A study on beam tilt angle of base station antennas for Base Station Cooperation systems

Base Station Cooperation (BSC) is one of the key technologies for next generation cellular systems. The BSC can improve channel capacity at the cell-edge unlike conventional single cell transmission. In this paper, we will study about beam tilt angle of base station antennas for the BSC systems. In conventional systems, beam tilt angle is designed to maximize the power of its own cell while minimizing the power from adjacent cells to reduce Inter-Cell Interference (ICI). Unfortunately, performance at the cell-edge cannot be improved since Signal-to-Interference Ratio (SIR) is unchanged regardless of the beam tilt angle. However, since the problem of ICI is removed in the BSC system, beam tilt angle is required to be designed differently from the conventional way. In this paper, we will derive optimal beam tilt angle for the BSC systems based on these considerations. For that purpose, an objective function to maximize average channel capacity of cooperative cell is defined, and the optimal beam tilt angle is derived by solving the problem. By numerical analysis, it is shown that the optimal beam tilt angle for the BSC system is smaller than that of the single cell transmission. By using the optimal base station antennas, channel capacity of the BSC system is greatly improved, especially at the cell-edge.