'Institute of Electrical and Electronics Engineers (IEEE)'
Abstract
Human sensing using WiFi signal transmissions
is attracting significant attention for future applications in ehealthcare, security and the Internet of Things (IoT). The
majority of WiFi sensing systems are based around processing
of Channel State Information (CSI) data which originates from
commodity WiFi Access Points (AP) that have been primed to
transmit high data-rate signals with high repetition frequencies.
However, in reality, WiFi APs do not transmit in such a
continuous uninterrupted fashion, especially when there are no
users on the communication network. To this end, we have
developed a passive WiFi radar system for human sensing
which exploits WiFi signals irrespective of whether the WiFi
AP is transmitting continuous high data-rate OFDM signals,
or periodic WiFi beacon signals whilst in an idle status (no
users on the WiFi network). In a data transmission phase, we
employ the standard cross ambiguity function (CAF) processing
to extract Doppler information relating to the target, whilst a
modified version is used for lower data-rate signals. In addition,
we investigate the utility of an external device that has been
developed to stimulate idle WiFi APs to transmit usable signals
without requiring any type of user authentication on the WiFi
network. In the paper we present experimental data which
verifies our proposed methods for using any type of signal
transmission from a stand-alone WiFi device, and demonstrate
the capability for human activity sensing
