BARCELONA, Spain – T-Mobile US’ 5G push gained spectrum momentum with a new carrier aggregation milestone resulting in speeds greater than 3 Gb/s, and continued expansion of its voice over new radio (VoNR) service that furthers its ability to drive more of its network traffic over 5G.

Neville Ray, president of technology at T-Mobile US, told a small audience at this week’s MWC Barcelona 2023 event, that the carrier ran a test aggregating four carrier channels of spectrum running across its 5G standalone (SA) network that produced network speeds of more than 3.3 Gb/s. Specifically, this involved integrating two carrier channels of 2.5 GHz spectrum and two carrier channels of 1.9 GHz spectrum for a total of 225 megahertz of spectrum.

The test ran over network equipment from Ericsson, Nokia, and Qualcomm Technologies, and a Samsung Galaxy S23 device. The carrier added that customers with those devices would be able to experience that capability later this year.

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.”

Ray announced last month that he would be leaving the carrier after 23 years this October. He will be replaced by current carrier exec Ulf Ewaldsson.

T-Mobile US just last year started trialing three-carrier aggregation that combined a pair of spectrum channels in the 2.5 GHz band and a single spectrum channel in the 1.9 GHz band to form a single 210-megahertz channel. Those tests produced download speeds in excess of 3 Gb/s.

Building on that “want,” T-Mobile US also expanded the reach of its VoNR service to four more markets: Cincinnati, New Orleans, New York, and Seattle. That service routes voice traffic over the 5G SA network, which will eventually allow T-Mobile US to turn off its current 4G LTE network that handles the vast majority of its voice traffic once it can migrate all of its end-users to voice devices compatible with the VoNR service. This will in turn allow T-Mobile US to turn off its 4G LTE network and re-farm the spectrum supporting that network to its 5G – or 6G – network.

Currently, voice calls for most operators in the U.S. is run over their 4G LTE networks using voice over LTE (VoLTE) technology. For 5G-compatible devices, carriers steer data traffic over their newer networks when it’s available.

This setup requires current 5G devices to also have a 4G LTE radio and antennas to support the voice traffic, which adds cost and complexity to those devices.

The challenge has been in getting voice quality traffic to meet that of legacy systems. Voice traffic is more sensitive to dropped or corrupted data packets than traditional data services.

The carrier had previously stated that the VoNR service might provide for faster call set-up times, but the real benefit will be in now being able to include voice services as part of its network slicing abilities.

T-Mobile US last year initiated its VoNR service in a pair of markets – Salt Lake City and Portland, Oregon – with plans to roll out the service to “many additional areas” in 2022. Those new areas bring total coverage to a half-dozen markets, with plans now to cover 100 million people with VoNR capabilities “in the coming months.”

T-Mobile US’ VoNR service is also reliant on the carrier’s 5G SA push. That push received a Cisco boost late last year when T-Mobile US turned on new Cisco routing and cloud equipment to power its 5G SA network.

A T-Mobile US spokesperson at that time explained that the carrier’s initial 5G SA core ran on an “older Cisco platform and only supported” the 5G SA core. “This new platform is cloud native and not only supports [5G SA] technology but legacy 4G technology all on the same converged node.”