Cellular Vehicle-to-Everything (C-V2X) is a frontier in the evolution of distributed communication introduced in 3GPP release 14 to advanced use cases. While research efforts continue to optimize the accessible bandwidth for transportation ecosystem, a bottom up analysis from the application layer perspective is necessary prior to deployment, as it can expose potential issues that can emerge in a dynamic road environment. This emphasizes on assessing the network using application-oriented metrics to evaluate its capacity of providing advanced vehicular services with stringent latency and throughput requirements. C-V2X enables advanced applications like autonomous driving and on-the-go transaction services where consecutive exchange of messages is required. For such services, the network level metrics fails to capture the edge case service quality as they express an average measure of performance. In this paper, we present an application-oriented analysis of a transaction service built on C-V2X protocol. We analyze different design choices that affects quality of service both from network-oriented and user-centric metrics and we highlight the issues regarding packet dissemination from infrastructures for vehicle-to-infrastructure (V2I) based service applications. We also present our study on the impact of batching in disseminating acknowledgement packets (ACK) and its consequence on both the service reliability and network congestion. Our results show that time-sensitive and mission-sensitive vehicular applications should aim for a balance between achieving the mission utility in shortest duration possible, while keeping minimal impact on the system-wide stability.

翻译：蜂窝车联网（C-V2X）是3GPP第14版为高级应用场景引入的分布式通信演进前沿技术。尽管研究界持续优化交通生态系统的可用带宽，但在部署前仍需从应用层视角进行自底向上的分析，以揭示动态道路环境中可能出现的潜在问题。本文强调使用面向应用的度量标准评估网络，检验其满足具有严格时延和吞吐量要求的高级车载服务的能力。C-V2X支持自动驾驶和移动交易服务等需要连续消息交换的高级应用。对于此类服务，网络级度量因仅表达平均性能指标而无法捕捉边缘服务质量的差异。本文对基于C-V2X协议的交易服务展开面向应用的分析，从网络导向指标和用户中心指标两个维度考察影响服务质量的不同设计选择，重点剖析基于车对基础设施（V2I）服务应用中基础设施侧数据包分发存在的问题。我们还研究了确认数据包（ACK）批处理机制对服务可靠性和网络拥塞的影响。结果表明，时间敏感型与任务敏感型车载应用应在最短时间内达成任务效用的同时，保持对系统稳定性的最小影响，从而寻求最佳平衡点。