Reference-free WiFi PHY preamble based passive radar for human sensing

In this paper, we deal with human target surveillance using the WiFi-based passive radar technology. Specifically, in the attempt of meeting the requirements for small sensor size, compactness, and easy deployment, we investigate the possibility of operating in a reference-free condition, where a good copy of the transmitted waveform is not available at the receiver. To this end, we apply a passive radar-based processing scheme to the invariant initial portion of the physical layer protocol data unit, namely the PHY Preamble, by building the corresponding reference signal according to the 802.11 standard. We investigate advantages and drawbacks of the proposed approach and present an effective practical strategy to handle the limitations of the considered operative scenario. The entire processing scheme is validated on real data collected in the 2.4 GHz WiFi band.