wi vi- wifi that see through walls

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Wi-Vi: See Through Walls With Wi-Fi

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Page 1: Wi vi- wifi that see through walls

Wi-Vi: See Through Walls With Wi-Fi

Page 2: Wi vi- wifi that see through walls

Outline

Introduction

What can Wi-Vi do?

Applications

Design Methodology

Results

Advantages

Limitations

Conclusion

Bibliography

Page 3: Wi vi- wifi that see through walls

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

Page 4: Wi vi- wifi that see through walls

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.

Page 5: Wi vi- wifi that see through walls

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.

Page 6: Wi vi- wifi that see through walls

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.

Page 7: Wi vi- wifi that see through walls

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 Detactable to move

Page 8: Wi vi- wifi that see through walls

Wi-Vi Setup

Page 9: Wi vi- wifi that see through walls

Applications Police avoids ambush Firefighters check for humans

Personal Security Gesture Interface from behind a wall

Page 10: Wi vi- wifi that see through walls

MIMO Nulling

Page 11: Wi vi- wifi that see through walls

Contd…

h2

h1

αx

X

y = h1 x + h2αxα = -h1 / h2

Static objects( wall, furniture, People move, therefore their Etc.) have constant channels. Channel change.y = h1 x + h2(- h1/ h2)x y = h1

’ x + h2’(- h1/ h2)x

= 0 = 0

Page 12: Wi vi- wifi that see through walls

ISAR

Direction of reflection

Direction ofmotion

Page 13: Wi vi- wifi that see through walls

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.

Page 14: Wi vi- wifi that see through walls
Page 15: Wi vi- wifi that see through walls

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

Page 16: Wi vi- wifi that see through walls

Detection Accuracy of Wi-Vi for Different Types of Obstructions

Page 17: Wi vi- wifi that see through walls

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.

Page 18: Wi vi- wifi that see through walls

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).

Page 19: Wi vi- wifi that see through walls

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

Page 20: Wi vi- wifi that see through walls

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.

Page 21: Wi vi- wifi that see through walls

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.

Page 22: Wi vi- wifi that see through walls

THANK YOU