FCC Tests Suggest WiFi Can Coexist With DSRC Car Networks

For automakers who want to use Dedicated Short-Range Communications vehicle-to-everything wireless technology, and companies eyeing the same frequencies for WiFi, there’s a bit of good news: The systems may be able to coexist.

Recent test results from the US Federal Communications Commission show the two types of networks might be able to share a designated spectrum band. But those findings are only for the first phase of a long process that might take too long, as an alternative to DSRC quickly emerges.

DSRC dates to the 1990s and is designed to prevent crashes and congestion. It could let cars communicate with each other about location, speed and road conditions, as well as with roadside infrastructure and pedestrians’ and cyclists’ phones. But despite efforts by the federal government to promote it, including setting aside a big chunk of radio spectrum, very few vehicles have DSRC yet.

Meanwhile, the cellular-based alternative, C-V2X, has official backing in China and is gaining momentum in the US and Europe.

Some advocates of more unlicensed spectrum for WiFi say that’s reason enough to knock DSRC out of the 75MHz of frequencies that are devoted to it. Automakers say the technology is still a good use for the spectrum because it’s now starting to be deployed and could save lives.

Early lab experiments suggest it may not have to be one or the other. In test results released on October 29, unlicensed devices were able to sense nearby DSRC transmissions and give them priority.

Still, this isn’t the end of the story. The first phase of tests only provides baseline data for analyzing other operational scenarios and real-world tests later on in the process, the FCC said. It’s seeking public comment on the results until November 28.

There have been methods proposed for preventing interference in the first place. In the tests, the FCC tried two of them. Both give DSRC traffic higher priority because it could involve public safety.

The first, Detect-and-Vacate, lets the two systems use the whole band but requires an unlicensed device to back off if it senses DSRC signals. The second, Re-Channelization, sets aside part of the band just for DSRC. The tests showed how well unlicensed devices responded to interference that happened despite the mitigation methods.

Re-Channelization might give WiFi users a bigger win if it were implemented. Because it assigns DSRC to a specific part of the band, it could leave WiFi free to use wide channels, up to 160MHz, like those used in the high-performance 802.11ac standard.

Still, the FCC kicked off the study of coexistence more than two years ago, and the rhetoric around it is heated. Last month, the cable operator organization NCTA called on the FCC to make the band unlicensed.

“The country can no longer afford to hold 75MHz of optimal spectrum in reserve with the hope that the next twenty years will somehow be different than the last two decades of stagnation,” wrote Rick Chessen, NCTA’s chief legal officer, in a letter to the FCC.

In response, the carmaker group Auto Alliance said no unlicensed use should be allowed unless it’s proven not to cause harmful interference.

Stephen Lawson is a freelance writer based in San Francisco. Follow him on Twitter @sdlawsonmedia.

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