Energy Efficiency of Multiuser Sparse Massive MIMO System using Orthogonalized Hybrid Beamforming

In this paper, we present an energy efficient two-stage hybrid beamforming for the multiuser massive multiple-input multiple-output (MIMO) downlink system. The millimeter wave (mmWave) technology provides high bandwidth but at the same time suffers from high path-, penetration-, and absorption-losses. In massive MIMO system, the large number of antennas at base-station side compensates the mmWave losses but causes high power consumption in the large number of radio frequency (RF) chains. In this paper, we propose a low complexity orthogonal hybrid beamforming (OHBF) design. We use the Householder reflectors generate the orthogonal analog precoding matrix. It reduces the dimension of the digital precoder as well as the inter-user interference in the beam domain. The proposed Householder based OHBF (HOHBF) scheme provides better energy-efficiency (EE) performance than the Gram-Schmidt based hybrid beamforming design in the real-World ill-conditioned massive MIMO channel. It has been shown that the beam domain orthogonality error remains less than 0.5 with 0.98 probability and the proposed OHBF provides 19.5% improvement in EE at 5 dB SNR as compared to the Gram Schmidt based hybrid beamforming.