Passive Radar based on 802.11ac Signals for Indoor Object Detection

Passive radars opportunistically capture communications signals to detect and track targets in the environment. Since Wi-Fi signals are widely available today, they can be used by passive radars in local areas. Until now, passive radars based on Wi-Fi signals have only been investigated for 11a/b/n standards. This paper investigates the recent 11ac signals of much wider bandwidth for passive radars. The passive radar works by observing the preamble at the beginning of each frame transmitted by the Wi-Fi access point and applies either a two-dimensional cross-correlation or a frequency/time domain channel estimation to build range/Doppler maps. It is shown that passive radar processing based on the time-domain channel estimation is the only viable solution since the other two techniques cause significant sidelobes in the range/Doppler map. Experimental results held in our research lab confirm that the passive radar is capable of detecting small objects in an indoor environment.