5G Vehicle-to-Everything (V2X) is a new technology developed by 3GPP to support inter-vehicle communication. In contrast to 4G V2X which allows only broadcast communication, 5G V2X enables groupcast and unicast communication. Such types of communication are needed for new V2X scenarios: platooning, extended sensors, remote driving, etc. To improve the data transmission reliability and assist in the selection of the transmission parameters in these scenarios, 5G V2X introduces a feedback channel that allows receivers to send acknowledgments in response to data packets. However, some part of the overall resource shall be allocated for the feedback channel, which reduces the amount of channel resources available for data transmission. In this paper, we consider a scenario with a platoon, which generates groupcast traffic, and surrounding vehicles, which generate legacy broadcast traffic. Using extensive simulations in NS-3, we analyze how the usage of the feedback channel influences the overall system capacity. Our results show that depending on the platoon size, groupcast, and broadcast traffic intensities, and their quality of service requirements, the usage of the feedback channel can in some cases significantly increase the system capacity (up to 2x), while in other cases it almost halves the system capacity. We explain the reasons for such effects and discuss how to adaptively select the feedback channel parameters.

翻译：5G车联网（V2X）是由3GPP开发的支持车辆间通信的新技术。与仅支持广播通信的4G V2X不同，5G V2X支持组播和单播通信。此类通信模式是新型V2X场景（如编队行驶、扩展传感器、远程驾驶等）所必需的。为提高这些场景中数据传输的可靠性并辅助传输参数选择，5G V2X引入了反馈信道，允许接收端针对数据包发送确认信号。然而，反馈信道需占用部分系统资源，从而减少了可用于数据传输的信道资源。本文研究包含生成组播流量的编队车辆与生成传统广播流量的周边车辆共存场景。通过在NS-3中进行大规模仿真，我们分析了反馈信道的使用对系统整体容量的影响。结果表明：根据编队规模、组播与广播流量强度及其服务质量要求，使用反馈信道在某些情况下可显著提升系统容量（最高达2倍），而在其他情况下可能使系统容量降低近半。我们解释了产生这种效应的原因，并讨论了如何自适应选择反馈信道参数。