 network, allows beamforming in the elevation and the azimuth dimension that is dynamic and more flexible (3D-beamforming). It is also evident that AAS architecture is critical in determining the number of antenna ports as well as the flexibility available for controlling the antenna array - thereby directly impacting the system performance as shown later. 11.4 Deployment Scenarios for Antenna Arrays The spectral efficiency of a system is maximized when the antenna array is able to focus a beam on a particular user in the system achieving user-specific beamforming gains and also able to separate multiple users in the spatial domain via beamforming achieving multi-user LTE Macro Cell Evolution Figure 11.5 An example AAS architecture where a TXRU is connected to all the co-polarized antenna elements contained in a single column [4] transmission gains. Conventional passive antenna systems including RRH installations are able to take advantage of user-specific beamforming and multi-user transmission gains in the azimuth (2D horizontal plane) dimension. This ability has been well studied in the literature and it is understood that the user-specific beamforming opportunity is not biased in any direction (within the sector pattern) which is a result of a uniform distribution of users within the sector in the 2D plane. This is no longer true in the elevation dimension. Figure 11.8 shows four users in the horizontal plane in NLOS condition (blocked by buildings) and their hypothetical mean elevation angle of departures. Simply from a geometrical point of view it is clear that the users closer to the base-station are more separable in the elevation dimension than the users that are far away. It is, therefore, natural to expect that the user-specific beamforming opportunity in the elevation dimension is biased favourably towards the users that are closer to the base-station. This shows that the angular distribution of the users in the elevation dimension in a particular LTE Small Cell Optimization Column-1 Column-2 Column-3