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What is C-Band 5G and why is it so controversial?

5G phone connected on 5G network
(Image credit: d3sign/Getty Images)

AT&T and Verizon are ready to launch revamped 5G networks that should mean faster download speeds that cover a wider area for more people with the best 5G phones. The initial 5G networks launched by those carriers only offered modest gains over LTE speeds. The areas that did have high-speed coverage were limited to select sections of a few cities. But this revamped form of 5G based on C-Band spectrum figures to dramatically improve things if you get your 5G service from either AT&T or Verizon.

So what's not to like? Plenty, if you happen to be running an airline.

AT&T and Verizon have kept pushing back the launch dates for C-Band 5G, amid concerns from the aviation industry that the new signals create potential safety hazards for planes. Even now, with the launch of C-Band-based 5G imminent, AT&T and Verizon have both agreed to dial back their launches by not activating the new service on towers near select airports. Even so, it's an issue dividing wireless carriers and airlines, even pitting government agencies against one another.

Here's a quick overview of C-Band 5G and why this new form of 5G is proving to be so controversial.

What is C-Band spectrum and what does it mean for 5G?

Up until now, 5G networks have relied on two different kinds of spectrum —sub-6GHz and millimeter wave (mmWave). The former has a broad reach, forming the backbone of most nationwide 5G networks, but it's not very fast. In our testing, sub-6Hz 5G installations have been only a little bit faster than the 4G networks they're meant to replace. mmWave 5G is the faster standard, but you've got to be within sight of a tower to enjoy fast speeds. Also, mmWave signals can't go around obstacles like buildings and windows.

C-Band is a relatively uncrowded part of the wireless spectrum that's been used to build out 5G in other parts of the world. Last year, the FCC auctioned off 5G spectrum to the highest bidder, with Verizon grabbing the largest share of spectrum, followed by AT&T. Those carriers are adding C-Band to their existing 5G networks, which will not only bolster speeds, but allow those faster speeds to have greater reach.

Take Verizon, which spent most of the past 2.5 years setting up mmWave-based coverage in parts of 87 cities. Those mmWave-based towers are fast, but to enjoy their speeds, you need to be within sight of one of those towers. C-Band's going to remove that obstacle, so that more Verizon customers will see faster 5G overall. (Our C-Band testing last month found that subscribers with the best 5G phones are going to enjoy faster speeds in more areas.)

What are AT&T and Verizon planning to do with C-Band 5G?

Both AT&T and Verizon are ready to throw the switch on their updated 5G networks. In Verizon's case, the carrier was ready to go two weeks ago, but postponed the launch at the request of U.S. government agencies — we're getting to why in a moment. Today (January 19) is the day Verizon's supposed to make its faster 5G available to more people, with service reaching some 90 million people — Verizon's original goal, touted two weeks ago, was 100 million people, but Verizon's refraining from launching its C-Band 5G on towers near select airports.

Verizon 5G c-band spectrum testing

(Image credit: Tom's Guide)

Likewise, AT&T is expected to launch its C-Band 5G today, though it's been less explicit about how may people will be covered by the faster speeds initially. Last October, AT&T said 70 to 75 million people in the U.S. would be covered by C-Band 5G by the end of 2022. We're expecting more details from AT&T shortly.

What about T-Mobile?

We haven't mentioned T-Mobile yet, because the carrier is taking a different approach to its 5G network. T-Mobile was the first to launch a nationwide 5G network, doing so at the end of 2019. In the subsequent two years, the Uncarrier has taken the spectrum acquired from its merger with Sprint to build up 5G speeds with its Ultra Capacity service that now reaches 200 million people. In Ookla's most recent report on wireless carrier performance, T-Mobile ranked first for both 5G speed and availability, so you can see why the other carriers are eager to launch C-Band 5G.

That's not to say that T-Mobile doesn't have any C-Band spectrum of its own to bolster its 5G network. But the carrier isn't planning any C-Band implementation until 2023.

Why are airlines and the aviation industry objecting to C-Band 5G?

As eager as AT&T and Verizon might be to get their new 5G deployments live, airlines are just as eager to pump the breaks on the upgrade. "The C-Band is closer to the frequencies used by airplane altimeters than previous 5G deployments," explained Avi Greengart, lead analyst with Techsponential. "In the U.S., the 5G we’ve been using has either been used before for prior wireless networks, or it is on really high frequencies with no ability to penetrate a piece of paper, let alone an airplane."

Specifically, the airline industry is concerned that C-Band 5G will interfere with altimeters and affect the ability to safely land planes in low visibility. A recent letter signed by the CEOs of 10 airlines warned that implementing C-Band 5G could lead to airlines scrapping flights out of safety concerns. On a typical day "more than 1,100 flights and 100,000 passengers would be subjected to cancellations, diversions or delays," the letter warned.

Similar frequencies [to C-Band 5G] are already in use in Europe with no problems observed. If the airplane’s altimeter filters are working properly, there should be no interference whatsoever.

— Avi Greengart, Techsponential

Is the aviation industry right to be concerned? "From a technical standpoint, not really," Greengart said. "There is a 200 Mhz buffer zone between C-Band and altimeter frequencies, and the part of C-Band that is opening up this week is even farther from that point. Additionally, similar frequencies are already in use in Europe with no problems observed. If the airplane’s altimeter filters are working properly, there should be no interference whatsoever."

There is a concern that older altimeters may not be in the clear, and that they'll need to be updated or replaced. That takes money, and that's at the heart of the aviation industry's objections. "The airlines don’t want to pay for those upgrades just because the FCC gave adjacent frequencies to wireless operators," Greengart said.

Nevertheless, fears of 5G interference has led to a cascade of U.S. flight delays and cancellations

Is this a new complaint?

Not hardly at all — and that's led to some noticeable frustration among wireless carriers who seem to be wondering why the situation hasn't been resolved by now. 

Both AT&T and Verizon had initially targeted 2021 launches for their respective C-Band 5G, only to table those plans at the request of federal aviation officials. A January 4 launch was delayed for two weeks when U.S. Transportation Secretary Pete Buttigieg intervened. And now, right before another launch, AT&T and Verizon both agreed to not enable C-Band 5G at towers near select airports — something neither carrier sounded particularly pleased by.

"The Federal Aviation Administration (FAA) and our nation’s airlines have not been able to fully resolve navigating 5G around airports, despite it being safe and fully operational in more than 40 other countries," Verizon noted in its statement.

"We are frustrated by the FAA’s inability to do what nearly 40 countries have done, which is to safely deploy 5G technology without disrupting aviation services, and we urge it do so in a timely manner," AT&T said in a statement of its own.

What happens next?

C-Band 5G sounds like it's going live today whether airlines like it or not — though not as widely spread as the carriers originally envisioned. "Barring someone walking in with a barrel of money to placate the airlines, carriers are going to turn on the frequencies with buffer zones around airports, and then we’ll see if the FAA actually mandates anything in terms of flight restrictions," Greengart said.

That will address the initial launch of C-Band 5G. But eventually, carriers are going to want their new networks to enjoy a wider reach. And that's a dispute that's going to need to be settled at some point in the near future.

Philip Michaels is a Managing Editor at Tom's Guide. He's been covering personal technology since 1999 and was in the building when Steve Jobs showed off the iPhone for the first time. He's been evaluating smartphones since that first iPhone debuted in 2007, and he's been following phone carriers and smartphone plans since 2015. He has strong opinions about Apple, the Oakland Athletics, old movies and proper butchery techniques. Follow him at @PhilipMichaels.