Channel Alignment for Hybrid Beamforming in Millimeter Wave Multi-User Massive MIMO

To assist hybrid beamforming in multi-user massive Multiple Input Multiple Output (MIMO) systems at millimeter wave frequencies, we propose Auxiliary Processing Network (APN) based multi-phase channel alignment techniques. The APN, which is realized in parallel to the main beamforming network, have two implementation architectures, namely the hybrid analog-digital APN based on antenna switching as well as the fully digital APN with low-resolution Analog-to-Digital Converters (ADCs). For different APN architectures, we design various channel estimation algorithms for the channel alignment procedure and evaluate the corresponding performance.