The New Odd Couple: LTE and Wi-Fi in Unlicensed Spectrum

Carl Weinschenk
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Fifteen Wi-Fi Predictions for 2015

One of the serendipitous things about the coexistence of LTE and Wi-Fi is that one runs in licensed spectrum and one does not. The LTE spectrum that is now used is more expensive, but due to that barrier to entry, is less chaotic and crowded. Unlicensed Wi-Fi, conversely, is the equivalent of a New York City subway at rush hour. It gets you there, but the ride is not necessarily for the faint of heart.

Because of this fundamental difference, Wi-Fi is attractive to carriers because there is no reason not to shuttle some LTE traffic from the licensed to the unlicensed spectrum. It’s the equivalent of telling your GPS to avoid the toll roads.

Using an unlicensed spectrum for LTE (LTE-U) creates some complexities, though. Sarah Thomas at LightReading explains that plans are to use LTE-U in the 5 GHz spectrum area. The problem is that the nature of the LTE signals can interfere with and even shut down the current Wi-Fi tenants. There is a way around that problem, which is aptly named the listen-before-talk (LBT) protocol.

The 3rd Generation Partnership Project (3GPP), which is in charge of LTE, has introduced LBT. However, that technique is available so far in only release 13 of the protocol. In the U.S., South Korea, China and India, Thomas writes, carriers are free to use earlier releases and, thus, aren’t forced to use LBT.


The good news for ISPs and their customers is that at least one U.S. carrier plans to include LBT. At the cable industry’s INTX trade show this week in Chicago, T-Mobile U.S. National Director Tony Silveira said that the company will abide by a “good neighbor policy” and use LBT to make sure that its signal plays nicely with the Wi-Fi signals currently using that spectrum.

T-Mobile’s intentions, as honorable as they may be, are only a small part of the overall landscape. Standards, rules and regulations are needed so that all players know what the landscape looks like. On Tuesday, the Federal Communications Commission (FCC) took a big step toward hashing them out. It released a public notice asking interested parties for comments focusing on a series of pertinent questions.

EE Times goes into the bits and bytes of LTE-U and a similar protocol called Licensed-Assisted Access (LAA) and their relationship to Wi-Fi. The story makes the point that the FCC’s involvement means that the macro picture – the way in which unlicensed spectrum will be used in the United States – now is in play:

Aside from the technical coexistence discussions on LTE-U/LAA and Wi-Fi, the FCC’s public notice is likely to trigger a whole new industry debate on how best the nation’s unlicensed spectrum should be appropriated and used, now that powerful cellular operators with licensed spectrum want to poach it.  And who should arbitrate that.

If it is allowed to stray into unlicensed waters, the gains for LTE may be great. Korea Times reported today that mobile carrier LG Uplus demonstrated LTE-U operating in the 5.8 GHz spectrum hitting speeds of 600 Megabits per second (Mbps). That is double the speed of the carrier’s tri-band LTE Advanced (LTE-A) service.

Though there is a lot at stake in the debate, the immediate issue is the relationship between LTE and Wi-Fi in the 5GHz band. The bigger picture is a recognition that Wi-Fi is changing, both in its use cases and sophistication. Thus, how it is administered by the government likely must change as well. How LTE-U is administered is the beginning of the debate about these changes.

Carl Weinschenk covers telecom for IT Business Edge. He writes about wireless technology, disaster recovery/business continuity, cellular services, the Internet of Things, machine-to-machine communications and other emerging technologies and platforms. He also covers net neutrality and related regulatory issues. Weinschenk has written about the phone companies, cable operators and related companies for decades and is senior editor of Broadband Technology Report. He can be reached at cweinsch@optonline.net and via twitter at @DailyMusicBrk.



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