A frequency-selective wall for interference reduction in wireless indoor environments

Modifying the indoor wireless physical propagation environment to reduce the interference level was investigated and demonstrated in this research. A common office partition wall (that was in the main propagation path) was transformed into a frequency-selective (FS) wall by attaching a custom-designed band-stop frequency-selective surface (FSS) as a cover on the wall surface. In-situ measurements showed that this frequency-selective wall filtered out signals operating at 5.4-6.0 GHz (IEEE 802.11a) by an additional attenuation of 10-15 dB compared to the unmodified wall, for incident angles ranging from 0 degrees-55 degrees in the azimuth plane and 0 degrees-20 degrees in the elevation plane. An attenuation of 10-15 dB in signal strength in the stop band is considered to be significant and beneficial in interference reduction, whereas in the pass-band region (such as 1.8 GHz for cellular telephones), signals experienced only marginally more attenuation than that through the unmodified wall. Results also suggest that the interactions between the FSS and the wall surface can be minimized with an appropriate FSS design, which leads to a feasible and practical product solution: frequency-selective wallpapers. In addition, installation issues, such as misalignment of FSS sheets on the wall, were also examined.