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

For 5G to offer an experience that’s noticeably better than 4G, it needs broad, dedicated channels, ideally 50MHz or wider. Enter C-Band, the frequency that may save 5G in the US.

By Sascha Segan

A half-dozen companies are ready to potentially spend $80 billion for C-Band, a new set of airwaves that promise to fix the perilous state of American 5G.

That’s a vast amount of money, and it shows how important C-Band is. 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? I can explain.

Recovering the Satellites

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 range from 3.7 to 3.98GHz.

This frequency had been used for satellite TV since the 1970s, but as C-Band satellite reception requires “big, ugly dishes” up to 10 feet in diameter, it got largely 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 sits immediately above CBRS, a band from 3.55–3.7GHz 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 auction off C-Band already; in terms of the number of countries, it’s probably the most popular 5G band in the world. The International Telecommunication Union (ITU) chopped C-Band up into three chunks: band n77, band n78, and band n79. Most European and Asian countries currently use n78, which stretches from 3.3 to 3.8GHz. We in the US will use n77, a larger band from 3.3 to 4.2GHz. Japan also already uses n77, so equipment and phones are out there.

Why Do We Need C-Band?

The state of 5G in the US 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&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&T and Verizon are delivering 5G that’s either no faster than LTE would be on the same frequencies or has poor range.

C-Band can fix this. The government is auctioning 280MHz of airwaves 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.

An estimate of 3.5GHz cell coverage in the capital of Slovenia.

Cell distance is a tricky thing. This paper from 2006 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.

Who Wants C-Band?

According to Light Reading, the top C-Band bidders are Verizon, AT&T, Comcast, and Charter (together, in a joint venture), T-Mobile, US Cellular, and Dish.

These are all either mobile network providers or cable companies. They’ve all expressed interest in running their own 5G networks, at some point. While the cable companies don’t run their own mobile networks yet (they resell service on Verizon’s network), they could build their own, or lease their spectrum to one of the three major wireless carriers in a partnership.

What Phones Support C-Band?

For a phone to support US C-Band, it needs two components. Its hardware must support it, and it must be approved by the FCC to work on it. If the hardware supports it but it doesn’t yet have FCC approval, the phone’s maker can file for a “class 2 change” with the FCC, but they have to do it. Phone makers sometimes choose not to file for changes because they cost money; they’d rather just make a newer model and sell that.

There’s a bit of a debate whether hardware support means band n77 or n78 appearing on a spec sheet, as parts of the US C-Band fall within n78. If a carrier only wins segments within the n78 group, n78 phones will probably work for them. That would open up a potential wider range of phones, as more phones currently have n78 than n77.

The iPhone 12 family are the first phones approved by the FCC for C-Band.

The iPhone 12 series are the first US phones approved by the FCC for C-Band. The Google Pixel 5 has C-Band on its spec sheet, but it hasn’t been approved for use on C-Band by the FCC yet. The same goes for many foreign phones; they may have n77 or n78, but they haven’t been cleared for US use on those frequencies by the FCC.

I expect the Samsung Galaxy S21 and many other phones released in 2021 will support C-Band.

When Will C-Band 5G Happen?

The current C-Band auction will run until the bidders don’t want to bid anymore, which is likely to be sometime in January or February 2021.

The C-Band frequencies are being auctioned off in 14 chunks of 20MHz each. The first five, 100MHz known as the “A block,” are the most important (and most expensive) because satellite companies can be paid to clear them for 5G use by the end of 2021. Cellular firms can start building their networks before the frequencies are cleared for use, so we’ll likely see the first C-Band systems at the end of 2021 or the beginning of 2022.

The other 180MHz in the C-Band is only scheduled to be cleared by the end of 2023. That would put other 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 14–55, 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 more than a year before it was supposed to, for instance.

Do I Need a C-Band Phone?

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.

  • For Verizon, I think that carrier is going in big on C-Band and will have major C-Band launches in late 2021 and early 2022. If you intend to keep a new phone for more than a year, it would help to get a C-Band phone on Verizon.
  • For T-Mobile, you don’t need C-Band. T-Mobile isn’t making a big investment in the frequency.
  • For AT&T, you don’t need C-Band now. I think AT&T will, by and large, go for the later clearing chunks of C-Band, which means you’ll want it in your 2024 phone.

We’ll be tracking the C-Band developments here on PCMag.com, and will tell you whether it’s available on every 2021 phone.

Originally published at https://www.pcmag.com.



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