Vehicles and road infrastructure are starting to be equipped with vehicle-to-everything (V2X) communication solutions to increase road safety and provide new services to drivers and passengers. In Europe, the deployment is based on a set of Release 1 standards developed by ETSI to support basic use cases for cooperative intelligent transport systems (C-ITS). For them, the capacity of a single 10 MHz channel in the ITS band at 5.9 GHz is considered sufficient. At the same time, the ITS stakeholders are working towards several advanced use cases, which imply a significant increment of data traffic and the need for multiple channels. To address this issue, ETSI has recently standardized a new multi-channel operation (MCO) concept for flexible, efficient, and future-proof use of multiple channels. This new concept is defined in a set of new specifications that represent the foundation for the future releases of C-ITS standards. The present paper provides a comprehensive review of the new set of specifications, describing the main entities extending the C-ITS architecture at the different layers of the protocol stack, In addition, the paper provides representative examples that describe how these MCO standards will be used in the future and discusses some of the main open issues arising. The review and analysis of this paper facilitate the understanding and motivation of the new set of Release 2 ETSI specifications for MCO and the identification of new research opportunities.

翻译：车辆和道路基础设施正开始配备车联网（V2X）通信解决方案，以提高道路安全性并为驾驶员和乘客提供新服务。在欧洲，其部署基于ETSI制定的一套第1版标准，以支持协作式智能交通系统（C-ITS）的基本用例。对于这些用例而言，5.9 GHz ITS频段中单个10 MHz信道的容量被认为足够。与此同时，ITS利益相关方正致力于多个高级用例，这些用例将导致数据流量显著增加，并需要多信道支持。为解决此问题，ETSI近期标准化了一种新的多信道操作（MCO）概念，以实现灵活、高效且面向未来的多信道使用。该新概念由一系列新规范定义，这些规范构成了C-ITS标准未来版本的基础。本文对这些新规范进行了全面综述，描述了在协议栈各层扩展C-ITS架构的主要实体。此外，本文提供了代表性示例，说明这些MCO标准在未来将如何应用，并讨论了由此产生的一些主要开放性问题。本文的综述与分析有助于理解并推动ETSI第2版MCO新规范的制定动机，同时识别新的研究机遇。