# Enhancing Route Guidance with Integrated V2X Communication and Transportation Systems: A Review
## 4 V2X Communication Architecture
### V2X Communications Protocols
#### 4.1.3 PC5 and LTE-Uu Interface-Enabled V2X  
In 2015, the 3 rd Generation Partnership Project (3 GPP) launched the V2X research item to investigate the service elements of LTE-based V2X communication, LTE-V2X or Cellular-V2X (C-V2X) technology based on Long-Term Evolution (LTE)/4 th Generation (4G) or 5 th Generation (5G) mobile network. It has described LTE advanced V2X services, architectures, radio access regulations, and four use case scenarios (V2V, V2I, V2N, and V2P). LTE-V2X has a high data rate and better QoS [82]. Some significant LTE-V2X components are user equipment, V2X server, V2X control function, and multimedia broadcast multicast service. It enables vehicles to share information with nearby vehicles and RSUs directly. Every vehicle communicates with a V2X server through unicast communication. Furthermore, V2I enables the delivery of data from and to any vehicle [93]. It includes two caller communication modes: the LTE-Uu interface, which is used for communication with the cellular station, and the PC5 interface, which is used for direct communication between nodes. PC5 communication has been developed rapidly to enable sharing of dynamic information such as position, speed, driving direction, etc. [95]. The ability of the current cellular network infrastructure to transmit data using C-V2X communication technology within an acceptable latency is questionable. Therefore, there is a significant need for integrated DSRC and C-V2X architectural solutions that provide reliable and efficient V2X connections. The fact that C-V2X uses existing network infrastructure has numerous benefits, but there are also drawbacks that need to be considered. For example, transmission delays for Uu interface sidelines rise with the number of interacting nodes. More detailed characteristics of LTE C-V2X can be found in [88; 96].  
C-V2X, which encompasses both PC5 (Direct Short-Range Communications) and LTE-Uu (Cellular Vehicle-to-Everything) interfaces, offers promising capabilities to enhance and enable a robust route guidance system. The combination of these technologies provides an extensive communication framework for vehicles to exchange data with other vehicles, infrastructure, and pedestrians, contributing to more efficient and effective route guidance. PC5 technology enables direct and low-latency communication between nearby vehicles. This allows for exchanging critical safety-related information, such as collision warnings and traffic conditions, cultivating real-time situational awareness [90]. By leveraging PC5, the route guidance system can receive and transmit crucial information promptly, assisting drivers in making informed decisions and taking appropriate actions. On the other hand, the LTE-Uu interface utilizes existing cellular networks to establish communication links between vehicles and infrastructure. This enables access to a broader range of information, including traffic data, weather updates, and points of interest. Leveraging LTE-Uu, the RGscan tap into comprehensive data sources, providing drivers with up-to-date and accurate information for route planning and guidance. By integrating PC5 and LTE-Uu technologies, the RGS can harness the benefits of direct vehicle-to-vehicle communication and access to a vast networked environment. This combination enables the system to deliver enhanced route guidance, considering local information from nearby vehicles and broader contextual data from infrastructure and other connected sources. Ultimately, the integration of C-V2X technologies enhances the capabilities of the route guidance system, empowering drivers with more comprehensive and reliable information for creating sufficient and efficient routes.