3GPP Officially Begins Study of ‘LTE Over Unlicensed' Technology in 5 GHz

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By Paul Barbagallo

Sept. 15 — The Third Generation Partnership Project, an industry standard-setting organization, has approved a proposal to study the feasibility of deploying LTE (Long Term Evolution) technology in unlicensed spectrum in the 5-gigahertz band.

The decision came at the end of a four-day plenary meeting of 3GPP's Radio Access Network technical specification group (TSG RAN) last week in Edinburgh, Scotland after several amendments were included to clarify language on the study's scope.

In official terms, “LTE Over Unlicensed,” or LTE-U, will now be considered as part of 3GPP's standards “Release 13,” which is not likely to be completed until 2016. But timing aside, the group's action is significant because it sets up a formal process to begin testing LTE Over Unlicensed, a potentially game-changing technology, on a global basis. Critics of the idea can also now begin formally organizing their opposition.

Impact to Wi-Fi?

As originally conceived by Ericsson and Qualcomm Inc., a supplementary 20-megahertz channel in the 5-GHz band would be combined with channels in licensed spectrum from 700 MHz to 2.6 GHz using LTE Advanced's carrier-aggregation mechanism. The companies' decision to target 5 GHz, out of all other spectrum bands, was an easy one: There already is more than 500 MHz available in the band on a shared basis, with hundreds of megahertz more slated to be freed up by regulators in the United States, Europe, and Asia in the coming years. The 5-GHz band is also where Wi-Fi is making its future home. Thus the technology that could help solve the so-called spectrum crunch—LTE Over Unlicensed—could at the same time ignite new battles with Silicon Valley, cable operators, and maybe even the world's communications regulators, none of whom will want to see a new technology annex unlicensed spectrum for the sole benefit of one industry segment—and limit the future development of Wi-Fi in the process.

For their part, the study proposal's sponsors—Ericsson, Qualcomm, Huawei Technologies Co. Ltd., and Alcatel-Lucent—underscored the importance of LTE coexisting with Wi-Fi.

“In some regions in the world, unlicensed technologies need to abide to certain regulations, e.g. Listen-Before-Talk [LBT],” they wrote in the document approved by 3GPP, “Study on Licensed-Assisted Access using LTE,” which was obtained by Bloomberg BNA Sept. 15. “Fair coexistence between LTE and other technologies such as Wi-Fi as well as between LTE operators is seen necessary. Even in countries without LBT, regulatory requirements exist to attempt to minimize interference with other users of the unlicensed spectrum. However, it is not enough to minimize interference simply for regulatory aspects. It is also essential to insure that a deployed system will operate as a ‘good neighbour,' and not significantly impact legacy systems. Therefore a study is required to determine a single global solution which enhances LTE to enable licensed-assisted access to unlicensed spectrum while coexisting with other technologies and fulfilling the regulatory requirements.”

Of the four nationwide wireless carriers—Verizon Wireless, AT&T Inc., Sprint Corp., and T-Mobile US Inc.—all four signed on as supporters of the study.

AT&T had initially raised some concern, however. In a presentation given during a workshop on the issue in June, AT&T said that if licensed networks (AT&T's own, even) were allowed to borrow capacity from unlicensed spectrum, then there would be less capacity left for unlicensed users (also AT&T). For this reason, the company urged 3GPP to “determine enhancements which enable LTE to coexist with legacy technologies in unlicensed bands.”

But AT&T is not the only carrier with Wi-Fi interests.

Last week T-Mobile US Inc. announced that its customers will be able to use Wi-Fi to make phones calls and text messages, helping them stay in touch even in dead spots in their homes or office buildings.

Next Steps

With the study approved, stakeholders will present findings to the 3GPP in March 2015, with possible final approval as early as June 2015.

Reporting contributed by Tim McElgunn

To contact the reporter on this story: Paul Barbagallo in Washington at pbarbagallo@bna.com

To contact the editor responsible for this story: Bob Emeritz at bemeritz@bna.com

For the full text of the study item, visit http://op.bna.com/der.nsf/r?Open=sbay-9nypb8