Clash of Carriers, Backing LTE-U, and Wi-Fi Boosters Intensifies on Interference Concerns

The LTE-U Forum and T-Mobile assured the FCC in a letter posted Thursday in docket 15-105 that LTE-unlicensed and Wi-Fi can peacefully operate together. LTE technology "has been carefully designed to coexist well with Wi-Fi so that consumers will enjoy better coverage, faster network speeds and reduced latency," Tom Sawanobori, CTIA chief technology officer, said in a statement.

But NCTA said "absent a broad technical consensus, millions of Wi-Fi consumers are at risk," in a filing. It was posted Wednesday to the docket urging that whatever coexistence features are adopted internationally for licensed assisted access (LAA) LTE apply to all types of unlicensed LTE.

NTIA Chief of Staff Glenn Reynolds said at the CTIA conference that the agency could provide guidance, doing testing through its lab in Boulder, Colorado, if necessary. “We’d be happy to get involved and help try to be the honest broker as far as unraveling some of these technology and engineering debates, in case anyone wants to approach us,” Reynolds said.

LTE-U already is "a better neighbor to Wi-Fi than Wi-Fi is to itself," said the LTE-U Forum and T-Mobile. LTE-U "was developed to provide consumers who choose to use it a great broadband experience without causing any adverse impact on those opting to use Wi-Fi," they said. The group has "been clear to the FCC and the public that it is critical that LTE-U and Wi-Fi coexist successfully,” it said. “Our companies are all strong supporters of Wi-Fi. Millions of our consumers rely upon Wi-Fi every day. We have deep, continuing business interests in Wi-Fi, and we have every incentive to ensure that these technologies operate alongside each other well. We would never have developed or pursued deployment of LTE-U if it would harm our customers’ use and enjoyment of Wi-Fi.”

The letter responds to an Aug. 5 letter from Office of Engineering and Technology Chief Julius Knapp asking questions about LTE-U. The forum was founded last year by Verizon in cooperation with Alcatel-Lucent, Ericsson, Qualcomm and Samsung, its website said.

FCC Wireless Bureau Chief Roger Sherman said during a CTIA panel discussion that he had yet to review the LTE-U Form response. FCC Chairman Tom Wheeler has sent a clear message that industry should work out its differences on LTE-U, Sherman said Wednesday.

'Disinformation'

There is a lot of “disinformation” swirling about LTE-U, T-Mobile Senior Vice President Kathleen Ham said, also during a panel talk on spectrum issues at CTIA: “The commission has to be careful that it doesn’t get roped in to what really is an industry fight between the cable industry and wireless industry.” T-Mobile is “a major, major user of Wi-Fi,” she said. “We want harmony with Wi-Fi.”

Verizon Senior Vice President Kathleen Grillo encouraged everyone who cares about the issue to give the LTE-U Forum letter a close review. “Facts matter all the time, but they matter here a lot because there’s a lot at stake,” she said. The U.S. has long been a leader in unlicensed technologies because of the low barriers of entry to using unlicensed spectrum, Grillo said. “You meet the Part 15 requirements and you can use the spectrum,” she said. "That encourages disruption.” The forum letter makes clear that LTE-U will be a “good neighbor” to Wi-Fi, she said.

The LTE-U Forum's three interference-prevention etiquette protocols are LTE-U's spectrum-sensing capability that has it look for open frequencies and transmit only on those channels, its automatic taking of the "least crowded" channel if none is open through carrier-sensing adaptive transmission (CSAT), and that traffic always defaults to an operator's licensed network, using unlicensed spectrum only when that network is congested, it said with T-Mobile. Some Wi-Fi equipment doesn't do channel-sensing accurately, while Wi-Fi nodes vary widely in their ability to share spectrum with each other and with other technologies, they said. LTE-U's CSAT is analogous to Wi-Fi's channel-sharing carrier sense multiple access (CSMA) protocol, except that CSMA sometimes results in separate Wi-Fi nodes transmitting on the same channel, they said.

Coexistence features are being discussed for LAA LTE, but LTE-U "does not meet even the minimal coexistence standards being advanced for LAA," NCTA said. That companies are developing LTE-U for the U.S. market means domestic customers might not get any benefit from the coexistence mechanisms being proposed to 3GPP for the LAA standard, NCTA said. Those mechanisms involve equitable spectrum access across all technologies, including "listen before talk" configurations; assurance that consumers can access their network of choice; and enabling coexistence testing, measurement and certification of LAA technology, and they should apply equally to all unlicensed LTE variations, NCTA said.

Wi-Fi and other technologies that use unlicensed spectrum work because they "all follow politeness rules," said John Solit, NCTA senior director-digital strategy, in a blog post Wednesday. "They listen out for each other’s signals and take steps to avoid interference. But LTE-U, which also relies on unlicensed spectrum, doesn’t want to follow these rules. LTE-U thinks it can bully technologies using unlicensed spectrum and prioritize itself over others. In doing so, LTE-U puts all unlicensed technologies at risk and could make Wi-Fi slower, less reliable, and less available."

Qualcomm 'Encouraged'

Qualcomm Senior Vice President Dean Brenner said he was encouraged by Wheeler's comments at CTIA noting that the FCC was looking at LTE-U. "We have filed a mountain of test results," Brenner said. "LTE-U devices, once they are submitted, will go through the FCC's regular approval process," he said in a written statement. "We are confident that at the end of the day, any fair person will conclude that LTE-U will not have any adverse impact on Wi-Fi. In developing LTE-U, we have collaborated broadly with the Wi-Fi community (of which we are part) in groups, individually, and via associations, and we plan to continue doing that to address questions, ease concerns, and resolve issues."

Verizon Vice President-Policy David Young said LTE-U offers much promise. “This isn’t old-school LTE technology, the kind mobile devices currently use,” he wrote in a blog post Thursday. “This is a technology specifically designed for the unique environment used in unlicensed bandwidth.” Verizon wants to make sure that LTE-U won’t degrade Wi-Fi, he said. “The reason is obvious: our customers use their mobile devices with Wi-Fi, either connecting to home and public hotspots, or using their phones and 'jet packs' to create their own hotspots.”

Bret Swanson, president of Entropy Economic, said in a blog post in Computerworld Thursday that LTE-U tests show the technology delivers better performance than Wi-Fi, doesn’t degrade Wi-Fi performance and “may in fact improve the performance” of nearby Wi-Fi networks. ”I will be looking for more real-world tests that either confirm or contradict the initially encouraging evidence,” he wrote. “Until then, we should not prejudge and block a potentially useful new technology. We should remain optimistic that cooler heads prevail.”