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LTE-Unlicensed Poses Threat to Cable WiFi

Don’t look now, but Long Term Evolution, the technology powering the mobile industry’s 4G wave, could soon crash cable’s WiFi party.

There’s a big movement afoot to enable LTE to operate in the unlicensed 5-Gigahertz band, the same spectrum that’s being used by the latest WiFi equipment. By offloading some traffic on that band using “small cells” deployed in high congestion areas, carriers see LTE-Unlicensed as an efficient method to keep capacity demands in check.

The idea has drawn concerns from the WiFi and cable industries. While WiFi was developed to be “polite” and share unlicensed spectrum, LTE operates differently — it’s not inherently fair from a bandwidth perspective, because it’s designed to work on exclusive, licensed spectrum. The fear is that use of LTE in unlicensed spectrum would dominate the traffic and not allow WiFi to get a word in edgewise.

The use of LTE in unlicensed spectrum is progressing on two fronts — a faster-track version that won’t include some mechanisms, such as “listen-before-talk,” that are foundational to the way WiFi operates; and a standardized version called Licensed Assisted Access (LAA) that is underway at the 3rd Generation Partnership Project (3GPP), which is expected to support listen-before-talk.

LTE-U was a hot topic at March’s Mobile World Conference show in Barcelona, Spain. Qualcomm, for example, announced it would extend LTE to the unlicensed spectrum in the 5-GHz band, with a system-on-chip for small cells slated for availability later this year.

The initial deployment of LTE-U is for a “supplemental downlink,” Mazen Chmaytelli, senior director business development at Qualcomm, said, adding that he expects some tier-1 operators in regions such as North America and Asia to start deployments of LTE-U in the first half of 2016.

While some mobile operators have eyed WiFi to balance the data load, LTE-U offers a “better air link” in terms of coverage and range, while also providing a more unified network architecture, Chmaytelli said.

The potential trouble posed by LTE-U/LAA comes as WiFi becomes an increasingly important cog in cable’s mobile broadband and voice ambitions.

Several cable operators, including those that are part of the Cable WiFi roaming consortium (Comcast, Time Warner Cable, Cox Communications, Bright House Networks and Cablevision Systems), have already deployed hundreds of thousands of hotspots at public venues and in business locations as a perk to their broadband service.

Cablevision, meanwhile, has launched a WiFi-only phone service called Freewheel.

CableLabs, the cable industry’s R&D house, and the Wi-Fi Alliance are among the groups that hope to mitigate the risk LTE-U poses to WiFi.

Edgar Figueroa, president and CEO of the Wi-Fi Alliance, said his group is eager to discover whether LTE-U can become a good neighbor. “But we don’t know exactly what the impact on WiFi will be when this equipment that implements LTE-U is out there,” he said.

Per the Wi-Fi Alliance, about 1 billion WiFi devices with 5-GHz capabilities were shipped in 2014.

“We want the technology to coexist well with WiFi,” Dan Rice, senior vice president of network technology at CableLabs, said.

Under the rules being developed, use of LTEU is limited to carriers that operate LTE services in licensed spectrum — messaging and control channels of those LTE services run in licensed spectrum, and would then use unlicensed spectrum to generate a data boost.

The cable industry, Rice said, is proposing a stand-alone mode for LTE-U that would also allow cable operators and others to utilize it, while still being a good neighbor to WiFi.

“We think that ecosystem could develop,” Rice said. “We’re working hard with 3GPP … to make sure that they co-exist well, but that work isn’t complete yet.”

“The main thing is to have a healthy dialogue,” said Figueroa. “The next few months and years will be important to establish good interaction among the stakeholders.”

But cable and the wider WiFi community have some concerns about some of the current standards proposals. One such issue involves the notion of an LTE “duty cycle,” whereby it turns on for about 200 milliseconds, and then off for another 200 milliseconds. The worry is that such a duty cycle could cause latency and impair real-time apps such as gaming, video streaming, and VoIP delivered on WiFi.

“Latency matters … it’s very important to the customer experience,” Rice said, hopeful that an algorithmic method could be introduced to the standard to enable better bandwidth-sharing. “We think we know how to modify it to make it work well.”

Of more immediate concern is the pre-standard LTEU technology on the way that doesn’t use this sort of listen-before-talk algorithm.

“We’re actually sort of worried about that,” Rice said. “It could cause some problems.”

Qualcomm, meanwhile, said co-existence is already being demonstrated. According to Chmaytelli, the demo at MWC highlighted coexistence algorithms alongside the data-enhancing capabilities of LTE-U.

Qualcomm has also conducted tests at its San Diego campus that highlight that co-existence mechanism.

“Our tests showed that in some situations, having an LTE-U small cell was a better neighbor to WiFi than adding another WiFi access point to the mix,” Chmaytelli said.