Adaptive Beamforming in TDD-Based Mobile Communication Systems: State of the Art and 5G Research Directions

Adaptive beamforming has been attracting considerable attention from both academia and industry for decades. It has already played an important role in modern wireless communication systems. This article provides an overview of adaptive beamforming and its application in cellular systems including the fundamental principle and schemes. This article points out that TD-SCDMA 3G spins off the commercial scale of adaptive beamforming in cellular networks. Beamforming-based spatial multiplexing is a breakthrough in adaptive beamforming and the symbolic technology of TD-LTE 4G. The standardization of adaptive beamforming in 3GPP LTE networks is summarized. To evaluate adaptive beamforming techniques, system simulation and field test results from commercial TD-LTE 4G networks are presented and associated with gains achieved through adaptive beamforming in different scenarios. Finally, future research areas of massive beamforming in 5G are envisioned.