Contents I. Introduction
Over the last few years, the demand for wireless connectivity has risen beyond all expectations. The proliferation of wireless networks and the increase in the bandwidth demand, has led to the shortage of the radio resources: for a given amount of power (limited by regulation or practical considerations) and a fixed amount of bandwidth, there is a finite amount of capacity (bits/sec/Hz/unit area) that operators can offer to their customers. Recent works [1], [2], [3] show how spatially selective transmissions, based on directive and smart antennas, constitute a powerful opportunity to substantially increase the wireless system capacity and coverage capability, but also show how a number of drawbacks emerge within a 802.11 environment, originally designed for omni-directional antenna operation [4], [5]. Space division techniques ideally allow to reuse the same frequency channel in physically separate regions (sectors), thus adding new interesting perspectives for broadband wireless access. The key advantage of directional-antenna solutions is then the enabling of intra-cell bandwidth reuse by multiplexing spatially separated users in the same radio channel.
