# 5G Physical Layer-Based Procedure to Support Time-Sensitive Networking
## 5 Using The 5G Physical Layer Signal for TSC Synchronization
### Performance Evaluation  
Numerical evaluations were conducted to assess the performance of Over-the-Air time Synchronization (OAS) using the method proposed in this paper. For these results, we have used 3 GPP-defined values of UE timing errors, given by [18], ensuring that the UE can afford up to +/ -0.1 ppm relative error, which is 0.2 \(\upmu\)s clock drift per second assuming errors in both sides of the communication. Under this assumption, the network would only need to deliver the GM reference time at most every 5 s to remain within the 1 \(\upmu\)s accuracy requirement. Moreover, the reference time granularity is 10 ns [13], which means that, once the UE gets a message containing the reference time GM, it gets its maximum accuracy that would start degrading at a pace of 0.2 ns per millisecond. In the analysis, the UE could synchronize every slot, via the Slot Indicator Signal, or could synchronize after several slots.  
Figure 9 plots the UE's synchronization accuracy depending on the Slot Indicator Signal period or, in other words, depending on how often the UE performs the synchronization process using the TESC. If the synchronization is made every slot, the accuracy would remain at 10 ns, but if the period of synchronization increases, after 50 ms, the drift would start affecting the accuracy. In the limit, if no resynchronization is made in any slot, the clock drift would reach 1 \(\upmu\)s in 5 s, in which a new reference time would be provided to the UE in the application layer.  
According to the results, when using TSN-enabled Small Cell we can maintain the most accurate clock, at 10 ns, which is required in scenarios such as coordinated maneuvering of autonomous vehicles, industrial automation in high-speed production lines, healthcare telesurgery, and AR gaming.  
Next, the impact of the number of UEs to be synchronized to the GM on the consumption of Resource Blocks (RBs) was evaluated. We considered 5G numerology with SCS 15 kHz and 10 MHz bandwidth configurations, which entailed a maximum number of RBs per slot of 52, yielding 260,000 RBs every 5 s [19]. Assuming that the GM reference time can be encoded in 76 Bytes [15], this is equivalent to 4 RBs using a Quadrature Phase-Shift Keying (QPSK) modulation scheme with \(\upmu\)z code rate.  
Figure 10 illustrates the rate of RB consumption as a function of the number of users in a cell. With the TESC proposal presented in this paper, only 0.0015% of the RBs are allocated to broadcast the GM reference time, transmitted once every 5 s to all UEs in the cell, and this rate remains constant regardless of the number of UEs. Consequently,  
Figure 9: UE’s clock accuracy level depending on the resynchronization period.  
this option proves highly advantageous in scenarios where the number of UEs is high and they require an accuracy level of less than 1 \(\upmu\)s. Conversely, in a conventional 5G system with an accuracy level of 1 \(\upmu\)s, the consumption of RBs increases as more UEs require synchronization. Furthermore, in a 5G system designed for 10 ns accuracy, the RB consumption rate experiences a rapid increase as the number of UEs grows, since the GM reference time has to be sent every 50 ms to every UE.