Shrub-blown time variability in attenuation and scattering at cellular frequencies

The interest in the electromagnetic behaviour of shrubs is growing in parallel with the extension of radio communication networks and the need for better coverage planning tools. When a tree is present in the vicinity of a radio link, a scattering process is likely to be induced in the propagation environment. Even though the trunk of the tree is usually kept stationary, the wind blowing on the canopy will force its leaves to oscillate, which induces time variability in the propagation channel. This study presents results of a measurement campaign aimed at the characterisation of the propagation channel time variability in vegetation media, at cellular wireless frequency bands. The results have shown that the presence of vegetation media will contribute to the received signal level enhancement, particularly in the side- and back-scattering regions, as opposed to the significant attenuation caused by absorption and scattering, in the forward-scattering region. Finally, the time variability was observed to significantly decrease the dispersive effects in vegetation media. The experimental results presented in this study provide an improvement in the electromagnetic modelling of the scattering around isolated trees.