WIBECAM: Device Free Human Activity Recognition Through WiFi Beacon-Enabled Camera

This paper presents WIBECAM, a Human Activity Recognition system which does not require neither user instrumentation, nor specialized infrastructure, nor active operation - it passively leverages Beacon frames periodically emitted by a single off-the-shelf Wi-Fi access point. As many other recent proposals, WIBECAM also exploits the different multipath conditions (and their temporal variations) induced by human activity. In most of the previously proposed systems, the classification is based on the characterization of the signal strength variations, caused by the human activity. WIBECAM's main distinguishing aspect is that it 'watches' the channel in the frequency domain where spectral metrics, calculated on the raw signal samples of the received Beacon frames, are like 'snapshots' of the channel taken in a regular and periodical way. The classification process uses properly selected features that measure the changes of consecutive 'snapshots'. WIBECAM adapts to any Wi-Fi access point (and may comply even with legacy 802.11b-only ones), as it does not exploit neither OFDM and CSI extracted from the receiver, nor MIMO/multiple antennas. WIBECAM has been built into USRP software radios. Its classification accuracy has been preliminarily assessed for four different activities in two different environments; the resulting confusion matrices show very promising performance.