What is C Band 5G?
What radio frequencies are we actually talking about, here? We'll focus on mid-band, but let's be thorough and start with low-band for context.
Low-band includes a large number of different bands, many of which have been in use for cellular networks for a very long time. The range in the US is around 600 – 2,400 MHz, or 0.6 – 2.4 GHz. (If 2.4 GHz sounds familiar, it's because low-band ends around where Bluetooth and Wi-Fi frequencies begin.) But that range includes AT&T's band 30, a relatively small (narrow), high-frequency outlier. Band 30 aside, the bulk of low-band in the US is 0.6 – 2.2 GHz, with a significant gap between 0.9 and 1.7 GHz.
When you see phones that support 4G LTE in bands 2, 4, 5, 12, 13, 30, 66, and 71, that's all low-band. And 5G has been deployed in low-band in the US as well, in bands 2, 5, 66, 25, 66, and 71. That's what carriers have thus far referred to as "nationwide" or "extended range" 5G; it's not a lot faster than 4G, but it is 5G.
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Mid-band in the US currently means 2.5 – 4.0 GHz. Within that, the C Band as it applies to 5G is 3.7 – 3.98 GHz, which the FCC auctioned off in Auction 107.
The C Band isn't just one lump of spectrum, though, it has sub-bands within it. Satellite operators are still using some of it, and are vacating different parts of the band in phases, a process called clearing.
The first, lower-frequency section of C Band cleared in December 2021, opening up 3.7 – 3.8 GHz for use by AT&T and Verizon in 46 of the top 50 areas (cities). (This section of the C Band is the "A" blocks. Read more about "blocks" below, and there's more detail on the clearing process and how it relates to satellite operators in the History section.)
December 2023 is the next big date. That's when C Band will first be available for 5G in more rural areas, as well as full availability in Washington/Baltimore, Atlanta, and Denver. That's also when the upper part of the band — 3.8 – 3.98 GHz — will clear, opening up even more bandwidth for carriers. It's also when T-Mobile will join the C Band party, since the licenses they won in Auction 107 are in this upper part of the C Band.
But as we touched on earlier, the C Band described above is only the upper part of the larger band 77, and band 77 is what will end up mattering in the end. The FCC is auctioning off the lower parts of band 77 in auctions 105 and 110.
Auction 105 took place in 2020 and covers 3.55 – 3.65 GHz. (This band technically extends up to 3.7 GHz, but licenses giving companies priority access were only made available up to 3.65 GHz.) In most key areas, Verizon bought up as much of this as they were allowed. Licenses were issued in March 2021, and Verizon has already deployed it for 4G LTE using band 48, a narrower subset of band 77. Verizon also plans to deploy 5G in this band in the future. When that happens, this band will complement C Band and further improve Verizon's mid-band 5G service.
Dish (Boost) was also a big player in Auction 105. When they launch their planned standalone 5G network, this band will presumably play an important role.
Auction 110 concluded in January 2022, and covers 3.45 – 3.55 GHz. AT&T and Dish won licenses nationwide, while T-Mobile snapped up some key areas around the country. This will likely be used by AT&T to add more capacity to its mid-band 5G network nationwide, and by T-Mobile to beef up capacity in key areas where its mid-band 5G network might otherwise be relatively weak. 5G could potentially be deployed in this band before the end of 2022, giving AT&T a way to expand its mid-band 5G coverage before December 2023. (Or it could take longer.)
Then there's T-Mobile's band 41, which spans around 2.5 – 2.7 GHz. It's been around for a while, first used for Sprint's ill-fated WiMAX network, then re-deployed for LTE and now re-deployed again for 5G by T-Mobile. It qualifies as mid-band as well. (For a visual, the graphic on the previous page shows band 41.)
T-Mobile owns a lot of band 41, but they don't own it all. A good amount of it is unclaimed, and the FCC will be auctioning off the rest of it in the upcoming Auction 108. The dates for that auction should be announced soon. It will be interesting to see if another major company deploys 5G in band 41.
Blocks and Regions
As with most radio bands allocated for mobile networks, these bands are sub-divided into blocks. When the FCC auctions off bands, they actually auction off specific blocks. And the bands are also divvied up geographically. Some bands/blocks are auctioned off in relatively large regions, while other bands are divided up into much smaller geographic divisions.
Some bands for mobile networks are "paired", with separate frequencies for transmitting vs. receiving. This is not the case with mid-band; all mid-band frequencies in the US are unpaired, meaning they are simple, singular chunks of radio spectrum. This type of band is typically used with TDD technology, which means the network tower and mobile device "take turns" sending and receiving.
Auction 107 for the C Band is evenly divided into 14 20-MHz blocks. The lowest five of those (the ones launching this month) are blocks A1 – A5, spanning 100 MHz (3.7 – 3.8 GHz). The remainder (clearing in Dec. 2023) are blocks B1 – B5 and C1 – C4, spanning 3.8 – 3.98 GHz.
The satellite operators have actually cleared the lower 120 MHz of the C Band, but block B1 (3.80 – 3.82 Ghz) will serve as an empty "guard band" to prevent interference between 5G and satellite operations between now and the end of 2023.
Auction 107 used PEAs (partial economic areas) as its geographical divisions. 406 PEAs cover the contiguous states and DC. These frequencies will not be available for 5G in Hawaii, Alaska, nor US territories. Only 46 of the top 50 PEAs cleared in Dec. 2021. Everyone that lives in the other 360 (mostly more rural) PEAs will have to wait until late 2023 to see C Band 5G from AT&T and Verizon.
Why only 46 of the top 50? Well, the satellite industry has to get out of the way before these frequencies can be used for 5G, and that's trickier where there are facilities on the ground that essentially control the old C Band satellites still in use. Unfortunately, the exempted cities are a few major ones: the Washington DC / Baltimore area, Atlanta, and Denver. If you live in these areas, you might have to wait until the end of 2023 for C Band 5G from AT&T and Verizon, although 5G could potentially launch before then in other mid-band frequencies (from auctions 110 and 105). Update: Verizon has found a way to launch 5G in C Band in those cities in 2022.
Auction 110, spanning 3.45 – 3.55 GHz, is also split up into the same 406 PEAs. Again, states and territories outside of the contiguous 48 states are left out of this one. The blocks are different, though. Here, the band is split into ten equal blocks of ten MHz each (designated blocks A – J). 10 MHz is relatively small for 5G, so carriers can combine several into one larger span.
AT&T bought four licenses (the maximum allowed by the FCC for this auction) in all 406 PEAs, giving them 40 MHz of new bandwidth nationwide, which should significantly boost their mid-band 5G network when deployed. Dish bought closer to three licenses per PEA in Auction 110.
Auction 105, covering 3.55 –3.65 GHz (band 48 / CBRS), was also divided up into ten equal blocks of 10 MHz each for priority access licenses, but the FCC only auctioned off seven blocks in any given area. And those areas are much smaller: auction 105 was divided up by county, not PEA. Verizon bought the maximum of four blocks in most key places.
Auction 108 should take place later in 2022, auctioning off the unused parts of band 41. The way this band is split up into blocks is rather complex. It was originally divided up into small, oddly-defined blocks, with a separate band called BRS wedged in the middle. In Auction 108, it's split into three larger channels. "New Channel 1" and "New Channel 2" take up the bottom portion of the band, spanning 2.5 – 2.6 GHz. They're each around 50 MHz wide. Oddball "New Channel 3" is smaller and broken into two parts, to weave around that BRS band. Geographically, this whole band is split up by county, like the CBRS band from Auction 105.
Finally, for complete context, we should mention mmWave, which in the US currently means 27.5 – 40 GHz. Now you might be thinking "whoa, that's a big jump from the other frequencies!" Well, yes... yes it is. And that's why mmWave has such different properties, like range measured in feet instead of miles, and why it has difficulty penetrating glass in some cases. The band numbers for mmWave in the US are 260 and 261.
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