# 5G V2X System-Level Architecture of 5 GCAR Project
## 3 Overall 5 GCAR Architecture Design
### Network Procedures  
Service delivery in mobile networks involves several procedures, such as network-application negotiation, connectivity establishment, mobility and user plane management, etc. [7]. Such procedures directly impact the service delivery, for instance in terms of introduced latency, while other impacts might be associated with required improvements to better handle V2X services. From this point of view, 5 GCAR introduced several features in terms of network procedures, introducing the following enhancements: (i) improved management of roaming scenarios; (ii) improved awareness of service requirements and additional related information for the network when delivering a certain vehicular use case; (iii) optimization of control and user plane paths; (iv) optimization of scheduling capabilities considering vehicle mobility; (v) providing resource configuration stability for local services; and (vi) network-driven setup of unicast sidelink. The technical components associated with enhancements (i-iv) listed above will be discussed in more detail in Section 4. In particular, the enhancements introduced by 5 GCAR on the interaction between network and applications will be given in Section 4.1, while additional improvements achievable by using enhanced application and service information are provided in Sections 4.2 and 4.3. More details on enhanced procedure allowing the ability to shorten the UP path for localized V2X communications are given in Section 4.4. Finally, more details on the enhancements for multi-operator scenarios will be provided in Section 4.5. The remainder of this Section will provide more information on enhancements (v) and (vi). One enhancement introduced by 5 GCAR is related to the concept of SM-Zones as a solution to provide resource stability for local services that are provided by using roadside units (RSUs), either in the form of UE- or eNB-type RSUs. In this context, 5 GCAR considers RSUs as logical architectural nodes delivering local services. The RSUs, as considered in 5 GCAR, can be grouped to form smart radio access service areas, referred to as Smart Zones (SM-Zones). SM-Zones might be configured to be local to targeted individual roads (covering just road areas). In this case, radio transmissions, as well as the end-to-end service flows of V2X communications between UEs on roads, may be kept local to individual roads, which is rather desirable for the efficient utilisation of spectrum and network resources while meeting QoS requirements of advanced V2X services. This comes with the deployment cost of RSUs along targeted individual roads, to be mounted on roadside lamps for instance. While the exploitation of RSU may bring benefits in terms of increasing overall capacity of supported V2X traffic acting as \"local hot spots\" for local services, an aspect that might cause performance variation is related to different resource configurations associated with different RSUs. From this point of view, a vehicle may experience performance variation/degradation when moving from one RSU to another. The goal of resource stability among the RSUs within an SM-Zone is achieved by the enhancement that, when entering a certain SM-Zone, a UE is provided with a communication configuration which is kept within the whole SM-Zone even if the zone is composed of several RSUs. This allows the UE to achieve stable communication within the whole SM-Zone. Given the local nature of SM-Zones, ad-hoc configurations tailored for specific SM-Zones can be considered to optimize performance and network resource utilization considering the local connectivity requirements and scenarios (expected vehicle density, road traffic pattern, service characteristics, etc.). The work done in 5 GCAR with respect to SM-Zone optimization can be further extended considering approaches similar to those in [16], where aspects such as user pause probability, user arrival, and departure probabilities are derived and used for evaluating the user mobility performance in a hotspot-type 5G small cell network.