Name: What Is C-Band, and What Does It Mean for the Future of 5G?
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What Is C-Band, and What Does It Mean for the Future of 5G?

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PCMag editors select and review products . If you buy through affiliate links, we may earn commissions, which help support our testing.It came. You saw. Planes did not fall out of the sky.AT&amp;T and Verizon recently turned on their C-band 5G networks after with the airlines and FAA. And, knock on wood, so far we've seen neither major flight disruptions nor any danger to air safety. After two years of AT&amp;T's and Verizon's "nationwide 5G" networks feeling much like 4G, C-band could finally majorly multiply speeds. But what is C-band, and what does it mean for 5G? Do you need a C-band phone? Is C-band a new frequency? Should you be scared of C-band? We can explain.According to wireless testing firm Rohde and Schwarz, the C-band is all frequencies between 4 and 8GHz. When US wireless geeks talk about C-band, though, they're talking about 3.7 to 4.2GHz—and specifically, in this case, the ranges from .There's another chunk of airwaves involved, too, from 3.45 to 3.55GHz. Nobody has really settled on what to call these—they're "3.45," "DoD" (the military used them), or even "Andromeda." But they have a lot in common with the C-band spectrum, so we include them in this explainer.The main C-band frequencies have been used for since the 1970s, but because C-band satellite reception requires "big, ugly dishes" up to 10 feet in diameter, they largely got replaced by more flexible systems with smaller dishes on the Ku band, such as Dish and DirecTV. C-band is currently used for the "satellite downlink" for broadcast television distribution.With more advanced methods of digital encoding than they had in the 1970s, the satellite companies can now "repack" their broadcasts into the upper portion of the C-band, leaving the lower portion available for cellular companies to use.(The chart above shows the primary wireless carrier user of each band; it does not include minor users)C-band sits between the two Wi-Fi bands, which are at 2.4GHz and 5GHz. It's slightly above and very similar to the 2.6GHz band that Clearwire and then Sprint used for 4G starting in 2007, and which T-Mobile currently uses for mid-band 5G. And it adjoins CBRS, a band from 3.55 to 3.7GHz that's currently being deployed for 4G. So its transmission characteristics are very well known, and its safety is well established.Most of the rest of the world started to use C-band already; in terms of the number of countries, it's probably . The International Telecommunication Union (ITU) chopped C-band up into : band n77, band n78, and band n79. Most European and Asian countries currently use n78, which stretches from 3.3 to 3.8GHz. In the US, we will use n77, a larger band from 3.3 to 4.2GHz, in part so carriers can combine 3.45GHz, CBRS, and C-band for wider channels if they have the licenses available. Japan also already uses n77, so equipment and phones are out there.Mid-band, including C-band, is the world's most popular form of 5G.The is pretty rough right now. For 5G to offer an experience that's noticeably better than 4G, it needs broad, dedicated channels, ideally 50MHz or wider. For 5G to cover entire cities, it needs to be on a frequency below about 6GHz, so it can get decent range from towers. Right now, AT&amp;T and Verizon aren't using any airwaves that fit these bills. Verizon may be able to pull something together using the new CBRS airwaves just below the C-band, but the jury's still out on that. So by and large, AT&amp;T and Verizon are delivering 5G that's either would be on the same frequencies or has poor range.C-band can fix this. The government auctioned off 280MHz of airwaves in the main C-band, and another 100MHz in 3.45, that are likely to go up to about a half-mile from each tower, so plenty of bandwidth for several different wireless carriers to have solid 5G using mostly existing cell sites.Verizon's C-band network showed decent range in testing in a dense part of Queens, NY.Cell distance is a tricky thing. estimates that 3.5GHz networks can go up to 1.2 miles from each site in an urban area and up to 6.2 miles in a rural area. According to CellMapper.net, there are up to 2.5 miles between T-Mobile's 2.6GHz sites in suburban Dallas, but only 0.6 miles between sites where I live in Queens, New York. So I'm saying a half-mile for the 3.5GHz networks to be safe.Our show about a 0.37-mile range in very dense Queens, NY. That seems to be limited not by the power of the airwaves, though, but by Verizon not wanting its cell sites to interfere with each other. So half a mile in much of the country still feels good to me.First, AT&amp;T and Verizon. Later, T-Mobile and Dish.The main C-band frequencies from 3.7-4.2GHz are rolling out in two chunks. The first 100MHz are now available in around 50 major markets across the US, covering about 60% of the US population. Verizon and AT&amp;T split those "A block" airwaves 60/40. So Verizon will be just above, and AT&amp;T just under, the 50MHz rule of thumb I've been using for real 5G differentiation.Another 180MHz is scheduled to clear by the end of 2023. That includes more Verizon and AT&amp;T spectrum, along with airwaves purchased by T-Mobile, US Cellular, and some local phone companies. At that point, Verizon will end up with an average of 160MHz of spectrum and AT&amp;T with an average of 80MHz—both able to deliver a truly different 5G experience.That calendar puts those networks on a late 2023 or 2024 launch. Those launches may happen earlier in 2023, though, if the precedent from the 600MHz band holds. T-Mobile took a lot of the 600MHz band, which was previously TV channels 14 to 55, in 2017. That had a clearance schedule that went out to July 2020. But T-Mobile worked with (and paid) broadcasters to clear early, getting New York City cleared before it was supposed to, for instance.AT&amp;T, Dish, and T-Mobile are the primary purchasers of the 3.45GHz frequencies. AT&amp;T and Dish have said that they plan to turn them on as soon as equipment becomes available, which would be later in 2022 or early 2023. T-Mobile is holding its 3.45GHz in reserve for when it needs the capacity.The C-band networks were initially supposed to launch on Dec. 5, 2021, but the airline industry and the FAA argued that C-band signals would be picked up by airplane radio altimeters, which judge airplanes' distance from the ground for landings in poor weather. Those altimeters aren't designed to use the same band as the 5G network—the airlines' frequency is 400MHz away from the 2022 launch networks—but some were designed not to filter out surrounding frequencies, because those frequencies weren't being used as heavily at the time the altimeters were built.The FAA and carriers agreed on "exclusion zones" two miles long around many airport runways where the carriers wouldn't initially launch C-band. That caused Verizon to notch its initial projected population coverage from 100 million Americans down to 90 million, as it cut out parts of cities including Chicago, Dallas, New York, and San Diego that are too near the airports. Our tests show Verizon appears to be well outside the two-mile boundary, at least in New York City.The C-band exclusion zones extending from Midway Airport knock out some in-city Chicago neighborhoods.(Image: Rene Ramos)The FAA is also working to verify and approve which altimeter models have the right filters, although some observers question why the agency couldn't have done this a year ago when the spectrum was auctioned.Once the networks launched on Jan. 19, the CEO of American Airlines said the conflict appeared to be past.None of the airline conflict affects any frequencies below 3.7GHz. That means it doesn't affect CBRS, or T-Mobile's mid-band, or AT&amp;T's 3.45GHz. That gives AT&amp;T and T-Mobile a key advantage over Verizon for now, as they're able to install mid-band systems in spots near airports where Verizon isn't.For a phone to support US C-band, it needs three components: Its hardware must support it, it must be approved by the FCC to work on it, and it must have the appropriate firmware. That last bit has created some delays, for example with Verizon's Pixel 6. The Pixel 6 had the hardware and the FCC clearance, but C-band support was delayed for a while because the firmware was missing. (It's fixed now.)The key to look for on the spec sheet is whether it supports band n77, but ultimately it's up to the carriers to implement the right firmware.The iPhone 12 family was the first set of phones approved by the FCC for C-band.(Photo: Sascha Segan)We have a list of all the phones . AT&amp;T's C-band list is similar, but there's an extra twist, in that not all AT&amp;T C-band phones support 3.45GHz. Right now, the only phones we know of that will support the new 3.45GHz for AT&amp;T are those in the Samsung Galaxy S22 series and the Google Pixel 6a, but AT&amp;T has promised more details on that later this year. The iPhone 14 series will probably be the first iPhones with 3.45GHz.Right now, deciding whether you need a C-band phone is about trying to foresee whether your carrier will launch a C-band network before you get a new phone.We'll be tracking the C-band developments and will tell you whether it's available on every phone we review, so make sure to buy a model that supports the airwaves you want to use.Sign up for Fully Mobilized newsletter to get our top mobile tech stories delivered right to your inbox.This newsletter may contain advertising, deals, or affiliate links. Subscribing to a newsletter indicates your consent to our and . You may unsubscribe from the newsletters at any time.Your subscription has been confirmed. 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PCMag editors select and review products . If you buy through affiliate links, we may earn commissions, which help support our testing.It came. You saw. Planes did not fall out of the sky.AT&amp;T and Verizon recently turned on their C-band 5G networks after with the airlines and FAA. And, knock on wood, so far we've seen neither major flight disruptions nor any danger to air safety. After two years of AT&amp;T's and Verizon's "nationwide 5G" networks feeling much like 4G, C-band could finally majorly multiply speeds. But what is C-band, and what does it mean for 5G? Do you need a C-band...

What Is C-Band, and What Does It Mean for the Future of 5G?

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