# 5G Beyond 3 GPP Release 15 for Connected Automated Mobility in Cross-Border Contexts
## 4 Cross-Border Use Case Implementations
### Vehicle Platooning  
The vehicle platooning use case has some similarities with advance driving, but here participants are not just exchanging information to facilitate a safe manoeuvring, as shown in Figure 5. Instead, some participants with a common path enrol in a platoon and receive instructions from the leading vehicle. This use case brings a big challenge in the cross-border domain, as it involves a higher number of actors which will move across different borders and networks. Here, the synchronised acknowledgement among the platoon vehicles and the leader is mandatory, where the gPTP protocol is key to providing reliable time synchronisation as declared in 3 GPP TS 23.501 [28], granting a common time base for all participants. This becomes more complex as the membership dynamics need to be managed by the platoon, for example, when a vehicle joins or leaves the platoon, requiring the re-arrangement of the vehicles. In order to ease the communication between the platoon vehicles and to keep the connection alive, the sidelink communications, such as PCS C-V2X and 5G NR  
Figure 4: Advanced driving scenario of the proposed solution.  
sidelink [22], play a significant role. Furthermore, the multicast communications minimise the potential inconsistencies for a common awareness distribution when sharing information along the platoon. Here, FeMBMS technology and the advances to include feedback in the next releases [24] will facilitate information sharing and actuation coordination. The multicast communications would also simplify the platooning protocol, reducing overheads. Last, the mid/long distance covered makes this use case more prone to failures, that is, communications interruptions when performing cell handover or cross-border roaming, requiring low-latency and reliable performance.  
From the latency perspective, advanced roaming techniques [11] and sidelink communications [22] make again the difference. Furthermore, broadcast and multicast [24] help to simplify coordination messaging by removing acknowledgement and clock messaging for common shared information while granting distributed awareness at once. Ensuring consistent timing and synchronous distribution of messages [28] for broadcasting gets intricate in cross-borders where different systems operate by different operators with shifted time zones get place.  
Additionally, the same benefits from extra features apply. Accurate positioning of 5G NR [19] complements onboard sensor-based measures; edge computing [11] provides a higher level vision of the driving situation, gathering data from all the members in place and the QoS management of the traffic from a platoon when managing co-located services. The network slicing techniques [29] provisioning virtual/logical network assets devoted to specific traffic and isolating the performance from concurrent traffic flows could reinforce the use case results, adding data accuracy while enabling cost-performance trade-offs.  
This use case embraces RSUs, V2V and broadcast/multi-cast communications as proposed in [40]. Furthermore, part of the processing load and the clustering of information to the platoon's region of interest can be managed by the edge computing infrastructures to gain scalability.