How MU-MIMO Can Change the FWA Game for T-Mobile and Verizon

A recent study highlights a new flavor of 5G hiding in T-Mobile’s regular radio frequency landscape that should result in a significant capacity upgrade for Fixed Wireless Access (FWA) — and for other carriers’ service.

Drawing on field testing conducted in December, Signals Research Group found that a combination of Sounding Reference Packet Shaping (SRS) and Multi-User Multiple Input Multiple Output (MU-MIMO) resulted in up to 75% throughput gains compared to single user MIMO, taking Average throughput from 901 Mbit/s to 1,576 Mbit/s.

“This is important,” said Michael Thelander, SRG President and Founder. “If the operator can get a 10% gain in capacity for very little effort, they’d love it.”

The Independence, Minn., company conducted this research using the OnePlus 10 Pro and Galaxy S22 smartphones as well as a not-yet-shipped FWA receiver from Arcadyan. T-Mobile provided technical support, including instructions on where to find Ericsson MU-MIMO n41 cell locations in Southern California.

Thelander emphasized that this power boost withstood having receivers in close proximity.

“Without MU-MIMO, if a second mobile device starts receiving data, they’ll basically share that speed,” he said. With it: “You get your second phone, and your max data speed stays the same.”

Don’t move!

SRG published a preview of these results in the December 16th edition of Signals Flash! newsletter, then published the details in the Jan. 10 issue of its Signals Ahead report. This longer post also revealed hints of T-Mobile testing a new TDD frame structure that increases downlink capacity.

The FWA part of the company’s research comes in its finding that the SRS packet-forming communication and response protocol (Thelander described the dialogue between cell site and user equipment to optimize signal optimization, “Marco yelled, they’re back Polo”) worked better with receivers that were less movement.

It could mean very good things for T-Mobile’s once-booming FWA business — the carrier now expects to have 7 to 8 million customers by 2025 and is considering deploying millimeter wave spectrum to increase FWA capacity in urban areas.

“If you get fixed, CPE will never move,” Thelander said. “So multiuser MIMO tends to work better.”

In addition, when carriers already provide fixed wireless customer equipment to subscribers for free, it is easier for them to push for upgrades than to persuade customers to upgrade phones with their own money. Thelander said that while “some iPhone models support it,” he wasn’t sure about the general level of MU-MIMO support among current smartphones.

T-Mobile hasn’t talked much about its MU-MIMO deployment since its 2020 press release about a test of the technology that delivered 5.6Gb/s speeds above 2.5GHz’s 5GHz — a marked contrast to its publicity for mid-band 5G.

But a spokesperson confirmed that the carrier’s current FWA CPE supports MU-MIMO. However, older customer equipment does not, and the company is not moving to replace it with MU-MIMO-compatible equipment.

T-Mobile’s publicist also said that the carrier will finish upgrading non-Ericsson bases to support SRS and MU-MIMO by mid-2023.

Not just T-Mobile

SRG’s December research only covered T-Mobile locations, but previous testing showed Verizon 5G service near Minneapolis with performance characteristics that match MU-MIMO, as covered in the September 27 Signals Flash! problem.

“I was doing software testing in Minneapolis last September, and I discovered that Verizon was trying to use multi-user MIMO on its network,” Thelander said in January. “I don’t know where they put it from.”

Verizon has been as quiet as T-Mobile regarding public announcements about its MU-MIMO deployment, but a company publicist confirmed that the carrier has lit up both packet-forming and MU-MIMO.

“Yes, we’ve rolled out MU-MIMO and packet-shaping to the vast majority of our network, and we’re definitely seeing service gains from these technologies in both mobility and FWA,” spokeswoman Karen Schulz said via email. “We will continue to roll it out this year across the rest of our network.”

It has not specified which Verizon fixed wireless CPE models support these upgrades.

Thelander pointed out some of the limitations of MU-MIMO, saying “You need relatively decent signal conditions to make this happen.” But capacity gains in those places come at much lower costs than traditional carrier tools: “New cellular sites or buying new spectrum, that’s the expensive side of the house.”

He was confident that this cost-benefit calculation would lead each carrier to deploy these upgrades.

“If they don’t do it or try it today, I can guarantee they will very soon,” he said. “It’s simple—simple in quotes—upgrading software, and as long as you have the jumper in place, then you get it.”

– Rob Pegoraro, Light Reading. follow him @employee.