University of Oulu

S. Kondo et al., "Bi-Directional Beamforming Feedback-Based Firmware-Agnostic WiFi Sensing: An Empirical Study," in IEEE Access, vol. 10, pp. 36924-36934, 2022, doi: 10.1109/ACCESS.2022.3165029

Bi-directional beamforming feedback-based firmware-agnostic WiFi sensing : an empirical study

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Author: Kondo, Sota1; Itahara, Sohei1; Yamashita, Kota1;
Organizations: 1Graduate School of Informatics, Kyoto University, Kyoto 606-8501, Japan
2Centre of Wireless Communications, University of Oulu, 90014 Oulu, Finland
3School of Engineering, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8550, Japan
4Department of Integrated Information Technology, Aoyama Gakuin Univeristy, Chuo-ku, Sagamihara-shi, Kanagawa 252-5258, Japan
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.6 MB)
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Language: English
Published: Institute of Electrical and Electronics Engineers, 2022
Publish Date: 2022-08-26


In the field of WiFi sensing, as an alternative sensing source of the channel state information (CSI) matrix, the use of a beamforming feedback matrix (BFM) that is a right singular matrix of the CSI matrix has attracted significant interest owing to its wide availability regarding the underlying WiFi systems. In the IEEE 802.11ac/ax standard, the station (STA) transmits a BFM to an access point (AP), which uses the BFM for precoded multiple-input and multiple-output communications. In addition, in the same way, the AP transmits a BFM to the STA, and the STA uses the received BFM. Regarding BFM-based sensing, extensive real-world experiments were conducted as part of this study, and two key insights were reported: Firstly, this report identified a potential issue related to accuracy in existing uni-directional BFM-based sensing frameworks that leverage only BFMs transmitted for the AP or STA. Such uni-directionality introduces accuracy concerns when there is a sensing capability gap between the uni-directional BFMs for the AP and STA. Thus, this report experimentally evaluates the sensing ability disparity between the uni-directional BFMs, and shows that the BFMs transmitted for an AP achieve higher sensing accuracy compared to the BFMs transmitted from the STA when the sensing target values are estimated depending on the angle of departure of the AP. Secondly, to complement the sensing gap, this paper proposes a bi-directional sensing framework, which simultaneously leverages the BFMs transmitted from the AP and STA. The experimental evaluations reveal that bi-directional sensing achieves higher accuracy than uni-directional sensing in terms of the human localization task.

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Series: IEEE access
ISSN: 2169-3536
ISSN-E: 2169-3536
ISSN-L: 2169-3536
Volume: 10
Pages: 36924 - 36934
DOI: 10.1109/access.2022.3165029
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 Ministry of Internal Affairs and Communications/Strategic Information and Communications R&D Promotion Programme (MIC/SCOPE) under Grant JP196000002, and in part by the Japan Society for the Promotion of Science (JSPS) KAKENHI under Grant JP18H01442.
Copyright information: © The Author(s) 2022. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see