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Visible Light Communication: Concept, Technology,
Challenges and Possibilities Navin Kumar (PhD)
MIEEE, IET(UK), IAEG(HK), IE, IETE(India)
CMR Institute of Technology, Bangalore -India
Jiao Tong University Shanghai
3/25/2013
2
Agenda
Introduction
Optical Wireless
Visible Light Communication
Infrared
Free Space Optics
Basic Components and Configuration
Motivation
LED Advancement
Agenda …
3
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Characteristics
Applications
Technical Details
Architecture and VLC System
Modelling Development
Prototype, Testing & Results
Progress & Current Status
Conclusion
Introduction
Visible Light Communication ?
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0 1 0
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0
1 0 1
0 1
1 0
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0
1 0 0 1
1 0 1
0 1
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0 1
1 1
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Tx
Rx
Communication using visible light Wirelessly.
Introduction: History
Smoke signals of the ancient tribes
The use of fire or lamp
Beacon fire, lighthouse, ship-to-ship comm.
5 3/25/2013 Traffic Signal
Information delivery using mirror reflection (Heliograph): is a wireless solar telegraph that signals using Morse code flashes of sunlight reflected by a mirror. Traffic light : R/G/B color multiplexing (Walk/Stop)
Introduction: History …
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Alexander Grahm Bell’s Photophone (1880)
Optical source: sunlight Modulation: vibrating mirror Receiver: parabolic mirror Distance: 700 ft (213m)
Source: http://www.freespaceoptic.com/
In 1920, somewhat by accident, Losev foresaw the usage of optical links to relay information.
In 1969, Gfeller presented “Wireless In-House Data Communication via Diffuse Infrared Radiation”. It became the stepping stone to VLC.
Facts, Figures, and Trends of Wireless Networks and Technology
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Several Technologies move in the same direction
4G Many
Access Networks
5G
Introduction
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Introduction
Wireless data transmission via optical carriers: opportunity, many yet unexplored.
Optical Wireless Communication (OWC): Significant technical and operational advantages.
OWC, in some applications:
–a powerful alternative to radio frequency (RF) and,
–complementary to existing RF wireless systems. 9 3/25/2013
Frequency Spectrum
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1024 1022 1020 1018 1016 1014 1012 1010 108 106 104 102 100 ν(Hz)
λ(m)10-16 10-14 10-12 10-10 10-8 10-6 10-4 10-2 100 102 104 106 108
Increasing Frequency(ν)
Increasing Wavelength(λ)
380nm 780nm
γ rays X rays UVMicrowaveIR FM AM
Radiowave
Longwave
Visible Spectrum
Licensing Area/ISMSpecial purposed Area
Non-Licensing Area
1024 1022 1020 1018 1016 1014 1012 1010 108 106 104 102 100 ν(Hz)
λ(m)10-16 10-14 10-12 10-10 10-8 10-6 10-4 10-2 100 102 104 106 108
Increasing Frequency(ν)
Increasing Wavelength(λ)
380nm 780nm
γ rays X rays UVMicrowaveIR FM AM
Radiowave
Longwave
Visible Spectrum
Licensing Area/ISMSpecial purposed Area
Non-Licensing Area
Low Frequency (High wavelength)
Large Coverage Mobility
High Frequency (Small wavelength)
High Bandwidth Security
IrDA : 334THz(900nm) to 353THz (850nm)
Introduction …
Variations of OWC can be employed in a diverse range of communication applications:
–very short-range (on the order of millimetres) optical interconnects within integrated circuits
–outdoor inter-building links (on the order of kilometres)
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Optical Wireless Communication and Systems
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Usually, OWC includes:
–Infrared (IR): for short range [Kahn & Barry, 1997],
- approximately 1 to 400 THz frequency
band,
(Much of the energy from the Sun arrives on Earth in the form of infrared radiation).
J. M. Kahn, and. J. R. Barry, "Wireless infrared communications," Proc. of the IEEE, pp. 265-298, 1997.
OWC – Infrared …
Used for -night vision equipment when there is insufficient visible light to see.
• Infrared imaging (capturing invisible infrared images and making them visible)
• as heating source
• IR data transmission in short-range communication
• These devices usually conform to standards published by IrDA, (Infrared Data Association).
• Remote controls, etc.
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OWC – Free Space Optics
Free-Space Optics communication: for longer range
This line-of-sight technology approach uses invisible beams (193.5GHz and 382.2GHz: 1550 nm, 785 nm) of light to provide optical bandwidth connections.
–A technology that can be installed license-free worldwide,
–can be installed in less than a day.
–Offers optical fiber like bandwidth and data speed
–Normally so called, Wide band Home Access or Last Mile Access Network
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FSO: Applications
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Fig.: A Simple Point-to-point FSO Connection
Fig.: FSO Corporate Networks
FSO: Applications
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FSO: System Requirement and Design Issues Tracking
The requirements for tracking systems in carrier-class free-space optics systems.
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Scintillation and atmospheric effects Scintillation effects and techniques for mitigating the detrimental effects of scintillation.
Power Control and Eyesafety The benefits of power control for long-term laser reliability and eyesafety
FSO: System Requirement and Design Issues
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Fig.: Atmospheric Issues
FSO: System Requirement and Design Issues ….
Ex.: Attenuation because of Fog/Snow storm
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Taken from - Scott Bloom, The Physics of Free-space optics, white paper AirFiber Inc.
FSO: Overall Functional Blocks
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Transmitter Laser, Lens, Driver
Receiver
Photo Detector Front End Amplifier
Tracking
Microprocessor based tracking/alignment system
Fig.: Overall FSO Block Diagram
BASIC COMPONENTS: OPTICAL WIRELESS
Transmitter
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Optics
Array of sources can also be used
Source
LED or Laser diode Eye safety regulation means that high power requires sources to be modified Three ranges:
Visible (used for both illumination and data transmission) Near infrared
700nm>Wavelength<1400nm- Low cost Wavelength>1400nm- Eye safe
OWC – Basic Components …
Receiver consists of:
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Photo Detector
- Optical power to photo current
Input radiation
Photodetector (or array of detectors)
Optical filter
Supported by: Optical filter
Rejects ‘out-of-band’ ambient illumination noise
Concentrator
AMP
Amplifier and following processing
Concentrator or Lens Collection of radiation
Preamplifier (or number of preamplifiers) normally Transimpedance
Amp. and signal processing
OWC Configuration
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Lin
e-o
f-sig
ht
(LoS)
Non LoS
BASIC CONFIGURATION: LoS OR DIFFUSE
Configuration Characteristics
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Diffuse -Multipaths from Transmitter to Receiver Robust to blocking
o Large coverage
- Path loss More - Subject to multipath dispersion
LoS - Single path from Transmitter to Receiver
No dispersion Path loss Less
o Very high bandwidth available
Difficult to provide coverage
OWC Characteristics
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MERITS - Very High Bandwidth
o 200THz carrier frequency
-Secure (LoS) -Cost Effective -Interference
o Suitable for RF sensitive
environments
-Potential for low power
Problems and possible Solutions - Noise from ambient light
o Optical filtering o Electrical filtering in receiver
- Less sensitive than radio - Link Blocking
o Geometrical solutions o Diffuse channels o Combine with RF
- Available components optimised for fibre-optic applications
o Higher performance available if optimised for OW
Development
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Optimal Integration into 4G Infrastructures
Emerging Area Visible Light Communication
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Visible Light Communication (VLC)
That is, Communications of information using light (visible to the human eyes).
VLC offers short/medium range data communication
Visible Light Communication is a Novel kind of Optical Wireless Communication which uses visible light (400THz to 790THz) from Light Emitting Diodes (LEDs) as a medium for data communication.
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VLC Motivation
Intrinsic Characteristic of VLC •Visibility •No interference /No regulation
Environmental trend •Energy saving •Green Technology
Communication Community trend •Ubiquitous (Connected anywhere, anytime) •Security
LED Advancement •LED technical evolution (efficiency, brightness) •LED illumination infrastructure
Advancement in LEDs Technology.
Mostly in terms of Illumination
characterisitics & Switching speed.
LEDs as brighter as our conventional lights (Fluorescent or Incadescent lamp)
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VLC Motivation …
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VLC Motivation – LED Illumination
0
20
40
60
80
100
120
140
160
180
200
2 7 1020
3040
47
115
136
186
200lm/WLuminous Efficacy
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VLC Motivation –LED Advancement
Therefore, Visible Light emitted from LED can be modulated to send information data i.e. Simultaneous operation of Lighting and Switching.
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VLC Motivation…
Free Spectrum (Best things in life are free )
At the same time, LEDs can switch at high rate (over 10 MHz) [as such they are Semiconductor devices]
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VLC Motivation – LED Applications
Illumination moving from incandescent/ fluorescent to solid state sources (LEDs) - Predicted to become predominant method for room illumination - Used extensively in traffic systems (traffic signals, rear light cluster) - Headlight is being also used - Extra wireless capacity available at (potentially) low cost
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LED- The VLC Source
Single chip LED spectrum
Red Green Blue Higher cost Higher bandwidth For WDM Modulation without colour shift
Blue LED & Phosphor Low cost Phosphor limits bandwidth Modulation can cause colour shift
General Characteristics:
Ubiquitous: Omni-presence.
Harmless for human body and electronic devices.
Available visible light bandwidth is about 300THz. It is considerably larger than the current available radio frequency bandwidth (about 300GHz)
Achievable at Low Cost and on Existing Infrastructure or with slight modification
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VLC Characteristics
Ambient interference:
Obstacles: Must obtain a Line-of-Sight (LoS).
Interferences from other visible light sources (sun, bulbs…)
Also suffer from the multi-path effect as light reflects.
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VLC Characteristics
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VLC Characteristics: Relative Advantages and Disadvantages with Radio and Infrared (IR) Communication Parameters Radio Infrared VLC
Bandwidth Around 300GHz Few 100 THz 300 THz
Data Rate Few 100 Mbps Few 10 Mbps Dependent on distance and limited by LED switching speed
Spectrum Regulation
Licensed Regulated & Licensed Not licensed
Safety Issue Susceptible to the biological damages to humans by the electromagnetic wave.
Eye safety problem No danger to eyes or biological effect. Easily used with medical instruments or even on airplane.
Usage Everywhere with cell phones and the wireless LAN, etc
Notebook, Cell Phone, PC etc.
Getting popularity
Suitability Wide applications and popularity. Restricted in Hospital and airplane
Short range (mostly indoor)
Short & Medium, both indoor and outdoor
Implementation and cost
Complex, Costly Easier, cost effective Cost effective, Used on existing infrastructure or with slight modification
Security Many complex algorithm needed
May be secured (very short distance)
Secured (What you see is what you transmit)
Complex and Challenging VLC Can be a supplementary and not replacement to Radio
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RF or Optical Link?
OW OW
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VLC Applications
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VLC Applications
Indoor
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VLC Applications …
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VLC Applications: Indoor
LiFi Configuration
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VLC Applications: Indoor …
Music Broadcast Parallel Transmission (Taken from Nakagawa Lab, Japan)
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VLC Applications: Outdoor
UNDERWATER
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VLC Applications: Outdoor
Intelligent Transportation Systems
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VLC Applications: Outdoor
5m
7m
3m
30mLED Lights
A scenario of VLC in ITS Ubiquitous Communication with Road Illumination
Intelligent Transportation Systems
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VLC Applications: Outdoor
What’s behind the bend?
Integration of VLC with ITS
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VLC Applications: ITS-Road Safety
VLC For Advanced Driver Assistance Systems
SMART LIGHTING
MOBILE CONNECTIVITY
HAZARDOUS ENVIRONMENTS
VEHICLE & TRANSPORTATION
DEFENCE & SECURITY
HOSPITALS & HEALTHCARE
WiFi SPECTRUM RELIEF
AVIATION
UNDERWATER COMMUNICATIONS
LOCATION BASED SERVICES 3/25/2013 50
Summary of Top 10 Applications: VLC
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The System and Technique: VLC
Technical Details
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Overall Architecture
Fig. A VLC System (Overall Architecture)
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VLC Transmitter and Receiver
Emitter Characteristics and Model:
LED (Lambertian Model):
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VLC Modelling
where θ is the viewing angle and E0(d) is the irradiance (W/m^2), also given in luminous flux (lm) on the axis at a distance d from the LED.
Fig.: Lambertian Emitter Source
(1)
The number m is given by the half power angle, θ1/2 an angle provided by the manufacturer, defined as the view angle when irradiance is half of the value at 0°.
The relation between θ1/2 and m can be expressed,
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VLC Emitter Model …
(2)
(3)
Radiation Pattern
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VLC Emitter Model
Fig.: Radiation Pattern for different m Fig.: Normalized Radiation Pattern for different m
Multiple Emitting Sources
Single Circular Ring case:
Multiple ring case:
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LED Emitter Model …
(4)
(5)
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Emitter Circuit
V = Vcc = +24VR1 = 15KΩR2 = 490 ΩR3 = 850ΩRin1 = 51ΩRin2 = 300ΩCin = 100nFQ(β) = 102.64
+
V+V+
Vdata
R1
R2 R3
Rin1
Rin2 Cin
Q
HB-LED
Discrete Current-sink Optoelectronic Emitter
Topology
ID@ different Frequency (a)@ 100KHz (b) @ 1 MHz (c) @ 10MHz (d) Constant Value
Vdata
Logic high
(3v) 38.1 mA 39.0 mA 40.0 mA 34.6. mA
Logic Low
(0V) 10.4 μA 12.6 μA 42.9 μA
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Performance: Switching
0 2,5 5 7,5 100
10
20
30
40
50a) f = 100kHz
[ms]
[mA]
0 0,25 0,5 0,75 10
10
20
30
40
50b) f = 1MHz
[us]
[mA]
0 25 50 75 1000
10
20
30
40
50c) f = 10MHz
[ns]
[mA]
0 0,1 0,2 0,3 0,4 0,50
10
20
30
40
50d) constant value
[s]
[mA]
Optoelectronic Emitter- time domain Response at Different Frequencies
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Performance
Optoelectronics Emitter- gain/phase Response (ID⁄IRin2 )
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VLC Receiver Model
The RECEIVER is defined by the active area and is a function of field of view and incident angle.
where Ad is the area of the detector
σ is the angle of incident
FOV is the field of view
Photo Detector
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Receiver Circuit
Block Diagram of Optoelectronic VLC Receiver
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Receiver Circuit …
Preamplifier Topology
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Pre-Receiver Circuit Response
Phase/Gain plot for different values of RF and CPD
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Receiver Circuit
Photo Detector
Transimpedance Front-End Preamplifier
Low Pass Filter(2nd Order) High Pass Filter
(3rd Order)
Output Amplifier, ADC Driver, Voltage Limiting
Impedance Matching
SMA Connector
Output
Receiver Circuit Diagram (OrCAD Captured Schematic)
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Response of Overall Receiver
1 10 100 1k 10k 100k 1M 10M 100M 1G
-100
-50
0
50
100
Gain (Vout/Iin)
[Hz]
[dB]
1 10 100 1k 10k 100k 1M 10M 100M 1G-360
-270
-180
-90
0
90
[Hz]
[º] Phase (Vout/Iin)
Response curve of Overall Receiver
Both Possibilities
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VLC Modelling - Indoor
Typical Arrangement in a room
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VLC Modelling - Indoor
1m
2.15m 3.15m
5m
From One Single LED
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Experimental Measurement
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Experimental Measurement
LED Modulation Received Signal Appox. 2Mbps
Signal–to–noise ratio distribution in the room
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Simulation Performance
SNR 35 – 50 dB
Data rate over 1 Mbps
MULTILANE ROAD Traffic Light Set-up
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Traffic Light Arrangement for the Channel Model: Outdoor (ITS)
Important Parameters
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Traffic Light Arrangement for the Channel Model ….
Channel Gain vs Distance
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Channel Gain over Distance.
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Field Programmable Gate Array & Hardware Implementation
PN Code
Sequence Corr. Pk
Partial Corr. Pk
Observations
Novel Designed
+1+1+1-1-1 -1+1-1-1+1
±10
±2
-DC Balanced -Low resources -Easy Implementation -PG = 10dB
Barker +1+1+1-1-1-1+1-1-1+1-1
±11
±1
-Nearly DC Bal. -High Resource -Complex -PG = 10.4dB
PN Code
Input Data
MicroBlaze
DPLB
IPLBILMB
DLMB INTR
BRAM
INTC UART
LMB
LMB
PLBClock
IRQ Lines
50 MHzMB
PLBLMB
SIK
DataBuffer
+Frame
Processing
Binary
DSSS EMITTER CORE
AWGN(channel SNR
simulation)
Bipolar to
Unipolar
Output to Optoelectronics
GPIO
Frame
Processing
ClockManager
Unipolar to Bipolar
ADC
GPIO
Output Data
MicroBlaze
DPLB
IPLB ILMB
DLMBINTR
BRAM
INTCUART
LMB
LMB
PLB Clock
IRQ Lines
50 MHzMBPLBLMB
DSSS RECEIVER CORE
Input from Optoelectronics
SYNC
Matched Filter
PN Code
Treshold Detector
PER Bipolar to Unipolar
EMITTER ARCHITECTURE RECEIVER ARCHITECTURE
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VLC Prototype Development
OPTOELECTRONICS AND FPGA DEVELOPMENT
VLC Receiver
OPTOELECTRONICS & FPGA
Receiver
FPGA Rx
FPGA Tx
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VLC Prototype Development and Experimental Set up
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VLC Prototype: Experiment- Laboratory Test
(1) Domingos Terra, Navin Kumar, Nuno Lourenço, Luis Nero Alves, and Rui L. Aguiar,” Design, Development and Performance Analysis of DSSS-based Transceiver for VLC”, IEEE EUROCON, Lisbon, Apr. 2011
(2) Navin Kumar, Domingos Terra; Nuno Lourenço; Luis Nero Alves, and Rui L. Aguiar,” Visible Light Communication for Intelligent Transportation in Road Safety Application”, IEEE IWCMC 2011, Vehicular Communications Symposium, Istanbul, Jul 2011.
Traffci Light Emitter FPGA Rx
Software Running Laptop
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Experiment- Laboratory Test
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Experiment Outdoor
Bright Sky, Directly Under Sun at Noon time – Detector facing the Sun
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Experiment: Pavilion (60 x 40m)
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Experimental Results
0.0E+0
2.0E-6
4.0E-6
6.0E-6
8.0E-6
1.0E-5
1.2E-5
1.4E-5
1.6E-5
1.8E-5
2.0E-5
0 10 20 30 40 50 60 70
Receiv
ed
Po
wer (
W/
cm
2)
Distance (m)
Received Average Power over Distance
Axial Distance Received Power
Received Power at 3.5m Offset
from Axis
Received Average Power
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Experimental Results …
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10
Messag
e H
it [%
]
Signal-to-Noise ratio [dB]
25 Chars
50 Chars
100 Chars
256 Chars
Message
Received Message
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Experimental Results …
0
20
40
60
80
100
0 10 20 30 40
Messag
e H
it [%
]
Distance [m]
Outdoor Night
Outdoor Night - Height Offset
Outdoor DayLight
Environment Test
(2,5m)
Percentage of Received Message
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Experimental Results …
Packet Error Rate
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Experimental Results …
1,0E-7
1,0E-6
1,0E-5
1,0E-4
1,0E-3
1,0E-2
1,0E-1
1,0E0
0 10 20 30 40 50
Pac
ket
Erro
r R
ate
Distance (m)
Environment Test:
Control: Dark (Height Offset 1,65m)
Outdoor Bright Sun Light
Outdoor: Night
Packet Error Rate
2003: The Visible Light Communications Consortium (VLCC) is established between major Japanese companies to develop, plan, research and standardise Japan’s own visible light communication systems.
Its brief is to develop, test, investigate, plan and standardise ubiquitous high-speed biologically-friendly VLC LED systems.
21 members
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Progress & Current Status
www.vlcc.net
2007: The standardisation work undertaken by VLCC leads to the creation of the Japan Electronics and Information Technology Industries Association’s JEITA standards (2007) for a “visible light ID system”.
VLCC is also involved in preparing and publicising proposals for safe visible light communication technology standards for a variety of applications and fields of industry.
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Progress and Current Status …
2008: EU-funded OMEGA project seeks to develop global standards for home networks, including the use of optical wireless using infrared and VLC technology.
2009: Research continuing in Japan to increase viable communication distances for VLC to hundreds of meters.
–Such work will allow the transmission of information by light from billboards, and from new generations of traffic lights to automobiles and trains
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Progress and Current Status …
2009-12: IEEE 802.15 WPAN™ Task Group 7 (TG7) Visible Light Communication
–The IEEE 802.15.7 Visible Light Communication Task Group has completed a PHY and MAC standard for Visible Light Communications (VLC).
3/25/2013 91
Progress and Current Status …
http://www.ieee802.org/15/pub/TG7.html
2010: The data transmission speeds of VLC systems are shown to be rapidly improving, with a frequency-modulated white LED being shown by Siemens researchers and the Heinrich Hertz Institute in Berlin to be capable of transmitting information over 5 meters at a rate of 500 Mbps, significantly faster than present Wi-Fi technologies (that can operate at rates of up to 150 Mbps).
2010: Demonstration undertaken successfully in Japan showing the combination of VLC with indoor Global Positioning System (GPS).
3/25/2013 92
Progress and Current Status …
A £5M Research Programme on Visible Light Communications…
–‘Ultra-parallel visible light communications (UP-VLC)’,
–Collaboration between leading research groups at the Universities of Strathclyde, Edinburgh, St Andrews, Oxford and Cambridge.
–Its basis is the >1Gb/s modulation capability recently shown for individual micro-sized gallium nitride LEDs
3/25/2013 93
Current Status …
http://gow.epsrc.ac.uk/NGBOViewGrant.aspx?GrantRef=EP/K00042X/1 .
LiFi
Noise Sources
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Challenges & Opportunities
–Minimizing the effect of external noise (artificial or natural)
–Ambient lights effect
–Interference minimization
Uplink design
Long range communication (LoS link required), and many more ....
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Challenges & opportunities ..
High data rate (limitation of LED/photo diode switching)
–Different modulation including Optical MIMO
–Adaptive Modulation technique for different applications
–Using Equalization
Front end with gain control
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Challenges & Opportunities ..
V-LAN
–V-LAN on aeroplane
–Ubiquitous high data rate communication
Integration with Infrastructure
–RF/VLC Integration
–UP Link / Retrofitting
3/25/2013 97
Challenges & Opportunities …
VLC is cost effective and secured transmission system.
VLC Offers many challenging, novel and potential applications (both Indoor and outdoor).
Offers relief to RF based system
Need to be exploited further
System though has many challenges.
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Conclusion
Thank You for Your
Attention !
3/25/2013 99
Jiao Tong University Shanghai
3/25/2013 100
Contact: [email protected], [email protected]
Jiao Tong University Shanghai
Jiao Tong University Shanghai
