we demonstrate a lightweight VLC system

and it's application in indoor positioning

More details can be found in our Mobisys 2015 paper

We used three demo scenarios

to explain our design motivation and innovation

Existing schemes on establishing communication

between smart devices and lighting lamps

mostly relying on modulating light intensity

Those schemes

requires increasing the pulse rate

above 1000Hz to avoid flickering

The high pulse rate

however

adds high processing overhead

for resource constrained devices

Instead of modulating the light intensity

we come out the idea to control the polarization of light

which human eyes can not perceive

We borrow the liquid crystal and polarizing film from the LCD technologies

with those technologies we can control the polarization of light by applying different voltages

In LCD, the back light is first polarized by a polarizing film

When the voltage of the liquid crystal is low

the structure of liquid crystal can twist the polarization of the polarized light by 90 degree

so that the light will pass the second polarizing film and LCD illustrates bright

When the voltage of the Liquid Crystal is high

the liquid crystal will not change the lights' polarization properties

so that the light will be blocked by the second polarizing film

and LCD illustrates black at this time

Our basic idea is very similar to the LCD

Since human eyes can not perceive polarization changes

we move the second polarizing film to receiver side

In this way the modulation can only be detected by equipped receivers

In the prototype system

the VLC transmitter consists of a polarizing film

a liquid crystal layer, a disperser and a control board

The two electrodes are connected to the control board

which is continually changing the voltage of the liquid crystal layer

For convenience we used LED lamps in this demonstration

Note that any other light such as florescent light

solar light can also be used as light source

The transmitter works by simply attaching to the lamp

and facing to the light source

As we can see

the modulated light has no difference from normal light

However if we view through a polarizing film

it can be see that colors change significantly because of the modulated light

Our VLC design

can benefit a vast range of smart devices

including those with limited computational resources

we have verified our system in wearables

such as Google glass

but for better illustration

we use the Samsung Galaxy s2 smartphone in this video

This is the default camera application

Similar as human eyes

the camera requires a polarizing film

to reveal the modulated signal

After we attached the polarizing film in front of the camera

we can use our application to decode VLC messages

The VLC transmitter

is currently transmitting word “Hello”

repeatedly in baud rate of 14 Hz

As each character is encoded in 8 bits

and occupies one packet

it take about 1 second to receive one character

The client perform localization algorithm

to determine its location in 3D space

Our VLC design

can be seamlessly applied in indoor localization application

When broadcasting messages of a VLC transmitter represent the transmitter’s location

mobile client can localize itself

through comparing transmitters locations in the image

and the corresponding locations in real coordinates

To demonstrate this

four transmitters are deployed as left

They are broadcasting the assigned IDs

which can be mapped to real locations

Our receiving client

due to mobility

has opportunity to receive signals

from one or multiple transmitters

As expected, it can successfully decode them in all the scenarios

Once it successfully decoded messages

from three or more transmitters in the same image

the client perform localization algorithm to determine its location in 3D space.

We appreciate your time for viewing our video

Thank you