Journal
IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY
Volume 71, Issue 8, Pages 8739-8755Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TVT.2022.3176389
Keywords
Radio frequency; Massive MIMO; Array signal processing; Power demand; Channel estimation; Antennas; Uplink; Cell-free massive MIMO; hybrid beamforming; mmWave communication; RF chain activation
Categories
Funding
- National Research Foundation of Korea (NRF) through Basic Science Research Program - Ministry of Education [NRF2019R1A6A1A03032119, NRF-2016R1D1A1B03933122]
- Academy of Finland through 6G Flagship Program [346208]
- EERA project [332362]
- Infotech Program - University of Oulu Graduate School
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This paper investigates hybrid analog-digital beamforming architectures for uplink cell-free millimeter-wave massive MIMO systems and proposes two HBF schemes, namely decentralized HBF (D-HBF) and semi-centralized HBF (SC-HBF). It is shown that the analog beamformers generated in these two schemes provide approximately the same achievable rates, despite the lower complexity and lack of CSI requirement of D-HBF. Furthermore, a novel adaptive RF chain-activation scheme is proposed to reduce power consumption while achieving significant improvement in energy efficiency.
In this work, we investigate hybrid analog-digital beamforming (HBF) architectures for uplink cell-free (CF) millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) systems. We first propose two HBF schemes, namely, decentralized HBF (D-HBF) and semi-centralized HBF (SC-HBF). In the former, both the digital and analog beamformers are generated independently at each AP based on the local channel state information (CSI). In contrast, in the latter, only the digital beamformer is obtained locally at the access point (AP), whereas the analog beamforming matrix is generated at the central processing unit (CPU) based on the global CSI received from all APs. We show that the analog beamformers generated in these two HBF schemes provide approximately the same achievable rates despite the lower complexity of D-HBF and its lack of CSI requirement. Furthermore, to reduce the power consumption, we propose a novel adaptive radio frequency (RF) chain-activation (ARFA) scheme, which dynamically activates/deactivates RF chains and their connected analog-to-digital converters (ADCs) and phase shifters (PSs) at the APs based on the CSI. For the activation of RF chains, low-complexity algorithms are proposed, which can achieve significant improvement in energy efficiency (EE) with only a marginal loss in the total achievable rate.
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