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TMO warns that 3.5 GHz could be a US “orphan band” as Korea trials 5G

In many countries, notably China (see separate item), the 3.5 GHz band is being identified as an important one for 5G. Traditionally allocated for fixed wireless, it is being opened up by regulators for mobile 4G and 5G, and possibly for shared access using emerging technologies like MulteFire. Last week, SK Telecom announced South Korea’s first trial of 5G systems in the band.

Although many of the new developments in 3.5 GHz have been spearheaded in the US – where the FCC has introduced an innovative, if complicated, three-tier system of access – that early movement risks leaving the US out of the band plan mainstream again, if the rest of the world adopts a different approach and moves quickly to 5G in 3.5 GHz.

With companies in China, South Korea and elsewhere demonstrating 5G NR in the band, T-Mobile USA has stepped up its campaign to get the FCC to amend its proposed rules for the shared access element of its 3.5 GHz plan, known as CBRS (Citizens Broadband Radio Service), in order to take better account of global 5G harmonization.

“T-Mobile has asked the FCC to re-examine its rules for the 3.5 GHz band,” wrote TMO’s CTO Neville Ray, in a blog post. “The 3550-3700 MHz spectrum is ideal to meet the midband needs for 5G networks.”

Ray argues that combining 3.5 GHz with the bands above and below it would create a total of 1100 MHz of midband spectrum “with better coverage characteristics than high band spectrum, meaning that it can help deliver the promise of 5G to rural areas.”

“Over time, we would be passing up the opportunity to auction potentially 1100 MHz of midband spectrum, which will certainly generate tens of billions of dollars in auction proceeds,” Ray continued, warning that 3.5 GHz could end up as an “orphan band” in the US.

While Google and Federated Wireless are finessing their geolocation databases to manage shared access in 3.5 GHz, there are also two non-shared tiers. The highest level of protection from interference goes to the incumbent federal users, while there will also be an auction for licensed access, which will be protected from interference from the ad hoc sharers. The licences will be for a term of three years and the current rules dictate that they will be based on census tracts, so that a local WISP or enterprise could obtain a licence for a very localized area. Of course, the MNOs are lobbying to change that approach in favor of conventional licensing geographies and terms.

Meanwhile, in South Korea, SK Telecom has been talking up its demonstrations of 5G in that band with Samsung and Nokia. These were the first in the country, using an end-to-end network with a 5G virtualized core, virtualized RAN, distributed baseband uit and radio unit, and a test device based on the 3GPP 5G New Radio specs.

The operator went into some detail about its 5G NR test system, developed with Samsung. It uses subcarrier spacing of 60 kHz, transmit time interval (TTI) length of 0.25ms, a subframe structure that simultaneously supports downlink data and uplink feedback, and LDPC channel coding. SK Telecom also worked with Nokia to develop 5G base station equipment and test device for the 3.5 GHz spectrum and achieved gigabit throughput realised Gbps-level throughput using carrier aggregation.

SK Telecom said it plans to deploy commercial 5G networks using 28 GHz spectrum in downtown areas of concentrated traffic, while covering wide areas with 3.5 GHz or a combination of the two.

“SK Telecom has secured all key technologies for building commercial 5G networks using 3.5 GHz and 28 GHz frequency bands,” said Park Jin-hyo, SVP and head of the operator’s Network R&D Center. “We will maintain our leadership in 5G by enhancing our technologies for both above-6 GHz and below-6 GHz frequencies, while playing an active role in the standardization and commercialization of 5G technologies.”

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