Wi-Vi

WIRELESS VISION TECHNOLOGY

Presented ByDr. SK. Mastan Vali

A SEMINAR ON:

INTRODUCTION:

o Wi-Vi, Wireless Vision or Wi-Fi vision, is a see-through-

wall device that employs Wi-Fi signals in the 2.4Gz ISM

band.

o It identifies number of people, their locations and motion

in a closed room.

It can be used for gesture-based communication

without any transmitter.

PRINCIPLE:

It uses the principle:

RF signals can traverse a wall and reflect off objects

behind to wall and reach back the transmitter.

The reflected back signal is imprinted with the signature

of the reflectors.

This is similar to radar and sonar imaging.

DESIGN:

Wi-Vi uses Wi-Fi OFDM signals in the ISM band (at 2.4GHz) and

typical Wi-Fi hardware.

It is a 3-antenna MIMO device : two of the antennas being

transmitters and the other a receiver.

It also employs directional antennas to focus the energy toward the

wall or room of interest.

Its design incorporates two main components:

1. The first component eliminates the flash reflected off the wall.

2. The second component tracks a moving object by treating the

object itself as an antenna array.

FLASH EFFECT:

Transmitted RF signals through a wall, get reflected not

only from behind the wall objects but also from the wall.

These are much stronger and prevent ADC from

registering the minute variations due to reflections from

behind the wall.

This is known as ‘FLASH EFFECT’.

OPERATION:

Wi-Vi is operated in two modes:

In mode1, it can be used to image moving objects behind a wall

and track them.

In mode2, Wi-Vi functions as a gesture-based interface from behind

a wall that enables humans to compose messages and send them to

the Wi-Vi receiver.

Wi-Vi operation uses two basic techniques:

1. MIMO based Nulling to eliminate flash effect

2. Inverse Synthetic Aperture Radar (ISAR) for tracking human

motion

ELIMINATING THE FLASH

Wi-Vi uses interference nulling to cancel both the wall

reflections and the direct signal from the transmit to the receive

antenna.

To eliminate flash, a sample x is transmitted on each

transmit antenna separately and the ratio p is calculated.

Then x and px are transmitted concurrently to get the

perceived channel at the receiver.

The process repeats until channel estimates in step1 are

perfect so that the received signal is zero.

TRACKING HUMANS:

Wi-Vi uses Inverse Synthetic Aperture Radar, ISAR technique for

tracking humans behind the wall.

It has one receive antenna that captures one single measurement at

any point of time.

As the target moves, he/she samples the received signal at

successive locations in space corresponding to successive spatial

locations of the moving target.

Wi-Vi emulates an antenna array and uses it to track motion behind

the wall.

TRACKING HUMANS:

Continued..

Single human Multiple human

GESTURE-BASED COMMUNICATION:

Wi-Vi enables a human who does not carry any wireless

device to communicate commands or short messages to a

receiver using simple gestures.

It designates a pair of gestures as a ‘0’ bit and a ‘1’ bit.

A human can compose these gestures to create messages that

have different interpretations.

Gesture Encoding:

Gestures are encoded using any scheme such that:

The gestures must be composable i.e. at the end of each bit the human

should be back in the same initial state as the start of the gesture

The gestures must be simple so that a human finds it easy to perform

them and compose them.

The gestures should be easy to detect and decode without requiring

sophisticated decoders.

Here a ‘0’ bit is a step forward followed by a step

backward; a ‘1’ bit is a step backward followed by a step forward. This

modulation is similar to Manchester encoding.

Wi-Vi detection of gestures:

Gesture Decoding:

Since each bit is a combination of two steps, forward,

Wi-Vi applies two matched filters: one for the step forward

and one for the step backward.

Next, Wi- Vi uses a standard peak detector to detect the

peaks/troughs and match them to the corresponding bits.

Wi-Vi DESIGN MODEL:

Wi-Vi is built using USRPN210 software radios with SBX daughter boards.

The system uses LP0965 directional antennas, which provide a gain of 6 dBi.

The system consists of three US- RPs connected to an external clock so that they

act as one MIMO system. Two of the USRPs are used for transmitting, and one for

receiving.

A standard Wi-Fi OFDM modulation is implemented, each OFDM symbol

consisting of 64 subcarriers including the DC. The nulling procedure is

performed on a subcarrier basis.

RESULTS:

Wi-Vi correctly decoded the performed gestures at all distances

less than or equal to 5m.

A 93.75% accuracy for 6-7m and 75% for 8m was obtained and

above 9m Wi-Vi could not identify any of the gestures.

Continued..

ADVANTAGES:

Cheap, small, feasible to general public.

No need to carry transmitting device for communication.

Accurate detection and good efficiency.

APPLICATIONS:

1. Law Enforcement

2. Emergency Situations

3. Personal Security

4. Smart Sensing

5. User Interface Design

6. Entertainment

ADVANCEMENTS:

Can be extended for indoor localization, sensing

and control.

It can be extended to develop virtual reality

systems.

CONCLUSION:

Wi-Vi is a new form of user interface which rely solely

on reflections of a transmitted RF signal to identify

human gestures.

It can be envisioned, promising new direction in virtual

reality.

REFERENCES:

Wi-Vi system uses Wi-Fi to see through walls Gizmag

. www.seminarsonly.com

{fadel,dk}@mit.edu

Massachusetts Institute of Technology