Antenna Arrays and Space Division Multiple Access

Adaptive base station antennas also called smart antennas have recently become a hot research topic. In principle the adaptive antenna concept consists of an antenna array and a flexible beamforming network. In terms of commercial exploitation there are mainly two driving factors for introducing adaptive base station antennas, (i) range extension, (ii) capacity enhancement. The issue of range extension is briefly discussed in Section 2, but the main emphasis is put on capacity enhancement of adaptive base station antennas. As sketched in Figure 1, an adaptive antenna array typically creates a narrow beam in the direction of the desired mobile station and thereby reduces the co-channel interference level in other azimuth directions. This is called spatial filtering. There are two methods to exploit a capacity gain from spatial filtering: In the concept of Same Cell Reuse (SCR), the physical radio channels (timeslot, frequency channel) = (t,f) are