Hybrid beamformer design for millimeter wave MIMO OFDM downlink systems

Abstract

Hybrid beamforming consisting of digital precoding and analog beamforming is considered as a practical way to implement efficient beamforming for large-scale antenna systems in next generation mmWave wireless communication systems. Most of prior works focused on hybrid beamforming in narrow band mmWave systems. However, with consideration of wide bandwidth associated with wireless communication in the mmWave band, it is necessary to extend hybrid beamformer design to wideband mmWave systems. The main constraint of hybrid beamforming in the wideband system is that the analog beamformer should be common to every frequency component used for communication whereas the digital beamformer can be designed separately for each frequency component. In this paper, we propose an efficient hybrid beamformer design algorithm for mmWave multi-user MIMO OFDM systems with the above constraint. The proposed algorithm is based on maximization of the sum of signal-to-leakage-plus-noise ratio (SLNR) often used in multi-user MIMO broadcast downlink. Numerical reusults show that proposed algorithm achieves good performance compared to the beamformer design targeting narrowband mmWave systems.