Power Optimization in RIS-Assisted P-NOMA for Full-Duplex 6G Vehicular Networks

In this paper, we propose a new full-duplex transmission reconfigurable-intelligence-surface (RIS)-assisted vehicular communication framework aimed at enhancing vehicular communications among connected vehicles under congested urban areas. By integrating power-domain non-orthogonal multiple access (P-NOMA) and enabling spectrum reuse between the RIS-assisted vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) communications, the proposed framework facilitates concurrent data transmission to multiple vehicles via a single sub-channel, effectively enhancing data rate performance without requiring additional bandwidth. To further improve the spectrum efficiency, we incorporate NOMA as a cross-tier interference coordination mechanism and employ successive interference cancellation (SIC) for mitigating interference originating from V2V communication, rendering our solution highly suitable for vehicular applications. We derive optimal values for transmit power and NOMA pair coefficients, and employ a successive convex approximation (SCA) technique to optimize RIS phase shifts. The superiority of the proposed approach is evaluated in comparison to the dominant interference scenario and orthogonal multiple access (OMA) technique with respect to the data rate.