AT&T in no hurry to test and deploy LTE-Unlicensed

Unlike rivals Verizon Wireless (NYSE: VZ) and T-Mobile US (NYSE:TMUS), AT&T Mobility (NYSE: T) is not in a rush to trial and deploy LTE-Unlicensed (LTE-U) technology, according to an AT&T executive. AT&T might use LTE-U, but only if it can assure that it will not harm Wi-Fi, according to AT&T's Tom Keathley, who said that the carrier would be willing to wait for a standardized version of the technology known as a Licensed-Assisted Access.

"We don't have any hard plans to trial [LTE-U]," Keathley, AT&T's senior vice president of network and product planning said in an interview last week with FierceWirelessTech at AT&T's wireless headquarters in Atlanta.

Philosophically, he said, AT&T does support the use of unlicensed spectrum for capacity to be aggregated with what he called "a foundation LTE carrier." However, he said that AT&T would do so only if it could "assure fair use to any technology vying for that spectrum, i.e. Wi-Fi."

Wi-Fi proponents worry that the control and scheduling in LTE-U will always be run over the licensed channel since it is centrally-scheduled, meaning that carriers will hold the balance of power over how much spectrum is devoted to LTE and how much to unlicensed Wi-Fi. The Wi-Fi Alliance urged caution and cooperation with Wi-Fi users in February.

AT&T is a major Wi-Fi proponent itself and currently owns and operates around 34,000 Wi-Fi hotspots at restaurants, bookstores, hotels and other locations.

Keathley noted, importantly, that LTE-U in the U.S. would not contain a so-called "listen before talk" methodology. That term means that devices listen to see if there is Wi-Fi activity on a channel and if there is, they do not transmit. Keathley said that LTE-U, as currently envisioned, would only use a "duty cycle" methodology, meaning that it has the capability of transmitting and listening through some pre-set cycle that would attempt to guarantee fair use.

The 3GPP standards body is currently working on standardizing LAA, but has not yet done so, so some carriers are moving ahead with the unstandardized LTE-U. LAA likely will be enabled in LTE Release 13.

"LAA is listen before talk," Keathley noted. "To get to LAA requires a 3GPP LTE standards change. LTE-U will not include that standards change. So by definition it cannot be listen before talk."

The current thinking on LTE-U is that it will be most appropriate in the 5 GHz band, though the 3.5 GHz band is also an option. Qualcomm (NASDAQ:QCOM), which is a major proponent of both Wi-Fi and LTE-U, has noted that using channel selection, "LTE-U small cells always try to select a clean channel to avoid interference with nearby nodes, based on continuous channel measurements. Considering that multiple 20 MHz channels are available in 5 GHz, channel selection is very effective in low to medium density scenarios."

However, Qualcomm notes that in some markets, including the U.S., South Korea and China, there are no requirements for listen before talk, also known as LBT. In those scenarios where there are no LBT requirements, Qualcomm proposes several techniques to ensure that Wi-Fi is not harmed, including "carrier-sensing adaptive transmission," which senses channels for a longer period of time and then gates off or blocks LTE transmissions proportionally. Another method is called "opportunistic secondary cell operation," in which LTE-U small cells would release the unlicensed carriers and fall back to the main carrier in licensed spectrum at low traffic levels.

In the meantime, other carriers are moving ahead. T-Mobile has said it will be one of the first carriers to deploy LAA in 5 GHz spectrum in 2016, and is teaming up with Qualcomm and Alcatel-Lucent (NYSE: ALU) to use LTE in the unlicensed spectrum, with trials beginning this year using LTE-U enabled small cells from Alcatel-Lucent that are equipped with Qualcomm Technologies' FSM99xx family of small cell system-on-chip (SoC) solutions. Commercial products are expected in the first half of 2016.

Verizon earlier this year announced that it plans to deploy LTE-U technology in the 5 GHz and 3.5 GHz bands starting in 2016.

"I'm not saying that that won't be fair use," Keathley said. "It may. It's not guaranteed and we haven't finished our evaluation on the 'U' piece of whether or not that will guarantee fair use."

Keathley noted that if AT&T does go with LTE-U "then we will have validated it provides a fair use. Now, even if we don't go with it doesn't mean it won't [provide fair use]."

The AT&T executive noted that LTE-U is designed primarily for small cells at this point. "So it might just make more sense to wait for LAA if LAA comes quickly," Keathley said.

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