Time Synchronization in V2X Communications

The proliferation of Vehicle-to-Everything (V2X) networks and services is growing, driven by the increase of V2X communications on roadways. These services include navigation, entertainment, emergency assistance, and support for autonomous driving. Precise time accuracy forms the foundation of the data generation in services like Intelligent Transport Systems (ITS). For this basis to be achieved, accurate time sources, and time synchronization must be achieved throughout the entire network. The high mobility of the networks results in high packet loss, asymmetrical latency, and jitter, that can influence traditional network protocols like Network Time Protocol (NTP). This paper proposes a set of practical time synchronization approaches in V2X scenarios, exploring the use of NTP, Precision Time Protocol (PTP), and Global Navigation Satellite System (GNSS) to synchronize the various network nodes to a given reference clock. Additionally, we also take into consideration the impact of synchronization tools, and technologies like Pulse-per-second (PPS) in GNSS. These approaches were tested in a city-scale platform, the Aveiro Tech City Living Lab (ATCLL), in static and mobility scenarios. The obtained results show that it is possible to achieve sub-microsecond accuracy at all times in a vehicular network, even with high mobility and no network connection.