Optimized hybrid beamforming method with limited feedback in Massive MIMO systems

Abstract

Due to the limitation of digital chains' number, the hybrid beamforming structure may be utilized for massive Multiple Input and Multiple Output (MIMO) systems, where the eNodeB may maintain a number of analog Tx beams. To achieve higher spectral efficiency, two analog beam interpolation methods are further proposed to enhance the accuracy of downlink analog beamforming, which based on amplitude or angle interpolation algorithm. In this paper, the typical channel state information(CSI) from user equipment (UE) is used to determine the candidate Transmitting (Tx) beams. Especially, by exploiting the spatial correlation of neighbor candidate beams, the best downlink analog Tx beam for each UE can be generated by interpolating the two strongest Tx beams from the Uplink Control Informat ion (UCI) report. Moreover, we develop a limited CSI feedback to alleviate the feedback load in traditional frequency division duplexing (FDD) Massive-MIMO systems, giving rise to better coverage and spectrum efficiency. Simulation results show that with the help of analog beam interpolation, the downlink spectrum efficiency can be significantly increased.