Hybrid Beamforming for Downlink Massive MIMO Systems with Multiantenna User Equipment

In this paper, a novel hybrid precoding algorithm is proposed for the downlink of a multiantenna multiuser massive multiple-input multiple-output (MIMO) system. Firstly, a modified block diagonalization precoding technique is presented. Then, it is shown that combining the modified block diagonalization with hybrid beamforming can achieve a similar sum-rate as block diagonalization with digital beamforming can. Moreover, the performance of the presented algorithm is comparable to the achievable rate in the single-user scenario where there is a full collaboration among the receivers. In a sparse scattering channel, the proposed technique has significantly higher sum-rate compared to a zero- forcing based hybrid beamformer. When digital phase shifters with 3-bits of resolution are used at the RF beamformer, the proposed algorithm achieves the performance of a hybrid beamforming algorithm with analog phase shifting.