. This approach allows massive connectivity, and it enhances the sum rate. According to the simulation results, adding RIS improves the sum rate performance of near-far (NF) and near-near far-far (NNFF) pairing for hybrid NOMA with four users. Adding $N=8$ RIS increases the sum rate by $\sim 71.79 \%$ in NF pairing and $\sim \mathbf{6 4. 7 0 \%}$ in NNFF pairing.