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 802.1 Ia) by an additional attenuation of 10-15 dB compared to the unmodified wall, for incident angles ranging from 0°-550 in the azimuth plane and 0°-200 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.
A three-dimensional parallel implementation of the finite-difference time-domain (FDTD) method has been used to identify and isolate the dominant propagation mechanisms in a multistorey building at 1.0 GHz. A novel method to visualize energy flow by computing streamlines of the Poynting vector has been developed and used to determine the dominant propagation mechanisms within the building. It is found that the propagation mechanisms depend on the level of internal clutter modeled. Including metallic and lossy dielectric clutter in the environment increases attenuation on some propagation paths, thereby altering the dominant mechanisms observed. This causes increases in the sector-averaged path loss and changes the distance-dependency exponents across a floor from 2.2 to 2.7. The clutter also reduces Rician -factors across the floor. Directly comparing sector-averaged path loss from the FDTD simulations with experimental measurements shows an RMS error of 14.4 dB when clutter is ignored. However, this is reduced to 10.5 dB when the clutter is included, suggesting that the effects of clutter should not be neglected when modeling propagation indoors.
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