An experimental and theoretical analysis on precoding-based vertical plane beam control for LTE systems

Most current cellular mobile communication systems employ 1-cell frequency reuse to achieve high spectrum efficiency. With 1-cell frequency reuse, the co-channel interference among cells remains as a critical barrier to achieving further improvement in the spectrum efficiency. Vertical plane beam control at base station is one approach to mitigating the co-channel interference. As a conventional method of vertical plane beam control, antenna beam tilting has been widely used. In the antenna beam tilting, the tilt angle is generally fixed per base station. If the vertical plane beam can be changed dynamically for each mobile station, it is possible to significantly improve the reception environment. Given this background, we have proposed precoding-based vertical plane beam control. In the proposed method, the vertical plane beam pattern for each mobile station is easily changed dynamically by just the precoding (phase control of digital baseband signal) operation without changing conventional antenna configuration drastically. To demonstrate the feasibility and performance of the proposed method, we developed a prototype system, in which the proposed scheme is implemented on an LTE-based system, and conducted a field experiment. This paper overviews the prototype system and field experiment results. Measured results clarify that the proposed method is effective in mitigating interference level to the neighbor cells as well as improving the desired signal level in the serving cell. We also conducted theoretical analysis and confirmed that the experimental results are well in line with the theoretical results.