Spectrum-starved Wi-Fi vendors look at DSRC band, sharpen knives

A mostly-unused slice of radio spectrum set aside for connected cars in 1999 could soon be shared with Wi-Fi, with the Federal Communications Commission seeking comment on the future of the 5.9 GHz band.

On Monday, the FCC presented the results of tests conducted by Cisco, Qualcomm, KEA Tech, Broadcom, and CAV technologies to see how well Wi-Fi devices (in regulatory-speak “unlicensed national infrastructure”, U-NII, devices) can share spectrum with Dedicated Short Range Communications (DSRC) systems for the Intelligent Transportation Service (ITS).

Since vendors have worked for years learning how to “play nice” with other spectrum – for example, in the “LTE unlicensed versus Wi-Fi” debate resolved last year – it should come as no surprise to learn that Wi-Fi kit can obey “detect and vacate” rules in the 5.9 GHz band.

Coexistence has been on the agenda for much of this decade. In response to an FCC proposal, the IEEE kicked off what it called a “Tiger Team” in 2013 (Cisco and Qualcomm were part of that process). That group presented its study (PDF) in 2015, and in 2016 the group of vendors kicked off the “Phase 1” tests.

The vendors and the FCC now agree on the most important requirement if two applications are sharing spectrum: Wi-Fi kit can reliably detect if there are DSRC signals present, and back off so as not to interfere with vehicle communications, if there are any.

With 1,450 individual tests collecting more than a million data points, the FCC said, “the prototype U-NII-4 devices were able to detect a co-channel DSRC signal and implement post detection steps as claimed by the submitters”.

The test results are now open for public comment until November 28, with follow-up comments closing December 13, 2018.

The FCC noted that there are other developments in the market since the test process began, and said comments can include the impact of autonomous vehicle developments, emerging cellular “vehicle-to-everything” (C-V2X), and the “limited deployment of DSRC”.

Some of the FCC's commissioners think there's way too much process going on. Commissioner Michael O'Rielly reckons “the results are not all that surprising”, and said “the Commission should move past this and initiate a rulemaking to reallocate at least 45 megahertz of the band, which is completely unused today for automobile safety.”

Commissioner Jessica Rosenworcel also criticised the snail's pace of the deliberations, and said: “We need to start a rulemaking to take a fresh look at this band and its real possibilities”.

The Internet and TV association NCTA wants the FCC to free up 75 MHz of the spectrum immediately.

The Auto Alliance doesn't agree. Last week, the group said 5.9 GHz DSRC technology is “already deployed on some cars”, and one day might “reduce up to 79 per cent of crashes”. ®