If unlicensed Wi-Fi spectrum is like a cool, independently run cafe, then mobile operators using those frequencies for LTE may sound like a corporate chain buying out your favorite spot.
There goes the neighborhood. Or does it?
LTE is coming to the fat 5GHz unlicensed radio band that much of consumers' Wi-Fi use now depends on. The idea drew skepticism at first, but the mobile industry is starting to agree on some steps to make sure wireless LANs don't get trampled under LTE's feet. The first trial deployments are expected to begin this year, and users could get faster service as the technology is rolled out.
Huawei and NTT DoCoMo demonstrated the technology last August, Qualcomm showed it off at International CES last month, and T-Mobile USA plans a trial deployment later this year. More plans for unlicensed LTE may be revealed next month at Mobile World Congress in Barcelona, where the quest for more mobile capacity will be a hot topic.
LTE was designed to run over frequencies exclusively licensed to mobile operators, for which some carriers have paid billions of dollars. In its current form, LTE lacks crucial features to prevent one type of network from drowning out others in unlicensed spectrum.
That would seem to make LTE a poor fit for unlicensed bands. But growing demand for cellular capacity can make mobile operators act a little crazy: In the U.S. last week, the Federal Communications Commission tallied up more than US$40 billion in bids for new cellular spectrum. Most carriers are also turning to Wi-Fi, a completely different technology from cellular, even though they need to adopt new technologies to automatically move subscribers between the two systems.
In that light, sending LTE signals over unlicensed frequencies doesn't look so outlandish. In the 5GHz band, there's more than 400MHz of unlicensed spectrum available in most countries. That's more than most mobile operators have in all their licensed bands combined. No one will be able to use all 400MHz at one time, but an average subscriber who walks into range of an unlicensed LTE cell might get twice as much spectrum, according to Tolaga Research analyst Phil Marshall. And more bandwidth typically means more speed.
Using that deep well of spectrum without giving up the familiar controls and guarantees of a cellular network was what early proponents of unlicensed LTE, such as Qualcomm, had in mind. LTE is also tuned to use spectrum more efficiently than Wi-Fi does, proponents say. But the concept was controversial when it was first proposed at 3GPP, the standards body that oversees LTE.
Wi-Fi users already face crowded airspace in some areas, often the very kinds of mobile meccas where carriers might deploy unlicensed LTE: business districts, convention centers, and hotels. The idea of letting LTE networks use the same, already taxed spectrum raised alarm bells for some in the industry, especially carriers that use Wi-Fi to supplement their networks.
The main worry was that service providers would build LTE networks, without any coexistence mechanisms, that relied totally on the "free" unlicensed frequencies in 5GHz, said Tom Peters, an engineer at law firm Hogan Lovells and a former chief engineer of the Wireless Bureau of the FCC. Wi-Fi is designed to "back off" when it senses another device using a channel, but this feature assumes that other technologies in the unlicensed band will treat it the same way.
"If somebody were to deploy unlicensed LTE as a stand-alone service in an unlicensed band, you very likely wouldn't be able to use Wi-Fi," Peters said.
However, unlicensed LTE was really conceived as a way to supplement regular licensed LTE networks, he said. Backers of the technology eventually agreed to change its name to LAA (Licensed Assisted Access) to reflect this. "That calmed a lot of people down," Peters said.
3GPP plans to include features in the next version of LTE, due to be finished around the end of this year, to help it coexist with other networks in unlicensed bands. And though different countries have different rules in this area, all unlicensed LTE products should be safe for Wi-Fi.
Ericsson, one of the world's largest mobile equipment makers, will build its gear to meet the demands of its customers in each market, said Eric Parsons, head of mobile broadband LTE at Ericsson. But all of its equipment will coexist peacefully with Wi-Fi, meaning that adding an unlicensed LTE cell won't have any more effect than adding another Wi-Fi access point, he said.
Parsons and other backers of LAA say it will do more for subscribers than the Wi-Fi services many carriers offer today. Rather than be handed off from one network to another, users will stay on the cellular network, so calls and data sessions are more likely to stay up without a glitch, they say.
"The handoff between any network boundary is a pain, and it often results in failures due to latency," Tolaga's Marshall said. "You don't want to be doing that if you don't have to."
Cisco Systems, which sells Wi-Fi gear to carriers around the world, says there's no difference. Its systems already allow carriers to manage unlicensed spectrum as if it were licensed, according to Kelly Ahuja, Cisco's senior vice president of service provider products and solutions. But the company is agnostic when it comes to the two technologies, he said.
Vendors, carriers and service providers have worked long and hard to make roaming among Wi-Fi networks or between cellular and Wi-Fi as seamless as possible. So-called Hotspot 2.0 technology, as well as parts of the LTE standard allowing handoffs between cellular and Wi-Fi, are gradually being implemented in devices and networks.
Will all that work go to waste if carriers can make unlicensed spectrum part of their cellular systems?
Not everywhere, and certainly not soon.
For one thing, carriers are far from being the only network providers turning to Wi-Fi for mobile services. Many cable operators, including Comcast in the U.S. and Liberty Global in Europe have extensive Wi-Fi networks to keep their subscribers connected while they're away from home. Those two providers announced a roaming deal last year. Companies that bundle access to many different Wi-Fi hotspots, such as Boingo, are also taking advantage of Hotspot 2.0 technology.
Meanwhile, unlicensed LTE still needs to prove how well it will work with licensed networks and how much of a boost it can give subscribers, Ovum analyst Daryl Schoolar said. It will require new features in both network equipment and mobile devices. Qualcomm's involvement suggests the technology will get out into handsets, but Schoolar doesn't expect those devices to ship until next year. And some mobile operators, such as AT&T, have built out vast Wi-Fi networks that they probably won't swap out for LAA-capable small cells any time soon, no matter what the promised benefits.
However, in the coming years, LAA may be major step toward mobile using any kind of spectrum that's available, a trend that next-generation 5G networks coming in 2020 are expected to continue.
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