Common amplitude-weighted analog beamforming in multiuser millimeter wave communication systems

In millimeter wave (mmWave) Multiple-Input Multiple-Output (MIMO) multiuser communication systems, Hybrid BeamForming (HBF) has been widely studied to make a balance between performance and hardware costs. However, the design of HBF requires either full Channel State Information (CSI) or the knowledge of equivalent channel, which brings heavy training and feedback overhead. In the paper, we propose a novel pure Analog BeamForming (ABF) method to reduce the training overhead and suppress the inter-user interference without digital beamforming. More specifically, we split the whole ABF process into two stages: standard beamforming at a special direction and spatial angle modulation. The former is realized by a common amplitude-weighted network shared by all links, while the latter is realized by a phase shifter network. Compared with the existing HBF methods, the proposed two-stage ABF method does not require extra analog hardware components, and the digital beamforming process is removed. The training overhead of channel estimation can also be greatly reduced. Both theoretical analysis and numerical results show that this two-stage ABF method can outperform the HBF methods, especially in the medium and low SNR regime of pilot signals.