Transcript
1
Visible Light Communication
Le Tien Anh - 80623864Nakagawa lab – Keio university
Advanced course in Digital Communications3rd July 2007
2
Overview
1. Introduction
2. Technology
3. Applications
4. Conclusion
5. Question & Answer
3
Characteristics
• What is VLC:– Stands for “Visible light communication”.– Communications of information using light that is visible to the
human eye.
• How is VLC:– Ubiquitous: Omni-presence.– Harmless for human body and electronic devices. Power has not
been limited.– The available visible light bandwidth is about 300THz (450-750
THz). It is considerably larger than the current available radio frequency bandwidth (about 300GHz)
Introduction Technology Applications Conclusion Referenceｓ Q&A
4
History
Radio waves
Microwave Infrared Ultra-Violet X-rays Gamma-rays
Visible light
Tribes used smoke, fire as
optical wireless communication
long ago
June 3, 1880, Alexander
Graham Bell transmitted the
first wireless telephone
message on "photophone”
Introduction Technology Applications Conclusion Referenceｓ Q&A
5
Difficulties
• Ambient interference: – Obstacles: Must obtain a LOS.– Interferences from other visible light sources
(sun, bulbs…)– Also suffer from the multi-path effect as light
reflects.
Introduction Technology Applications Conclusion Referenceｓ Q&A
6
Modulation schemes
• There are 4 popular baseband modulation schemes used in VLC:– Pulse Position Modulation (PPM):
• 2-PPM, 4-PPM.• I-PPM.
– Sub-carrier Pulse Position Modulation (SC-PPM):• SC-PPM.• SC-I-PPM.
– Sub-carrier Frequency Shift Keying (SC-FSK)– Sub-carrier Phase Shift Keying (SC-PSK)
• The main output uses OOK (on/off keying), one kind of Intensity Modulation-Direct Detection (IM-DD).
Introduction Technology Applications Conclusion Referenceｓ Q&A
7
Pulse Position Modulation (PPM)
Introduction Technology Applications Conclusion Referenceｓ Q&A
Adopted from: Ref [2]
8
Sub-carrier Pulse Position Modulation (SC-PPM)
Introduction Technology Applications Conclusion Referenceｓ Q&A
Adopted from: Ref [2]
9
SC-FSK/PSK
Introduction Technology Applications Conclusion Referenceｓ Q&A
Adopted from: Ref [2]
10
Baseband modulation:PPM/I-PPM,
SC-PPM/SC-I-PPMSC-FSK/SC-PSK
Data Visible light modulation
Baseband demodulation:PPM/I-PPM,
SC-PPM/SC-I-PPMSC-FSK/SC-PSK
DataVisible light
demodulation
Limitations of the VLC technology Baseband modulationData RF modulation
Baseband demodulationData RF demodulation
BPF
BPF
Introduction Technology Applications Conclusion Referenceｓ Q&A
11
Applications
• Audio systems:– Silent concert
• Indoor:– VLC and PLC (power-line communication),– Smart super market,– Museum,– Hospital.
• Outdoor:– Intelligent Transport System
• Underwater
Introduction Technology Applications Conclusion Referenceｓ Q&A
12
Audio systems
Introduction Technology Applications Conclusion Referenceｓ Q&A
13
Indoor applications
Introduction Technology Applications Conclusion Referenceｓ Q&A
Adopted from Ref.[3]
14
Outdoor applications
• ITS: Intelligent Transport System:– Pedestrians support:
• Roadside information terminal– Driver and passenger support:
• Toll collection,• Traffic information, road map…• Ground to train communications.
– Vehicles support:• Logistic.
Introduction Technology Applications Conclusion Referenceｓ Q&A
15
Conclusion
• VLC can lead to many interesting applications.
• No international standard or protocol has been developed.
• VLC still has to overcome many limitations both in the transmitter’s LED and in the receiver’s PD.
• “Best things in life are free”
Introduction Technology Applications Conclusion Referenceｓ Q&A
16
Questions and Answers
Thank you
Introduction Technology Applications Conclusion Referenceｓ Q&A
17
References
• [1]. M.Z.Afgani et.al. Visible light communication using OFDM. IEEE 2006.
• [2]. H.Sugiyama, S.Haruyama, M.Nakagawa. Experimental investigation of modulation method for visible-light communications.IEICE transection
• [3]. LED lamp http://en.wikipedia.org/wiki/Image:Ampoules.jpg
• [4]. NEC’s ITS
Introduction Technology Applications Conclusion Referenceｓ Q&A
top related