I. Introduction
With the rapid advancement of wireless communication techniques, connected smart vehicles are anticipated to be an inseparable part of our daily lives, where mobile nodes communicate through radio-based vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications. The hybrid communication model allows vehicular ad hoc networks (VANETs) to be a key part of the intelligent transportation system (ITS) and offers many attractive applications, such as road safety, traffic management, and infotainment services [1]. Next-generation ITS technologies, including connected vehicles are finishing their last phase toward large-scale worldwide deployment, whereas a large-scale pilot project for connected vehicles is conducted in the city of Doha, Qatar [2]. However, the dynamic topology, high mobility, resource constraints, and recurring interruptions impose considerable challenges for reliable data transmission in vehicular networks. Moreover, in highways with inadequate fixed infrastructures, deployment and maintenance of road side units (RSUs) are costly. Additionally, the conventional terrestrial infrastructure is not enough to guarantee the typical 5G key performance indicators (KPIs) due to its design and intrinsic limitations such as the coverage issue.