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A November 2020 ruling from the Federal Communications Commission (FCC) means C-V2X will be the de facto technology format for future automotive safety communications. (Valeo)

Vehicle safety communications landscape clarified with controversial FCC ruling

The vehicle-to-everything communications-technology debate has been “solved” by federal regulators – and DSRC appears to be the loser.

After years of transportation-industry tussle over competing technologies to enable communications between vehicles and a “connected” environment, the Federal Communications Commission (FCC) has decided the matter. On Nov. 18 the FCC ruled it will allow a portion of the 5.9-GHz “Safety Spectrum” long reserved for the transportation sector to be allocated to unlicensed private usage such as Wi-Fi internet connectivity. The ruling effectively eliminates the future for Wi-Fi-based Dedicated Short-Range Communications (DSRC) and locks in the advancing alternative, cellular vehicle-to-everything (C-V2X).

Despite many experts’ opinion that the decision to now limit transportation communications to just the upper 30 MHz of the 75-MHz spread within the 5.9-GHz (5.850-5.925 GHz) Safety Spectrum has not been sufficiently researched, the FCC said in a statement that the ruling will enhance automotive safety. Many are concerned that interference from other radio signals now permitted to be close to the Safety Spectrum may adversely affect the bandwidth’s performance and reliability.

In a letter to FCC chairman Ajit Pai just prior to the FCC’s final ruling, General Counsel for the Department of Transportation (DOT) Steven Bradbury said, “FCC’s reallocation of the 5.9 GHz Band is unworkable and undermines innovation in transportation safety,” adding that, “DOT remains convinced that all 75 megahertz (MHz) of spectrum previously allocated for V2X should remain available for that purpose. Reducing that allocation by more than half, to 30 MHz, jeopardizes both the existing deployment of, and innovation in, V2X technology. DOT also disagrees with FCC’s conclusion that 30 MHz is adequate for V2X.”

Moving on despite concerns
The reallocation of the 5.9-GHz spectrum sees the upper 30 MHz of the spectrum previously allocated to DSRC now assigned to C-V2X. The lower 45 MHz now is allotted to so-called “unlicensed” wireless use, generally assumed to be Wi-Fi. The FCC said it has its own conclusion about the reallocation of the portion of the safety spectrum now given over to unlicensed use, saying the action “modernizes” the 5.9-GHz spectrum.

“Increasing the amount of spectrum available for unlicensed operations is critical for meeting our nation’s connectivity needs,” the FCC said in a statement. Adding that the reallocation is earmarked to deliver economic benefits, it noted the value created by Wi-Fi in the United States is projected to double by 2023 to nearly $1 trillion.

A lengthy roster of entities, from political representatives to Fortune 500 corporations, publicly supported the FCC decision. Charter Communications said, “We applaud the Chairman’s leadership and efforts to take significant steps to accelerate America’s 5G transition and promote innovation in the unlicensed ecosystem.” Citizens Against Government Waste said in its blog, “The FCC will be taking a much-needed and significant step to improve the availability and use of spectrum, which is a limited resource owned by the taxpayers.”

The FCC’s action had been expected. As a parrying move, in April 2020, the Alliance for Automotive Innovation (AAI) proposed a 5-year plan that provided for one of the competing formats to prove itself – and claim the entire 5.9-GHz spectrum. But the gambit did not sway the FCC’s intent to reallocate the Spectrum’s lower 45 MHz for other purposes.

A key facet of the tussle over the Safety Spectrum was that automakers and other transportation interests had, since the Spectrum’s initial allocation in 1999, done little to demonstrate the safety benefits of DSRC – and by extension, the need for the entire bandwidth of the Safety Spectrum. Few automakers ever deployed DSRC-equipped production vehicles in the U.S. or elsewhere. GM’s Cadillac was the only brand ever to outfit production models with DSRC capability and the number amounted to fewer than 50,000 vehicles.

“The FCC’s decision to take 45 MHz of spectrum away from automotive safety was unfortunate, but not surprising given the industry’s slowness in actually rolling out V2X communications,” said Sam Abuelsamid, principal e-mobility analyst at Guidehouse Insights. “The decision to reassign the remaining 30 MHz of spectrum from DSRC technology to C-V2X was really just an affirmation of facts on the ground, as no automaker has committed to DSRC rollout and the momentum has shifted almost entirely to C-V2X.”

Next alternatives
The transportation sector enters 2021 with the certainty that some of its 5.9-GHz bandwidth is no longer going to be available. And although there is a certain value in knowing the lingering debate about the merits of DSRC and C-V2X has culminated in the tacit formation of a standard safety-communications protocol, apprehension about the efficacy of C-V2X squeezed into its new 30-GHz slice is unabated. Those concerns primarily center around what critics say has been inadequate testing or understanding of the potential for interference from other radio sources operating on adjacent frequencies.

“I think all of us are concerned with the level of out-of-band emissions the V2X channel will endure,” one electronics-industry source told SAE International. In early 2020, John Kenney, director and senior principal researcher at Toyota InfoTech Labs, said at SAE International’s Government/Industry Meeting, “If the FCC proceeds with its plan and the bandwidth is used for non-automotive services, interference from Wi-Fi could render the V2X spectrum useless.” He added that if automotive lost 60% of its V2X spectrum, the industry would lose 60% of potential V2X benefits.

Some sources have suggested allotting perhaps a 10-MHz buffer within C-V2X’s 30 MHz of bandwidth to allay concerns about interference. Many electronics- and automotive-industry engineers say, at minimum there has not been sufficient study of the potential for cross-interference or overloading of the spectrum in which C-V2X now must operate.

Guidehouse’s Abuelsamid sees something of an optimistic turn of events borne from the FCC’s settling of the lengthy dialogue about the Safety Spectrum and which format should prevail: “Ford has publicly announced its intention to deploy C-V2X from 2022 and numerous other automakers have hinted at doing the same,” he said. “Numerous C-V2X pilots are running. And now that the FCC has made a decision, we will likely see many more OEMs make announcements in the next year or two, probably in conjunction with the rollout of 5G [cellular] technologies.”

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