Nokia's US CTO isn't expecting high-speed 5G millimeter wave networks will ever blanket the country in the way that 4G LTE networks do now, simply because the technologies are different.

Talking to me Tuesday, Michael Murphy, CTO of North America at Nokia Corp. (NYSE: NOK), explained that he expected high-speed millimeter wave, which will initially be deployed in the 28GHz and 39GHz bands in the US, to be used to create high-speed broadband "5G islands or zones" in select American cities.

"It's not going to be deployed nationwide like 4G was," Murphy said. "There's pretty much zero chance of that happening, maybe forever."

This is because millimeter waves at 28GHz can deliver gigabit speeds over short distances in the air using "beamforming" that connects the signal to a single device over the best possible path, but is subject to foliage interference, line-of-sight issues and other problems. In contrast, 4G LTE at 700MHz has been used by AT&T Inc. (NYSE: T) and Verizon Wireless to cover the US population. (See Helping Millimeter Wave Achieve Its Potential.)

High-speed 5G broadband zones, which could promise services at least ten times faster than 4G, would be deployed in major cities, likely in the areas where a carrier could get the best return on their investment.

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Murphy expects that a lower-band layer of 5G will have to provide coverage and incrementally better performance over LTE. "Yep, that's how a lot of countries are looking at it now."

Murphy suggests that 3.5GHz is becoming a de-facto option for low-band 5G. Europe and CHina are almost 100% confirmed for N42 and N43 [3.4-3.6GHz bands]," he says.

Since China Mobile Ltd. (NYSE: CHL) can encourage the development of a 3.5GHz-based silicon and hardware infrastructure by itself, that makes the availability of low-cost 3.5GHz chipsets much more likely. (See Google, LTE-U & the Question of a Wireless Broadband Future and Tech Giants Team Up on 3.5GHz Initiative.)

3.5GHz is a shared public band in the US, still Murphy still thinks it could be used by carriers and "new entrants" for low-band 5G.

In tests so far, however, Nokia is not finding that applying beamforming techniques to the lower band offers much performance improvement.

"5G gives you better gains the higher the frequency," he says. This is because the higher you go the smaller the antennas can be and the more can be packed into an array.

— Dan Jones, Mobile Editor, Light Reading