Abstract
Presence of foliage in propagation path plays a significant role in the propagation of radio waves. The foliage medium provides a rich scattering environment which largely affects the spatial and temporal characteristics of the received signal in wireless communications systems. A better understanding of the effects of foliage on the radio channel characteristics allows us to better evaluate the performance of multi-antenna systems such as diversity combining and MIMO systems. In the past years, in many studies in the field of radio wave propagation through foliage, there have been a number of theoretical as well as empirical path loss models developed in literatures [1]. A theoretical description of penetration into vegetation is given by the theory of radiative energy transfer. These models are generic and applicable to any foliage wave propagation scenario, but are more complicated than the empirical models. The empirical models are based on specific measured data and fail to relate the foliage path-loss to the foliage dependent parameters such as tree species and density. All the models, as mentioned above, are focused mainly on path loss characteristics. An important aspect in the understanding of radio wave propagation in rural areas are the spatio-temporal characteristics of the channel. Of special note is the angular spread of the radio channel, which is essential parameter for diversity combining and MIMO systems. Currently, there are few studies on the directional analysis of the dispersion effects of foliage in the radio channel. The spatio-temporal channel characteristics on the MS side in the foliage environment based on measurements using a channel sounder has been studied [2]. The results show that some large spreads in azimuth and the distance of the nominal azimuth values from zero may be related to the dispersion caused by the foliage. However, this result only investigated the direct path with the location of the MS fixed. Further investigation is essential to extract the effects of other paths that may be present in the environment. © 2012 IEICE.