Performance analysis and comparisons of antenna and beam selection diversity

Smart antennas can greatly improve the performance of wireless communication systems by providing better link quality and immunity to interference. A simple smart antenna structure is fixed beamforming and beam selection. More complex structures require combining of the signals from multiple receivers. In this paper we compare the performance of beam and antenna selection and combining techniques. Our results are based on recently reported statistical and measurement based spatial channel models and in most cases include impact of co-channel interference. We derive the probability density function (pdf) of SINR in space- and frequency-selective multiple clustered Rayleigh fading channel with finite angle spread (AS). We also analyze the outage capacity and probability of beam selection in flat fading assuming both correlated and independent fading between the antennas. Our analysis also includes the impact of erroneous beam or antenna selection. Furthermore, theoretical bounds for a hybrid of beam/antenna selection and maximal ratio combining (MRC) are presented. We show that beam selection techniques can be very effective against both multipath fading and co-channel interference. We also show that simple fixed beamforming networks such as Butler matrices are nearly as effective as more complex fixed beamforming networks.