Real-time status update in future vehicular networks is vital to enable control-level cooperative autonomous driving. Cellular Vehicle-to-Everything (C-V2X), as one of the most promising vehicular wireless technologies, adopts a Semi-Persistent Scheduling (SPS) based Medium-Access-Control (MAC) layer protocol for its sidelink communications. Despite the recent and ongoing efforts to optimize SPS, very few work has considered the status update performance of SPS. In this paper, Age of Information (AoI) is first leveraged to evaluate the MAC layer performance of C-V2X sidelink. Critical issues of SPS, i.e., persistent packet collisions and Half-Duplex (HD) effects, are identified to hinder its AoI performance. Therefore, a piggyback-based collaboration method is proposed accordingly, whereby vehicles collaborate to inform each other of potential collisions and collectively afford HD errors, while entailing only a small signaling overhead. Closed-form AoI performance is derived for the proposed scheme, optimal configurations for key parameters are hence calculated, and the convergence property is proved for decentralized implementation. Simulation results show that compared with the standardized SPS and its state-of-the-art enhancement schemes, the proposed scheme shows significantly better performance, not only in terms of AoI, but also of conventional metrics such as transmission reliability.

中文翻译：

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信息时代通过基于 Piggyback 的协作优化 V2X Sidelink 中的 MAC


未来车辆网络的实时状态更新对于实现控制级协同自动驾驶至关重要。蜂窝车联网（C-V2X）作为最有前途的车载无线技术之一，采用基于半持久调度（SPS）的媒体访问控制（MAC）层协议进行侧链路通信。尽管最近一直在努力优化 SPS，但很少有工作考虑 SPS 的状态更新性能。在本文中，首先利用信息时代（AoI）来评估 C-V2X 侧链路的 MAC 层性能。 SPS 的关键问题，即持续数据包冲突和半双工 (HD) 效应，被认为会阻碍其 AoI 性能。因此，相应地提出了一种基于搭载的协作方法，车辆协作以相互通知潜在的碰撞并共同承担 HD 错误，同时只需要很小的信令开销。针对所提出的方案导出了封闭式 AoI 性能，从而计算了关键参数的最佳配置，并证明了分散式实施的收敛性。仿真结果表明，与标准化的SPS及其最先进的增强方案相比，所提出的方案不仅在AoI方面，而且在传输可靠性等传统指标方面都表现出明显更好的性能。