Comparison Study of RF Beamforming Schemes in Hybrid Precoding for Cell-Free MmWave Massive MIMO UDN System

Cell-free Massive MIMO (multiple-input multiple output), where all the access nodes (ANs) cooperate to coherently serve all the user equipments (UEs) and to overcome the inter-cell interference limitation in ultra-dense network environments, has attracted significant attention from both academia and industry as a promising technology for 5G and future wireless communication. In this paper, we investigate the impacts of RF beamforming schemes to be combined with zero-forcing baseband precoding on cell-free mmWave massive MIMO UDN systems.