# Evaluation of Radio Access Protocols for V2X in 6G Scenario-Based Models
## 1 Introduction  
The fifth generation of mobile communications (5G) began the process of installing the mobile infrastructure required to enable and accelerate the full digital transformation, namely, incorporating the concept of the Internet of Things (IoT). In turn, the sixth generation of mobile communications (6G) brings the beginning and strengthening of the so-called Industry 5.0. Furthermore, 6G technology will support the Internet of Verticals (IoV), known as 6G-IoV. This new concept will make it possible to have an adaptable and reconfigurable network infrastructure to meet the demands of the different sectors of industry and society. With 5G, and with the emergence of 6G, new use cases will require the support of higher data rates, improved mobility, higher connectivity, lower latencies, and a higherdensity of connected devices, among other capabilities. In this context, mobile network services supported by 5G have been classified by the International Telecommunication Union (ITU) into three categories: (1) Enhanced Mobile Broadband (eMBB); (2) Ultra-Reliable, Low-Latency Communications (uRLLC); and (3) Massive Machine-Type Communications (mMTC) [1]. Enhanced Mobile Broadband (eMBB) focuses on supporting use cases with high bandwidth requirements, such as high-definition video streaming, virtual reality (VR) and augmented reality (AR), with high coverage. The URLLC service aims to meet the expectations of the highly demanding Industry 4.0 [2] and focuses on latency-sensitive services, such as autonomous driving and remote surgery. Finally, mMTC focuses on addressing services that require connecting many (eventually low-power) devices which enable large-scale IoT deployments, such as interconnecting sensors utilized in smart cities. While 5G communications play an important role in autonomous driving as they support URLLC [3], with 6G, these three use cases will be unified in the so-called Mobile Broadband Service and Reliable Low-Latency Machine-Type Communication (MBBRLLMTC) to offer a high data rate, latency, coverage, spectral energy, cost efficiency, intelligence level, networking, and massive connectivity, and autonomous driving is one of the areas that will benefit [4]. In autonomous driving, transmission latency must be less than 1 ms and requires very low bit error rates (BERs) [5]. With the deployment of 6G, V2V communications will be improved and can be carried out without the need to use base stations [6]. Given the restricted line-of-sight capability of autonomous vehicles, the concept of vehicle-to-everything (V2X) communication was created with the aim of increasing the safety and efficiency of transport through direct communication between vehicles, infrastructure, and other devices. One of the protocols created for this purpose was LTE-V2X [7]. V2X is made up of a set of communication protocols, namely 802.11p, 802.11 bd, LTE-V2X, and 5G New Radio V2X (NR-V2X), which enable vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications, as shown in Figure 1.  
In 2010, the Institute of Electrical and Electronics Engineers (IEEE) proposed the first standard for V2X communications: the 802.11p protocol [8]. This standard is an evolution of the IEEE 802.11a wireless local area network (WLAN) standard and mainly defines the rules for controlling physical access to the medium. In March 2018, the Next-Generation V2X Study Group was formed to create the evolution of the 802.11p protocol, and in January 2019, the IEEE 802.11 bd Task Group was created. This group published a document that defined the technical details of the new standard, namely, the 802.11 bd protocol [9] and updated in [10]. Figure 1: V2X communication. The 3 rd Generation Partnership Project (3 GPP) also defined, in 2016, a protocol for V2X communications in its 3 GPP Release 14. It can be considered that the LTE-V2X specification was completed gradually between Releases 14 [7] and 16 [11], but with continuous improvements in later releases.