Download - Wi Vi technology

Transcript
Page 1: Wi Vi technology

“Wi-Vi Technology”

- Seeing through walls using Wi-Fi

Technical Seminar On

Presented by:Liju P Thomas1HK10EC030

Page 2: Wi Vi technology

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

Page 3: Wi Vi technology

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

Page 4: Wi Vi technology

KEY IDEA

Wi-ViDevice

Page 5: Wi Vi technology

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

Page 6: Wi Vi technology

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

Page 7: Wi Vi technology

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

Page 8: Wi Vi technology

Algorithm for Wi-Vi Nulling

Page 9: Wi Vi technology

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 changey = h1‘ x + h2‘(- h1‘/ h2‘)x y = H1

’ x + H2’(- h1‘/ h2‘)x

Not Zero0

MIMO Nulling

Page 10: Wi Vi technology

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?

Page 11: Wi Vi technology

Direction of reflection

θ

Antenna Array

Tracking MotionRF source

Page 12: Wi Vi technology

θ

Antenna Array

Direction of motion

At any point in time, we have a single measurement

Tracking Motion

Page 13: Wi Vi technology

θ

Antenna Array

Direction of motion

θDirection of motion

Tracking Motion

Page 14: Wi Vi technology

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

Page 15: Wi Vi technology

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

Page 16: Wi Vi technology

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.

Page 17: Wi Vi technology

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.

Page 18: Wi Vi technology
Page 19: Wi Vi technology

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

Page 20: Wi Vi technology

Gesture Encoding

Gestures as Angles:Gestures as detected by Wi-Vi:

Page 21: Wi Vi technology

Gesture DecodingOutput of matched filter: Decoded bits:

Accuracy of Gesture Decoding as a Function of Distance

Page 22: Wi Vi technology

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.

Page 23: Wi Vi technology

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).

Page 24: Wi Vi technology

Applications

Law Enforcement Emergency Situations

Personal Security Smart Sensing

Page 25: Wi Vi technology

ApplicationsUser Interface Design Intruder Detection

Gaming

Page 26: Wi Vi technology

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

Page 27: Wi Vi technology

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

Page 28: Wi Vi technology

Thank You….


Top Related