Hybrid Beamforming for Uniform Circular Arrays in Multi-User Massive MIMO Systems

This paper proposes a new hybrid 2-stage RF-baseband precoding scheme for massive-MIMO systems using uniform circular arrays (UCA) via phase mode transformation. In particular, the baseband digital precoding stage has two sub-blocks: normalization and regularized zero-forcing (RZF). At first, the analog RF-beamforming stage and normalization sub-block are jointly designed for the phase-mode transformation, without requiring channel knowledge. Then, the RZF sub-block is constructed via the reduced-size effective channel state information (CSI) to suppress inter-user interference. The design of the proposed hybrid beamforming scheme is analytically derived and numerical results on its achieved sum-rates in comparison with the fully digital RZF precoder are presented for different scenarios. It shows that the proposed hybrid beamforming can significantly outperform the fully digital RZF precoder for the same hardware cost/complexity.