# 5G Physical Layer-Based Procedure to Support Time-Sensitive Networking
## 3 Time-Sensitive-Enabled Small Cell  
### Concept and Architecture  
As described above, providing a wireless TSN network poses some challenges. Implementations that use a dedicated TSN system, separate from the primary wireless network, may increase the complexity and cost of the UEs. To address such challenges, we develop a physical-layer procedure that disciplines the device clock using a timing signal extracted from the 5G NR radio frame sub-slot or Orthogonal Frequency Division Multiplexing (OFDM) symbol to achieve the desired synchronization accuracy. In some specific implementations of the proposed idea, the SC-TT embedded in the Small Cell (SC) is a gPTP instance that guarantees the synchronization and the accuracy of the 5G NR radio frame to maintain enforcement of the synchronization across the 5G industrial network. Figure 2 illustrates a private industrial network that contains multiple small TSC-enabled Small Cells (TSC-SCs): The three SCs communicate with the UPF to access the internet and industry controller; each TSC-SC may provide wireless connectivity to multiple equipment instances; the Network TSN Translator (NW-TT) interfaces the 5G and internet systems; and equipment instances (robots) wirelessly communicate with SCs. The arrows in red highlight the scynrhonization using gPTP, while the arrows in green highlight the synchronization using 5G NR radio frame. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type of UE** & **UE with** & **UE with** & **All Type** \\  & **No PTP** & **PTP** & **of UE** \\ \hline Synchronization method & (c) & (a) and (b) & TESC \\ \hline Accuracy level & \textless{}10 \(\upmu\)s & \textless{}1 \(\upmu\)s & \textless{}0.01 \(\upmu\)s–1 \(\upmu\)s \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The accuracy level provided by the configuration methods of 3 GPP and TEC. Figure 1: Time-Sensitive Communication-enabled Small Cell (TESC) versus 3 GPP integration. Network components have a local clock for local timekeeping. The local clocks may all be synchronized to a reference clock to provide a common understanding of time across the network components, forming a virtual clock domain. For example, a grand master clock may provide a time from an atomic clock, such as an atomic clock affiliated with the GPS or a national timekeeping system. The controller clock is synchronized with the reference clock and provides the Controller with a local time, which may be used in scheduling events or interpreting incoming signals. As shown in Figure 2, SC clocks are synchronized with the reference clock, and UE clocks are synchronized with SC clocks. The synchronization of the UE clocks with an SC clock, and synchronization between the SC clock and the reference clock, provides synchronization between the UE clocks and the reference clock. In this way, each clock in the virtual clock domain has a common reference time. Thus, when the Controller schedules instructions for the robots to coordinate an assembly process, all the robots will be able to execute their respective portions of the assembly process at the prescribed time without interfering with each other. The SC that provides access for UEs to the core network may communicate with other network components through wired connections and communicate with the UEs through wireless connections. For example, in Figure 2, the small cells and industry controller are each wired to the UPF, as indicated by the solid lines; the small cells wirelessly communicate with equipment instances (robots), as indicated by the three-arc wireless symbol; the wired connection may communicate using an Ethernet protocol; and the wireless connections may communicate through 5G or beyond 5G. Thus, network components that communicate through wired connections may be synchronized through a first-timing protocol using gPTP [14], and network components that communicate through wireless connections may be synchronized through a second-timing protocol based on using a 5G NR radio frame as explained in Sections 4 and 5.