AT&T tested spectrum aggregation models on the oft-overlooked uplink channel that the carrier claimed was an industry first and resulted in network speeds that could help meet growing 5G traffic demands.

Jason Sikes, AVP for device architecture at AT&T, explained in a blog post that the carrier completed an uplink data call running on its 5G standalone (SA) network core that aggregated two different spectrum frequency bands. The test was in AT&T’s labs using Nokia’s 5G AirScale equipment running on MediaTek’s mobile test platform.

Sikes explained in an email to SDxCentral that the test used 10-megahertz of AT&T’s low-band 850 MHz spectrum combined with varying amounts of the carrier’s C-band spectrum. With 40-megahertz of C-band spectrum the carrier was able to increase uplink speeds by 100% to more than 70 Mb/s compared with just the base 850 MHz spectrum. It witnessed a 250% increase in speed to more than 120 Mb/s using 100-megahertz of C-band spectrum.

“Think of this as adding more lanes in the network traffic highway,” Sikes wrote in the blog. “No one in the U.S market has successfully aggregated two carriers in 5G SA uplink – until now.”

Sikes added that AT&T’s mobile network has witnessed a 30% increase in uplink capacity demand per year.

“This new age of connectivity is not only about consuming more content but also generating more content than ever before,” he noted of the increase. “Whether you are uploading large files, on a video call with family, live streaming, cloud gaming or using extended reality applications, the network is facing surging upstream traffic demands it never has before.”

The latest test followed one conducted by the carrier last fall that involved a four-channel downlink call that traversed its 5G SA network. That call aggregated a pair of frequency division duplex (FDD) carriers and a pair of time division duplex (TDD) carriers running in the C-band and the 3.45 GHz spectrum bands.

FDD is where different bands of frequency are used by users; one for uplink and the other for downlink. TDD is where one frequency band will be used for uplink and downlink, switching between the two from moment to moment.

Sikes also noted that AT&T was deploying a “two-layer uplink” multiple-input, multiple output (MINO) technology on TDD across its C-band spectrum. “This feature will not only improve uplink throughput but also enhance cell capacity and spectrum efficiency,” he wrote, though he further added that the carrier did not use MIMO during the most recent uplink test.

The carrier is planning to launch 5G New Radio Dual Connectivity (NR-DC) capabilities “in the coming months.” This will allow for the aggregation of low- and mid-band spectrum with AT&T’s millimeter-wave (mmWave) spectrum using the 5G SA core.

Sikes noted this capability has resulted in lab test downlink speeds up to 5.3 Gb/s and uplink speeds up to 670 Mb/s.

“This technology gives customers high-speed mobile broadband for both downlink and uplink in stadiums, airports and other high-density venues,” Sikes wrote.

In the follow-up email, Sikes added that "over time, private 5G and fixed wireless will benefit from these uplink and downlink enhancements."

While Sikes noted the carrier’s most recent tests were an industry first, the industry has been prolific in testing different downlink carrier aggregation combinations.

T-Mobile US, for instance, recently ran a test aggregating four carrier channels of spectrum running across its 5G 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.

Verizon last year plugged quasi-licensed Citizen Broadband Radio Service (CBRS) spectrum into a 5G data session trial with Ericsson that showed it was able to use both the shared and licensed versions of the CBRS spectrum to boost network capacity.

CBRS spectrum includes 150 megahertz of spectrum in the 3.5 GHz band. Access to that spectrum is through a multi-tiered access program that includes tier-one incumbents with “protected status,” including the Department of Defense for use by Navy ship radars and registered fixed satellite receiving stations; a tier two for “priority access licenses” (PAL); and tier three for “general authorized” channels.

Verizon said it plans to use that spectrum to supplement the current use of its licensed C-band and millimeter-wave (mmWave) spectrum for its 5G network.

AT&T also remains steadfast toward more broadly rolling out commercial 5G SA capabilities.

“We have said that we plan to deploy standalone 5G when the ecosystem is ready, and AT&T is charging forward to advance SA ecosystem readiness,” Sikes explained. “Businesses and developers will be first to take advantage of this technology as we move from research & development to deployment.”

Commercial 5G NSA networks rely on an operator’s legacy 4G LTE core for base processing and routing. A 5G SA core, which consists of the user plane, control plane, and shared data layer network functions, allows operators to deliver a more resilient core network and support highly-touted 5G services like network slicing, automation, orchestration and mobile edge computing (MEC).

AT&T late last year said it had begun supporting commercial customers on its 5G SA network core, which aligned with more high-profile moves by its competitors.

“We haven’t made a big splash about standalone core, but we have a standalone core deployed, and we do have commercial users on it, and we’re slowly moving more commercial users onto it,” Chris Sambar, network EVP at AT&T, said at that time. “We’re marching down the road on standalone core just like everyone else is, and I think everyone is in the place where we need to have it well distributed. We’ve already done that with non-standalone because [of] the architecture we used there – we were at the forefront of that – so our standalone core will follow in the same locations.”

Sikes added that the carrier is approaching its uplink carrier aggregation plans in the same manner. "We will introduce when the ecosystem is ready, including devices," he wrote.