University of Oulu

O. L. A. López, H. Alves, S. Montejo-Sánchez, R. D. Souza and M. Latva-aho, "CSI-Free Rotary Antenna Beamforming for Massive RF Wireless Energy Transfer," in IEEE Internet of Things Journal, vol. 9, no. 10, pp. 7375-7387, 15 May15, 2022, doi: 10.1109/JIOT.2021.3107222

CSI-free rotary antenna beamforming for massive RF wireless energy transfer

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Author: López, Onel L. A.1; Alves, Hirley1; Montejo-Sánchez, Samuel2;
Organizations: 1Centre for Wireless Communications, University of Oulu, 90014 Oulu, Finland
2Programa Institucional de Fomento a la I+D+i, Universidad Tecnológica Metropolitana, Santiago 8940577, Chile
3Department of Electrical and Electronics Engineering, Federal University of Santa Catarina, Florianópolis 88040-900, Brazil
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.7 MB)
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Language: English
Published: Institute of Electrical and Electronics Engineers, 2022
Publish Date: 2022-08-26


Radio-frequency (RF) wireless energy transfer (WET) is a key technology that may allow seamlessly powering future massive low-energy Internet of Things (IoT) networks. To enable efficient massive WET, channel state information (CSI)-limited/free multiantenna transmit schemes have been recently proposed in the literature. The idea is to reduce/null the energy costs to be paid by energy harvesting (EH) IoT nodes from participating in large-scale time/power-consuming CSI training, but still enable some transmit spatial gains. In this article, we take another step forward by proposing a novel CSI-free rotary antenna beamforming (RAB) WET scheme that outperforms all state-of-the-art CSI-free schemes in a scenario, where a power beacon (PB) equipped with a uniform linear array (ULA) powers a large set of surrounding EH IoT devices. RAB uses a properly designed CSI-free beamformer combined with a continuous or periodic rotation of the ULA at the PB to provide average EH gains that scale as \(0.85\sqrt{M}\), where \(M\) is the number of PB’s antenna elements. Moreover, a rotation-specific power control mechanism was proposed to: 1) fairly optimize the WET process if devices’ positioning information is available and/or 2) avoid hazards to human health in terms of specific absorption rate (SAR), which is an RF exposure metric that quantifies the absorbed power in a unit mass of human tissue. We show that RAB performance even approaches quickly (or surpasses, for scenarios with a sufficiently large number of EH devices, or when using the proposed power control) the performance of a traditional full-CSI-based transmit scheme, and it is also less sensitive to SAR constraints. Finally, we discuss important practicalities related to RAB such as its robustness against non line-of-sight (LOS) conditions compared to other CSI-free WET schemes, and its generalizability to scenarios where the PB uses other than a ULA topology.

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Series: IEEE internet of things journal
ISSN: 2372-2541
ISSN-E: 2327-4662
ISSN-L: 2327-4662
Volume: 9
Issue: 10
Pages: 7375 - 7387
DOI: 10.1109/jiot.2021.3107222
Type of Publication: A1 Journal article – refereed
Field of Science: 213 Electronic, automation and communications engineering, electronics
Funding: This work was supported in part by the European Commission through the H2020 Project Hexa-X under Grant 101015956; in part by the Academy of Finland through 6Genesis Flagship under Grant 318927 and EE-IoT under Grant 319008; in part by RNP/MCTIC 6G Mobile Communications Systems, Brazil, under Grant 01245.010604/2020-14; and in part by ANID FONDECYT Iniciación, Chile, under Grant 11200659.
EU Grant Number: (101015956) Hexa-X - A flagship for B5G/6G vision and intelligent fabric of technology enablers connecting human, physical, and digital worlds
Academy of Finland Grant Number: 318927
Detailed Information: 318927 (Academy of Finland Funding decision)
319008 (Academy of Finland Funding decision)
Copyright information: © 2021 The Author(s). This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see