(Note: This is a fictionalized account of how a journalist may have covered the paper, “Holography of Wi-fi Radiation” by Philipp M. Holl and Friedemann Reinhard. None of the quotations below are true and must be interpreted as fiction only.)
Technische Universität München
Researchers at the Technische Universität München have demonstrated a way to form 3D image reconstructions of the environment from the radiation emitted by common wi-fi routers.
“A plethora of microwave and radar imaging techniques exist currently that allow one to image targets in situations where optical cameras may fail, such as in foggy environments,” says the first author of the study. “However, most such techniques require custom-built emitters that are expensive to build and deploy. In addition, the current hardware setups to support the extremely large frequency bandwidths required are bulky, which makes their usage impractical for small laboratory setups. We have sought to break this roadblock by using pre-existing wi-fi routers for the same purpose.”
The crux of their technology lies in the idea of thinking about wi-fi radiation as holograms that encode information about the surrounding environment. Similar to how lasers form optical holograms, the coherent nature of wi-fi radiation forms electromagnetic holograms as it traverses through the environment.
To capture the holographic information, the researchers use a setup similar to that of synthetic aperture radar by moving an antenna across a 2D plane to sample the radiation at multiple points. As their method does not assume any prior knowledge of the signals being transmitted by the router, a reference antenna is also used for normalizing the sampled data. The images are then reconstructed from the data via backprojection, which is a well-known algorithm in the radar and microwave imaging community.
As the frequency bandwidth of current wi-fi standards lie in the 2.4 – 5 GHz range, their system currently only supports centimeter-scale spatial resolution. However, with the upcoming 5G and 802.11ad specifications and the shift towards the 60 GHz frequency band, the researchers say the resolution may improve to a few millimeters in the near future, making their system resolution equivalent to the state-of-the-art in high-frequency radar imaging.
“The only concern is the lack of privacy in wireless communication our research foretells,” says the first author of the study. “It is disturbing that malicious individuals may invade the privacy of others from vantage points outside with no more sophisticated hardware than a wi-fi router. Research on making wireless communication immune to such attacks would be an important future direction.
“However, on an optimistic note, we believe our work is an exciting step towards enabling applications such as 3D indoor localization with low-cost off-the-shelf hardware,” he says. “The distributed city-wide imaging system in the movie The Dark Knight may well be reality soon,” he adds with a smile.
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