Verizon and AT&T were hoping to light up their new mid-band 5G networks in the coming weeks, but they might have to wait a bit longer. The C-band rollout was previously set for December 5th, but the Wall Street Journal now reports it will be January 5th, at the earliest. At issue is the potential interference with the safety systems of some aircraft.
5G connectivity in the US is in a rough place right now, and the C-band spectrum is seen as a major milestone in making 5G live up to the hype. Verizon and AT&T spent billions of dollars on the licenses for this spectrum recently because they’ve been trying to piece together a functional 5G network with scraps. I’m sure the carriers would dispute that description, but their focus on millimeter wave 5G speaks louder than any protestation. These signals have high speeds, but the range is abysmal — it doesn’t even work indoors.
Mid-band 5G (like the C-band) can handle more data throughput than lower LTE-like frequencies, but they still have respectable range. There just isn’t a lot of this to go around. In the absence of a proper mid-band spectrum, Verizon has resorted to using dynamic spectrum sharing (DSS) to run a 5G network in the same bands as 4G. The results are not amazing, but C-band is supposed to fix all that.
The spectrum AT&T and Verizon want to use is in the 3.7-4GHz range, which is just part of this block of the C-band. The C-band used to be reserved for satellite TV signals, but satellite transmissions in this range required enormous 10-foot and larger dishes — you might remember seeing them pretty often in the 80s and 90s. They’ve mostly been replaced by Ku-band technology, which can use smaller 1-foot dishes. With modern technology, it’s possible for operators to compress their remaining C-band usage, opening up wide swaths of these optimal frequencies for 5G. And that’s what they’re doing; operators will be done with the lower C-band on December 5th.
The aviation industry has been expressing concerns about C-band interference for some time, and this prompted the Federal Aviation Administration (FAA) to finally step in this week. It issued a “special information bulletin” that noted the potential for C-band interference with radio altimeters. These devices measure the height of the aircraft above the ground using radio waves between 4.2 and 4.4GHz, which is adjacent to the new 5G C-band. The FAA believes C-band transmissions could leak into the altimeter range, causing potential safety issues.
Industry experts stress that there’s no evidence of issues like this in other regions where mid-band 5G is more developed. Still, this is a “better safe than sorry” situation. The carriers are working with regulators to understand the FAA’s concerns. It’s likely the rollout will go ahead in early 2022, but you never know. Meanwhile, T-Mobile is sitting pretty on the big pile of the spectrum it got from Sprint. The Band 41 (2.5GHz) block is generally faster than LTE and has better range than mmWave, so it’s already in a good place for 5G. T-Mobile also acquired a piece of C-band spectrum that won’t be clear until 2023. AT&T and Verizon will be pushing hard to get started with C-band in order to catch up to Tmo.
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