Sprint's CTO said Wednesday that he is not sure that using millimeter waves to deliver 5G services is a practical economic use of the high-band spectrum and that Sprint will be focusing on using its existing bandwidth to deploy 5G, at least initially.
"What is the cost to deliver a bit over millimeter waves? Where is the business case on that?" John Saw asked at the Citi conference in Las Vegas.
The logic here is that using sub-6GHz networks to deliver 5G -- Sprint Corp. (NYSE: S) is using 2.5GHz -- will allow operators to get better coverage than mmWave (typically 28GHz or 39GHz) and re-use its infrastructure.
What we've seen so far of millimeter wave tests suggests signal ranges of a quarter of a mile or less. So, millimeter wave deployments will require many, many more small cells, repeaters, and sundry antennas than we have ever seen before in cellular network deployment. It could require a small cell -- or more -- per city block for mobile coverage. (See High-Band 5G: Let's Address the Range Question, Shall We?)
"We need to solve the cost challenges before you can scale millimeter wave," Saw said.
He did say that mmWave could be useful as a hotspot "overlay" to a lower band 5G network, but he added that "the laws of physics say it won't propagate very far."
Of course, Saw couldn't do much with millimeter bands even if he wanted to. As things stand in the US today, Sprint doesn't have access to the 24GHz and higher bands. The FCC has yet to set a date for millimeter-wave band auctions, so it could be a while before Sprint even has an opportunity to buy some of that spectrum.
In the meantime, Sprint is upping its capex as it builds a bridge from 4G to 5G on its 2.5GHz spectrum. Sprint is expecting to spend $5 billion to $6 billion on capital expenditure in the fiscal year that begins April 1. (See Sprint's 2.5GHz LTE Spend Will Grow in 2017.)
Saw says that the network spending priorites will be: rolling out 2.5GHz coverage to "nearly" all sites; adding new "destination sites, where customers like to roam in the summer;" and upgrading from antennas with eight transmit and receive elements (8T8R) to "massive MIMO" 64T64R units. (see Sprint COO on Massive MIMO Deployment: 'You Ain't Seen Nothing Yet'.)
"It's going to be a bridge to 5G," Saw said. (See Sprint Says Massive MIMO, Coming in 2018, Is the Bridge to 5G.)
This is because, like T-Mobile US Inc. , Sprint can now deploy 3GPP 5G New Radio (NR)-ready gear as it upgrades in 2018 and use its existing spectrum to host both 4G and 5G, Saw said. (See Sprint Gets Ready for Massive MIMO, Eyes 2.5GHz for 5G.)
"I can run LTE and NR on the same massive MIMO site, without climbing the tower again in 2019," the CTO said. "It kills two birds with one stone."
Saw said that Sprint will focus solely 5G on mobile broadband initially, with an eye on IoT in the future. His comments suggest a likely timeline of a later in 2019 or 2020 software update to switch on 5G on the Sprint network after the 5G-ready equipment is deployed.
— Dan Jones, Mobile Editor, Light Reading