# 5G V2X System-Level Architecture of 5 GCAR Project
## 4 Detailed Analysis of Selected Features
### Multi-Operator Solutions for V2X Communications
When using Uu interface, edge cloud schemes used for processing the data need to provide this information to vehicles of the other operator (e.g., in the case of HD maps use case and vehicles that are associated with different edge clouds owned by an operator). This requires Multi-access Edge Computing (MEC) sharing the same schemes with local breakout solutions described above to reduce the time for sharing this information. Additionally, multicast/groupcast requires duplication of the messages in the two (or more) operators' spectrum. The previous analysis shows that enhancements are required for dealing with the proper (in terms of delay and reliability) communication of the vehicles belonging to different operators if we want to avoid complex deployments. Additionally, we should consider the case of the cross-country border crossing, where interruptions are going to occur since the UE should register to the other country's operator. The latter procedure requires a significant amount of time (i.e., at least some seconds; it has to be noted that the registration/attach procedure is in the range of 330 ms [31]), and thus a significant interruption in the service, which is not acceptable according to 3 GPP requirements, where it is mentioned that \"regardless of actual scenarios in place, from passenger experience point of view, automated driving should not be interrupted even when the vehicles cross borders as long as automated driving is permitted by regulation\" [32]. The challenges related to increased delays or limited reliability can be solved if the multi-operator problem may be simplified to a single operator based on agreements among operators for a regional split, as for example depicted in Figure 10. Splitting the overall area into regions where only one operator is responsible simplifies the multi-operator environment and enables efficient V2X communication. PC5 communication is efficiently handled by one operator without requiring complex coordination among multiple operators. Also, the edge cloud solutions do not require any further enhancements since a single operator offers such service. In order to minimize the transition time from one operator to another, when crossing the boundaries of an area, the devices will be registered in advance to all available operators. For example, in the case of a vehicle, while performing a typical attachment to its Home Public Land Mobile Network (HPLMN), the subscriber server of the HPLMN triggers through the core network the attachment (i.e., registration of the same vehicle) in all other available operators. Upon attach  
Figure 10: Split of a highway. a device is considered to be \"connected\" to only one of them while being in an \"idle\" state in the others. To which operator a UE should be connected is dictated by the network; this may be done by direct indication form the operator or via pre-configurations, or the tracking area updates (TAUs). This pre-registration allows to minimize the time needed to steer a device from one operator to another, because it will be RRC connected to the operator who is indicated to serve it and idle for all the other operators in the area under consideration (Figure 11a). It should be noted that the registration to all the operators takes place via interactions among the operators. The selection of through which operator a UE should communicate with the other UEs in the vicinity and the network depends on the geographical location of the device or specific instructions from the network. In the latter case the UE attaches to an operator, who instructs the UE to attach to another UE (Figure 11b). Further enhancements, where the UE may be connected in both operators or connected to the one operator and idle to the other but listening to the downlink signalling channels with higher frequency may further reduce the delays and increase the reliability.