Polarization characteristics under indoor micro/pico cell environments

For the radio communication and the radio LAN within indoor environments, such as buildings, underground shopping centers and subway stations, it is necessary to design a micro- or pico-cell system to increase the traffic capacity. In such a small sized cell, the propagation environments are based on the line-of-sight(LOS) path, and the diversity gain obtained by using the space diversity technique to eliminate the fast fading is not expected because the fading structure is Rician. However, the use of polarization diversity at the base station is assumed to increase the average up-link level when hand held terminals are used at a tilted angle. The conventional cellular systems use vertical polarization and a few references have reported the use of horizontal polarization or circular polarization to reduce the fading effects. On the other hand, the optimum polarization for the transmitting antenna as the base station has not been considered from the view point of expanding or restricting the cell size. When the propagation environments are changed, the optimum polarization is assumed to be different for the micro- or pico-cell. The paper presents the polarization characteristics of an indoor propagation environments obtained by experiments and by ray tracing methods.