Autonomous vehicles and Intelligent Transport Systems (ITS) have started to become a reality in recent years. However, shortcomings of these early intelligent vehicles demonstrate a need to increase an intelligent vehicle’s perceptual bubble beyond the vehicle’s onboard sensors. Vehicle-to-Everything (V2X) communications is a technology intended to enable intelligent vehicles to increase their perceptive range via communication with the outside world i.e. other vehicles, road users, and infrastructure. One of the critical layers of V2X communications is that of the underlying wireless access. There remains an open debate on which technology (or technologies) will ultimately be adopted as the de facto wireless access technology for V2X communications. Presently, a myriad of unconnected threads of work are being undertaken to this end, resulting in an unclear picture of the current state of wireless access for V2X communications. In this tutorial review, we collate current research on wireless access for V2X communications to showcase recent developments and the challenges facing candidate technologies. To allow the reader to engage with the debate, we present an overview of the field of V2X communications, its history, and standardisation. Following this, we provide an overview of the key candidate wireless access technologies that may enable V2X communications. Through this work, we aim to provide a comprehensive first step into the discipline of wireless access for V2X communications.

Vehicle-to-Everything (V2X) communication technology aims to enhance intelligent vehicles’ coordination and perception by enabling interactions with other vehicles, road users, and infrastructure. Although 4th and 5th generation cellular technologies (4G LTE and 5G NR) can support non-safety V2X communication, their design, rooted in multimedia and telephony, doesn’t align well with safety-critical applications. Despite the advancements of 5G NR over 4G LTE, ensuring reliable Quality-of-Service (QoS) metrics remains a notable concern. The process of handover, a core cellular network function, significantly contributes to the challenges in cellular communication reliability. To assess handover’s impact on latency in V2X communication scenarios, a driving-focused measurement campaign was executed on an early 5G NR-enabled commercial cellular network. Findings reveal that, in terms of its effect on end-user latency, the more mature 4G LTE network displays on average 63% (intra-freq.) and 36% (inter-freq.) lower latency costs when performing handovers compared to early 5G NR deployments. Notably, inter-generation handovers (4G to 5G and vice versa) exhibit 24% (intra-freq.) and 10% (inter-freq.) higher average latency costs with respect to other handover types. Furthermore, discernible variations in network reliability emerge between distinct V2X scenarios such as urban and rural environments. The prevailing reliability concerns tied to present handover algorithms hold substantial weight, as they undermine intelligent vehicles’ trust in network-received information. Consequently, these outcomes underscore the urgency for designing and implementing handover strategies better suited to the dynamic mobility characteristics of intelligent vehicles across diverse V2X scenarios.

Advancements in intelligent vehicles and Intelligent Transport Systems (ITS) have shown that they are now feasible in both technology and commerce. However, there are still significant challenges to overcome, particularly regarding the perception and coordination of intelligent vehicles in unfavourable conditions. Vehicle-to-Everything (V2X) communications is a technology that aims to enable intelligent vehicles to communicate with other road users and infrastructure to increase their range of perception and coordination capabilities. While the 4th generation of cellular technology (4G LTE) is capable of supporting V2X communications to some extent, its multimedia and telephony-centric design does not translate well to safety-critical applications. As a result, the 5th generation of cellular technology (5G NR) is being developed to improve V2X communications. To investigate the effectiveness of 5G NR in V2X communications, a driving-based measurement campaign of a commercial cellular network with early 5G NR deployments was conducted. Results showed that the existing 4G LTE network is limited in its capability, and early 5G NR deployments can in fact outperform it. However, neither 4G LTE nor 5G NR can reliably support advanced V2X applications. Early 5G NR deployments suffer from significant reliability issues compared to existing 4G LTE deployments. These reliability issues are of particular concern, as they impact the vehicle’s ability to trust the information it receives. These findings highlight the need for further design and implementation of intelligent vehicles and future 5G NR networks to address these reliability concerns and ensure the safe and efficient operation of intelligent vehicles in all conditions.

Cellular Vehicle-to-Everything (C-V2X) communications is a technology that enables intelligent vehicles to exchange information and thus coordinate with other vehicles, road users, and infrastructure. However, despite advancements in cellular technology for V2X applications, significant challenges remain regarding the ability of the system to meet stringent Quality-of-Service (QoS) requirements when deployed at scale. Thus, smaller-scale V2X use case deployments may embody a necessary stepping stone to address these challenges. This work assesses network architectures for an Intelligent Perception System (IPS) blind road junction or blind corner scenarios. Measurements were collected using a private 5G NR network with Sub-6GHz and mmWave connectivity, evaluating the feasibility and trade-offs of IPS network configurations. The results demonstrate the feasibility of the IPS as a V2X application, with implementation considerations based on deployment and maintenance costs. If computation resources are co-located with the sensors, sufficient performance is achieved. However, if the computational burden is instead placed upon the intelligent vehicle, it is questionable as to whether an IPS is achievable or not. Much depends on image quality, latency, and system performance requirements.