This is because Kansas City-based Sprint Corp. (NYSE: S) is likely to be the first operator to get its hands on so-called "Massive MIMO" smart antenna arrays, which will boost the speed and capacity of its 2.5GHz 4G network. Sprint already has 8x8 antenna arrays in its network, and expects to test 64x64 arrays at 2.5GHz this year. (See Sprint Lights Fire Under High-Band 4G, Builds for 5G.)

"The coming benchmark" is 64x64, Nokia Corp. (NYSE: NOK)'s North American CTO, Michael Murphy, told me recently. "Customers are asking for it."

And the first customer in the US is likely to be Sprint. Murphy says that 64x64 antenna arrays "will be coming very soon" for higher frequency TDD networks, such as Sprint's 2.5GHz LTE network, for example.

This is because the higher frequency the network, the simpler it is to build denser antenna arrays in a smaller space. Sprint's single-channel time division duplex (TDD) operates at a higher frequency than any of the other big three's cellular networks in the US.

By contrast, for 2-channel low and medium band networks in the US, Murphy is expecting 8X8 antenna arrays to arrive in 2017. 64X64 arrays are "not too far in the distance," Murphy says, but he does not give an actual date.

Sprint clearly already has some prototypes from Nokia kicking around. CTO John Saw brought one with him to New York City in December 2016 (see photo below).

Sprint parent SoftBank Corp. has been testing such large arrays and started deploying 128-element MIMO systems in Toyko late last year. (See Massive MIMO Key to 5G, Says SoftBank.)

Along with other LTE-Advanced Pro (4.5G) features, such as bonding together radio channels to boost performance, upgraded MIMO should help Sprint head towards gigabit LTE and give it more know-how about a 5G future. (See Sprint Ups the 4G Speed Ante to 230 Mbit/s.)

Users, however, will -- as usual -- need to upgrade their devices to get the most out of MIMO upgrades on a network. (See New Qualcomm Chip Promises 'Gigabit' 4G.)

— Dan Jones, Mobile Editor, Light Reading