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

This article presents two novel hybrid beamforming (HYBF) designs for a multi-cell massive multiple-input-multiple-output (mMIMO) millimeter wave (mmWave) full duplex (FD) system under limited dynamic range (LDR). Firstly, we present a novel centralized (C-HYBF) scheme based on alternating optimization. However, C-HYBF presents many drawbacks such as high computational complexity, massive communication overhead to transfer complete channel state information (CSI) to the central node every channel coherence time (CCT), and requirement of expensive computational resources. To overcome these drawbacks, we present a very low complexity, per-link parallel and distributed HYBF (P$\&$D-HYBF) scheme based on cooperation. Due to per-link decomposition, it enables each FD base station (BS) to solve its local sub-problems independently and in parallel on multiple processors, which leads to significant reduction in the execution time. It requires that each FD BS cooperates by exchanging information about the beamformers with the neighbouring BSs which allow each FD BS to adapt its beamformers correctly, and consequently, P$\&$D-HYBF exhibits negligible performance loss compared to C-HYBF. Moreover, its complexity scales only linearly with the network size and density, making it highly scalable. Simulation results show that both designs achieve similar performance and outperform the fully digital half duplex (HD) system with only a few radio-frequency (RF) chains.