Sprint CTO describes “bridge to 5G”, cold on mmWave spectrum

Sprint CTO John Saw has thrown cold water, again, over the hype about millimeter wave spectrum for 5G. With Verizon and AT&T vying to be first to deploy 5G (initially for fixed wireless) in high frequency spectrum, Sprint is focusing on its biggest asset – its plentiful holdings of midband spectrum in 2.5 GHz.

The US operator was crowing recently when the 3GPP adopted its 2.5 GHz band – which it already uses for high capacity LTE – as an official spectrum option for 5G New Radio (NR). This gives Sprint the chance to refarm 2.5 GHz spectrum in future for 5G, and to make use of some of the airwaves which are currently unused.

At the Citi conference in Las Vegas, Saw questioned the economics of using mmWave bands like 26 GHz, 28 GHz and 39 GHz for 5G, at least in the first wave of deployment, because of their short range, which will require very large numbers of base stations to achieve coverage.

“What is the cost to deliver a bit over millimeter waves? Where is the business case on that?” he asked.

Saw pointed out that, at the power levels permitted in the US, signals will only reach a quarter of a mile or less, which could mean a small cell for every city block to achieve coverage as well as the high capacity that these frequencies support. Initially, the two largest US MNOs are using the spectrum more conservatively for fixed wireless, though AT&T has promised to add mobile services as soon as devices are available.

There are very divided opinions among MNOs round the world about the near term potential of mmWave. For instance:

  • The technology remains experimental, though many trials are starting to give a clearer picture of its real world performance.
  • Chips and devices are at a very early stage.
  • There is no global harmony around the bands (the US is pursuing 28 GHz while the ITU has identified 26 GHz as the 5G candidate band in this area of the spectrum, for instance).
  • Although mmWave could be used to support very targeted small cell networks for exceptionally high bandwidth users or applications, many operators believe they still have plenty of mileage in exploiting newly available, or currently underused, midband options for 5G, including (in Release 16) unlicensed.

“We need to solve the cost challenges before you can scale millimeter wave,” Saw said, adding that the main economic use for mmWave would be as a hotspot “overlay” for a lower band 5G network, to add capacity in selected areas.

Sprint, of course, is bound to focus on 2.5 GHz, where it has a significant advantage over rivals, rather than mmWave, where it has no holdings (except the potential to use the 60 GHz WiGig technology, which is has sometimes discussed as a possible small cell backhaul option). Verizon and AT&T have acquired 28 GHz and 39 GHz airwaves through various transactions but Sprint has not, and the FCC has not set a date to auction new spectrum above 24 GHz, despite its very supportive approach to opening up these airwaves to seize a 5G headstart.

After slashing its capex budget in 2016-17, Sprint – with fresh funds from its parent Softbank – is boosting its investment this year, with 2.5 GHz densification being the top priority to enhance 4G and prepare for 5G. It is expecting to spend $5bn to $6bn in capex in the fiscal year that begins on April 1.

Saw set out the capex priorities as:

  • Deploying 2.5 GHz LTE in “nearly” all sites. Most of the operator’s LTE traffic is carried over its current 2.5 GHz spectrum holdings, but that band is supported on only 70% of its cell sites, covering 200m POPs.
  • Adding new “destination sites, where customers like to roam in the summer”.
  • Upgrading from 8T8R MIMO base station antenna arrays to Massive MIMO (64T64R).

The combination of densification and antenna upgrades will be a “bridge to 5G”, he said, adding: “I can run LTE and NR on the same massive MIMO site, without climbing the tower again in 2019.  It kills two birds with one stone.”

He added: “Because we have so much spectrum at 2.5, I can allocate half of my spectrum to LTE Advanced and other half for 5G … So as we build massive MIMO this year, we’re really starting to build a 5G network that also supports LTE Advanced …  And then over the same Massive MIMO base stations, we’re going to launch 5G NR when it’s available. So it’s a more pragmatic plan.”

Sprint is expected to start switching on 5G in 2019 or 2020 and Saw said that, like most major MNOs, it will focus on mobile broadband enhancement first before addressing the challenges of IoT and critical communications services.

There are no plans to add fixed wireless, which would make little commercial sense unless Sprint were prepared to deploy a wide-scale (and very expensive) network to offer a wireless alternative to wireline operators’ services. The same goes for T-Mobile, which has thrown scorn on the big two carriers’ fixed 5G plans. However, for Verizon and AT&T, the model makes sense to fill gaps in fiber coverage, to penetrate markets where they have no wireline footprint, and to replace ageing DSL cheaply in some rural and suburban markets.

“We have no plans to launch fixed wireless at the moment,” Saw said. “Right now I think our focus is on mobile broadband; the economics are so much better. Maybe when you look into the 5G world, when we have more spectral efficiency, and potentially new spectrum, we can revisit the opportunity for fixed wireless.”

Meanwhile, Verizon and AT&T were continuing their tit-for-tat about which operator will be first to 5G. AT&T has said that it will move rapidly to mobile services in its early stage 5G network, partly because it is using fully standardized 3GPP specifications, and so should have earlier access to mobile devices.

However, Verizon CTO Hans Vestberg told the audience at the Consumer Electronics Show last week that his firm “will be first” to 5G and will discuss its live 5G network at next year’s CES in January 2019. The carrier will deploy fixed wireless services in mmWave spectrum, based on its own pre-standard specifications, in the second half of this year, starting in Sacramento, California. It will later migrate the network to support full 3GPP 5G NR standards.

He insisted that, like AT&T, Verizon has ambitious plans to move beyond fixed wireless and towards mobile and IoT 5G services. He said: “From 5G you can do different slices. We are now focusing on one slice, which is basically residential broadband to deliver superior performance quicker to market…That’s one use case, we can talk about many others.”

He also told the Citi event audience that 5G would change Verizon’s economics because “the core network, the transport network, the fiber network, all is the same. It’s one slice out of that software and the antenna that is doing the broadband, and the rest is the same investment”. Like most MNOs, Verizon plans to use a combination of spectrum including a lower frequency coverage layer with mmWave zones to support specific high performance services or locations.