Per-Link Parallel and Distributed Hybrid Beamforming for Multi-Cell Massive MIMO Millimeter Wave Full Duplex

This paper presents two hybrid beamforming (HYBF) designs for a multi-cell massive multiple-input-multiple-output (mMIMO) millimeter (mmWave) full duplex (FD) system under limited dynamic range (LDR). Firstly, we present a centralized HYBF (C-HYBF) scheme based on alternating optimization. In general, the complexity of C-HYBF schemes scales quadratically as a function of the number of users and cells, which may limit their scalability. Another major drawback is that significant communication overhead is required to transfer complete channel state information (CSI) to the central node every channel coherence time. The central node also requires very high computational power to jointly optimize many variables for the uplink (UL) and downlink (DL) users. To overcome these drawbacks, we present a very low-complexity and scalable cooperative per-link parallel and distributed (P$\&$D)-HYBF scheme. It allows each FD base station (BS) to update the beamformers for its users independently in parallel on different computational processors. Its complexity scales only linearly as the network size grows, making it desirable for the next generation of large and dense mmWave FD networks. Simulation results show that both designs significantly outperform the fully digital half duplex (HD) system with only a few radio-frequency (RF) chains, achieve similar performance, and the P$\&$D-HYBF design requires considerably less execution time.