Wi-Vi: See Through Walls With
Wi-Fi
Outline
Introduction
 What can Wi-Vi do?

Applications
Design Methodology
Results
Advantages
Limitations

Conclusi...
Through Wall RADAR
 Eliminate “Flash Effect” by isolating signals reflected off
the wall from the signals reflected off t...
Wi-Vi
 Wi-Vi stands for Wi-Fi Vision.
 Demonstrated by Dina Katabi, a professor in MIT’s
Department of Electrical Engine...
Contd…
 Wi-Vi is essentially a 3-antenna MIMO device: two of the
antennas are used for transmitting and one is used for
r...
What can Wi-Vi Do?
 Detect the Number of Moving Humans in a Closed Room.
 Determine the Relative Locations of Moving Hum...
Contd…
Transmit two waves that cancel each other when they reflect

off the Static object but not the Moving object.
Wall ...
Wi-Vi Setup
Applications
Police avoids ambush

Personal Security

Firefighters check for humans

Gesture Interface from behind a
wall
MIMO Nulling
Contd…
X

h1
y = h1 x + h2αx

α = -h1 / h2

αx

h2

Static objects( wall, furniture,
Etc.) have constant channels.

People...
ISAR

Direction of
reflection

Direction of
motion
Results
A prototype of Wi-Vi using USRP N210 radios software
was implemented and evaluated in two office buildings by

Fad...
Contd…
Wi-Vi depends on the amount of movement. To achieve a
narrow beam the human needs to move by about 4

wavelengths ...
Detection Accuracy of Wi-Vi for Different Types of
Obstructions
Advantages
 Wi-Vi requires only few MHz of bandwidth and operates in
the same range as Wi-Fi. It operates in ISM band.
 ...
Limitations
 Display has very low resolution.

 We cannot detect humans behind concrete walls thicker than
8".
 To achi...
Future Scope
 Wi-Vi could be built into a Smartphone or a special
handheld device.
 Can be used in search-and-rescue mis...
Conclusion
Wi-Vi, a wireless technology that uses Wi-Fi signals to detect

moving humans behind walls and in closed rooms....
Bibliography
 http://people.csail.mit.edu/fadel/wivi/

 Fadel Adib and Dina Katabi, See Through Walls with Wi-Fi,
ACM SI...
THANK YOU
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Wi vi- wifi that see through walls...

  1. 1. Wi-Vi: See Through Walls With Wi-Fi
  2. 2. Outline Introduction  What can Wi-Vi do? Applications Design Methodology Results Advantages Limitations Conclusion Bibliography
  3. 3. Through Wall RADAR  Eliminate “Flash Effect” by isolating signals reflected off the wall from the signals reflected off the objects behind the wall.  Isolation can be achieved in Time or Frequency domain which requires UWB (Ultra-Wideband Widths) of the order of 2GHz.  Difficult to capture the reflections.  Narrowband RADARs use Doppler Shift to detect moving objects behind the wall but can be done only in free space with no obstruction or with low attenuation standing wall
  4. 4. Wi-Vi  Wi-Vi stands for Wi-Fi Vision.  Demonstrated by Dina Katabi, a professor in MIT’s Department of Electrical Engineering and Computer Science, and her graduate student Fadel Adib.  Wi-Vi uses Wi-Fi OFDM signals in the ISM band (at 2.4 GHz) and typical Wi-Fi hardware.  Wi-Vi limits itself to a 20 MHz-wide Wi-Fi channel, and avoids ultra-wide band solutions used today to address the flash effect.
  5. 5. Contd…  Wi-Vi is essentially a 3-antenna MIMO device: two of the antennas are used for transmitting and one is used for receiving.  It also employs directional antennas to focus the energy toward the wall or room of interest.  It is relatively a low-power, low-cost, low-bandwidth, and accessible to average users.
  6. 6. What can Wi-Vi Do?  Detect the Number of Moving Humans in a Closed Room.  Determine the Relative Locations of Moving Humans.  Enable Communication through a Wall without Carrying a Wireless Device.  Identify Simple Gestures from Behind a Wall.
  7. 7. Contd… Transmit two waves that cancel each other when they reflect off the Static object but not the Moving object. Wall is Static Disappears People tend to move Detactable
  8. 8. Wi-Vi Setup
  9. 9. Applications Police avoids ambush Personal Security Firefighters check for humans Gesture Interface from behind a wall
  10. 10. MIMO Nulling
  11. 11. Contd… X h1 y = h1 x + h2αx α = -h1 / h2 αx h2 Static objects( wall, furniture, Etc.) have constant channels. People move, therefore their Channel change. y = h1 x + h2(- h1/ h2)x = 0 y = h1’ x + h2’(- h1/ h2)x =0
  12. 12. ISAR Direction of reflection Direction of motion
  13. 13. Results A prototype of Wi-Vi using USRP N210 radios software was implemented and evaluated in two office buildings by Fadel Adib and Dina Katabi, Massachusetts Institute of Technology (MIT), Results are as follows: Wi-Vi can detect objects and humans moving behind opaque structural obstructions. This applies to 8" concrete walls, 6" hollow walls, and 1.75" solid wooden doors.
  14. 14. Contd… Wi-Vi depends on the amount of movement. To achieve a narrow beam the human needs to move by about 4 wavelengths (i.e., about 50 cm). Table. Accuracy of Automatic Detection of Humans
  15. 15. Detection Accuracy of Wi-Vi for Different Types of Obstructions
  16. 16. Advantages  Wi-Vi requires only few MHz of bandwidth and operates in the same range as Wi-Fi. It operates in ISM band.  Wi-Vi can perform through-wall imaging without access to any device on the other side of the wall.  Wi-Vi employs signals whose wavelengths are 12.5 cm.  Extend human vision beyond the visible electromagnetic range, allowing us to detect objects in the dark or in smoke.
  17. 17. Limitations  Display has very low resolution.  We cannot detect humans behind concrete walls thicker than 8".  To achieve a narrow beam the human needs to move by about 4 wavelengths (i.e., about 50 cm).
  18. 18. Future Scope  Wi-Vi could be built into a Smartphone or a special handheld device.  Can be used in search-and-rescue missions and law enforcement
  19. 19. Conclusion Wi-Vi, a wireless technology that uses Wi-Fi signals to detect moving humans behind walls and in closed rooms. In contrast to previous systems, which are targeted for the military, Wi-Vi enables small cheap see-through-wall devices that operate in the ISM band, rendering them feasible to the general public, without carrying any transmitting device.
  20. 20. Bibliography  http://people.csail.mit.edu/fadel/wivi/  Fadel Adib and Dina Katabi, See Through Walls with Wi-Fi, ACM SIGCOMM'13, Hong Kong August 2013.
  21. 21. THANK YOU
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