In their paper, “3D Through-Wall Imaging with Unmanned Aerial Vehicles Using WiFi,” researchers from the University of California, Santa Barbara, reported their research and demonstrated 3D through-wall imaging of a completely unknown area. Instead of using RF signals for through-wall imaging, which has proven to be quite challenging, they used Wi-Fi received signal strength indicator (RSSI) and unmanned aerial vehicles (UAVs) navigating around the outside of the area of interest to collect Wi-Fi measurements. In disaster management, surveillance, and search and rescue, assessing the situation prior to entering an area can be very crucial.
The experimental testbed used two octo-copters to localize, navigate, and collect the wireless data. The measurements utilized a line of sight (LOS) model for the received signal power, and calculations based on sparse signal processing, loopy belief propagation, and Markov random field modeling for solving the 3D imaging problem. In the experiment, one drone transmits 2.4GHz radio waves and the drone on the other side of the wall receives and measures the power of the signals.
A key part of the experiment was the aerial route design for the UAVs for collecting the wireless measurements, since the transmit/receive (TX/RX) locations where the measurements are collected play a key role in the 3D imaging quality. With proper design of the control paths to optimize the locations of the TX/RX from the UAVs, the researchers were able to autonomously and efficiently collect the measurements that are the most informative for 3D imaging, something the researchers say would be prohibitive with fixed sensors.