e 10-35. As the inter-cell interference is most severe in the cell edge, the evaluation of Co-MIMO performance is performed in the cell-edge area. The cell-edge area is characterized by the cell-edge length in the simulation, as shown in Figure 10-35. We assume a 19-cell collaborative-zone configuration in the simulation. The users are randomly dropped with a uniform distribution in the cell-edge area, one user per sector. The system performance with different sizes of cell-edge area is evaluated by setting the cell-edge length to 150 m, 100 m, and 50 m. In each collaborative region, three coordinated base stations communicate with three mobile stations located in their cell-edge areas, allocating the same time and frequency resource. Each MS in the cell-edge area will be served by two coordinated base stations, and each BS serves two mobile stations simultaneously. The precoding matrices for the two served mobile stations are calculated indepen- dently within each single sector of a coordinated BS. Each coordinated BS transmits with full power and equal power allocation to the two mobile stations. A single narrowband sub-carrier is assumed in the system without loss of generality. A conventional SU-MIMO scheme is used as the benchmark for comparison where three mobile stations in the cell-edge area are served independently by different base stations without any coordination in frequency reuse 1 deployment. As shown in Figure 10-36, even though there remains a certain amount of residual inter-cell interference, the interference power from neighboring cells within the collaborative zone is considerably reduced. 10.4 Multi-antenna transmission schemes Serving Cell Cell Edge Cell Edge Length Interfering Sectors Collaborative Zone FIGURE 10-35 An example of cell configuration and cell edge area in a collaborative zone [26] Interference from Cells within Co-MIMO Zone Single-user MIMO: 50m Collaborative MIMO: 50m Single-user MIMO: 100m Collaborative MIMO: 100m Single-user MIMO: 150m Collaborative MIMO: 150m Interferenc