Wi-Fi signals used to perform a head count
Having previously used Wi-Fi signals to look through walls, a team of researchers in professor Yasamin Mostofi's lab at the University of California, Santa Barbara, has now turned the wireless signals to the task of counting the number of people walking in a particular area – even if they aren't carrying any Wi-Fi-enabled devices.
The technology is basically the same asthat previously used by Mostofi's team to look through walls. But rather thanidentifying the position and outline of stationary objects within a walledstructure, the changes in the strength of the sent and received Wi-Fi signalswas used to estimate how many people were walking in a given area.
To put the technology to the test, theresearchers used two Wi-Fi cards, placing one at each end of a target area ofroughly 70 sq m (753 sq ft). Using the received power measurements of the linkbetween the two cards, it was possible to estimate the number of people walkingwithin the area using a probabilistic mathematical framework.
This largely relied on two key things – thedrop in the signal as a person crosses the direct line of sight between the twocards, and the scattering of the signal being reflected backto the receiving card when the person is not in the direct line of sight, whichis known as multi-path fading.
The researchers have successfully testedthe technology with nine people in both indoor and outdoor settings, withMostofi believing it could find applications in energy efficiency and searchand rescue given the near-ubiquity of Wi-Fi signals in many areas.
In terms of energy efficiency, she suggeststhe technology could be used to estimate the number of people in a building,and adjust the heating and cooling automatically. Similarly, this kind of information could help with search and rescue operations.
Mostofi says she plans to eventually bringthe two Wi-Fi-based technologies together, which could result in a system thatcould estimate the number of people moving in a given area, but also locatepeople behind solid walls.
The video below explains the head-countingWi-Fi technology, with the team's paper scheduled for publication in theInstitute of Electrical and Electronics Engineers Journal on Selected Areas inCommunications.
Source: UC Santa Barbara
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