Building Materials and Propagation
Background and context
The propagation of radio signals into, out of and around buildings is important for a range of communication services, including mobile phone use, radio listening and TV viewing on both mobile devices and conventional portable TV sets. We wished to better understand the impact of building materials and techniques on the use of wireless devices indoors, in particular any reduction in indoor percentage locations availability in the bands of frequencies use for broadcasting and by mobile networks.
A particular focus is the possible impact of changes in building construction intended to increase energy-efficiency, which may result in the passage of radio waves being blocked in addition to heat and/or infra-red. Although the main focus of the study is propagation into and out of buildings, we also wished to understand the extent to which evolving construction techniques are likely to have significant impacts on indoor propagation, including in the bands used by Wi-Fi.
As wireless signals pass through objects, such as walls, windows or doors, they become weaker due to reflections off, or absorption by, these objects. This effect is known as building loss and different materials will exhibit different levels of building loss at different frequencies.
Measuring the effects of construction materials on indoor coverage
Our study measured the building losses of several properties with a range of different construction materials, including foil-backed plasterboard and metallised double glazing. The approach is described below.
Step 1 – Baseline, transmitter outside
Step 2 – Transmitter inside and calculation of building loss
The following frequencies were measured as they are broadly representative of typical wireless services that are accessed while indoors:
- 88MHz - FM radio;
- 217MHz - DAB radio;
- 698MHz - Digital terrestrial television, mobile broadband (for high coverage);
- 2.4GHz - Wi-Fi, mobile broadband (for high capacity); and
- 5.7GHz - Wi-Fi.
Two high level findings from the study are:
- Broadly, building loss increases with frequency, i.e. higher frequency signals will experience a greater reduction in signal strength when passing through an object than lower frequency signals. This is the reason why lower frequencies are preferred for delivering wide area and in-building coverage for mobile networks; and
- The use of common materials such as foil-backed plasterboard and metallised double-glazing has a tangible effect on in-building coverage. On average, the presence of these materials reduced the strength of incoming signals by between 6 and 11 dB, compared to standard wall construction and single glazed windows.
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