# Distributed Edge Computing to Assist Ultra-Low-Latency VANET Applications
## 3 System Structure  
In this part the proposed structure for a novel VANET system is introduced. The system comprises two main technologies; SDN technology at the core network and MEC at the RAN. Introducing an SDN paradigm to the VANET became a demand, since it achieves various benefits that include the higher security, latency performance improvement, network congestion reduction and higher routing efficiency. MEC technology provides computing capabilities near to vehicles, which reduces the communication latency and solves the problem of high traffic density. With the introduction of SDN and MEC technologies, traffic from vehicles does not have to pass through the network core; it can be managed and handled at the edge of the access network. Figure 1a provides the general structure of the VANET system. The system deploys distributed stationary roadside units (RSUs) to assist vehicles. The core network provides an interface to the application server that provides additional services for the vehicles. Vehicles interact with each other, i.e., V2V, and with surroundings, e.g., V2X, over the appropriate reliable radio access interface, e.g., dedicated short range communication (DSRC) and cellular V2X (C-V2X) [34]. DSRC are based on the IEEE 802.11 standard group, which have been modified for vehicular communication. The IEEE 802.11p is the most common radio access technology that has been developed for Mobile ad hoc networks (MANETs), including ad hoc networks for vehicles [35]. The physical layer and the MAC layer of the IEEE 802.11P have been derived from the IEEE 802.11a standard. The technical requirements of the IEEE 802.11p standard are targeted to speed up to 200 km/h, response time around 100 ms and a communication range of up to 1 km. IEEE 802.11P provides unacceptable performance for ultra-low latency applications, which makes it proper only for safety applications [34; 36]. Furthermore, for high density vehicular networks, IEEE 802.11P indicates low performance due to packet collision. This makes the C-V2X more desirable for these applications. To overcome these limitations of the IEEE 802.11.P, and to increase the performance of DSRC compared to that of C-V2X, a new radio access protocol, i.e., IEEE 802.11 bd, has been developed. IEEE 802.11 bd offers higher modes of operation at a higher throughput. Figure 1: (**a**) General structure of the traditional vehicular ad-hoc network (VANET). (**b**) The end-to-end system structure of the proposed novel VANET system. One of the main design goals of the IEEE 802.11 bd was to achieve a throughput at least twice that of IEEE 802.11P at a higher mobility, i.e., the targeted speed of up to 500 km/h. Furthermore, another main advantage of 802.11 bd is increasing the communication distance to double of that covered by the IEEE 802.11P. However, IEEE 802.11 bd achieves higher benefits and performance compared to the IEEE 802.11P, the main problem associated with the deployment of the 802.11 bd is the compatibility with existing systems [36]. The proposed system introduces the multilevel MEC structure and an intelligent core network to the general VANET system structure, as illustrated in Figure 1b. The proposed system comprises three types of communications. The first is the communication between vehicles and referred to as the vehicle-to-vehicle (V2V) communication. The second interaction is the data transferred between vehicles and stationary road infrastructure, i.e., RSU, and is referred as vehicle-to-infrastructure (V2I) communication. The third communication may be hold between vehicles and other surrounding devices, which is referred to as vehicle-to-everything (V2X). These communications are done over appropriate communication interfaces, such as the IEEE 802.11 standard group. The proposed VANET structure can be viewed as a four layer system, as presented in Figure 2. The first layer represents the physical hardware layer that includes vehicles powered with On-Board Units (OBUs) able to communicate with the distributed RSUs.