Polarization Diversity for Multiband UWB Systems

Ultra-wideband (UWB) transmission provides a fast local range wireless connection using the same frequency spectrum assigned to other narrowband communication standards. A precise knowledge of the indoor transmission channel is necessary to obtain high performance. Several channel models have been presented in the literature, but normally without considering the distortion effect caused by a real UWB antenna. A detailed antenna model shows that the radiation pattern varies with frequency, i.e., different receiver positions and antenna orientations result in different antenna frequency responses. In order to obtain a more uniform coverage over the indoor area, two transmitting antennas with orthogonal polarization can be used. The receiver can use a single antenna whose orientation and position is arbitrary within the coverage area, resulting in a special case of a 2:1 MISO system in which a space-time encoding is used at the transmitter. The target is to employ the polarization diversity to obtain a constant quality of symbol detection while the receiver moves around in the coverage area. The proposed polarization diversity scheme is applied in an UWB multiband scenario and it is compared to both a single antenna scheme and a classical space diversity scheme employing a single polarized antenna array.