V2X communications — the ability of a vehicle to communicate with another, or with ambient infrastructure – could vastly enhance transportation safety if deployed on a mass scale. But it remains an unfulfilled dream because there isn’t a universal agreement on communications protocols.
There are two leading contenders for such a communications standard: Dedicated Short Range Communications (DSRC) and Cellular Vehicle-to-Everything (C-V2X) technology that leverages the commercial cellular network and field equipment managed by Mobile Network Operators (MNOs)
The 5G Automotive Association (5GAA), whose founding members include Ericsson, Intel, Huawei, Nokia, Qualcomm, Audi, BMW Group and Daimler AG, is lobbying for C-V2X, claiming superior capabilities over DSRC, on more than one front.
DSRC is championed by the US NHSTA which estimates that safety applications enabled by V2X could eliminate or mitigate the severity of up to 80 percent of non-impaired crashes, including crashes at intersections or while changing lanes.
DSRC is based on the IEEE 802.11p standard, which defines enhancements to IEEE’s 802.11 standards (the basis of Wi-Fi) to support wireless access in vehicles. In Europe, 802.11p serves as a basis for the ITS-G5 standard, supporting the GeoNetworking protocol for V2X communications.
According to its adherents, IEEE 802.11p was designed with every V2X application in mind and with the most stringent performance specifications. IEEE 802.11p operates in the 5.9 GHz band that was set aside for V2X in 1999 by the U.S. Federal Communications Commission (FCC). The standard, approved in 2009, has been extensively field-tested in several prototypes under the supervision of the Department of Transportation.
Obviously, for V2X to be effective, it has to be universally installed – on cars and on infrastructure.
Recognizing this reality, the NHSTA issued a Notice of Proposed Rulemaking in December 2016 that would mandate V2V communications on all new light-duty vehicles. The proposal includes V2V communication performance requirements predicated on the use of on-board DSRC devices to exchange two-way Basic Safety Messages (BSM) about a vehicle’s speed, heading, brake status, and other information with nearby vehicles.
The public-comment period for the proposed Federal Motor Vehicle Safety Standard rulemaking closed in mid April. What will happen next is unclear, says a mid-May report in EE Times, “since the promulgation of a clear V2V mandate has stagnated with the slow pace of nominations by the Trump administration. Many cabinet agencies – including the National Highway Traffic Safety Administration (NHTSA) – remain stuck in staffing limbo.“
What is clear, however, is that the proposed rule making effort is hotly contested
The C-V2X camp claims that DSRC is dead on arrival. It argues that today’s extensive cellular networks could be upgraded to the next generation of wireless technology, while DSRC relies on roadside units that are not ubiquitously deployed in the U.S. “As soon as 5G and its corresponding highly reliable, low-latency mission critical services are available for V2X applications, ADAS and CAD will be significantly enhanced” according to a whitepaper commissioned by 5GAA.
For its part, the DSRC side maintains that its approach is simple and fast; since the communication link between vehicles and infrastructure is short lived, there is no need to establish a so-called basic service set, with the associated authentication procedures, before exchanging data. The IEEE 802.11p amendment defines a way to effect this data exchange.
(Many of the comments to the rule-making proposal echo this one from Verizon, as reported in RCR Wireless News, “NHSTA should not prescribe specific technology that must be deployed to meet its proposed mandate, since limiting possible solutions to a specific type of spectrum or technology will unnecessarily hamstring innovation.” BMW, too, “urge(s) the agency to consider rewriting the requirements of this rule to be performance-oriented and technology neutral.”)
But, the most trenchant argument in favor of DSRC comes from Cisco. In its comments on the NHSTA proposal, Cisco points out that DSRC is “the only mature communication option that meets the latency requirements to support vehicle communication based crash avoidance.”
That DSRC is indeed the “only mature communications option” is clear: It works reliably (in field trials it has been repeatedly demonstrated to the satisfaction of the Department of Transportation); the costs are well defined since components exist; the DSRC functionality would simply be part of a standard infotainment package sold and maintained by the automotive OEM. Unlike a cellular approach, there would be no subscription fee
And, just two months ago, the world’s third largest automaker provided the biggest endorsement yet of DSRC. General Motors’ Cadillac division introduced the first production vehicle – the 2017 CTS — capable of V2V communications. Cadillac claims that the CTS system, which happens to be based on DSRC, can handle 1000 message per second from vehicles up to nearly 1,000 feet apart. Cadillac uses a Delphi-supplied module running application software developed by Cohda Wireless on NXP Semiconductors’ IEEE 802.11p chipset.
True that, at the moment, a Cadillac can only communicate with another similarly equipped Cadillac. But this represents the first large-scale experiment in V2X.
Perhaps even more importantly, Cadillac’s coup demonstrates that DSRC is here, now.
In contrast, there is general agreement that current versions of cellular can only address basic V2X use-cases, but not safety-while-driving, which needs extremely low latency. Next generation 5G cellular may be the Holy Grail, promising manifold benefits but given the fact that the specification has not even gelled yet, it remains a distant hope.