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  • 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 wordHello

  • 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

In this video

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B1 中級

動画で見る屋内測位用の軽量可視光通信 (Video: Lightweight Visible Light Communication for Indoor Positioning)

  • 205 8
    陳連城 に公開 2021 年 01 月 14 日
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