PHY/MAC Cross-Layer Design using NOMA for Next Generation C-V2X

As vehicle-to-everything (V2X) communication becomes essential for autonomous and connected vehicle ecosystems, enhancing performance through advanced multiple access techniques is increasingly vital. This paper introduces a novel cross-layer design integrating non-orthogonal multiple access (NOMA) in the physical (PHY) and medium access control (MAC) layers of cellular V2X (C-V2X) systems, with a focus on improving system throughput, reliability, and resource efficiency. Through analytical modeling and simulation, we evaluate the impact of NOMA-based resource allocation and user pairing strategies compared to traditional orthogonal multiple access (OMA) methods. Simulation results confirm that NOMA significantly boosts throughput and spectral efficiency, particularly in low-to-moderate user densities; however, as the number of users rises beyond 10, interference among far users and the complexity of successive interference cancellation (SIC) for near users present performance trade-offs in packet error rate (PER) and throughput. These findings highlight the need for advanced power allocation, interference management, and hybrid solutions to sustain NOMA's advantages in dense vehicular environments.