Sprint CTO explains how carrier plans to win the 5G race

Sprint MIMO radios antennas (Sprint)
Massive MIMO antennas are part of Sprint's secret weapon in the race to 5G. (Sprint)

Sprint CTO John Saw used an appearance at a IEEE conference in Kansas City, Missouri, to thank some of the masterminds behind technologies like Massive MIMO, a technique the operator is deploying on the path to 5G.

Saw reiterated at the IEEE International Conference on Communications (ICC) today that Sprint is one of only a few operators globally that can truly deliver LTE and 5G simultaneously on the same spectrum band using 100-200 megahertz of spectrum, and that’s a differentiator for Sprint, he said.

Sprint is launching 5G initially in nine markets, which he described as rollouts that will not be hot zones but will cover a substantial portion of a metro area. For example, it will cover 230 square miles in Phoenix, and in New York, it will cover all of Manhattan.

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Earlier this month, Sprint added three more cities to its list of 5G markets, which now include New York, Phoenix and its hometown of Kansas City, as well as Atlanta, Chicago, Dallas, Houston, Los Angeles and Washington. Sprint expects to launch its nationwide 5G network in the first half of 2019.

Sprint has never been shy about talking about its boatload of 2.5 GHz spectrum and Saw did not let the opportunity pass without giving its due at the IEEE conference. Sprint has more spectrum than anyone else, primarily in the 2.5 GHz band, and it’s going to simultaneously enable LTE and 5G in the same footprint, which is not easy to do with millimeter wave spectrum, which other carriers are using.

“With 5G, for the first time, we’re pretty much going to use up every megahertz we have in the 2.5 band,” he said. “We’re going to simultaneously enable LTE and 5G on the 2.5 band. What that means is we’re able to have the same footprint, in terms of coverage, within 5G and 4G. It’s not easy to do if you are building a 5G network on millimeter wave and your LTE network is running on cellular channels.”

But for Sprint to do it right, in split mode, “we can do that. It also means we don’t have to look for so many new towers, which takes time to build, but we can leverage existing towers” and upgrade them with Massive MIMO to enable split-mode LTE and 5G.  

RELATED: Massive MIMO to play role in T-Mobile/Sprint 5G readiness

Of course, Sprint says its 5G network will be better with T-Mobile, and Saw took the opportunity to say the two of them can build a better 5G network and build it faster if they’re together. T-Mobile has a lot of 600 MHz spectrum and some millimeter.

By putting T-Mobile and Sprint together, “you can essentially build the first nationwide 5G network ubiquitously, with ubiquitous coverage 5G,” he said, adding that there is low band for rural, midband for metro and millimeter band for dense urban areas. Together, they can get wide coverage and capacity faster than if they were to go it alone, he said.

Massive MIMO is a big part of Sprint’s strategy, and he thanked the academics and researchers in the audience who made contributions that make it a reality today. Saw noted that the 2.5 GHz band in the U.S. is TDD, the same as that used in China, Japan and India. TDD is ideal for Massive MIMO, which doesn’t work so hot at FDD, he said.

Sprint will be upgrading thousands of cell sites with Massive MIMO to support LTE and 5G at the same time. Its vendors are also providing clever software to enable the operator to pull this off, he noted.

Sprint’s Massive MIMO antenna is actually shorter but slightly wider than the existing antenna it uses. In the present 2.5 GHz configuration, Sprint uses an 8T8R system where the antenna is separate from the Remote Radio Head (RRH) and a coax cable connects the two of them. So it’s more cumbersome. With its Massive MIMO, everything is in one box, so it’s a slightly smaller box, but the radio and the antennas are built into one unit to minimize degradation. It might be slightly heavier, he said, but so far, in the zoning and permitting applications they’ve done, “we have not run into a lot of structural issues,” he said.

Opportunities remain for academics and researchers to contribute to future efforts as well. Still in the works are 3GPP’s Release 16, V2X, network security and a number of areas.

“I would not be up here talking about Massive MIMO had you not figured out the details behind it,” he said. “A big thank you. But if you look ahead, there are a lot of other things that we need to be focused on. 5G NR. It’s not done yet. We have the Non Standalone; we still need to lock down the Standalone specs... Immense number of areas that still need your help and your creativity to get those problems solved.”

Editor's Note: Article updated May 24 with additional information on the Massive MIMO product.

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