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27 November 2019

FCC proposals would sound the death knell for DSRC for V2X

Ajit Pai, chair of the FCC, has run out of patience with the US-developed DSRC (Dedicated Short Range Communications) technology for vehicle-to-everything (V2X) connectivity, and is now giving new hope to Cellular-V2X to become a near-global standard. The 3GPP solution could now gain two dedicated 10 MHz chunks of spectrum in the USA’s 5.9 GHz V2X band.

The FCC said it would “take a fresh look” at the 5.9 GHz band, 75 MHz of which was allocated to DSRC in 1999. Pai believes that, in 20 years, DSRC has failed to build on its opportunity to develop and deploy useful services. There has been little evolution of the technology and a disappointing level of deployment, critics say, and alternatives like C-V2X have leapfrogged some of its capabilities, are more international in scope (which helps the auto ecosystem to scale), and has a roadmap to 5G.

Under the new proposals, C-V2X would gain 20 MHz of the 5.9 GHz band, and 45 MHz would be added to the store of unlicensed spectrum for WiFi. That will help towards Pai’s target of opening up as much as 1.6 GHz of new midband spectrum for unlicensed use by 2025, to keep pace with rising usage.

As for C-V2X, this supports low latency messaging between vehicles and between them and roadside infrastructure such as traffic lights. It currently uses LTE as transport and will also use 5G in future, and requires less spectrum than DSRC.

The barrier may come from the US Department of Transport, (DoT), which controls the 5.9 GHz spectrum and is reluctant to let go of dedicated spectrum, or the years of investment in DSRC.

An earlier idea of developing a spectrum sharing regime to enable WiFi and DSRC to coexist in the band seems to have fallen out of favor, despite the high interest in the spectrum access system (SAS) created for the CBRS band, and potentially to be adapted for other occupied midbands in future.

However, Pai is leaving the door open for a compromise solution, though it is clearly not his preferred option. “I’m proposing that we seek public input on whether to allocate the remaining 10 MHz of spectrum in the 59 GHz band for DSRC or C-V2X,” he told an even in Washington DC last week.

Pai discussed other transport-related initiatives the FCC has taken under his tenure. “Automotive safety has been an important priority,” he said in a recent speech. “Back in 2017, I led an effort to allocate a large swathe of contiguous spectrum in the 76-81 GHz band exclusively for vehicular radars. These radars have proved especially useful for emergency braking and adaptive cruise control.”

And he noted that some of the capabilities for which DSRC was devised are now provided by other means. “Applications like Waze help with traffic management and provide alerts far in advance of road hazards ahead. Blind spot detection and lane departure warnings have become common features on the latest cars,” he said.