Multi-RAT Diversity in Intelligent Vehicular Networks: A Review of Design and Implementation Issues

In the context of the Intelligent Transportation System (ITS), the exchange of information among vehicles and other entities is made possible through Vehicle-to-Everything (V2X) communications. This includes interactions with roadside infrastructure units, cycles, and pedestrians, in addition to other vehicles, thus enabling a broad array of advanced applications, including safety and non-safety infotainment applications. To support V2X, two primary Radio Access Technologies (RATs) are utilized: Dedicated Short Range Communications (DSRC) and Cellular Networks (C-V2X). However, with the anticipated increase in the number of vehicles on the roads and the emergence of more advanced applications, it is unlikely that a single technology will satisfy the Quality-of-Service (QoS) requirements for the increased number of vehicles in the near future. Hence, exploring multi-RAT diversity for effective V2X communications is proposed. This paper encapsulates a detailed overview of V2X RATs based on their state-of-the-art, evolutions, and limitations to determine the design and implementation issues in multi-RAT scenarios. Generally, this review study intends to provide a solid platform that will reduce time and effort for the research community working on V2X multi-RAT and heterogeneous contexts. Additionally, it addresses new open issues for potential future research directions and identifies trends and future technologies that will lead to more efficient V2X multi-RAT deployment.