The Telecom Infra Project performed testing last year specifically looking at penetration losses in indoor environments at 28 GHz and 60 GHz. TIP’s testing gives some insights into the challenge of achieving outdoor-in coverage for 5G at millimeter-wave frequencies, but also paints an intriguing picture of the spectrum’s coverage capabilities within the indoor environment.
Part of TIP’s testing was meant to mimic an outdoor-in scenario and assess the path loss caused by low-emissivity, double-paned glass. That glass was meant to represent the most “lossy” glass that would commonly be encountered as a barrier between outdoors and indoors, and it did have significant impacts to the signals. The low-e glass caused an average loss of 33.2 dB at 60 GHz and 22.4 dB of loss at 28 GHz. Comparatively, single-paned, clear glass – the type that would be likely to be used in indoor environments – showed losses of 3 dB for 28 GHz and 3.3 dB for 60 GHz. The TIP research paper also noted that other researchers have found that tinted glass attenuation for 28 GHz measured at 19 dB/cm. JMA Wireless, in its own testing, has calculated losses for tinted glass to be between 13-15 dB.
The Telecom Infra Project, in addition to testing 28 GHz and 60 GHz losses through low-e glass, also measured losses for those frequencies when they encountered a number of common indoor materials, including:
- Simple, single-pane clear glass: Average loss for 28 GHz was 3 dB and 3.3 dB for 60 GHz.
- Wood (specifically, three types of plywood) resulted in an average loss of 2.9 dB/cm at 28 GHz and 4.7 dB/cm at 60 GHz.
- Drywall was penetrated much more easily, with loss of 0.8 dB per layer of drywall for 28 GHz and 1.2 dB/layer for 60 GHz.
- Foliage (dense, medium-density and sparse, tested with a single plant of each foliage type): The peak loss across the three types was calculated as 19.2 dB for 28 GHz and 21.1 dB for 60 GHz. While foliage might usually be assumed to be an outdoor obstacle, indoor plants and small, live trees in offices or atriums could also potentially have significant impact signal propagation, depending on their placement, and that may need to be accounted for in link budgets.
In addition, TIP concluded that based on its testing, losses through typical internal wall materials at both 28 GHz and 60 GHz “are sufficiently small that reflections through these materials can be utilized for NLOS communication. … While typical wall constructions include more layers than [the simple wood and drywall compositions that were tested], these measurements indicate a strong potential for using both mmWave bands for LOS communication through interior wall constructions. … Despite the challenges faced by technologies operating in the mmWave spectrum, when transmitting though lossy channels link budgets can account for known losses and reliable links can be deployed when these factors are considered.”
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