Fine Time Measurement based Time Synchronization for Multi-AP OFDMA Wireless Industrial Environments

Sugandh H. Mohan, Rute C. Sofia, Florian Wiedner, Jonas Andre and Georg Carle

May 2023


Industrial Internet of Things (IIoT) systems require synchronized communication among devices for sensing, computing, and actuation for some specific types of traffic. These systems typically use a wired, deterministic infrastructure that offers tight synchroniza- tion, bounded latency, and low to zero packet loss. To achieve these demands, precise time synchronization across all wired networked devices is guaranteed through the use of the Precision Time Protocol (PTP) at the Local Area Network (LAN) level. Industrial networks are undergoing change with the integration of new wireless standards such as Wi-Fi 6/7. Although PTP can support time synchronization across wireless networks, it is based on a point-to-point UDP protocol. Wi-Fi, on the other hand, has specific time synchronization mechanisms that are more effective in achieving precise and tight synchronization across wireless networks. One such mechanism is the Fine Time Mea- surement (FTM) protocol. Also, with the increase in the number of wireless devices that are incorporated into these networks, it is crucial to account for new features such as multi-AP coordination which demand accurate time synchronization. Aiming at con- tributing to the time synchronization solution across multi-AP IIoT environments, this master thesis proposes a approach based on multi-level hierarchical methodology to time synchronize the devices. It also proposes a method to select a best FTM Responder to distribute time when multiple FTM responders and initiators are functioning in the network. The assessment of the multi-level hierarchical approach’s performance indi- cates that the newly implemented mechanism allows for achieving the desired level of synchronization accuracy by successfully synchronizing all devices within the network and the evaluation of the best FTM responder selection also reveals that the algorithm performs as expected.

subject terms: IIoT, Wi-Fi 6, TSN, wireless