1. Wi-Vi: See Through Walls With
Wi-Fi

2. Outline
Introduction
 What can Wi-Vi do?
Applications
Design Methodology
Results
Advantages
Limitations
Conclusion
Bibliography

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. 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. 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. 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. 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. Wi-Vi Setup

9. Applications
Police avoids ambush
Personal Security
Firefighters check for humans
Gesture Interface from behind a
wall

10. MIMO Nulling

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. ISAR
Direction of
reflection
Direction of
motion

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.

15. 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

16. Detection Accuracy of Wi-Vi for Different Types of
Obstructions

17. 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.

18. 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).

19. 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

20. 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.

21. 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.

22. THANK YOU