Verizon, T-Mobile push unlicensed LTE forward - but concerns remain

Mike Dano

BARCELONA, Spain--A major topic at this year's Mobile World Congress trade show here is whether, how and when wireless operators should conduct LTE transmissions over unlicensed spectrum. And based on comments from those in the industry, it appears this technology is well on its way to being deployed broadly starting next year. But  Wi-Fi proponents are concerned that the technology could affect the Wi-Fi industry.

And hanging over the whole issue is the nagging notion that allowing wireless operators to butt into unlicensed spectrum is fundamentally unfair.

But let's start at the beginning. For the past few years or so, vendors including Qualcomm (NASDAQ:QCOM), Ericsson (NASDAQ: ERIC) and others have floated the idea that overloaded LTE networks could make use of unused, unlicensed spectrum by combining an LTE transmission in licensed spectrum with an LTE transmission in unlicensed spectrum via carrier aggregation. The general idea is that an LTE user would instigate a transmission in a carrier's licensed spectrum band and then, once that licensed connection is established, the technology would expand into an unlicensed spectrum band to increase the size of the available downlink channel--basically making a user's connection to the Internet faster by downloading content simultaneously in both a licensed spectrum band and a separate, unlicensed spectrum band.

To work, the technology requires new hardware in both the user device and the operator's access point--meaning that you would have to buy a new phone and your operator would also have to install a new base station or small cell before you could enjoy faster downloads.

Initially called LTE Unlicensed, or LTE-U, the technology is part of the 3GPP's Release 12. A more specific version of the technology is also under discussion for inclusion in the 3GPP's forthcoming Release 13. (The 3GPP recently renamed LTE-U as Licensed-Assisted Access, or LAA. But Verizon still calls it LTE-U. It's unclear which name will ultimately stick.)

Now here's where it gets a little murky, but based on the discussions I've had this week, it appears that Verizon (NYSE: VZ), Vodafone and other carriers last year decided they wanted to make LTE-U a reality--and they decided they didn't want to wait for the 3GPP to standardize the technology. So they teamed up with some network technology companies to design real-world tests of the technology.

This week, Verizon released the parameters of the tests it wishes to conduct to determine exactly how it can deploy LTE-U. And Verizon clearly has high hopes for the tests and the technology--it has said that it plans to commercially deploy it in the 5 GHz and 3.5 GHz bands in 2016.

Verizon is not the only carrier that supports LTE-U/LAA. T-Mobile announced this year that it too will deploy what it calls LAA in the 5 GHz band in 2016. T-Mobile CTO Neville Ray said he believes the carrier can get LAA-capable handsets this year. Qualcomm said that SK Telecom, Vodafone, Verizon, T-Mobile and LG U+ are all evaluating LTE transmissions in unlicensed spectrum. A recent test by Vodafone Spain showed LTE-U speeds of up to 600 Mbps.

However, not all carriers are on board.

"That's not standardized yet," said Tom Keathley, SVP of wireless network architecture and design for AT&T, in response to questions on whether AT&T would support LTE-U. "We have not finished our analysis."

Specifically, Keathley said that current approaches to LTE-U are vague about how exactly to check for existing users in unlicensed bands, and how long LTE users can occupy unlicensed spectrum.

Eric Parsons, one of Ericsson's top LTE-U executives, explained that the issue revolves around how LTE-U technologies check for existing users in an unlicensed band (called "listen then talk" or "clear channel assessment") and how long a user should sit in the unlicensed band (called the "duty cycle" or the "occupancy.") He said there are very specific guidelines in Europe and Japan that cover these areas, but countries like the United States don't have specific guidelines. But Parsons said that Ericsson has developed LTE-U technology that doesn't affect existing Wi-Fi users--he hinted that concerns over the deployment of LTE-U are more related to business questions than technology problems.

But AT&T isn't alone in voicing concern over LTE transmissions in unlicensed spectrum.

The Wi-Fi Alliance issued a statement in February that basically said it is still evaluating LTE-U and LAA and that more work is required. "There is a risk that LAA, and especially pre-standard systems deployed ahead of coexistence work being done in the industry, will negatively impact billions of Wi-Fi users who rely on 5 GHz today for networking and device connectivity," the group said. Parsons said Ericsson and other vendors are working to explain the technology to the Wi-Fi industry and get them on board.

After reviewing tests of LTE-U, Derek Peterson, CTO of Wi-Fi provider Boingo, said he thinks that they still have some work to do. However, he added that he expects the engineers who are working on the technology to eventually be able to address his concerns.

And EJL Wireless Research analyst Maury Wood recently issued a post with detailed concerns about Qualcomm's implementation of LTE-U.

Clearly there is a lot of interest among wireless operators in LTE-U technology, and that doesn't come as a surprise. As LTE networks become increasingly stretched out by users' data demands, operators are looking for new and effective ways to satiate that desire. What better way to do so than to step into unused, unlicensed spectrum while at the same time being able to keep a tight rein on a user's experience.

But there's something fundamentally unfair about allowing cellular carriers to butt into unlicensed Wi-Fi spectrum. Unlicensed spectrum is currently being used by cable companies, MVNOs and startups to offer new and innovative services--services that in some cases compete directly with those offered by regular cellular carriers. To have cellular carriers step into the unlicensed arena and potentially take up space that could be used by other, smaller players feels like a smear on the spirit of the freewheeling Wi-Fi industry.

And if carriers begin widespread deployments of LTE-U, will that diminish their financial motivation to improve their operations on licensed spectrum bands?

Of course, unlicensed spectrum is just that--unlicensed--which means that anyone, including wireless carriers, can do what they wish. Further, normal people don't care whether their Facebook News Feed is delivered over Wi-Fi or LTE, as long as it's snappy and cheap.

LTE-U, LAA or whatever the technology ends up being called is definitely interesting, and could have major future implications. But the wireless industry will need to tread carefully in the unlicensed world or risk the wrath of regulators, public-interest groups, Wi-Fi proponents and regular Wi-Fi users like me. --Mike | @mikedddano

Read more on