Impact Analysis of Directional Antennas and Multiantenna Beamformers on Radio Transmission

The impact of directional antennas and multiantenna beamformers on radio transmission is formulated in terms of the gain of the Rician -factor, the reduction of the root-mean-squared delay spread, and the gain of the signal-to-noise ratio at the receiver for Rician fading channels in multipath environments. The analysis is based on a double-directional channel model. For the analytical formulation, the joint channel spectrum is assumed to be decomposable into separate spectra in time and angular domains. By way of illustration, closed-form expressions for the impact of hypothetical cosine-shaped antenna patternsand conventional beamformers are derived for channels with uniform angular spectra and an exponential decaying delay spectrum. The impact factors are explicitly related to the antenna beamwidth and the number of antenna elements. In addition, the effect of misalignment between the antenna main beam and the direct path is included in the analysis. The quantitative analysis given in this paper is important for radio system design, particularly for the design of antennas and multiantenna beamformer configurations.