T-Mobile pulls more out of 2.5 GHz in MU-MIMO 5G demo with Ericsson

T-Mobile said the demo achieved "astonishing" spectral efficiency of 50 bps/ Hz. (T-Mobile)

T-Mobile boasted spectral efficiency gains in a new 5G demo with Ericsson that saw eight devices on the same cell hit speeds of 700 Mbps.

The test leveraged 16-layer multi-user multi-input multi-output (MU-MIMO) technology and reached peak cell throughput of 5.6 Gbps operating on 2.5 GHz spectrum.

MU-MIMO boosts capacity, enabling more users to be served at the same time using the same radio resources. In this case the spectrum was a single 100 MHz channel of T-Mobile’s 2.5 GHz. MU-MIMO sends different layers to users via separate narrow beams simultaneously, with beamforming targeting streams in a specific direction. 

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T-Mobile indicated that it means the operator could reuse more of its cell site infrastructure to reach many people without a degraded experience.

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“At scale, this technology means T-Mobile could connect massively more devices to the same cell infrastructure and still deliver blazing fast speeds to all of them without compromising performance and that means wireless companies will be able to deliver even better 5G performance to even more people,” the announcement stated.

16-layer MU-MIMO isn't available today, but T-Mobile said it expects to start deploying the technology starting in 2021. Currently, T-Mobile supports up to 8-layers for its 2.5 GHz 5G and up to four layers in FDD mid-band. 

In a video of the demo, an antenna array was affixed to the top of a building, combined with “some sophisticated software,” Egil Gronstad, senior director of Technology, Development & Strategy at T-Mobile, explained in the clip. OnePlus 8 5G smartphones were placed around a parking and the test used a commercially available Ericsson massive MIMO radio with 64 antennas. 

T-Mobile transmitted 16 data streams – two to each of the eight devices. Each stream could hit more than 350 Mbps, combining for over 700 Mbps to some end users. Speeds across the handsets averaged between 650 Mbps and 733 Mbps.

“We are able to create beams with the antenna array that enables the energy to be directed in pencil beams,” Gronstad said in the video. “Now we’re able to send it in a narrow beam to just one specific device.”

In addition to the device data speeds, T-Mobile’s demo achieved what the operator called “astonishing” spectral efficiency. Spectrum is a scarce resource, so operators want to make the most of what they have and look for ways to increase efficient use.

By using the same radio resources, the demo attained spectral efficiency of more than 50 bits per second per hertz (50 bps / Hz). For comparison, typical spectral efficiency seen today is in the single digits, according to T-Mobile. 

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“Typically, in these kinds of systems with conventional radios you’re sort of sending the energy across the whole cell, now we’re able to send it in a narrow beam” to individual devices, Gonstad said, getting more out of the spectrum to serve more people who can then use more data.

These types of capabilities can be particularly effective in dense or busy settings where numerous users are accessing the network at the same time. 

“This is what you get when you pair T-Mobile’s unmatched spectrum portfolio with the best damn team in wireless – innovation that changes the game for the entire industry,” said Neville Ray, president of Technology at T-Mobile, in a statement. “We have a 5G network that’s second to none, and it’s getting better by the day thanks to our amazing engineers and partners.”

T-Mobile has been activating its newly acquired mid-band 2.5 GHz spectrum for 5G and at the beginning of September was on pace to turn on 1,000 sites per month. Its low-band 5G network using 600 MHz covers 250 million people.

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