What is C Band 5G?
Where did the C Band come from? Radio frequency bands cannot simply be created out of thin air. (Well, radio waves are just air, in a sense, but....) Nearly all useful frequencies were allocated to something specific many decades ago. So when mobile networks need more bandwidth to handle more devices, using more data, the FCC has to find frequency bands that can be re-allocated from something else.
C Band
In the case of C Band, that something was satellite communications, mainly satellite TV.
The steady evolution of television technology has been a huge benefit to the mobile industry over the last decade. In the 4G era, it was the death of analog broadcast TV (the kind you picked up with "bunny ears" or even a large antenna on your roof, if you're old enough to remember such things) that made room for "new" frequency bands allocated to 4G networks. Most people had moved on to cable, satellite, or streaming. And for the over-the-air TV signals still being broadcast, new digital signals were more efficient and took up less of the airwaves. That's what made room for bands 12, 13, and 71. Those bands are now the foundation of 4G (and in some cases, low-band 5G) networks in the US.
As it was with analog broadcast TV, the same has now happened with satellite TV. C Band is the original, old-school band for TV broadcasts from space. To receive it, you needed your own massive, 10-foot dish. (Hey, kids: Yes, this was a thing!) But fewer people are using satellite TV services. What remains of the satellite TV industry has moved on to modern digital signals and/or the Ku band, which uses much smaller dishes on the ground. So the C Band was sitting there under-utilized, and the frequencies were ideal for new mobile networks.
But "under-utilized" does not mean abandoned. Satellite companies still owned FCC licenses for C Band frequencies — a legal contract — and they are still using them. Crucially, they had satellite hardware in orbit that was designed to use those specific frequencies and none other.
So the FCC had to broker a deal where the mobile companies would effectively pay the satellite companies to take over the lower part of the C Band, pay for it to happen sooner rather than later (an "accelerated" schedule), and, in some cases, pay for some of them to launch new, replacement satellites.
None of that was cheap. Intelsat and SES together are launching ten new satellites to space to make this happen. There are also a bunch of things that need to happen on the ground, such as replacing equipment and installing filters. The satellite companies need to coordinate these upgrades with their customers, a complex and expensive process.
Fortunately, the satellite companies were able to effectively stop using the lowest part of the C Band (at least in ways that would interfere with 5G in most populated areas) before the new satellites were fully operational. This is the first phase of the "clearing" process, and what allows AT&T and Verizon to start using the 3.7 – 3.8 GHz part of the C Band (the A blocks) in most metro areas now.
Most... but not all. As we mentioned, some key cities like DC/Baltimore, Atlanta, and Denver are exempted from this first phase. That's because this transition process needs to work around not only existing satellites in orbit, but the corresponding Telemetry, Tracking, and Command (TT&C) sites those satellites communicate with on earth (often via C Band frequencies).
The remainder of the C Band, 3.8 – 3.98 GHz (the B and C blocks) won't become available until the new satellites are up and running. And the TT&C sites need to be consolidated and/or reconfigured in order for those three metro areas to open up for 5G. The deadline for those things is December 2023.
At that point, the clearing process will be complete, and satellite companies still using the C Band will be restricted to 4.0 – 4.2 GHz. But with modern digital technology, that should be enough to do everything they did before with 3.7 – 4.2 GHz. That includes digital TV broadcasts and satellite data services.
Sharing the 3.5 GHz Bands
As for the lower portion of band 77 (below C Band), there were — and remain — a variety of existing, or "incumbent", users of these frequencies. These include the Department of Defense, some RADAR systems, some ground stations that receive signals from satellites in orbit, and more.
Some of these incumbent users are relocating to other frequencies. However, some incumbent users will continue using these frequencies, and wireless carriers will need to share these frequencies with those incumbents.
For the 3.55 – 3.65 GHz portion (AKA CBRS, from Auction 105), automated commercial clearinghouses called Spectrum Access Systems (SASs) coordinate this sharing, allowing Verizon to use to it for 4G LTE service (in band 48) — and soon, 5G — whenever it's not being used by an incumbent.
The process to commercialize the CBRS band started in 2012, but Auction 105 didn't conclude until August 2020, and Verizon wasn't permitted to deploy 4G in this band until March 2021.
Another, lower level of priority allows others to use this band without a license, although they must use an SAS to make sure they don't interfere with incumbents or licensees like Verizon, and SASs can charge fees.
The 3.45 GHz band (spanning 3.45 – 3.55 GHz) was enabled by the Beat China by Harnessing Important, National Airwaves (Beat CHINA) for 5G Act of 2020. It directed the federal government to clear federal users out of this band wherever possible, and to auction these frequencies off for 5G. The NTIA (National Telecommunications and Information Administration) and FCC did just that. The FCC concluded Auction 110 for this band in January 2022.
The FCC has declared that, in "most" areas of the country, license winners (AT&T was the biggest) will have unrestricted access to the 3.45 GHz band. However, some federal users — the Department of Defense in particular — will retain some priority access to the band. This will only apply to certain areas, such as near military bases, including San Diego. This will require carriers to defer to the DoD or share frequencies in part of the band and/or during certain time periods (expected to last 1-2 months each year). The process for this coordination will be more manual than the SAS system for CBRS.
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