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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.

That sounds fair enough – but people still have a problem?

Yeah – the thing about duty cycling is that the carriers are the ones in charge of scheduling those pauses, and they’re under no real obligation to provide a decent window of time for Wi-Fi to coexist. Remember, it’s unlicensed spectrum! But since Wi-Fi is what’s known as a polite protocol, it will politely stop talking when the LTE-U is transmitting – and even if it didn’t, all that would happen is the signals crashing into each other and getting garbled. Basically, LTE-U’s coexistence mechanisms aren’t very convincing to some people, and there’s no standards group that has the authority to force it to play nice.

Well, that’s no good – what are the alternatives?

There’s a technology called Licensed Assisted Access or LAA that does roughly the same thing as LTE-U, but folds in a standard called “listen before talk” (LBT), which does pretty much what it sounds like. (Wi-Fi does this.) It’s not a perfect solution to the main coexistence problem, but LTE-U critics say it’s considerably more even-handed than Qualcomm’s plan. LBT is actually a legal requirement in the EU and Japan, so LAA is the only game in those particular towns.

Huh. So why not just use that instead?

Because LAA is a 3GPP standard, and as such is going through a lengthy process of testing and approval – which means that, in places that don’t legally mandate the use of LBT, including the U.S. and China, companies could rush LTE-U to market quicker and help take the pressure off their networks.

If the carriers have this huge demand problem, wouldn’t they want to make it easier for people to use Wi-Fi instead?

Certainly, and LTE-U’s backers have been making this very point at great volume as evidence that LTE-U won’t pose a coexistence problem. Realistically, it doesn’t seem likely that any version of LTE-U that the carriers would release would cause Wi-Fi Armageddon, and the problem seems more likely to be a matter of degrees – if LTE-U helps ease a carrier’s network load, even if it has minor deleterious effects on Wi-Fi networks in an area, they can probably live with that, given that there aren’t any real consequences for them.

Uh-oh.

To be fair, there’s no need to freak out just yet – Verizon and T-Mobile, the strongest advocates for LTE-U, have said that they’re not planning to roll the technology out until next year, and a lot can happen between then and now. Discussions among industry players are continuing, and FCC chairman Tom Wheeler has hinted that that agency could get involved if the companies can’t come up with a more convincing solution to the coexistence problem.

 

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