Robust and Low Complexity Hybrid Beamforming for Uplink Multiuser MmWave MIMO Systems

In a millimeter-wave (mmWave) multiple-input multiple-output (MIMO) system, a large number of antennas can be placed into a very limited space. It is not practical to equip each antenna with one independent radio frequency (RF) chain. Fortunately, the hybrid analog/digital beamforming (HBF) can be utilized to greatly reduce the number of RF chains, while providing an acceptable performance. However, the conventional multiuser MIMO beamforming algorithms cannot be directly applied to the mmWave system with HBF structure. In this letter, based on the idea that interuser interference reduction should be done for both analog beamforming and digital beamforming, we propose a novel HBF algorithm for the uplink multiuser scenario, which has low computational complexity. Simulations indicate that the proposed algorithm performs very close to the full digital algorithm, and its robustness is verified by comparisons with other existing algorithms under two different channel assumptions.