Abstract
This study delves into the capabilities of reconfig- urable intelligent
surfaces (RISs) in enhancing bidirectional non- orthogonal multiple
access (NOMA) networks. The proposed approach partitions RIS to optimize
the channel conditions for NOMA users, improving NOMA gain and
eliminating the re- quirement for uplink (UL) power control. The
proposed approach is rigorously evaluated under four practical
operational regimes; 1) Quality-of-Service (QoS) sufficient regime, 2)
RIS and power efficient regime, 3) max-min fair regime, and 4) maximum
throughput regime, each subject to both UL and downlink (DL) QoS
constraints. By leveraging decoupled nature of RIS portions and base
station (BS) transmit power, closed-form solutions are derived to
demonstrate how optimal RIS partitioning can meet UL-QoS requirements
while optimal BS power control can ensure DL-QoS compliance. Our
analytical findings are validated through simulations, highlighting the
significant benefits that RISs can bring to the NOMA networks in the
aforementioned operational scenarios.