Vehicle-to-everything (V2X) communication is the passing of information from a vehicle to any entity that may affect the vehicle, and vice versa. It is a vehicular communication system that incorporates other more specific types of communication as V2I (Vehicle-to-Infrastructure), V2V (Vehicle-to-vehicle), V2P (Vehicle-to-Pedestrian), V2D (Vehicle-to-device) and V2G (Vehicle-to-grid).
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The main push for V2X is safety, with energy savings also being important. However, there are still obstacles preventing the roll-out of this technology, mainly legal issues and the fact that, unless almost the totality of the existing vehicles adopt it, its effectiveness is rather limited. British weekly "The Economist" even argues autonomous driving is more regulatory than technology driven.
V2X communication is based on WLAN technology and works directly between vehicles or the infrastructure, which form a vehicular ad-hoc network, as two V2X senders come within each other’s range. Hence it does not require any infrastructure for vehicles to communicate, which is key to assure safety in remote or little developed areas. It is particularly well-suited for V2X communication, due to its low latency and the ability to communicate instantly. It transmits messages known as Common Awareness Messages (CAM) and Decentralised Notification Messages (DENM) or Basic Safety Message (BSM). The data volume of these messages is very low. The radio technology is standardised as part of the WLAN IEEE 802.11 family of standards and known in the US as WAVE (Wireless Access in Vehicular Environments) and in Europe as ITS-G5.
Use-cases
Through its instant communication V2X allows road safety applications such as (non-exhaustive list):
The US National Highway Traffic Safety Administration’s (NHTSA) report “Vehicle-to-Vehicle Communications: Readiness of V2V Technology for Application“ lists the initial use cases envisioned for the US. European standardisation body ETSI and SAE published standards on what they see as use cases. Early use cases focus on road safety and efficiency.
In the medium term V2X is perceived as a key enabler for autonomous driving, assuming it would be allowed to intervene into the actual driving. In that case vehicles would be able to join platoons, the way HGVs do.
Standardisation history
WLAN-based V2X communication is based on a set of standards drafted by the American Society for Testing and Materials (ASTM). The ASTM E 2213 series of standards looks at wireless communication for high-speed information exchange between vehicles themselves as well as road infrastructure. The first standard of this series was published 2002. Here the acronym Wireless Access in Vehicular Environments (WAVE) was first used for V2X communication.
From 2004 onwards the Institute Electrical and Electronics Engineers (IEEE) started to work on wireless access for vehicles under the umbrella of their standards family IEEE 802.11 for Wireless Local Area Networks (WLAN). Their initial standard for wireless communication for vehicles is known as IEEE 802.11p and is based on the work done by the ASTM. Later on in 2012 IEEE 802.11p was incorporated in IEEE 802.11.
Around 2007 when IEEE 802.11p got stable, IEEE started to develop the 1609.x standards family standardising applications and a security framework (IEEE uses the term WAVE), and soon after SAE started to specify standards for V2V communication applications. SAE uses the term DSRC for this technology (this is how the term was coined in the US). In parallel at ETSI the technical committee for ITS was founded and started to produce standards for protocols and applications (ETSI coined the term ITS-G5). All these standards are based on IEEE 802.11p technology.
Between 2012 and 2013, the Japanese Association of Radio Industries and Businesses (ARIB) specified, also based on IEEE 802.11, a V2V and V2I communication system in the 700 MHz frequency band.
In 2015 ITU published as summary of all V2V and V2I standards that are world wide in use, comprising the systems specified by ETSI, IEEE, ARIB, and TTA (Republic of Korea, Telecommunication Technology Association).
3GPP announced for 2017 a first set of LTE-V physical layer standards for V2I and V2V communication that uses a radio technology different from IEEE 802.11 WLAN.
US
In 1999 the US Federal Communications Commission (FCC) allocated 75 MHz in the spectrum of 5.850-5.925 GHz for intelligent transport systems. Since then the US Department of Transportation (USDOT) has been working with a range of stakeholders on V2X. In 2012 a pre-deployment project was implemented in Ann Arbor, Michigan. 2800 vehicles covering cars, motorcycles, buses and HGV of different brands took part using equipment by different manufacturers. The US National Highway Traffic Safety Administration (NHTSA) saw this model deployment as proof that road safety could be improved and that WAVE standard technology was interoperable. In August 2014 NHTSA published a report arguing vehicle-to-vehicle technology was technically proven as ready for deployment. On 20 August 2014 the NHTSA published an Advance Notice of Proposed Rulemaking (ANPRM) in the Federal Register, arguing that the safety benefits of V2X communication could only be achieved, if a significant part of the vehicles fleet was equipped. Because of the lacking immediate benefit for early adopters the NHTSA proposed a mandatory introduction. On 25 June 2015 the US House of Representatives held a hearing on the matter, where again the NHTSA, as well as other stakeholders argued the case for V2X.
Europe
To acquire EU-wide spectrum, radio applications require a harmonised standard, in case of ITS-G5 ETSI EN 302 571, first published in 2008. A harmonised standard in turn requires an ETSI System Reference Document, here ETSI TR 101 788. Commission Decision 2008/671/EC harmonises the use of the 5 875-5 905 MHz frequency band for transport safety ITS applications. In 2010 the ITS Directive 2010/40/EU was adopted. It aims to assure that ITS applications are interoperable and can operate across national borders, it defines priority areas for secondary legislation, which cover V2X and requires technologies to be mature. In 2014 the European Commission’s industry stakeholder “C-ITS Deployment Platform” started working on a regulatory framework for V2X in the EU. It identified key approaches to an EU-wide V2X security Public Key infrastructure (PKI) and data protection, as well as facilitating a mitigation standard to prevent radio interference between ITS-G5 based V2X and road charging systems. The European Commission recognised ITS-G5 as the initial communication technology in its 5G Action Plan and the accompanying explanatory document, to form a communication environment consisting of ITS-G5 and cellular communication as envisioned by EU Member States. Various pre-deployment projects exist at EU or EU Member State level, such as SCOOP@F, the Testfeld Telematik, the digital testbed Autobahn, the Rotterdam-Vienna ITS Corridor, Nordic Way, COMPASS4D or C-ROADS.