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Hybrid fusion for 802.11ax Wi-Fi-based passive radars exploiting beamforming feedbacks

par Willame, Martin;Yildirim, Hasan Can ;Storrer, Laurent ;Horlin, François ;Louveaux, Jérôme
Référence (10-13 September, 2024: Lucca, Italy), Proc. of the 25th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
Publication A Paraître, 2024-09

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Résumé :

Passive Wi-Fi-based radars (PWRs) are devices thatenable the localization of targets using Wi-Fi signals of opportunity transmitted by an access point. Unlike active radars thatoptimize their transmitted waveform for localization, PWRs alignwith the 802.11 amendments. Specifically, during the channelsounding session preceding a multi-user multiple-input multipleoutput downlink transmission, an access point isotropically transmits a null data packet (NDP) with a known preamble. Fromthese known symbols, client user equipments derive their channelstate information and transmit an unencrypted beamformingfeedback (BFF) back to the access point. The BFF comprisesthe right singular matrix of the channel and the correspondingstream gain for each subcarrier, which allows the computationof a beamforming matrix at the access point. In a classicalPWR processing, only the preamble symbols from the NDP areexploited during the channel sounding session. In this study,we investigate multiple target localization by a PWR exploitinghybrid information sources. On one hand, the joint angle-of departure and angle-of-arrival evaluated from the NDP. Onanother hand, the line-of-sight angle-of-departures inferred fromthe BFFs. The processing steps at the PWR are defined and anoptimal hybrid fusion rule is derived in the maximum likelihoodframework. Monte-Carlo simulations assess the enhanced accuracy of the proposed combination method compared to classicalPWR processing based solely on the NDP, and compare thelocalisation performance between client and non-client targets.