NTT DoCoMo is claiming a solution for one of the big problems that faces millimeter wave (mmWave) 5G -- transmitting the high-band signal through treated low-emissivity (low-E) glass. The operator tested a new window material which allows 28GHz signals to pass through, making it suitable for unobtrusive use in the windows of buildings and vehicles, DoCoMo claims.

Millimeter Wave 5G has amazing raw speed, getting downloads of 1-gigabit plus wirelessly, but has terrible coverage range (1,000 feet to 2,000 feet) and can't penetrate energy-saving low-E glass, as well as grass hedges and concrete walls. This means that early high-band 5G networks don't work inside buildings, a major failing for the newest high-band cellular standard.

NTT DoCoMo has now tested a new window material that it calls a "prototype dynamic transparent metasurface." The material is manufactured by Japanese global glass manufacturing company AGC, and can be used in the windows of buildings and cars. "The metasurface, an artificially engineered material, comprises a large number of sub-wavelength unit cells placed in a periodic arrangement on a two-dimensional surface covered with a glass substrate [underlying layer]," DoCoMo says in a statement.

Figure 1: DoCoMo transparent dynamic metasurface, designed by DoCoMo and manufactured by AGC.
(Source: NTT DoCoMo)

In the trial, 28GHz radio waves were beamed to measure penetration in two modes: full penetration, where the glass substrate and moveable transparent surface were attached to each other; and full reflection, where the two were separated by more than 200 micrometers.

DoCoMo says that the prototype material can be used with frequencies higher than the millimeter wave band (traditionally listed at 30GHz to 300GHz). This means it can be used in 6G communications that go up into the 120GHz and even the Terahertz (THz) range.

Why this matters
The prototype window material allows mmWave signals to pass through the new glass. This is technically important for 5G cellular.

So far, DoCoMo has only tested this technology on a small piece of prototype glass. The much larger issue is the cost of new and replacement glass that would be needed in millions of buildings around the world. It is way too early for DoCoMo to have any figures on how much it might cost to replace all existing windows with its new glass substrate, but it would doubtless be incredibly expensive!

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— Dan Jones, Mobile Editor, Light Reading