Frequency-selective wallpaper for indoor interference reduction and MIMO capacity improvement

This paper presents the design and features of frequency-selective wallpaper-based on periodic and symmetric metallic hexagons-intended to be attached to standard walls for filtering out 5GHz signals (e.g., IEEE 802.11a systems)without blocking other selected radio communication services (e.g., cellular mobile communication signals). It analyzes the characteristics of the radio channel-as found within standard indoor environments-with both regular walls and walls with the proposed frequency-selective wallpaper, examined using a ray-launching programfor single-input single-output (SISO) and multiple-input multiple-output (MIMO) systems. This allows the harvesting of parameters, including channel capacity, power delay profile, and signal-to-interference ratio, for proper comparison between the two environments under study: with and without the presented wallpaper. The achieved results clearly show that the use of the proposed frequency-selective wallpaper in an indoor scenario reduces interference levels by an additional attenuation of up to 20 dB in comparison to an unpapered wall. Additionally, with MIMO systems, radio channel characteristics, such as capacity, are improved due to the increase in the magnitude of all singular values of the channel transfer matrix compared to the unpapered wall case, thereby leading to the existence of more relevant subchannels.