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Sprint to Be 1st in US With Massive MIMO?

Dan Jones
2/7/2017

It is entirely possible that towards the end of this year -- or into 2018 -- Sprint will be able to claim the fastest 4G LTE network speeds in parts of the US with a completely straight face.

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

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Gabriel Brown
Gabriel Brown
2/8/2017 | 8:02:58 AM
Re: Device is impportant in this equation
A good point by Sr.Manag64649.

These massive MIMO base stations are more about system capacity than peak end-user speeds. Experience from Japan (SoftBank, notably) shows how these networks perform very well with existing devices, which are mostly 2x2 MIMO today. Over time we'll see more 4x4 devices in the market.
DanJones
DanJones
2/7/2017 | 10:57:55 PM
Re: Device is impportant in this equation
Yep, probably also explains why KT seems to be looking at tablets for its first mobile offerings with 28GHz MIMO too. Size/battery life.
Sr.Manag64649
Sr.Manag64649
2/7/2017 | 9:55:39 PM
Re: Device is impportant in this equation
To be clear, 64x64 antenna arrays are different from 4x4 MIMO. 

 

What's interesting about 4x4 MIMO is the ability to deliver 4 individual spatial streams (or 4 layers as it's also known) from the tower to the device. 

 

That would not change with a massive antenna array. The 64x64 antenna array would still only deliver 4 layers of data to the receiving device with its 4 individual physical antennas. The larger number of antenna elements helps with beamforming, including "full dimension MIMO" (FD-MIMO), so that the beam direction can be controlled in both elevation and azimuth. But even as all those many antenna elements work together to direct the beam more accurately at the device, only 4 layers of data are delivered.

 

We will only get to 16, 32, or 64 antenna arrays in devices with mmWave. Anything above 4 antennas for sub-6 GHz frequencies is simply not tenable. 
DanJones
DanJones
2/7/2017 | 3:36:20 PM
Device is impportant in this equation
I think 4x4 MIMO is currently pretty much the gold standard on the device side at the moment, still rare. I wonder how many more 2.5GHz elements can be squeezed onto a chipset and if Sprint has the ecosystem clout to make it commonplace?
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