Cellular vehicular-to-everything (C-V2X) systems offer the potential for improving road safety, in part through the exchange of periodic basic safety messages (BSMs) between nearby vehicles. The reliability and latency of these messages is a key metric. Hybrid automatic repeat request (HARQ) retransmissions are one technique used to this end. However, HARQ may come at the expense of consuming the limited available wireless resources, especially in highly congested scenarios. This paper studies BSM transmission latency and reliability when HARQ retransmissions are used with the semi-persistent scheduling (SPS) in C-V2X transmission mode 4. We do so through extensive system-level simulations that closely follow the SPS process. Furthermore, we provide an analytical model for the tail behavior of the BSM latency distribution with HARQ retransmissions that is a good approximation to the simulation results. Our study reveals the impact of several deployment settings (e.g., bandwidth configurations and vehicle density).

翻译：蜂窝车联网（C-V2X）系统通过邻近车辆间周期性交换基础安全消息（BSM），为提升道路安全提供了潜力。这些消息的可靠性与时延是关键指标。混合自动重传请求（HARQ）重传是实现该目标的技术之一。然而，HARQ可能以消耗有限的无线资源为代价，尤其是在高度拥堵的场景中。本文研究了在C-V2X传输模式4中采用半持续调度（SPS）时，HARQ重传对BSM传输时延及可靠性的影响。我们通过紧密遵循SPS流程的大规模系统级仿真开展分析，并进一步构建了一个分析模型，用于描述HARQ重传下BSM时延分布的尾部行为，该模型与仿真结果吻合良好。我们的研究揭示了多种部署参数（如带宽配置与车辆密度）的影响。