Want similar presentation ideas? Interact and follow me in Quora : https://www.quora.com/profile/Liju-Thomas-13 or Connect with me through Facebook : http://www.facebook.com /lijuthomas24 Researchers have always tried to build a device capable of seeing people through walls. However, previous efforts to develop such a system have involved the use of expensive and bulky radar technology that uses a part of the electromagnetic spectrum only available to the military. Now a system is being developed by Dina Katabi and Fadel Adib, could give all of us the ability to spot people in different rooms using low-cost Wi-Fi technology. The device is low-power, portable and simple enough for anyone to use, to give people the ability to see through walls and closed doors. The system, called “Wi-Vi,” stands for "Wi-Fi" and "vision." is based on a concept similar to radar and sonar imaging. But in contrast to radar and sonar, it transmits a low-power Wi-Fi signal and uses its reflections to track moving humans. It can do so even if the humans are in closed rooms or hiding behind a wall. Simple definition for Wi-Vi is, as a Wi-Fi signal is transmitted at a wall, a portion of the signal penetrates through it, reflecting off any humans on the other side. However, only a tiny fraction of the signal makes it through to the other room, with the rest being reflected by the wall, or by other objects. Wi-Vi cancels out all these other reflections, and keeps only those from the moving human body. Previous work demonstrated that the subtle reflections of wireless inter signals bouncing off a human could be used to track that person's movements, but those previous experiments either required that a wireless router was already in the room of the person being tracked. Wi-Fi signals and recent advances in MIMO communications are used to build a device that can capture the motion of humans behind a wall and in closed rooms. Law enforcement personnel can use the device to avoid walking into an ambush, and minimize casualties in standoffs and hostage situations. Emergency responders can use it to see through rubble and collapsed structures. Ordinary users can leverage the device for gaming, intrusion detection, privacy-enhanced monitoring of children and elderly, or personal security when stepping into dark alleys and unknown places. The concept underlying seeing through opaque obstacles is similar to radar and sonar imaging. Specifically, when faced with a non-metallic wall, a fraction of the RF signal would traverse the wall, reflect off objects and humans, and come back imprinted with a signature of what is inside a closed room. By capturing these reflections, we can image objects behind a wall. Wi-Vi is a see-through-wall technology that is low-bandwidth, low-power, compact, and accessible to non-military entities. Wi-Vi is a see-through-wall device that employs Wi-Fi signals in the 2.4 GHz ISM band.

1. - Seeing through walls using Wi-Fi
Technical Seminar On
Presented by:
Liju P Thomas
1HK10EC030

2. CONTENTS
Introduction.
Challenges faced in designing Wi-Vi
Flash Effect.
Tracking Human movements.
Methods used to overcome the challenges.
Implementation.
Results.
Advantages and limitations.
Applications
Conclusion and Future Scope

3. Wi-Vi
- Wireless Device
- Captures moving
objects behind the
wall
- Through Wall
Imaging
- Relatively Low
power
- Low Cost
- Low Bandwidth
- It is 3 antenna MIMO Device
- Two transmitting and one
receiving antenna.
- Limits itself to a 20 MHz-
wide Wi-Fi channel, and
avoids ultra-wide band
solutions
- Two modes of use:
- Image moving
objects behind the
wall
- Gesture based
interface
- Uses Wi-Fi signals
in ISM
band(2.4Ghz)
- Typically Wi-Fi
Hardware
INTRODUCTION

4. KEY IDEA
Wi-Vi
Device

5. Challenges Faced in Designing Wi-Vi
 Challenge #1: “Flash” Effect
 RF signals penetrate walls:
• Reflect off objects on other side of wall
• Distinguish reflectors by their arrival times
 At low bandwidth:
• Wall reflection much stronger than reflections coming from behind
the wall.
• Flash effect: wall reflection saturates the ADC

6. Challenges Faced in Designing Wi-Vi
 Challenge #2: Identifying and tracking Humans
Traditional System:Array of Spaced Antennas
 Previous attempts to track moving targets through
walls have done so using an array of spaced antennas.
 This would be too expensive and bulky.
Angle of Arrival

7. How Can We Eliminate the Wall’s Reflection?
 Wi-Vi uses interference nulling to cancel both the wall reflections and the direct signal
from the transmitting to the receiving antenna, hence increasing its sensitivity to the
reflections of interest.
NULLING TO REMOVE THE FLASH
 MIMO systems can pre-code their transmissions such that the signal received at a
particular antenna is cancelled.
 This property can be tailored to eliminate the flash effect as well as the direct signal from
the transmitting to the receiving antenna, thereby enabling Wi-Vi to capture the
reflections from objects of interest with minimal interference.
 At a high level, Wi-Vi’s nulling procedure can be divided into three phases:
• Initial nulling
• Power boosting
• Iterative nulling

8. Algorithm for Wi-Vi Nulling

9. h2
h1
px
X
y = h1‘ x + h2‘px
p = -h1’ / h2‘
Static objects (wall, furniture,
etc.) have constant channels
People move, therefore
their channels change
y = h1‘ x + h2‘(- h1‘/ h2‘)x y = H1
’ x + H2
’(- h1‘/ h2‘)x
Not Zero
0
MIMO Nulling

10. ISAR – Inverse Synthetic Aperture Radar
 Inverse synthetic aperture radar uses the movement of the target
to emulate an antenna array.
 In ISAR, there is only one receive antenna; hence, at any point in
time, we capture a single measurement. since the target is
moving, consecutive measurements in time emulate an inverse
antenna array – i.e., it is as if the moving human is imaging the
Wi-Vi device.
 By processing such consecutive measurements using standard
antenna array beam steering, Wi-Vi can identify the spatial
direction of the human.
How Can We track the movement of Humans?

11. Direction of
reflection
θ
Antenna Array
Tracking Motion
RF source

12. θ
Antenna Array
Direction of motion
At any point in time, we
have a single measurement
Tracking Motion

13. θ
Antenna Array
Direction of motion
θ
Direction
of motion
Tracking Motion

14. IMPLEMENTATION
USRPs connect to a
host computer through
a high-speed USB or
Gigabit Ethernet link,
Universal Software Radio Peripheral (USRP N210)
Products are open
source USRP models also
integrate the general
functionality of a host
computer with an
embedded processor
Commonly used by
research labs and
universities etc.
Comparatively
inexpensive
hardware platform
for software radio
Designed and sold
by Ettus Research

15. IMPLEMENTATION
MIMO nulling is
implemented directly
into the UHD driver, so
that it is performed in
real-time.
• LP0965 directional
antennas
• 3 USRP’s are
connected to an
external clock and
they act as one
MIMO system.
Application areas include:
 Wi-Fi
 Wi-Max
 S-band transceivers
 2.4 GHz ISM band
transceivers
Capable of MIMO
and provides upto
40 MHz bandwidth
Dual-band
operation
• Wide bandwidth
transceiver
• Power output: Upto
10mW
• Noise Figure: 5dB
SBX Transceiver

16. Wi-Vi Setup & Working
Any objects that the signals hit including the wall create identical
reflections, they too are cancelled out by this nulling effect.
Only those reflections that change between the two signals, such
as those from a moving object, arrive back at the receiver.

17. Tracking of 2 humans Tracking of 3 humans
 Tracking of multiple people can be done by Smoothed Music Algorithm.
 This algorithm computes w x w correlation matrix R[n]
 It then performs an Eigen decomposition of R[n] to remove the noise and keep
the strongest Eigen vectors, which in our case correspond to the few moving
humans, as well as the DC value.

19.  For a human to transmit a message to a computer wirelessly,
they typically has to carry a wireless device.
 Wi-Vi can enable a human who does not carry any wireless
device to communicate commands or short messages to a
receiver using simple gestures.
 Wi-Vi designates a pair of gestures as a ‘0’ bit and a ‘1’ bit.
 At this stage, Wi-Vi’s interface is still very basic, yet we
believe that future advances in through-wall technology can
render this interface more expressive.
Through-Wall Gesture-Based Communication

20. Gesture Encoding
Gestures as Angles:Gestures as detected by Wi-Vi:

21. Gesture Decoding
Output of matched filter: Decoded bits:
Accuracy of Gesture Decoding as a Function of Distance

22. Results of Wi-Vi
Using USRP N210
Detect movements behind opaque
structural obstructions
Wi-Vi device pointed at a closed room with 6” hollow walls
supported by steel frames can distinguish between 0, 1, 2,
and 3 moving humans in the room. Computed over 80 trials
with 8 human subjects, Wi-Vi achieves an accuracy of 100%,
100%,90%, and 85% respectively in each of these cases.
A single person sending gesture
based messages, Wi-Vi correctly
decodes all messages performed at
distances equal to or smaller than
5 meters.
The decoding accuracy decreases to 75% at distances
of 8 meters, and the device stops detecting gestures
beyond 9 meters.
It also removes clutter from all
static reflectors, rather than
just one wall.
This includes other walls in the
environments as well as
furniture inside and outside the
imaged room.

23. Advantages
 Wi-Vi is relatively a low-power, low-cost, low-
bandwidth, and accessible to average users.
 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 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.
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).

24. Applications
Law Enforcement Emergency Situations
Personal Security Smart Sensing

25. ApplicationsUser Interface Design Intruder Detection
Gaming

26. 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.
Wi-Vi could be built into a Smartphone or a special handheld device.
Evolution of seeing humans through denser building material and with a
longer range.
High quality images.
Future Scope

27. REFERENCES
[1] Fadel Adib and Dina Katabi, "See through wall with WI-FI", Massachusetts
Institute of Technology. In ACM SIGCOMM, 2013.
[2] Q. Pu, S. Gupta, S. Gollakota, and S. Patel, "Whole-home gesture
recognition using wireless signals", University of Washington.
[3] T. Ralston, G. Charvat, and J. Peabody. “Real-time through-wall imaging
using an ultra-wideband multiple-input multiple-output (MIMO) phased
array radar system.” In IEEE ARRAY, 2010.
[4] “Advanced trends in wireless communication” Edited by Dr. Mutamed
Khatib
[5] "Seeing through walls"- MIT's Lincoln Laboratory, http://www.youtube.
com/watch?v=H5xmo7iJ7KA.
[6] www.people.csail.mit.edu/fadel/wivi