T-Mobile US has started rolling out a spectrum aggregation combination that in tests provided 5G download speeds in excess of 3 Gb/s, with one analyst noting a real-world deployment sample could show a strong focus for the spectrum cocktail to serve T-Mobile's growing fixed-wireless access (FWA) service.

The carrier this week said it was now supporting four-carrier aggregation in parts of its network, with nationwide availability set for the “coming weeks.” This technology uses 5G standalone (SA) network standards to combine four different spectrum channels across different spectrum bands to act as a single, larger transmission path.

In this case, T-Mobile is combining two channels of its deep 2.5 GHz spectrum, one channel of its 1.9 GHz spectrum and one channel of its 600 MHz spectrum to form a single transmission channel. More spectrum basically acts as a bigger pipe to send data traffic through.

“That’s like taking four separate highways and turning them into a massive superhighway where traffic can zoom faster than before,” the carrier noted in a statement.

Neville Ray, former president of technology at T-Mobile US, noted during a press conference at this year’s MWC Barcelona event that a trial of this spectrum combination resulted in 3.3 Gb/s of download network speed.

Ray explained that the test showed technical prowess in being able to aggregate time division duplex (TDD) spectrum (2.5 GHz) and frequency division duplex (FDD) spectrum (1.9 GHz) to form this single channel. TDD spectrum allows operators to adjust the uplink and downlink capacity of a spectrum channel based on need, while FDD spectrum is typically fixed in splitting its channel capacity evenly between the uplink and downlink.

“We’re in a position now [where] I can combine FDD and TDD spectrum assets across low- and mid-band,” Ray said. “I want that to be just one very large network pipe. I don’t want to be worried about migrating between bands, only being able to use mid-band. I want mid-band and low-band together. And I want every asset that we have in the company ultimately to be dedicated to that 5G layer.”

Access to this new spectrum combination is currently limited to Samsung’s recently launched Galaxy S23 smartphone as it’s the only device that includes the necessary antennas and software to accept the wide channel width. The carrier expects to add more devices in the future.

More spectrum to power T-Mobile's FWA growth

That increased device support could include FWA devices to connect T-Mobile US customers to higher speed broadband services.

Michael Thelander, president of SRG Research and Consulting Services, noted in a LinkedIn post that he had run across the embiggened T-Mobile network in the wild. This involved regular network testing work his firm was conducting in rural South Carolina that found a 220-megahertz wide band of four-carrier aggregated spectrum running on Ericsson equipment and tied to a 10 Gb/s backhaul link.

Thelandar noted this infrastructure and location indicated a focus on FWA services.

“Without question, T-Mobile is targeting its 5G assets for fixed-wireless access (FWA) and some of our testing this week is more than proving this point,” Thelander wrote. “There is no way in heck the operator needs this much capacity for eMBB (enhanced mobile broadband) where we are testing at the moment, yet the capacity is there in black and white – most notably in neighborhoods where there are slim, if any, pickings for any other type of broadband service.”

T-Mobile US added approximately 600,000 new FWA customers during the first quarter, pushing its customer base to 3.2 million subscribers. Chief Marketing Officer Mike Katz said those customers are using “hundreds of gigs a month on average,” including strong usage in rural areas, which he added for some was “the first high-speed option that existed, and it only happened because of 5G.”

However, some analysts have questioned the financial viability of 5G-based FWA services, noting the cost differential of using a finite spectrum resource compared with more unlimited potential of a fiber-based broadband offering.

T-Mobile’s management has said it was currently targeting support for up to 8 million FWA customers by 2025, with a focus on profitable expansion.

“I also will remind everybody that we’re not – this particular model on fixed wireless – we will take it into high single-digit penetration, and we don’t have illusions that it’s going to take over half the market,” CEO Mike Sievert told attendees during a recent investor conference. “But for the market we’re trying to serve, it’s a highly profitable, accretive, incremental business with little to no capital allocated. It’s a beautiful thing.”