Practical IEEE 802.1AS-Based TSN Time Synchronization over Wi-Fi for Bare-Metal Devices

Recent advances in wireless technologies providing flexibility, mobility, low wiring costs and high reliability have generated significant interest in extending Time-Sensitive Networking (TSN) capabilities over wireless networks. As an example, the integration of OPC Unified Architecture (OPC UA) - a successor of Open Platform Communication (OPC) over Wi-Fi TSN networks has gained significant importance in industrial automation and the Internet of Things (IoT) since it enables reliable and deterministic communication in wireless networks. This is essential in high-interference and low-latency environments. However, given the stochastic nature of wireless communication channels, enabling TSN capabilities — originally designed for Ethernet networks —comes with certain challenges, with time synchronization being one of them. This is especially true for low-cost embedded commercial off-the-shelf (COTS) devices that often lack dedicated hardware support. We present a prototype implementation that is mostly compliant to standard time synchronization over Wi-Fi, on a low-cost embedded platform and without additional components. We use a bare-metal generalized Precision Time Protocol (gPTP) implementation that we adopted to support Wi-Fi links in addition to traditional Ethernet networks to enable heterogeneity. We highlight the challenges, especially with respect to the HW / SW requirements and show the current status and performance of our developments which show that we can achieve a synchronization accuracy in the range of below $10, \mu \mathrm{~s}$, with low power consumption and using standard devices.