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Visible Light Communication
- Tutorial -
Visible Light Communication
- Tutorial -
2008. 03. 172008. 03. 17
Samsung ElectronicsSamsung Electronics
802.15 DCN: 15-08-0114-00-0000
2/29802.15 DCN: 15-08-0114-00-0000
Storyline(Tutorial on Visible light communication)
VLC introductionIdentity : Definition, Differentiation from other standardsHistory : VLC related activities in historyMotivation : LED infra, No regulation, No interference, Security…
LED introductionLED technical evolutionLED market evolutionLED applications/advantagesLED modulation characteristics (B+Y, RGB, RCLED)
VLC potential applicationVLC applicable services (Indoor, ITS, NFC) VLC categorization (I2M, M2M, M2F)VLC killer application
Indoor LBS High-speed video streaming
VLC demo Demo map PI, IB, VL (including movie)
SummaryTechnical issues (Oxford)
Source, Channel, ReceiverLink simulationLink ExperimentSystem resultTechnical challenge
3/29802.15 DCN: 15-08-0114-00-0000
Outline
Part 1 (Samsung)
VLC introduction
LED introduction
VLC potential application
Part 2 (Oxford univ.)
VLC components
Technical challenges
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VLC introduction
VLC (Visible Light Communication)
: New communication technology using “Visible Light”.
Visible Light
: Wavelength between ~400nm (750THz) and ~700nm (428THz)
General Characteristic
Visibility : Aesthetically pleasing
Security : What You See Is What You Send.
Health : Harmless for human body and electronic devices
Unregulated : no room to use more radio frequency
Using in the restricted area : aircraft, spaceship, hospital
Eye safety
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1900s Current405 B.C. 1800s280 B.C. 1880~
FireFire
SunlightSunlight
LampLamp
LEDLED
Heliograph
Beacon
Fire
Pharos
Lighthouse
Ship-to-ship
Comm.
Photophone
By Bell
Traffic Light
/Signboard Light
800 B.C.
Burning KiteIn Battle
VLC history
VLCVLC
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Information delivery through reflection by mirror (Heliograph)
The use of fire or lamp
• Beacon fire, lighthouse, ship-to-ship comm. by Morse code
Traffic light : signal discrimination by color (Walk/Stop)
Morsecode
VLC history – Low speed
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Bell’s Photophone (1880)
• Optical source : sunlight
• Externally modulation by vibrating mirror
• Receiver : parabolic mirror with crystalline selenium cells
• 700 ft (213m) sound transmission
VLC history - Photophone
Excerpted from: The New Idea Self-Instructor edited by Ferdinand Ellsworth Cary, A. M. (Monarch Book Company, Chicago & Philadelphia, 1904)
http://www.freespaceoptic.com/
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Low Frequency(Long wavelength)
CoverageMobility
visibleIR UV
700nm 400nm100μm
RF
3cm1m 1nm
428THz 750THz3THz10GHz300MHz 300PHz
High Frequency(Short wavelength)
BandwidthSecurity
1mm
300GHz
IrDA
802.15.3c
IG-THz
IG-VLC802.11802.16
• IG-THz : contribution 15-07-0623-01, AT&T Labs discussed the Terahertz spectrum band which covers 300 GHz to 10 THz. • This mmWave WPAN will operate in the new and clear band including 57-64 GHz unlicensed band • The millimeter-wave WPAN will allow high coexistence (close physical spacing) with all other microwave systems in the 802.15 family of WPANs
Frequency band for VLC
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Data
rate
(bps)
115K
4M
100M
480M
16M
50M
UFIR
FIR
IR
VIR
VLC
HDR UWBHDR UWB
1 113
Distance (m)
2 6 20 50
UWBUWB
802.11a802.11a
802.11b802.11b
BluetoothBluetooth
ZigBeeZigBee
VLC Characteristic
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VLC Characteristic
1Mb/s, 1m
100Distance Speed (m
Mb/s)
10
100
Power consumption
Speed
1000
50 Mb/s, 50m
500 Mb/s, 3m
4 Mb/s, 1m
10
1 SAMSUNGSAMSUNG
Non-LOS
Interference
LOS
Security
Directivity + SimplicityDirectivity + Simplicity Optical connectivity saves powerOptical connectivity saves power
(mW/Mbps)
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VLC vs. RF Characteristic
Property VLC RF
Bandwidth Unlimited, 400nm~700nm Regulatory, BW Limited
EMI No High
Line of Sight Yes No
Standard IG-VLC Yes
Hazard NoYes (H2O reaction to
2.4GHz)
Mobile
To
Mobile
Visibility (Security) Yes No
Power Consumption Relative low Medium
Distance Short Medium
Power Budget Tight Medium
Infra
to
Mobile
Security Yes No
Infra LED Illumination Access Point
Mobility Limited Yes
Coverage (Distance) Short (~10m)Wide (Short ~ Long Range)
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VLC motivation
Communication community trendUbiquitous (Connect each other everywhere, every time)
Security
LED trendLED technology (efficiency, brightness)
LED Cost
Environmental trendHealth
Energy saving
Intrinsic characteristic of VLCVisibility
No interference / No regulation
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Outline
Part 1 (Samsung)
VLC introduction
LED introduction
VLC potential application
Part 2 (Oxford univ.)
VLC components
Technical challenges
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LED technical evolution
Source: Credit Suisse, 2006.11.2Brightness / Power ratio
Co
st /
Bri
gh
tne
ss r
atio
Incandescent Lamp
Halogen Lamp
HID (High-Intensity Discharge)
Fluorescent Lamp
LED
LED
LED
LED
Performance and Price comparison
2003
2005
2010
2015
50 100 1500
1
10
100
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Air PollutionsUNFCCC (United Nations Framework Convention on Climate Change), Kyoto Protocol to the UNFCCC
(Dec. 1997)Decreasing CO2(10 k ton/year, 2002 at Korea)
Waste Materials & Environmental HazardsRoHS (Restriction of the use of Certain Hazardous Substance): 1, July 2006.
Pb, Hg, Cd, Cr6+, Polybrominated biphenyls(PBB), Polybrominated diphenyl eters(PBDE)
WEEE (Electrical and Electronic Equipment ) Producer Responsibility
Energy saving effectElectricity at Korea
278 TWh(2002), 7.2 % of USA20% for Lighting:55.6 TWh50% saving by LED:27.8TWhEnergy Saving Effect:
3 Nuclear Stations (1GW/day) 2 B$/year
Source: KOPTI (The Korea Photonics Technology Institute)
LED driver
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LED Market Forecast
LED
DRAM
NAND
NAND, DRAMLED ※CAGR :15%
Source: Deutsche Bank, 2007. 22002 2010 2006 2006
29.2 billion $
12.4 billion $
2017
LED
LED
6.3 billion $
11billion $
29 billion $
LED market comparison with NAND, DRAM
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LED application
Economicalefficiency
Back LightingBack Lighting Mobile PhoneMobile Phone
Home applicationsHome applications
digital devicedigital device
TFT LCD TV TFT LCD TV
General General LightingLighting
CommunicatCommunicationion
DisplayDisplay
General Lighting General Lighting
Task LightingTask Lighting
Signal LampSignal Lamp
VLCVLC
Mobile to MobileMobile to Mobile
Infra to MobileInfra to Mobile
Exterior, interior Exterior, interior
displaydisplay
Sign & Sign & Architecture Architecture
displaydisplay
LED screenLED screen
LED Applications
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LED modulation characteristics
R+G+B LEDB + Phosphor LED RCLED
~40 Mb/s ~100 Mb/s ~500 Mb/s
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Outline
Part 1 (Samsung)
VLC introduction
LED introduction
VLC potential application
Part 2 (Oxford univ.)
VLC components
Technical challenges
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VLC application
BandwidthBandwidthSecuritySecurity
CoverageMobility
IRIRU
VU
V
780nm
380nm
1nm
100μm
RF
RF
3cm
1m
visi
ble
visi
ble
PeripheralInterface
LAN
BankingBanking Door LockDoor Lock In PlaneIn PlaneDigital Digital
HospitalHospital
ITS (Navigation)ITS (Navigation)SAMSUNG
Sign BoardSign Boarde-booke-book
VisibleLAN
RFProhibited
InformationBroadcast
SecuritySecurity
E-display
Contents Contents MachineMachine
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Indoor applicationIndoor application
Mobile-to-MobileMobile-to-Fixed
LED Illumination Infrastructure
Mobile-to-InfraFixed-to-Infra
Ubiquitous
Security
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Requirements (Indoor application)Requirements (Indoor application)
Mobile to Mobile Mobile to Fixed Mobile to Infra Fixed to Infra
Link Bi-direction Bi-direction Bi or Uni Bi or Uni
Reach ~1m ~1m ~3m ~3m
Rate ~100M ~100M ~10M ~10M
Application Contents sharing File transfer
Video streaming
M-commerce
Indoor navigation
LBS
Networked robot
Data broadcast
Alternative IrDA, Bluetooth, UWB
IrDA, Bluetooth, UWB
WLAN
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Outdoor applicationOutdoor application
Vehicle-to-Vehicle
Traffic control Infrastructure
Vehicle-to-Infra
Outdoor advertising
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VLC application evolutionVLC application evolution
LED penetration
MobileDisplay
SignITS
Illumination
100MIndoor
10MIndoor
10MOutdoor
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Indoor navigation schemeIndoor navigation scheme
Uni-direction Bi-direction Hybrid Hot spot
Link
Rate Down : ~10k Down : ~10M
Up : ~100M
Down : ~10k
Up : ~10M
Down(light) : ~10k
Down(HS) : ~100M
Infra Lighting with optical ID
Lighting with optical ID
Receiver
In-building network
Routing server
Lighting with optical ID
RF access point
In-building network
Routing server
Lighting with optical ID
Hot spot
Mobile Receiver
Large storage
Map info
Routing software
Receiver
Transmitter
Receiver
RF connectivity
Receiver
Large storage
Routing software
Other service
LBS
Ad-hoc connection
LBS
Rx TRx Rx Rx
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High-speed High-speed high-security connectivity connectivity
What You See Is What You Send(WYSIWYS)
E-Contents Vending Machine
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Mobile to Mobile
(100Mbps,Samsung)
Music broadcasting
(6Mbps, Oxford Univ.)
Tx, Rx
(~30Mbps,Oxford Univ.)
Infra to Mobile
(10Mbps, Tamura Inc.)Infra to Mobile(VLAN)
(4Mbps, Samsung)
Infra to Mobile, VLCC (Keio Univ., NEC, Toshiba, Sony, Matsushita, Casio etc. )
(4.8kbps, illuminations, visible light ID, sign board, applications based on JEITA)
Sign board
(10Mbps, Samsung)
LowLowspeedspeed
HighHighspeedspeed
LED array
(~1Gbps, Keio Univ.)
Audio system
(100kbps, Hongkong Univ.)
Demonstrations
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VLC demonstrationVLC demonstration
100 Mb/s, 1mBidirection
20 Mb/s, 3mUnidirection
4 Mb/s, 3mBidirection
Mobile to mobile Infra to mobileInfra to mobile
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Mobile-to-mobile demo
PDA/UMPC
Spot @ 30 cm
What You See Is What You Send (WYSIWYS)
120 Mb/s, 1m, Full duplex
File transfer and video streaming
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Mobile-to-mobile (protocol)
D LSTS
Standby Transmitting
Beam guiding User alignmentDevice discovery Start steaming Temporal blocking
( < 8 sec.)Streaming end
D LS D LSTS D LSTS
SecondaryScreen
PrimaryScreen
Link
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Mobile-to-mobile (Link performance)
20 40 60 80 100 120-10
-5
0
5
10
Distance (cm)
20 40 60 80 100 120-10
-5
0
5
10
Distance (cm)
Cov
erag
e (c
m)
120 Mb/s 240 Mb/s
20 40 60 80 100 120-10
-5
0
5
10
0
2
4
6
8
10
Distance (cm)
320 Mb/s -log(BER)
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RGB WDM transmission
20 Mb/s, 3m, Uni-direction
Information broadcast from sign board
Infra-to-mobile demo
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Transmitter (RGB Sign-Board) Receiver (Silicon PD)
Data Rate = 10 Mb/s
Power Meter
-11
-10
-9
-8
-7
-6
-5
-4
0 1 2 3 4 5 6
REDBLUEGREENRED+BLUERED+GREENBLUE+GREENWHITESAMSUNG
Data Rate = 20 Mb/s
Infra-to-mobile (Link performance)
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TDMA-based P2MP
4 Mb/s, 3 m, bi-direction
Secure indoor LAN
Infra-to-mobile
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Downstream : White LED
Upstream : LD
Infra-to-mobile (Link performance)
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Summary (Part 1)
VLC introductionIdentityVLC historyMotivation
LED introductionLED technical evolutionLED market forecastLED applicationLED modulation characteristics
VLC applicationApplication categoryIndoor : Navigation, High-speed connectivityOutdoor : ITS, AdvertisingDemonstration
Mobile-to-mobile Infra-to-mobile
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Part 1 (Samsung)
VLC introduction
LED introduction
VLC potential application
Part 2 (Oxford univ.)
VLC components
Technical challenges
802.15 DCN: 15-08-0114-00-0000
Visible Light Communications
Dominic O’Brien, University of Oxford,
dominic.obrien@eng.ox.ac.uk
Contributions from Communications Group at Oxford
802.15 DCN: 15-08-0114-00-0000
Overview
> Visible Light Communications> Transmitter> Channel> Receiver
> Technical challenges> Higher bandwidth> Enabling mobility and reliability
> Conclusions
802.15 DCN: 15-08-0114-00-0000
VLC Sources
> Blue LED & Phosphor> Low cost> Phosphor limits bandwidth> Modulation can cause colour
shift
> RGB triplet> Higher cost> Potentially higher bandwidth> Potential for WDM> Modulation without colour
shift
Single chip LED spectrum RGB LED spectrum
802.15 DCN: 15-08-0114-00-0000
LED Modulation
> Opto-electronic response
Page 5
0 10 20 30 40 50-25
-20
-15
-10
-5
0
freq ( MHz)
Rel
ativ
e re
spon
se (
dB)
White response
Blue response
Measured LED small-signal bandwidth
sR dVL
sC
dC
V
I
Luxeon LED
Rs = 0.9727 L = 33.342 nHCs = 2.8 nFCd = 2.567 nFtt = 1.09 ns
SPICE Model
802.15 DCN: 15-08-0114-00-0000
Improvement of LED response
> Using blue-response only (blue filtering)
Page 10
350 400 450 500 550 600 650 700 750 8000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wavelength( nm)
Inte
nsity
(no
rmal
ised
)
~130 ns
~25 ns
Measured optical spectrum Measured impulse response
> Issue: Only 10% of signal power is recovered Reducing SNR, link distance
> LEDs with more blue energy [1] could be used to gain more filtered power, however the balance of white colour is shifted
Blue filtering
[1] Grubor, J., et al., "Wireless high-speed data transmission with phosphorescent white-light LEDs", Proc. ECOC 07 (PDS 3.6), pp. 1-2. ECO [06.11], 16-20 Sep. 2007, Berlin, Germany
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Improvement of channel response
> Receiver equalisation
Page 11
Fitting falling time curve
Equalization
Measured LED impulse response
Improved LED transmission BW
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Improvement of LED bandwidth
> Pre-equalization: Resonant driving circuit
Page 12
0 10 20 30 40 50-40
-35
-30
-25
-20
-15
-10
-5
0
Frequency ( MHz)
Res
pons
e no
rmal
ised
to m
axim
um(
dB)
C=2200pF white1000pF white680pF white330pF white68pF white
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
0 10 20 30 40 50 60
Bandwidth (MHz)
Tra
nsm
issi
on
(d
B)
A single resonant driving circuit
Multiple resonant points (normalized)
Bandwidth of 16 LED source
802.15 DCN: 15-08-0114-00-0000
Channel modelling
> Two propagation paths:> Line of sight (LOS): strong paths calculated using the illumination patterns from
LED arrays> Diffuse: modelled by assuming the room is equivalent to an integrating sphere> Channel impulse response is calculated for each point in the room
Page 6
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VLC modelling
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Room Power Distribution
> Assume > 1% modulation of typical
illumination power> Typical receiver
performance
> Conclusions> Very high SNR available
> SNRmin = 38.50dB> SNRmax = 49.41dB
> Modulation limited by source bandwidth
802.15 DCN: 15-08-0114-00-0000
Noise sources
> Optical noise> Daylight
> Generates DC photocurrent> Blocked at receiver due to AC coupling > Creates shot noise
> Other optical sources> Fluorescent, Incandescent
> Creates electrical interference photocurrent harmonics
> Mitigated by> Optical filtering
> Wavelength is in band of desired signal> Electrical filtering
802.15 DCN: 15-08-0114-00-0000
Optical receiver
> Receiver consists of> Optical filter
> Rejects ‘out-of-band’ ambient illumination noise
> Lens system or concentrator> Collects and focuses radiation
> Photodetector (or array of detectors)> Converts optical power to photocurrent
> Incoherent detection> Preamplifier (or number of preamplifiers)
> Determines system noise performance> Post-amplifier and subsequent processing
Optical filter
Optical system
Photodetector
Amplifier
Output
Input radiation
802.15 DCN: 15-08-0114-00-0000
Optical receiver: constant radiance theorem
> Optical ‘gain’ of receiver limited by required field of view
i
Ai
Ao
Aii<=Ao
Aii<=Ao
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Receiver performance: figure of merit
> Receiver Figure of Merit (FOM)> Fibre systems
> Performance determined by sensitivity (given sufficient detector area)
> FOV usually not relevant> Free space systems
> Etendue crucial determinant
min
2
P
ARFOM b
Detector Area A
Receiver sensitivity Pmin
Field of view 2Sr
Bit rate Rb
802.15 DCN: 15-08-0114-00-0000
Typical link: components
Page 22
Transmitter
•16 Luxeon LEDs
• PILLUM = 1.5W
• LED pitch = 60 mm
• IDC = 220 mA
• Mod-index = 0.1
• 45o wide-beam lens
• 7 resonant freq.
• Flat BW of 25 MHz
Transmitter and receiver specifications
2Rillum = 3 m
LLOS = 2 mReceiver
• Concentration lens
D = 50mm
F = 60mm
• Detection area
35 mm2
• Pre-Amp
• Post-Amp
(ampl. limiting)
Range
L = 2 m
Rillum = 1.5 m
Rcomm = 0.5 m
802.15 DCN: 15-08-0114-00-0000
Typical link: illumination
Power distribution in receiving plane
-20
-25
-30
-35
-40
-25
x coordinate(m)
y co
ordi
nate
(m)
Received power in dBm/cm2
0.5 1 1.5 2 2.5 3 3.5 4
0.5
1
1.5
2
2.5
3
3.5
4
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30 35 40 45 5010
-9
10-8
10-7
10-6
10-5
10-4
10-3
10-2
Data rate (Mbit/s)
BE
R
L = 2mL = 2.5m
Typical link: BER performance
Page 23
Eye diagram
30 Mb/s
40 Mb/s
50 Mb/s
• System test in normal lighting condition (room filled with other high-power white light sources) • Longer distance SNR penalty (BER)
NRZ
Flat BW baseline wandering reduction
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Bandwidth improvement: post equalisation
> Pre- and post-equalization: single LED link
Pre-equalisation: experiment
Post-equalisation: simulation
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Retro-reflecting link
> Novel optical communications between reader and tag> Low power (tag has no source)> Long range (determined by illumination source )> Visibly secure (user can see beam of light)
Illuminating Source
Beamsplitter
ReceiverRetroreflectingTransceiver showing angle of rotation
Reader
Tag
Illuminating Source
Beamsplitter
ReceiverRetroreflectingTransceiver showing angle of rotation
Illuminating Source
Beamsplitter
ReceiverRetroreflectingTransceiver showing angle of rotation
Reader
Tag
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Retro-reflecting link: retro-reflectors
> Front surface reflector array on rigid plastic substrate> Metallised front face> Normal incidence reflection loss of 5.5dB (relative to
theoretical maximum)> Returns a polarisation state close to incident for all
angles of incidence
Schematic of retro-reflecting surface Photograph of surface
802.15 DCN: 15-08-0114-00-0000
Retro-reflecting link demonstration system
Rx
Decode
2400bits/s data
Data 2400bits/s
Rx
LED TX
SLM Tx
2400 bits/s reader to tag2400 bits/s tag to reader
Data code
Data retime
Memory
PIC
Data codeMemory
PIC
Terminal program
Terminal program
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Retro-reflecting link demonstration system
> Demonstrator> 2.4kb/s bi-directional communication over several metres
Tag ReaderTag Reader
Demonstration system
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Future developments: optical MIMO
> RF MIMO> Scattering provides invertible H matrix and decorrelation
(capacity gain)> Difficult to shape radiation pattern with small antenna> Optical MIMO> No decorrelation> Invertible H matrix achieved by system and geometry
design> Simple low-cost elements (lenses) can provide high
directivity and/or complex beamshaping
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MIMO VLC: simulation Model
Transmitting process
Receiving process
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MIMO VLC: simulation system
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MIMO VLC: preliminary Results
Page 31
Position of the receiverAggregate data rate is linearly proportional to the
number of channels and channel rate
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Future technical challenges
> Data rate> Equalisation> MIMO> Complex modulation
> Integration in infrastructure> Uplink
>Retro-reflecting link> RF/VLC integration
802.15 DCN: 15-08-0114-00-0000
Conclusions
>VLC offers>High SNR channel>Intuitive alignment>Visibly secure channel
>Challenges>Integration with Wireless infrastructure>Higher performance