IEEE 802.11bd & 5G NR V2X: Evolution of Radio Access Technologies for V2X Communications

Abstract

With rising interest in autonomous vehicles, developing radio access technologies (RATs) that enable reliable and low latency vehicular communications has become of paramount importance. Dedicated Short Range Communications (DSRC) and Cellular V2X (C-V2X) are two present-day technologies that are capable of supporting day-1 vehicular applications. However, these RATs fall short of supporting communication requirements of many advanced vehicular applications, which are believed to be critical in enabling fully autonomous vehicles. Both DSRC and C-V2X are undergoing extensive enhancements in order to support advanced vehicular applications that are characterized by high reliability, low latency and high throughput requirements. These RAT evolutions-IEEE 802.11bd for DSRC and NR V2X for C-V2X-can supplement today's vehicular sensors in enabling autonomous driving. In this paper, we briefly describe the two present-day vehicular RATs. In doing so, we highlight their inability to guarantee quality of service requirements of many advanced vehicular applications. We then look at the two RAT evolutions, i.e., IEEE 802.11bd and NR V2X and outline their objectives, describe their salient features and provide an in-depth description of key mechanisms that enable these features. While both, IEEE 802.11bd and NR V2X, are in their initial stages of development, we shed light on their preliminary performance projections and compare and contrast the two evolutionary RATs with their respective predecessors.

Congestion Control Mechanisms in IEEE 802.11p and Sidelink C-V2X

“…IEEE 802.11p has been tested in very large implementations and is currently considered a mature technology. However, in order to update it with the latest solutions, a new working group has been settled in 2018 to define the new IEEE 802.11bd [2]. The main objective is to add advanced coding schemes and other innovations (mainly at PHY layer) to improve the reliability, especially at high speed and with long packets.…”

“…The cellular ecosystem considers LTE-V2X as the baseline for short-range V2X communications and the upcoming NR-V2X will be mostly based on similar principles, with the addition of flexible numerology and enhancements for non-periodic traffic. NR-V2X is anyway imagined as a separate technology for advanced use cases and retro-compatibility is not addressed [2].…”

“…In this scenario, two wireless technologies have been developed for vehicle-to-everything (V2X) communications, often referred to as IEEE 802.11p and sidelink cellular vehicle-to-anything (C-V2X) [1]. The former, relatively old and well consolidated, is an adaptation of the classical Wi-Fi, with enhancements currently under definition as IEEE 802.11bd [2]. The latter, at an earlier stage regarding large scale testing, but pushed by a strong ecosystem, was firstly defined in the long term evolution (LTE) framework as LTE-V2X and will be also part of 5G as new radio (NR)-V2X (NR-V2X) [2].…”

“…The former, relatively old and well consolidated, is an adaptation of the classical Wi-Fi, with enhancements currently under definition as IEEE 802.11bd [2]. The latter, at an earlier stage regarding large scale testing, but pushed by a strong ecosystem, was firstly defined in the long term evolution (LTE) framework as LTE-V2X and will be also part of 5G as new radio (NR)-V2X (NR-V2X) [2]. Given the tremendous market potential and the fact that the same technology seems required on board of all vehicles (at least on a regional basis) to make them inter-operate, a hard discussion is ongoing, which involves all the interested stakeholders, including national governments and international bodies.…”

“…We will refer to such messages as beacons in the further to be agnostic to the standards. 2 By its nature, such traffic is proportional to the number of vehicles on the road and tends to saturate the available channel resources when the traffic density increases. A saturation of the channel implies an increase of packet losses and thus a thread for the safety of drivers and passengers.…”