## 2 Related Work
### NOMA with V2X Applications  
The application of NOMA in V2X communications shows great promise in enhancing system performance in high-mobility and densely connected environments. V2X encompasses diverse interactions, including vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), and vehicle-to-pedestrian (V2P), all of which demand reliable, low-latency communnication. In such vehicular networks, resource scheduling is particularly challenging due to high vehicle mobility and rapidly changing network topologies. Meeting the stringent requirements of V2X communication, such as low latency and high reliability, is critical to ensuring seamless interactions.  
Traditional orthogonal multiple access (OMA) schemes often face challenges in dense vehicular environments like urban areas, leading researchers to explore NOMA as a promising alternative. NOMA's capacity for massive connectivity and improved spectral efficiency makes it particularly suitable for V2X applications, which require high data throughput and real-time communication.For example, [PERSON] et al. [3] proposed a NOMA-based V2X framework tailored to ultra-dense vehicular networks, demonstrating its ability to significantly reduce latency and enhance reliability by efficiently managing spectrum resources. Their work also highlighted NOMA's practical benefits across unicast and broadcast V2X systems, excelling in spectrum allocation and interference mitigation in crowded networks. These findings underscore the importance of advanced resource management for the successful integration of NOMA in V2X applications.  
The dynamic and high-mobility nature of vehicular environments calls for advanced resource allocation strategies tailored to NOMA-enabled V2X communications. Previous studies have established a solid foundation in this area. [PERSON] et al. [18] highlighted the importance of adaptive resource allocation to address frequent topology changes in vehicular networks. [PERSON] et al. [3] demonstrated the advantages of NOMA in ultra-dense vehicular networks, showing its ability to reduce latency and improve reliability by efficiently managing spectrum resources. Similarly, [PERSON] et al. [19] introduced relay-assisted NOMA frameworks, including half-duplex and full-duplex schemes, to enhance spectral efficiency and reliability under poor channel conditions. [PERSON] et al. [20] proposed a hybrid approach combining centralized resource allocation with distributed power control, optimizing communication in highly dynamic environments. [PERSON] et al. [21] explored energy-efficient NOMA multi-casting systems, focusing on reducing energy consumption while maintaining high throughput under imperfect channel conditions.  
Despite these advances, significant challenges remain, particularly in joint optimization of the NOMA resource chain including association, user clustering, channel assignment and power assignment, computational complexity, and adaptive algorithm design for rapidly changing network conditions. Building on this prior work, our research introduces a novelty that specifically addresses the efficient computation of joint resource optimization in a general configuration with multiple RSUs with mobile users.