Key to LTE-U Deployment Said to be Coexistence Standards

LTE-U's backers and critics agree the technology shows immense promise. Beyond that, consensus starts to break down on how to best implement it so as not to cause interference with Wi-Fi, according to panelists at a Monday night FCBA seminar on Wi-Fi-LTE-U. "These unlicensed bands are great [and] there's promise we can still avoid the rocks," said panelist Paul Margie of Harris Wiltshire, whose clients include wireless companies and ISPs.

The seminar featured a pair of panels -- one on LTE-U technical issues and one on its policy and regulatory implications. Much of the discussion involved the issue of standards for LTE-U. The coexistence protocols agreed to by the LTE-U Forum were to ensure it was "polite" to other wireless spectrum users, said Patrick Welch, Verizon assistant vice president-federal regulatory affairs. But one of the main worries among critics is that coexistence specifications are "too loose," said Tom Peters, senior technical adviser at Hogan Lovells: "There's not a whole lot of detail -- it leaves a lot to interpretation." While FCC Part 15 rules are technology agnostic, Peters said, there seemingly are concerns at the agency about a negative effect on Wi-Fi "on their watch," making the Office of Engineering and Technology apparently reluctant to certify LTE-U devices. An FCC spokesman said Tuesday that the agency is waiting for standards bodies to discuss LTE-U/Wi-Fi issues, but it doesn't have any LTE-U devices before it to review and it will evaluate and ask technical questions about any that do come in.

LTE-U backers repeated their core message numerous times -- that Wi-Fi is a key part of their businesses, and doing anything to disrupt that would be business suicide. Every device T-Mobile sells is Wi-Fi calling enabled, and its customers make 11 million Wi-Fi calls daily, said Director-Spectrum Policy John Hunter. And when T-Mobile begins testing LTE-U equipment in Q1, the aim is "an augment to Wi-Fi, not a replacement," Hunter said. A Qualcomm executive pointed to LTE-U/Wi-Fi interference testing the company has done showing no change in throughput from Wi-Fi access points in the presence of an LTE-U signal (see 1509160039). But in CableLabs testing with aggressive implementation of LTE-U, "you see Wi-Fi fall off the map," Margie said, adding that raises red flags because Ericsson is working on applications with a similar duty cycle.

The cable industry has pushed for a "listen before talk" (LBT) protocol to be part of LTE-U to ensure no Wi-Fi interference (see 1509230078). Even that might not be a fix because LBT can degrade Wi-Fi as LBT has different implementations, some better than others, said Vinko Erceg, technical director at Broadcom, which also discussed its concerns with the FCC (see 1510060018). "Depending on the algorithm, it can bring vastly different results," he said. Robust coexistence mechanisms need to be global -- something LTE-U is not, Erceg said. Another big concern is that the U.S. is one of the few nations that doesn't include LBT, and that LTE-U coexistence features such as duty cycle can be individually configured by individual carriers, said Michael Calabrese, director of New America's Wireless Future Project. Carriers also will have the technical ability -- and business incentive -- to be anticompetitive, using LTE-U to fend off possible Wi-Fi-first competitors like Google's Project Fi, Calabrese said. While standards are being worked out through the 3rd Generation Partnership Project for licensed-assisted access, Margie said, "LTE-U is a different story." Part of LTE-U's problem is that sharing specifications are suggested but not required, meaning it could end up deployed without some key protections, Margie said.

Standards for unlicensed spectrum use are unnecessary, Welsh said, pointing to the hundreds of technologies launched in unlicensed spectrum that don't have standards. "Bluetooth didn't get permission from the Wi-Fi community," Welsh said. If there are interference problems, the FCC has the statutory authority to swoop in and stop the interfering operations, he said, saying it fined Marriott International and Marriott Hotel Services $600,000 last year for Wi-Fi blocking at the Gaylord Opryland Hotel and Convention Center in Nashville (see 1410060066). The difference with LTE-U is scope and scale, Margie said: "We're looking at a carrier scale nationwide deployment, not a toe in the water." However, Welsh said, currently no LTE-U devices are in the market. "This is going to be an iterative process," he said. "You don't scale a network overnight."