orresponding to four or eight transmit antenna ports. The CSI feedback is used at the base-station for precisely controlling the amplitude and phases at the transceivers driving the antenna array in order to adapt the data transmission to the particular user. In order to get around this antenna port limitation, there are two main approaches for supporting a Massive-MIMO base-station with Rel-8-Rel-12 specifications - sectorization-based approaches and reciprocity-based approaches. 11.5.1 Sectorization (Vertical)-Based Approaches In the sectorization-based approaches, a mobile device is assigned a subset of four or eight antenna ports which are chosen from the set of antenna ports available at a Massive-MIMO base-station. An example would be to configure a 16 antenna port Massive-MIMO array to LTE Small Cell Optimization Vertical sector-1 Vertical sector-2 Figure 11.12 An AAS with 16 transceivers configured for vertical sectorization. Each vertical sector is comprised of eight azimuth cross-polarized ports create two vertical sectors with 8 azimuth antenna ports in each (see Figure 11.12). A possibility is to deploy the two vertical sectors as two different cells. Alternatively Rel-11 onwards allows the possibility of deploying the two vertical sectors as two virtual cells enabling some flexibility of switching a mobile device from one vertical sector to the other without a laborious handover procedure. Rel-11 also allows dynamic coordination of scheduling between the vertical sectors. Figure 11.13 shows the simulated performance of the shared data channel with vertical sectorization achieved with AAS compared to 8 Tx performance of a conventional base-station. These results do not assume dynamic coordination across the vertical sectors. Note that both the AAS and the conventional base-station are using a cross-polarized array of 64 antenna elements arranged in 8 rows and 4 columns with the same spacing. The AAS is equipped with 16 transceivers (8 azimuth X 2 elevation) driving the array while the conventional bas