# 5G Physical Layer-Based Procedure to Support Time-Sensitive Networking
## 2 Literature Review
### Contribution to the State of the Art  
While all the proposed solutions thoroughly investigate synchronization, focusing on accommodating TSN-capable IoT devices, addressing a critical aspect of the IoT landscape is essential. What about the existing IoT devices that are already deployed and lack TSN support? This is a pertinent question as many real-world industrial environments consist of a mix of legacy and modern IoT devices. Balancing synchronization strategies to cater to TSN-capable and non-TSN IoT devices becomes imperative for achieving comprehensive and practical synchronization solutions.  
This paper presents a method and architectural framework designed to enable TSN functionality over a wireless channel within a 5G network. The approach involves incorporating TSN synchronization capabilities into a Small Cell gNB, effectively implementing what is known as the Small Cell TSN Translator function (SC-TT). This TSN-capable Small Cell provides TSN functionality over the wireless network, facilitating the synchronization of UEs with the Grand Master (GM). This synchronization is achieved by utilizing the 5G radio frame's physical layer signal as a flank for the clock adjustment while the absolute time reference is given by the transmission of the GM reference time over the air, as specified by Release 18. In such a scenario, the Small Cell can synchronize its clock with the TSN domain by acting as a gTPP slave device; it receives gTPP synchronization messages from the gTPP GM clock in the TSN network and adjusts its local clock accordingly. The synchronization messages contain timing information, such as the current time and synchronization correction values, which the Small Cell uses to align its clock with the TSN domain. Once the Small Cell is synchronized, it uses the physical layer signal of the 5G radio frame to provide high-precision synchronization to the UE. This integration is exemplified in Figure 1, where the TESC includes the Small Cell TSN Translator (SC-TT) responsible for translating TSN messages into 5G signaling. This integration simplifies TSN synchronization for Small Cell manufacturers and facilitates the expansion of their market into automated factories. Additionally, it minimally impacts 5G IoT UE, making highly accurate TSN-capable IoT devices feasible, utilizing low-cost local oscillators, and extracting time and synchronization information from the 5G Radio Frame through slot indication and symbol boundary signals.  
Drawing from the analysis of the current state of the art, the precision of Over-The-Air synchronization (OAS) is contingent upon the type of device. For UE equipped with PTP support, the precision level is achieved at less than 1 \(\upmu\)s. Conversely, low-cost and low-energy UEs lacking PTP support can ensure an accuracy level of less than 10 \(\upmu\)s [10, 11, 12, 13]. Employing TEC ensures an accuracy level within the range of 0.01 \(\upmu\)s to 1 \(\upmu\)s, even for economical and energy-efficient UEs lacking PTP support. Table 1 provides a summary of this comparison. Sections 4 and 5 explain how this accuracy is calculated.