Nokia North America CTO Mike Murphy confirmed at least one US broadband provider is preparing to launch 5G on 3.5GHz spectrum and explained operators face cost challenges as they plan deployments in mmWave bands.

Murphy told Mobile World Live Nokia is in conversation with several tier-1 and tier-2 mobile operators, as well as cable operators, about deploying 5G at 3.5GHz. He said he has “zero doubt” at least one, if not more, of those players will use 3.5GHz spectrum for initial 5G deployments.

In January, cable operator Charter Communications noted it was “actively testing” fixed-wireless applications at 3.5GHz. T-Mobile US and wireless industry association CTIA have also aggressively pushed the Federal Communications Commission to consider new rules for the band which would be more favourable for mobile 5G.

Murphy said the focus on 3.5GHz stems from a consensus among operators that low band spectrum will be needed to provide a nationwide 5G coverage layer while mmWave will be used more for “hotspot” deployments in urban areas requiring more capacity.

For low band deployments, the CTO explained operators will generally be able to use existing LTE sites. But mmWave rollouts will require much more site density, somewhere in the realm of two-and-a-half times what is seen in today’s LTE networks. The need translates to a much higher cost of deploying mmWave spectrum, which is a key challenge operators are trying to solve ahead of planned rollouts, he said. The problem is similar across key mmWave bands, including 28GHz and 39GHz, as Murphy noted there’s only a “very minimal difference” between the propagation and penetration characteristics of those two bands.

Murphy said some potential solutions to the cost problem include the use of relay nodes, wireless backhaul and lower-cost base stations. But he said the industry continues work on the issue as operators simultaneously seek relief from regulatory siting barriers to densification.