The FCC recently decided to “take a fresh look” at the 5.9 GHz band, 75 MHz of which was allocated to Dedicated Short-Range Communications (DSRC) in 1999. FCC Chairman Pai maintains that that the original intended purpose of the allocation - to enable ubiquitous vehicle communication - has not played out well and over 20 years there has been little evolution of the technology and a disappointing level of DSRC deployment, it’s claimed. Time, says Pai, for a rethink.

In fact, he appears to have already “re-thought” - no surprises there - and his plan involves making over 45 MHz of the band to unlicensed use (Wi-Fi - which is also celebrating a 20th birthday this year) and slipping two dedicated 10 MHz chunks to support the newish kid on the block, C-V2X - a low-latency messaging standard designed to connect on-the-go vehicles with each other and with roadside infrastructure such as traffic lights. It currently uses LTE as transport and will also use 5G in future. It can replace the ‘failed’ DSRC and do a better job while using much less spectrum Pai (and much of the industry) claims.

So with the reallocation Pai hopes he’s solved two problems in one hit. He’s placated the Wi-Fi enthusiasts who would obviously welcome another chunk of spectrum for general use. Pai acknowledges that all the focus on cellular and 5G seems to ignore the fact that most consumers rely on Wi-Fi for most of their wireless data traffic and so he says the US will need to allow unlicensed use of up to 1.6 GHz of new mid-band spectrum by 2025 if it’s to keep up with demand. It helps that the 45 MHz sits close to the 5.725-5.850 GHz spectrum already made over to unlicensed use (effectively to Wi-Fi) .

Secondly, he’s opened a path for the deployment of C-V2X, much to the delight of Qualcomm and other interested vendors who are keen to develop and deploy the technology.

Winners and losers

The only problem here is the Department of Transport, which has become attached to its big chunk of spectrum and doesn’t want to let go of that and its existing development work with DSRC. Once you have dedicated spectrum the rule is that you fight hard to keep it.

But DSRC, according to Chairman Pai, is incompatible with C-V2X and the earlier idea of developing a spectrum-sharing regime to enable Wi-Fi and DSRC to coexist in the band has fallen from favour.

The implication is that DSRC has had its chance and has now had its day.

To justify the move to prioritise an alternative technology, Pai implies that the agency has already done much for transport safety and credits it with enabling a raft of transportation innovations, such as keyless entry, tire pressure monitors, anti-theft systems, and security services to name a few.

“These are all technologies enabled by FCC actions and during my tenure, automotive safety has been an important priority. Back in 2017, I led an effort to allocate a large swathe of contiguous spectrum in the 76-to-81 GHz band exclusively for vehicular radars. These radars have proved especially useful for emergency braking and adaptive cruise control,” he said in a recent speech.

The message is that many of the features originally envisioned for DSRC are being provided today 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,” and so on. So no need for that big chunk of spectrum when C-V2X will be able to do a better job with less.