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LTE-U: A quick explainer

Jon Gold | Oct. 28, 2015
LTE-U is a wireless network technology that’s promising a lot, as well as ruffling a few feathers (especially in the Wi-Fi world). Here’s a brief rundown for the perplexed.

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LTE-U is a wireless network technology that’s promising a lot, as well as ruffling a few feathers (especially in the Wi-Fi world). Here’s a brief rundown for the perplexed.

OK, so what’s LTE-U?

LTE-U is a system of wireless communication designed to use unlicensed spectrum – which is open to everybody, within certain limits – to ease the burden on big mobile carriers’ networks. Regular LTE is the system they use to transmit and receive information across their licensed spectrum – to which only they have access. LTE-U (short for Long-Term Evolution in unlicensed spectrum) uses the same “language” to operate on the unlicensed spectrum, which the carriers don’t have to spend billions of dollars to acquire.


Oh, goodness, yes. The FCC has been busy auctioning off the rights to various parts of the spectrum lately – companies bid for the rights to such-and-such a frequency in specific geographic locations in the U.S. – and the last auction took in almost $45 billion.

Cripes, that’s real money, even for Verizon and AT&T.

Sure is. And the reason they’re willing to spend it is that their networks are creaking under the truly crazy demand for data that they’re facing – all that Netflix and YouTube and Twitch and even the stuff that isn’t video (although video is the biggest issue by a long shot) is creating serious capacity problems for the big carriers.

That’s why they’re doing everything they can to stay ahead of it – building new infrastructure, acquiring new spectrum and trying to impose data caps without looking like they’re imposing data caps. LTE-U is part of that, since it would let them offload some of the spiraling demand onto the unlicensed band.

Swell. So what’s the big deal?

Well, there’s this thing called Wi-Fi that operates on the unlicensed band in the 2.4GHz and 5GHz ranges. Which is exactly the piece of spectrum that LTE-U wants to use. Two radio waves in the same physical location at the same frequency means interference, which means crappy service and “ugh-why-doesn’t-this-stupid-thing-work?”

Oh, well, that’s going to annoy just about everybody, huh?

Yep. Qualcomm – which invented LTE-U – swears up and down that they’re incorporating coexistence features that will prevent it from harming existing Wi-Fi installations, and to be fair, it seems highly unlikely that they’re just planning to throw LTE-U out there, your home Wi-Fi be damned. The problem is, though, that we don’t really have any way of knowing that for sure, nor any guarantees that the system will operate the way it ought to.

How come?

Qualcomm didn’t present LTE-U to either of the big wireless industry standards bodies – 3GPP or IEEE – for formal testing and approval, even though they’ve been relatively up-front about what the technology is going to entail. The idea will be to use a system called CSAT (Carrier Sense Adaptive Transmission, before you ask) to make LTE-U stations pause their transmissions for tiny periods to allow Wi-Fi to make use of the same frequencies. The principle is called duty cycling.


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