Sweden Shows the Way on Non-GNSS Timing Synchronization

Sweden leads the world in alternatives to GPS and other global navigation satellite systems (GNSS) that offer the precise timing services needed for 5G, speakers said Wednesday during a Mobile World Live webinar. Sweden’s approach includes launching the nonprofit-owned Netnod, which the government and operators fund. In the U.S., questions have been raised on Capitol Hill about carrier reliance on GNSS (see 2403120073).

“It has been a long project, and we are finally seeing some success in customers relying on our time services,” said Karin Ahl, Netnod CEO. The company was created when the Swedish Post and Telecom Authority (PTS) required that carriers not rely on GNSS or any satellite-based synchronization service for 4G or 5G, Ahl said.

Netnod stands out in that it’s “neutral,” Ahl said. 5G operators need to distribute time from the national clock source to radio access networks across Sweden, she said. “It was very clear from the beginning that we had to have a national perspective and could guarantee a robust and secure time system” across the country, she said.

Regulators made clear that price couldn’t be a barrier, so Netnod offered low-cost services, Ahl said. The government also required the company to provide visibility into the service, so regulators could “trace what we do and see how we are scaling,” she said. Without a guaranteed funding source it would be difficult to launch a similar service, she said.

Timing nodes are located in the extreme north and south of Sweden and housed in military-built bunkers, Ahl said. Each of the six sites contains two cesium clocks that guarantee resilience, connected by fiber and all the sites produce a timescale “traceable to the Swedish national time,” she said. “It has been a long ride” and “a big investment,” and requires staff with a high-level of expertise, she said.

Ahl said Netnod is fielding questions from around the world and is happy sharing what it has learned. “Interest is rising,” not just from carriers but also from the energy, banking and finance, gaming and other industries, she said. Customers are becoming “more and more knowledgeable” about the importance of timing, she said.

Sweden realized early that overrelying on GNSS is dangerous, said Hans Sjostrand, product director-synchronization at Net Insight, a Swedish technology provider. “There are so many critical systems and functions that rely on GNSS,” he said. Nations worldwide are looking at how they can “mitigate” this reliance, he said. “Awareness that there has to be an alternative to GNSS … has risen,” he said.

The PTS mandate that operators had to have a national, GNSS-independent source for synchronization “kind of forced the transition to network-based timing,” Sjostrand said. Carriers traditionally distribute time through the network using precision time protocol (PTP), which means that every router and line system in the network must be “timing aware” and support PTP. To make changes to timing support is “very, very difficult and comes with a huge cost and complexity,” he said.

Swedish authorities have made use of GNSS-independent synchronization part of the rules for 5G spectrum auctions and that’s not likely to change, said Hakan Andersson, mobile transport network specialist at wireless carrier 3 Sweden. Distributing timing from the 5G network core to the access layer has been a “real challenge” for carriers, he said.