With the 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 (DSRCs) 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 the 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-the IEEE 802.11bd for the DSRC and NR V2X for C-V2X-can supplement today's vehicular sensors in enabling autonomous driving. In this paper, we survey the latest developments in the standardization of 802.11bd and NR V2X. We begin with a brief description of the two present-day vehicular RATs. In doing so, we highlight their inability to guarantee the quality of service requirements of many advanced vehicular applications. We then look at the two RAT evolutions, i.e., the IEEE 802.11bd and NR V2X, outline their objectives, describe their salient features, and provide an in-depth description of key mechanisms that enable these features. While both, the 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.
IEEE, published 27 May 2019