In order to reduce the cost and power consumption of radio frequency (RF) chains in a millimeterwave (mmWave) multiple-input multiple-output (MIMO) system, hybrid analog/digital beamforming (HBF) can be utilized to reduce the number of RF chains. The HBF consists of an analog beamforming (ABF) stage and a digital beamforming (DBF) stage. The ABF is always realized by using phase shifters and the DBF is done in a low-dimensional digital domain. However, phase shifters have several drawbacks, such as high power consumption and inconsistency of insertion loss. In this paper, we propose an energy-efficient HBF structure to handle these problems, which utilizes the Butler phase shifting matrix in the ABF stage. With the Butlermatrix- based ABF, several fixed beam directions can be obtained, and the best beam directions of different Butler matrices can be chosen by using exhaustive search. To reduce the high complexity of exhaustive search, we further provide a low complexity HBF algorithm. Simulations under the conditions of perfect channel state information (CSI) and estimated CSI verify the effectiveness of our proposed Butler-matrix-based HBF structure and related algorithms.
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This work was supported by National Basic Research Program of China (973 Program) (Grant No. 2012CB316002), National Natural Science Foundation of China (Grant No. 61201192), National High Technology Research and Development Program of China (863 Program) (Grant No. 2015AA01A701), Science Fund for Creative Research Groups of NSFC (Grant No. 61321061), International Science and Technology Cooperation Program (Grant No. 2012DFG12010), National S&T Major Project (Grant No. 2015ZX03002002), Key Grant Project of Chinese Ministry of Education (Grant No. 313005), Tsinghua University Initiative Scientific Research (Grant No. 2015Z02-3), Open Research Fund of National Mobile Communications Research Laboratory, Southeast University (Grant No. 2012D02), and Tsinghua-Qualcomm Joint Research Program.
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Li, J., Xiao, L., Xu, X. et al. Energy-efficient Butler-matrix-based hybrid beamforming for multiuser mmWave MIMO system. Sci. China Inf. Sci. 60, 080304 (2017). https://doi.org/10.1007/s11432-016-0640-5
- Butler matrix
- hybrid beamforming