Over-the-Air Time Synchronization for URLLC: Requirements, Challenges and Possible Enablers

TL;DR

This paper reviews the requirements and challenges of achieving ultra-precise over-the-air time synchronization in 5G URLLC systems, focusing on factory automation and smart grids, and discusses potential mechanisms and enhancements needed.

Contribution

It identifies specific synchronization requirements and challenges in URLLC, and explores potential over-the-air synchronization methods and necessary enhancements for 5G systems.

Findings

High-precision synchronization is crucial for URLLC applications.

Over-the-air synchronization mechanisms can meet strict jitter requirements.

Enhancements to 5G radio interface are needed for device-level timing accuracy.

Abstract

Ultra-reliable and low-latency communications (URLLC) is an emerging feature in 5G and beyond wireless systems, which is introduced to support stringent latency and reliability requirements of mission-critical industrial applications. In many potential applications, multiple sensors/actuators collaborate and require isochronous operation with strict and bounded jitter, e.g., \SI{1}{\micro\second}. To this end, network time synchronization becomes crucial for real-time and isochronous communication between a controller and the sensors/actuators. In this paper, we look at different applications in factory automation and smart grids to reveal the requirements of device-level time synchronization and the challenges in extending the high-granularity timing information to the devices. Also, we identify the potential over-the-air synchronization mechanisms in 5G radio interface, and discuss the needed enhancements to meet the jitter constraints of time-sensitive URLLC applications.