The Rocky Road To LTE-U And Use Of Unlicensed Spectrum

2015 ended on a difficult note for those following the LTE-U developments. A battle seemed to be brewing. What was a tense conflict about how LTE will operate on unlicensed spectrum has evolved into a feel good example of competitive sectors peacefully ironing out their differences.

The cellular industry, attracted by the availability of free spectrum, is bringing LTE to the 5GHz unlicensed spectrum. This spectrum, of course, is home to Wi-Fi.

That’s a big deal — and a big challenge: LTE was not designed to operate in such a roiling and open environment. A lot of clever engineering is required to make it possible. The root of conflict was that the approach some cellular carriers advocated was raising fear among the incumbent spectrum users (Wi-Fi vendors) that LTE be unable to act as a “good neighbor” and could cause potentially serious interferance issues for Wi-Fi users at home and in the enterprise.

If LTE was the source of the interference, there would be very little that vendors could do to solve the problem.

Cooler heads prevailed, however, and the nascent confrontation turned to cooperation. The Wi-Fi Alliance has released draft test procedures for Wi-Fi/LTE-U coexistence. Both sides realize that it is in their interests to work together.

LTE-U: Where we are now

There are three main approaches to LTE on unlicensed spectrum: LTE-U, License Assisted Access (LLA) and MuLTEfire. While LTE-U garners the most attention in the news, carriers vary in which approach they are likely to adopt.

Despite the presence of the trio, it doesn’t seem that cellular carriers are rushing to begin unlicensed operations. Indeed, the sense is that they are approaching the opportunity gingerly.

They are starting to move, however. Andrew Fuller at Android Headlines wrote at the beginning of March that AT&T is testing LTE-U and is interested in LAA. Verizon is moving toward commercial use of LTE-U while T-Mobile is going to LTE-LAA. Sprint seems to be undecided. Qualcomm, the vendor that is central to last year’s drama, is playing both sides of the fence: Rethink Wireless in February said that it will demonstrate LTE-U with Verizon in the United States and is working on LTE-LAA with Deutsche Telekom in Germany.

Any reticence may be due to a continued sense of uncertainty on which technique will dominate. The one least favored by the Wi-Fi players – LTE-U – is the one being pushed by a group led by Qualcomm. Late last year it looked like the two sides would battle and the Federal Communications Commission (FCC) would have to step in and settle matters. Indeed, there was a palpable sense of anger between the sides that rarely is present on technical engineering issues.

Now, however, those same engineers are working together to solve the issues that almost triggered war last year. Rob Alderfer, the Vice President of Technology Policy at CableLabs, referred in a blog to a tone of “cautious optimism” that is in “contrast to the tone of the LTE-U debate in 2015.”

According to Alderfer, a draft set of LTE-U validation procedures were released at a workshop in February. “Work is continuing expeditiously within the WFA toward a complete coexistence test plan, which is essential to addressing the technical concerns that have been raised around LTE-U.”

Alderfer wrote that work is proceeding on LAA in the Third Generation Partnership Project (3GPP). The international body finished the primary draft of the standard last December and has sent liaisons to the IEEE and Wi-Fi Alliance to review. Plans are to be finished in June. “[The] 3GPP has been very constructive in driving fair coexistence mechanisms for LAA with Wi-Fi,” Alderfer wrote.

The cellular industry no doubt is serious about using unlicensed spectrum for LTE. It is likely that they will take it very slowly, however. On one hand, they know that the Wi-Fi players and the FCC are watching closely. They also know that end users of their products won’t abide problematic services.

Carl Weinschenk is a long-time IT and telecommunications journalist. His freelance work appears at IT Business Edge, Energy Manager Today, and other corporate and journalistic sites.

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