MIT Technology Review: Wireless Network Modded to See Through Walls
MIT Technology Review reports on research into technology to see through walls. Last year, Slate’s William Saletan had an interesting story on aerial drones (also known as “Unmanned Aerial Vehicles (UAVs)”) and STTW, “sense-through-the-wall” technology. MIT Technology Review reports:
Researchers at the University of Utah say that the way radio signals vary in a wireless network can reveal the movement of people behind closed doors. Joey Wilson and Neal Patwari have developed a technique called variance-based radio tomographic imaging that processes the signals to reveal signs of movement. They’ve even tested the idea with a 34-node wireless network using the IEEE 802.15.4 wireless protocol, the protocol for personal area networks employed by home automation services such as ZigBee.
The basic idea is straightforward. The signal strength at any point in a network is the sum of all the paths the radio waves can take to get to the receiver. Any change in the volume of space through which the signals pass, for example caused by the movement of a person, makes the signal strength vary. So by “interrogating” this volume of space with many signals, picked up by multiple receivers, it is possible to build up a picture of the movement within it.
In tests with a 34-node network set up outside a standard living room, Wilson and Patwari say they were able to locate moving objects in the room to within a meter or so. That’s not bad, and the team says there is ample potential for improvement by increasing accuracy while reducing the number of nodes.
The researchers say, “Locating interior movement from outside of a building is extremely valuable in emergency situations, enabling police, military forces, and rescue teams to safely locate people prior to entering. [...] The cost of VRTI hardware is very low in comparison to existing through-wall imaging systems, and a single network is capable of tracking large areas.” They imagine different applications for the technology:
In a mission-critical application, we envision a building imaging scenario similar to the following. Emergency responders, miltary forces, or police arrive at a scene where entry into a building is potentially dangerous. They deploy radio sensors around (and potentially on top of) the building area, either by throwing or launching them, or dropping them while moving around the building. The nodes immediately form a network and self-localize, perhaps using information about the size and shape of the building from a database (e.g., Google maps) and some known-location coordinates (e.g., using GPS). Then, nodes begin to transmit, making signal strength measurements on links which cross the building or area of interest. The RSS measurements of each link are transmitted back to a base station and used to estimate the positions of moving people and objects within the building.
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