Editor’s Corner—From Sprint to T-Mobile, what’s all the fuss about massive MIMO?

Massive MIMO
Sprint has been a big proponent of massive MIMO.
Monica Alleven editor's corner

It seems as though almost every day someone has a new massive MIMO announcement, and there’s usually some kind of “first” tied to it.

Massive MIMO was certainly a hot topic leading up to and at the Mobile World Congress Americas (MWCA) trade show last month. In early September, Ericsson introduced a new radio product for massive MIMO and said frequency division duplex (FDD) massive MIMO was part of a trial with T-Mobile US on three sites in Baltimore, Maryland.

“This will be the first time that standardized Massive MIMO will be used to carry commercial LTE traffic using mid-band FDD spectrum,” Ericsson said at the time.

But talk about massive MIMO has been going on for quite a while. In February, Blue Danube Systems said it had completed the first commercial trials of its massive MIMO technology in licensed FDD LTE spectrum with AT&T and Shentel. And Verizon was talking back in 2016 about conducting massive MIMO tests.

There are good reasons for embracing massive MIMO. For one, it’s foundational to 5G. For another, with everybody offering “unlimited” data plans, operators are facing a massive capacity crunch and turning to every trick in the toolbox to meet demand.   

While it seems counterintuitive that Sprint would need to worry too much about crushing under the weight of so much demand, it has stood out as being particularly aggressive about pursuing massive MIMO. At MWCA, Sprint and Ericsson unveiled results of the first U.S. 2.5 GHz massive MIMO field tests conducted in Seattle and Plano, Texas, using Sprint’s spectrum and Ericsson’s radios.

Once again, Sprint’s plethora of 2.5 GHz spectrum comes into play, an asset frequently cited as a huge advantage—at least until it falls into the hands of T-Mobile, which could be any day now. Sprint is the rare operator that uses both FDD and TDD spectrum, and the combination of TDD and 2.5 GHz gives it a natural fit for massive MIMO.

Sprint staged one of the more memorable demos when it compared a massive MIMO network against standard LTE systems.

“It’s not even fair,” when you have 128 antenna elements compared to four, said Sprint CTO John Saw during a presentation at MWCA. That essentially turns it into a 3D beamforming system, where you can create a lot of capacity with good signal integrity supporting more users. In an unlimited world, that’s important, he said.

Sprint produced a video demonstrating how they took 100 cell phones from each carrier, put them in a signal-dense area (Seattle's Myrtle Edwards Park), and had them trigger a download. If they completed the download in 15 seconds or less, they held up signs. Each team wore either red, blue, yellow or magenta, and you can guess which team came out on top. Sprint’s yellow team achieved 100 out of 100 download attempts, whereas the other carriers only got 16 out of 100 or even as little as 6 out of 100.

Sprint and Ericsson executives stressed that the 2.5 GHz spectrum allows Sprint to introduce massive MIMO early and start moving toward 5G. But Ericsson isn’t the only one working with Sprint on this technology. Samsung also has done massive MIMO demos with Sprint and Nokia is supplying its 4.9G AirScale massive MIMO adaptive antenna, which uses 64 transmit and 64 receive streams.

Sprint has said it will be selective in how it deploys the technology, first targeting crowded high-traffic areas. Indeed, Ovum analyst Daryl Schoolar wrote in a “Massive MIMO Comes of Age” report (PDF) that dense urban traffic hotspots and high-rise buildings are key areas for deployment as beamforming can better reach indoor users.

Although 5G won’t be fully standardized until 2020, initial deployments based on early standards work are going commercial in 2018. “The nearness of the 5G timeline has accelerated massive MIMO interest,” Schoolar wrote.

Erik Ekudden, Group CTO and head of Technology & Architecture at Ericsson, likens it to having a bunch of flashlights targeting your users rather than a single floodlight. “Massive” typically means you have a lot of these antenna to form many beams at the same time, so with multiuser MIMO, it’s pointing flashlights and communicating with an array of antennae without the need for more power.

“The beams are narrower,” he said. It’s not just for high bands, either; it can apply to low bands as well, he added. ”You get higher capacity and higher bit rate for the user and at the same time, you actually could look at it as an optimization tool for the network without increasing the power.”

“It’s a big deal,” said Sherif Hanna, product management/product marketing for mobile at Qualcomm, of massive MIMO in general. “For 5G, it’s foundational,” and it’s already being introduced in LTE networks and devices today.

“What we’re trying to do with massive MIMO basically is increase the reuse of the spectrum,” Hanna said. “Because I can reuse the same spectrum multiple times for different users, I end up getting more throughput from the cell than transmitting to everyone at the same time.”

Woojune Kim, SVP of product and strategy for the Samsung Networks division at Samsung Electronics, said there are typically three ways for operators to increase capacity: add more spectrum, get more sites or use more technology. Massive MIMO, in some ways, is the easiest network upgrade an operator can do to add capacity.

“For operators, it’s a natural progression,” he said.

Samsung has said it will begin commercializing its massive MIMO solutions this month on the TDD band and in 2018 on the FDD band. Samsung has quite a bit of experience with TDD throughout the world, with the exception of China, where it doesn’t have a major presence.

All in all, there’s not much controversy about massive MIMO—unless you want to get into a debate about who can legitimately claim a “first,” and where. – Monica | @fiercewrlsstech