A team of scientists has found another use for wireless networks, other than transmitting data from one terminal to another. According to a research paper it just made public, wireless technology can be used to reveal what's going on behind closed doors, or through a wall. The team, based at the University of Utah, in the United States, says that its modifications rely on the variations that radio signals exhibit while circulating in these networks. Its new monitoring tool can keep track of how people move in the room, which could be of great assistance to law enforcement forces.

The new process has been entitled variance-based radio tomographic imaging, and a working prototype has already been demonstrated using a 34-node wireless network, employing the IEEE 802.15.4 wireless protocol. This protocol is also used by a large number of personal area networks, provided by home automation services, Technology Review informs. The prototype was tested from outside an average living room, and the team, led by experts Joey Wilson and Neal Patwari, has proven that the movement of objects can be accurately determined, with an accuracy of about a meter (three feet).

The two say that the basic principle employed in the creation of VBRTI is fairly simple. They explain that, at every point in a wireless network, the strength of the radio signal is determined by the sum of all the paths the radio waves can take to get to the receiver. Therefore, as the waves pass through solid or moving objects, their strength parameter changes. By “interrogating” the status of this parameter many times per second, the scientists were able to recreate the inside of the test living room on which the system was tried out.

“We envision a building imaging scenario similar to the following. Emergency responders, military 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 two experts envision a situation for their new observation and monitoring system to work in.

“The nodes immediately form a network and self-localize, perhaps using information about the size and shape of the building from a database (eg Google maps) and some known-location coordinates (eg using GPS). Then, nodes begin to transmit, making signal strength measurements on links which cross the building or area of interest. The received signal strength 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,” they conclude.