Multiple antenna systems are the new frontier for wireless communications including the actually third generation mobile communication systems, called Universal Mobile Telecommunication System (UMTS), the wireless LAN and the wireless PAN up to the future 4G mobile system focused on seamlessly integration of the existing wireless technologies. The use of multiple antenna systems improves the overall system performance in term of capacity and spectrum efficiency achieving high data rate wireless

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... services. The paper highlights the two main techniques: smart antennas with adaptive beamforming to cancel the interference signals (from other users or multipath) and MIMO systems to exploit the space-time properties of wireless channels.