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Fundamentals of Free Space Optical Communication‐1
Selami ŞAHİN, Ph.D.TUBITAK‐BILGEM‐UEKAE
What are the aims?
Wireless access schemes and FSOCA Brief HistoryFSOC and Radio ComparisonLink ConfigurationsApplication AreasSafety and RegulationsChallenges
2
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
By 2020,
The internet population > 80%
The Future of internet is Mobile
and based on application services
3G : 2 Mbps
4G : designed for 1Gbps
4G speed in AT&T and Verizon is
10‐12 Mbps
4.5G : designed for 6Gbps
...
3
Fundamentals of FSOC‐1
Demand for High‐Speed Communications...
4
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
Demand from Next Generation Wireless Communication...
Offer Higher Capacity
High Definition TV (4‐20 Mbps)
Computer Network Applications (up to 100 Mbps)
Mobile Videophones/Video Conferencing
High Speed Internet Access
…
Mobility
Performance (Lower Battery Consumption)
Energy Efficiency (Green Technology)
5
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What about mobile network backhaul bottleneck?
Microwave Radio links (installed or leased)
2 Mb/s/user (backhaul bottleneck)
6
MU BS
Microwave linkBackhaul “last mile”
Mobile switchingNode (MSN)
Core networkRF
PTSN
Switching centre
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What about RF wireless access schemes?
Bell Labs Analysis
Wireless (RF) data is a rapidly growing problem!!
7
Metro EdgeMetro Edge
CoreCore
Wireless AccessWireless Access
Fixed AccessFixed Access
Pow
er /u
ser (
W)
Pow
er /u
ser (
W)
0.10.1
20102010
1010
100100
0.010.01
11
20152015 20202020
Metro Edge
Core
Wireless Access
Fixed Access
Pow
er /u
ser (
W)
0.1
2010
10
100
0.01
1
2015 2020
10% per year improvement in wire line equipment efficiency(Moore’s law).
Assumes 9% per year improvement in wireless (RF) access.
Wireless RF access power could grow by a factor of 100 in 10 years.
By 2020 wireless RF access power consumption dominatesnetwork.
Wireless Access Schemes and FSOC
Fundamentals of FSOC‐1
What about RF spectrum?
Radio Spectrum Congestion and Famine!!
Smart phone usage
Stream youtube, facebook videos
Watch TV
Download and Store movies and music
Play games/Talk to each other
8
All of them Consume RF bandwith
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What about RF wireless access schemes?
FCC Analysis
Spectrum deficit problem for wireless communications by 2013!!
9
Cognitive Radio
Use of Microwave & lower THz‐Spectrum
Use unregulatedportion of thespectrum
Wireless Optical Communication
Infrared, visible andUltraviolet Light
Year2013201220112010 2014
400
300
200
100
0
-100
-200
-300
Avai
labl
e Sp
ectr
um (M
Hz)
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What is Wireless Optical Communication?
First of all, It is a complementary technology to RF.
10
Optical Communications
Indoor
Wired Wireless
OutdoorFree-Space
Optics
IR VLC
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What is Free Space Optical Communication?
Uses Laser as transmitter.
Uses PIN or APD as receiver.
The communication tool is LIGHT
The communication mediums are Air, Space, UnderWater etc.
There is no physical connection between Tx and Rx.
11
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What is Free Space Optical Communication?
12
ATMOSPHERIC CHANNEL
1010PH
OT
OD
ET
EC
TO
R
SIGN
AL
PRO
CE
SSOR
DA
TA
OU
TRECEIVER
1010
DA
TA
IN
LE
D/L
DD
RIV
ER
TRANSMITTER
1 Network traffic converted into pulses of invisible light representing 1’s and 0’s
2Transmitter projects the carefully aimed light pulses into the air
5 Reverse direction data transported the same way. (Full duplex)
3 A receiver at the other end of the link collects the light using lenses and/or mirrors
4 Received signal converted back into fiber or copper and connected to the network
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What are the advantages of FSOC?
Highly secure connectivity.Directed laser beam.Invisible light wavelength.
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F/O, LANConnection
F/O, LANConnection
IR binocolurs
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What are the advantages of FSOC?
Used in EW/EMCON.Harder to find communication.Harder to intercept communication. (Resistance to jamming)
Energy efficient usage.Close positioning without interference.Highly secure communication.
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2.5 mrad0.08 mrad
2.5 m8 cm
Range = 1 km
BeamwidthSpotwidth
Communication is only in cone beam.Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What are the advantages of FSOC?
Provides wide badwidth communication.Possiblity of more than 40 GHz optical modulation.Bandwidth about GHz – THz with multiplexing.
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Infrared
0.3 m 0.3 mm 0.3 μm
GHz THz PHz1015
Frequency
Microwaves UV
109 10121010 1011 1013 1014
Blue
tooth,
Mod
em
Radar
Satellite
Wavelenght
Visib
leLight
Optical Com
m.
0 Hz 100 GHz
Bandwidth(Linear Scale)
200 GHz
MHz GHz
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What are the advantages of FSOC?
Small, light, compact size, low power consumption. (SWAP)
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Optical TelescopeD=10 cm
RF antennaD=1 m
Terminal Dia. Wavelength Beamwidth Gain
Optical 10 cm 1.5 μm 0.0009° 106 dBRF (@30GHz) 1 m 1 cm 0.7° 47 dB
∼ 60 dB difference∼ 10 times
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What are the advantages of FSOC?
Small, light, compact size, low power consumption. (SWAP)
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L‐Band Antenna2.35 m
Ka‐Band Antenna2.35 m
Optical TelescopeRx: 25 cmTx: 12.5 cm
ARTEMIS (ESA)
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
SPOT‐4
What are the disadvantages of FSOC?
Required LOS especially in ourdoor applications.Cone‐shaped laser beam transmissionSolution : Acquisition, Tracking and Pointing Systems
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Beamwidth FOV
Pointer Laser(Beacon)
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What are the disadvantages of FSOC?
Effected by weather conditions.A Rain particle size : 200 ∼ 2000 μm → close to microwaveA Fog particle size : 5 ∼ 15 μm → close to light (laser)
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Rain : 3‐17 dB/km Snow : 6‐26 dB/km Fog : 20‐300 dB/km
Light Attenuation
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What are the disadvantages of FSOC?
Effected by particles in athmosphere.Absorption
o molecular(gases) o Aerosol (dust, water drops)
Scatteringo Rayleigh (object dia. << wavelength – fine ash)o Mie (object dia. ~ wavelength– aerosol particles)o Geometrical (object dia. >> wavelength – rain,snow particles)
Scintillationo Beam Wander due to changes in refraction index
(in low frequencies)o Changes in Ligth intensity(up to 1kHz)
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Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What are the disadvantages of FSOC?
Solution : Adaptive Optics
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Transmitter
OriginalWavefront
AtmosfericTurbulance
DistortedWavefront
AO system
TiltMirror
Partial repairedWavefront
RepairedWavefront
High VoltageAmplifier
WavefrontController
High SpeedSensor
DeformableMirror
CableFibre Cable
Optical Signal
Receiver
E/Oconverter
ElectricalBlock
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What are the disadvantages of FSOC?
Solution : Adaptive Optics
22
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What are the disadvantages of FSOC?
Solution : Error Correcting Coding
Repetition MIMO BI‐LDPC‐coded PAM (a) Transmitter (b) Receiver
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Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What are the disadvantages of FSOC?
Solution : Error Correcting Coding
BER performance of BI and MLC LDPC‐coded modulation
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Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
What are the disadvantages of FSOC?
Effected by Ambient Ligth Sources.
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IRUV
Wavelength (μm)
Normalise
d po
wer/unit w
avelen
gth
0
0.2
0.4
0.6
0.8
1
1.2
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
Sun
Fluorescent
1stwindo
w IR
2ndwindo
w IR
IncandescentAbove 1400 nm ‐almost completely absorbed by the eye
cornea
Below 1400 nm: focused onto the retina, power levels must be limited for eye safety
Fundamentals of FSOC‐1
Wireless Access Schemes and FSOC
A Brief History26
200 m
1790s Optical Telegraph – by Claude Chappe800 B.C Fire Beacons – by ancient Greek and RomansDate Invention/Development
1970s FSO mainly used in secure military applications1979 Indoor WOC systems – by F.R.Gfeller and G.Bapst1993 Open standard for IR data comm. – IrDA2003 The Visible Light Comm. Consortium – Japan2008 Standard for home networking – OMEGA (EU)2009 IEEE 802.15.7 – Standard on VLC
1960 Invention of Laser
1880 Photophone – by Allexander Graham Bell
“It’s the greatest invention I have ever made; greater than the telephone!”Alexander Graham Bell ‐ 1880
Fundamentals of FSOC‐1
Lecture 2 Basic Concepts of WOC
1790s Optical Telegraph – by Claude Chappe800 B.C Fire Beacons – by ancient Greek and RomansDate Invention/Development
1970s FSO mainly used in secure military applications1979 Indoor WOC systems – by F.R.Gfeller and G.Bapst1993 Open standard for IR data comm. – IrDA2003 The Visible Light Comm. Consortium – Japan2008 Standard for home networking – OMEGA (EU)2009 IEEE 802.15.7 – Standard on VLC
1880 Photophone – by Allexander Graham Bell
1960 Invention of Laser
A Brief History27
1970 Full‐duplex link /w He‐Ne Laser over 14 km (NEC‐Japan)
1963 TV signal trans. /w He‐Ne Laser over 190 km (NAA‐A.B.D.)
1995 LCE (Laser Comm. Experiment) CRL & JPL
1998 GEOLite (Geo. Lightweight Techn. Exper.) Lincoln
1998 SILEX (Semiconductor Intersatel. Link Exper.) ESA
1998 OGS (Optical Ground Station) ESA
2009 MLCD (Mars Laser Comm. Demo.) NASA
2013 Mona Lisa Experiment (LRC‐ NASA)
1960 Invention of Laser
1980 AFTS (Airborne Flight Test System) McDonnell
1990 RME (Relay Mirror Experiment) Ball Aerospace
ARTEMIS (ESA) – SPOT4 (Fransa)
ARTEMIS (ESA) – Aircraft
Relay Mirror Experiment (USA)
ARTEMIS (ESA) – OICETS (JAXA)
OICETS (JAXA) – GROUND (Japon)
2014+ EDRS (European Data Relay Satellite System) ESA
28 A Brief History
Fundamentals of FSOC‐1
Mona Lisa
29 A Brief History
Fundamentals of FSOC‐1
FSOC and Radio Comparison
Antenna Size 10 cm ∼ 30 cm 2 m ∼ 5 mSat. Size Small and Medium Scale Large Scale
Data Rate 1 Gbps ∼ 10 Gbps 100 ∼ 800 Mbps
Dedectability Very Low Probability Very High ProbabilityEMI/RFI Very Low Probability High ProbabilityLicence Not required RequiredCost Low High
Power Low HighBandwidth Wide (GHz) Narrow (MHz)
Resolution Very High High
Service Quality Secure Unsecure
Installation Requires Alignment ‐ LoS NonLoS or LoSAttenuation Fog RainChannel effect Atmosferic Turbulance Multipath Fading
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Fundamentals of FSOC‐1
The most comparable features!RFSpectrum is scarce and low bandwidthSpectrum is regulatedSuffers from multi‐path fadingSusceptible to eavesdropping Large components
FSOCA single FSO channel can offers Tb/s throughputSpectrum is large and license free (very dense reuse)Transmission range limited by weather conditionSecure and are very difficult to interceptSmall components
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FSOC and Radio Comparison
Fundamentals of FSOC‐1
The most comparable features!Fibre opticHigh cost (450000$ @ 700m)Requires permits for digging (Rights of Way)TrenchingTime consuming installationMobility impossible
FSOCLow Cost (18000$ @ 700m)No permits (especially through the window) No digging Faster installationMobility/reconfigurability possible
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FSOC and FO Comparison
Fundamentals of FSOC‐1
Block diagram of the FSOC system.
33Link Configurations
Modulatedinput current
Light sourceLED/LD
OpticalPowerx(t)
Drive circuit
Input
Photodetector – PIN, APD- Surface area >> Optical
wavelength
Ambient light
PhotocurrentIp(t)
Receiver output
λ/2
= 10,000λ
S. Area = 1 cm2
Fundamentals of FSOC‐1
Typically grouped into four system configuration.
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RX
TX TX
RX
TX RX RX
TX
Directed Nondirected
Diffuse Tracked
Link Configurations
Fundamentals of FSOC‐1
What about Directed LOS Link?
Main configuration for outdoor environment (FSOC)
Point‐to‐point links rather than point‐to‐multipoint.
Narrow beam and Low power requirement
High‐power flux density at the photodetector
Offer high data rate (Mbps and above)
Range from a few meters to 5 km
Does not suffer multipath‐induced distortion
Noise from ambient sources rejected due to narrow FOV
Data rate depends on free space path loss.
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RX
TX
Link Configurations
Fundamentals of FSOC‐1
What about Tracked Systems?
Narrow beam Tx and narrow FOV Rx
reduce ambient noise and ISI
1Gbps bit rates with mechanical steerable optics.
Mechanical steerable optics are expensive to realize.
Solid‐state tracked system, using multielement Tx and Rx array with
lens arrangement is a solution.
OMIMO improves channel quality due to spatial diversity.
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RX
TX
Link Configurations
Fundamentals of FSOC‐1
What about FSOC Application areas…Last mile access
Bridge between the end‐users and fibre backcone. From 50 m to 5 km and 1Mbps to 10 Gbps
37Application Areas
Fibre based backbone>2.5 Gbps
FSOC>2.5 Gbps
Enduser>2.5 Gbps
Fundamentals of FSOC‐1
What about FSOC Application areas…Optical Fibre Backup
In the event of damage or unavailability.
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Fibre Cable
FSOC Link
Application Areas
Fundamentals of FSOC‐1
What about FSOC Application areas…Cellular backhaul
Traffic between BSs and switching centres in 3G/4G networks.
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BTSeNB
MSUE
aGWBSC
IP gateway
PDN gateway
?? gateway
Application Areas
Fundamentals of FSOC‐1
What about FSOC Application areas…Disaster recovery Temporary link, Transport HD TV signal
40Application Areas
Fundamentals of FSOC‐1
What about FSOC Application areas…Multicampus communication network
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Fibre CableInternet
Campus
Application Areas
Fundamentals of FSOC‐1
What about FSOC Application areas…Difficult Terrain
Bridge accross a river, busy street, valley etc.
42Application Areas
Fundamentals of FSOC‐1
What about FSOC Application areas…Convoy Communication in military
43Application Areas
Fundamentals of FSOC‐1
What about FSOC Application areas…Fleet Communication in navy
44Application Areas
Fundamentals of FSOC‐1
What about FSOC Application areas…Intersatellite and Satellite‐to‐ground communication
ARTEMIS GEO (ESA)– SPOT4 LEO (France)(2001)ARTEMIS GEO (ESA)‐ OGS (ESA) (2001)ARTEMIS GEO (ESA)‐DRS1 (ESA) (under dev.)Terrasar X (German)‐NFIRE (USA) (2008)5500 km @ 5.5 Gbps
45Application Areas
Fundamentals of FSOC‐1
What about FSOC Application areas…Scout intelligence in army
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Boundary
RF
Application Areas
Fundamentals of FSOC‐1
What about FSOC Application areas…Intelligence or surveillance transfer
From HAP or LEO satellite.
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• Aircraft-to-aircraft• Aircraft-to-ground• Aircraft-to-satellite• Aircraft-to-HAP
Application Areas
Fundamentals of FSOC‐1
And at last…
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mm m km >10000 km
Application Areas
Fundamentals of FSOC‐1
What about safety?
Two kinds of injuryEyeSkin
The damaga on eye is more significant.The eye can focus wavelength 0.4‐1.4μm.
49Safety and Regulations
Fundamentals of FSOC‐1
What about safety?
Response/absorption of the human eye versus wavelength
50Safety and Regulations
Fundamentals of FSOC‐1
Accessible Emission Limits (AEL) for 850 nm and 1550 nm…
AEL depends on wavelength, geometry of the emitter and the intensity of the source.No wavelength is inherently dangerous or eye‐safe; it is the output power that determines the laser classificationIt is also important to understand that the regulation addresses the power density in front of the transmit aperture rather than the absolute power created by an LD inside the equipment.
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Average Optical Power Output (mW)Class 850 nm 1550 nm1 < 0.22 < 102 < 0.22 < 103R 0.22 ~ 2.2 10 ~ 503B 2.2 ~ 500 50 ~ 5004 > 500 > 500
Safety and Regulations
Fundamentals of FSOC‐1
What is Maximum Permissible Exposure (MPE)?
It is the highest radiation power or energy, measured in W/cm2 or J/cm2, that is considered safe with a negligible probability of causing damage.The MPE is measured at the cornea of the human eye or at the skin, for a given wavelength and exposure time.It is usually about 10% of the dose that has a 50% chance of creating damage under worst‐case conditions.The values for the skin are much lower since the skin is usually less sensitive to laser radiation.
52Safety and Regulations
Fundamentals of FSOC‐1
Example of MPE values (W/m2) of the Eye
53
ExposureDuration (s) 1 2 4 10 100 1000 10000
MPE @ 850 nm 36 30 25 20 11 6.5 3.6
MPE @ 1550 nm 5600 3300 1900 1000 1000 1000 1000
Safety and Regulations
Fundamentals of FSOC‐1
What about FSOC Challenges?
54Challenges
Sunlight
Building Motion
Alignment
WindowAttenuationFog
Scintillation
RangeObstructions
Low Clouds
Aerosol& Gases
Fundamentals of FSOC‐1
What about FSOC Challenges?
Compensating Building MotionAutomatic Pointing and Tracking
o Allows narrow divergence beams for greater link margino System is always optimally aligned for maximum link margino Additional cost and complexity
Large Divergence and Field of Viewo Beam spread is larger than expected building motiono Reduces link margin due to reduced energy densityo Low cost
55
2 – 10 mrad divergence
=2 to 10 meter spread at 1 km
0.2 – 1 mrad divergence
= 0.2 to 1 meter spread at 1 km
Challenges
Fundamentals of FSOC‐1
Optical Wireless Communications : System and Channel Modelling with MATLAB, Z.Ghassemlooy, W.Popoola, S.Rajbhandari, CRC Press, 2013.
Optical Wireless Communications: IR for Wireless Connectivity, R.Ramirez‐Iniguez, S.M.Idrus, Z.Sun, CRC Press, 2008
Wireless Infrared Communications, J.R.Barry, Kluwer Academic, 1994.
Coding for Optical Channels, I.Djordjevic, W.Ryan, B.Vasic, 2010
Lecture notesMaite Brandt Pearce
References56
Fundamentals of FSOC‐1
The End of The Lesson,Thank you for listening…
57Finish
Fundamentals of FSOC‐1