LAA/LTE-U makes appearance at Brooklyn 5G summit

Monica Alleven, FierceWirelessTech

It just goes to show. Some topics are so hot, you can't make it through a discussion about 5G and millimeter wave (mmW) bands without the subject coming up.

In this case, the subject is LTE-Unlicensed (LTE-U)/LTE Assisted Access (LTE-LAA), and it came up during the Q&A part of a "Spectrum for 5G" session during the Brooklyn 5G Summit in New York last week. The summit was presented by Nokia Networks (NYSE:NOK) and the NYU Wireless research center at the Polytechnic School of Engineering at New York University. Discussions centered on themes such as 5G massive MIMO and beamforming solutions for 6-100 GHz bands.

This particular panel featured speakers from Sprint (NYSE: S), T-Mobile US (NYSE:TMUS), Straight Path Communications and CableLabs, as well as Michael Ha, deputy division chief of the Policy and Rules Division in the Office of Engineering and Technology at the FCC. Takehiro Nakamura, vice president and director of the Radio Access Network Development Department at NTT DoCoMo, served as moderator.

The discussion clearly hit a nerve when it turned to philosophies pertaining to licensed versus unlicensed spectrum. During a Q&A after the presentations, a member of the audience asked about U.S. Wi-Fi spectrum and the kind of testing that should be done before deploying LTE-U/LAA to avoid interference.

"I'm not familiar with 'Wi-Fi spectrum,'" said Scott Migaldi, a research scientist and member of the technical staff at the Sprint. "I'm familiar with unlicensed spectrum, of which Wi-Fi is one of the many users who is in that spectrum. It's unlicensed spectrum, but it's to be used on a fair use basis, and I think that's the critical point" at the center of the question.

"What defines fair co-existence?... How do we best define it so we co-exist properly, not just because I want to be concerned about will LTE unlicensed destroy Wi-Fi. I want to make sure that Wi-Fi doesn't destroy an LTE thing… so we have to figure out a way to work together," he said, adding that he's glad to see discussions between 3GPP and the Wi-Fi Alliance. "As a company that has a lot of traffic that does go over Wi-Fi, we don't want to see an LTE unlicensed/LAA thing come on and start to hurt us either."

Of course, pretty much everybody has an opinion on the subject now, and Ha said the FCC is monitoring it and aware of IEEE, 3GPP and other industry discussions that are going on. However, it's premature for the FCC to say anything or jump to conclusions while the industry works things out, he said.

In fact, various parties in the FCC's 3.5 GHz proceeding, which is on the commission's agenda for this Friday, have argued for prohibiting the use of LTE-U/LAA in the band, while others say the FCC is doing the right thing by letting the market decide which technologies ultimately win out.

The FCC has said repeatedly that it's not going to dictate technology choices, a philosophy that has been in play at least since the PCS days back in the '90s, when the industry fought over GSM--the standard adopted throughout Europe--versus CDMA, a rival technology heavily promoted by Qualcomm (NASDAQ:QCOM), which happens to be a big supporter of LTE-U.

Dan Rice, senior vice president of network technology at CableLabs, said his non-profit organization, which includes cable operators that have deployed a lot of Wi-Fi, shares concerns but also sees "a big opportunity here," particularly if engineers can come up with better ways of using the technology.

"We think the definition of co-existence is very important; it can't just be throughput," he said. For example, CableLabs was involved in recent demos of co-existence between LAA and Wi-Fi that resulted in "getting pretty good throughputs," but there also was a lot of latency in the network that destroyed some of the real-time services. Still, Rice said that CableLabs thinks those problems are all solvable. "I think there's plenty of market motivation that will encourage the infrastructure vendors and operators" on both sides of the issue to work together to come up with a solution, he said.

With 2.5 billion Wi-Fi chipsets sold last year, "that's a lot to try and create problems for," Rice said. "So we're optimistic that those issues can be solved." He said that work is ongoing with IEEE, the Wi-Fi Alliance and 3GPP, and he encouraged session attendees to check out some of the work CableLabs has done in this area. "We're optimistic we'll see co-existence," he said.

In a separate panel Q&A session at the 5G forum, AT&T's (NYSE: T) Tom Keathley was asked about how AT&T views the sharing of unlicensed spectrum. As my colleague Phil Goldstein previously reported, AT&T views that spectrum as available for it to use, provided that it can be shared in a fair manner with other users of the non-licensed spectrum, and right now, "that other user is Wi-Fi," Keathley said.

"The real question now is can you do that with the duty cycle methodology, listen, and then transmit, but not listen before talk. That's the LTE-U methodology. Or do you have to wait for Licensed Assisted Access, where you will get a true listen-before-talk methodology implemented as that LTE standard changes," said Keathley, senior vice president of network and product planning at AT&T. "Right now, we don't know the answer to that. We're evaluating it, and we'll make a determination around a couple of items. If you can share it in a fair use manner, then we'll have to ask ourselves whether it's worth deploying that true, pre-standards version in advance of licensed assisted, and frankly, we don't know that."

It's unclear how much shared spectrum will be a part of 5G, but it's a pretty good bet that sharing spectrum will play a bigger and more critical role in the industry's future. No doubt, everyone can agree that reaching consensus on what constitutes proper and fair co-existence will be of utmost importance going forward.--Monica