Characterization of Indoor Channels with Directional Antennas and Performance Evaluation

Abstract

Recently UWB beamforming attracts significant research attention to obtain spatial gain in the form of antenna array. It is commonly believed that directional antenna based communication could improve the system performance. In order to further make clear the relationship between system performance and the antenna radiation pattern, UWB indoor channels extracted from practical measurements are combined with circular horn antenna to characterize the channel properties and to evaluate the system performance. The direction related channel parameters like angle of departure (AOD) and angle of arrival (AOA) are obtained by SAGE algorithm from the measurement results. Using directional antenna with a certain half power beamwidth (HPBW), the channel delay will decrease because the multipath components the receiver could collect are reduced. In the line of sight (LOS) environments, the channel capacity increases with the beamwidth decreasing and is always larger than that of an omnidirectional antenna. Similarly, the bit-error-rate (BER) performance of RAKE receiver is improved with the beamwidth becoming smaller. However in the non-line of sight (NLOS) environments, the conclusions are not so simple. The capacity and BER performance are not always better with directional antennas. And the variation trend between the system performance and the antenna beamwidth disappears. This is mainly because that there exist no dominant strong path components like in the LOS environments. This reminds us that when antenna beamforming is used to obtain array gain, the beamwidth should be carefully designed to obtain optimal performance, especially in the NLOS environments.