Non-feedback vertical plane beamforming for LTE-Advanced systems

In 1-cell frequency reuse, which is generally employed in current cellular mobile communication systems, the downlink Inter-Cell Interference (ICI) remains a critical barrier to achieving improvements in the spectrum efficiency. As one of the techniques for ICI in LTE-Advanced, we have proposed precoding-based vertical plane beamforming of eNB (evolved Node B) antenna and clarified the effectiveness of the proposed method through a field experiment. In general, an eNB generates a precoding matrix by reference to the channel state information sent back from a UE (User Equipment). Therefore, feedback error or delay causes a deterioration of downlink performance. On the other hand, in the vertical plane beamforming, the precoding matrix to be applied can be estimated from the distance between the eNB and the UE. The distance can also be calculated from the propagation delay obtained at the eNB by Timing Advance (TA) operation, which is an essential function for adjustment of the transmission timing of UEs. Therefore, in this paper, we propose the non-feedback vertical plane beamforming, in which the eNB estimates the distance from the UE by TA operation and applies the appropriate precoding matrix according to the distance. To demonstrate the feasibility and performance of the proposed method, we develop a prototype system, in which the proposed scheme is implemented on an LTE-Advanced-based system, and conduct a field experiment. This paper overviews the prototype system and the field experiment results.