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Video: Lightweight Visible Light Communication for Indoor Positioning

In this video 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

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