Vehicle-to-Everything (V2X) communication is expected to accomplish a long-standing goal of the Connected and Autonomous Vehicle (CAV) community to bring connected vehicles to roads on a large scale. A major challenge, and perhaps the biggest hurdle on the path towards this goal is the scalability issues associated with it, especially when vehicular safety is concerned. As a major stakeholder, 3rd Generation Partnership Project (3GPP) based Cellular V2X (C-V2X) community has long been trying to research on whether vehicular networks are able to support the safety-critical applications in high-density vehicular scenarios. This paper attempts to answer this by first presenting an overview on the scalability challenges faced by 3GPP Release 14 Long Term Evolution C-V2X (LTE-V2X) using the PC5 sidelink interface for low and heavy-density traffic scenarios. Next, it demonstrates a series of solutions that address network congestion, packet losses and other scalability issues associated with LTE-V2X to enable this communication technology for commercial deployment. In addition, a brief survey is provided into 3GPP Release 16 5G New Radio V2X (NR-V2X) that utilizes the NR sidelink interface and works as an evolution of C-V2X towards better performance for V2X communications including new enhanced V2X (eV2X) scenarios that possess ultra-low-latency and high-reliability requirements.

翻译：车辆与万物（V2X）通信有望实现网联与自动驾驶车辆（CAV）领域长期以来的目标，即大规模将网联车辆引入道路。而实现这一目标的主要挑战，或许也是最大的障碍，在于与之相关的可扩展性问题，尤其是在涉及车辆安全时。作为关键利益相关方，基于第三代合作伙伴计划（3GPP）的蜂窝V2X（C-V2X）领域长期致力于研究车辆网络能否支持高密度车辆场景下的安全关键型应用。本文尝试回答该问题，首先概述3GPP Release 14长期演进C-V2X（LTE-V2X）在低密度与高密度交通场景中使用PC5直连链路接口面临的可扩展性挑战；其次，展示一系列解决LTE-V2X网络拥塞、数据包丢失及其他可扩展性问题的方案，以推动该通信技术的商业化部署；此外，简要综述了3GPP Release 16第五代新空口V2X（NR-V2X）——该技术利用NR直连链路接口，作为C-V2X的演进方向，旨在提升V2X通信性能，包括针对具有超低时延与高可靠性需求的新型增强型V2X（eV2X）场景。