Nokia and U.K.-based operator BT conducted a series of 5G standalone (SA) network trials that aggregated four separate spectrum channels into a single transmission channel. The work used BT’s EE mobile service network and furthers efforts to deliver faster 5G services.

The four spectrum channels included two frequency division duplex (FDD) spectrum bands in the 2.1 GHz and 2.6 GHz bands, and two time division duplex (TDD) spectrum bands in the 3.4 GHz and 3.6 GHz bands. The FDD channels operate with uplink and downlink spectrum in channels separated by a guard band, while the TDD channels use the same spectrum channel with the uplink and downlink managed by time slots.

The initial four-carrier channel aggregation (4CCA) trial was conducted at BT’s Radio Lab in Bristol, England. The companies then conducted a similar trial using a BT-owned cell tower in a park in Suffolk, England.

The total amount of spectrum used and the network performance achieved were not revealed. The companies did claim the trials were the first in Europe to aggregate four different commercial spectrum bands on a 5G SA network as well as being the first conducted outdoors.

Commercial 5G non-standalone (NSA) networks are much more common and 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.

A recent LightCounting Market Research report found that just 10% of commercial 5G network deployments use an SA core. A similar report from Dell’Oro Group noted that only three new 5G SA networks were launched during the first half of the year (Dish in the U.S., KDDI in Japan, and China Broadnet), bringing the market total to just 27.

Carriers are also increasingly tapping into 5G carrier aggregation capabilities to further bolster their network performance. Carrier aggregation allows operators to combine spectrum from different bands into a single virtual channel to provide increased network speeds.

The 5G standard allows operators to combine spectrum into a single 100-megahertz channel as opposed to a maximum of a 20-megahertz channel for 4G LTE networks. Operators need to use guard bands, or fallow spectrum, in between channels to minimize interference. This results in some spectrum not actually being used to beam signals.

T-Mobile US earlier this year aggregated three different spectrum channels running over its commercial 5G SA network that produced network speeds in excess of 3 GB/s. The carrier is currently running all of its 5G data sessions over that SA network, with parts of it also supporting two-channel CA combining a pair of 2.5 GHz spectrum channels.