Fundamentals Free Space Optical Communication 1opticwise.uop.gr/attachments/article/93/TD3.pdf ·...

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


Demand for High‐Speed Communications...

4



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



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



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.



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



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)



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



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



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



What are the advantages of FSOC?

Highly secure connectivity.Directed laser beam.Invisible light wavelength.

13

F/O, LANConnection

F/O, LANConnection

IR binocolurs




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.

14

2.5 mrad0.08 mrad

2.5 m8 cm

Range = 1 km

BeamwidthSpotwidth

Communication is only in cone beam.Fundamentals of FSOC‐1



Provides wide badwidth communication.Possiblity of more than 40 GHz optical modulation.Bandwidth about GHz – THz with multiplexing.

15

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




Small, light, compact size, low power consumption. (SWAP)

16

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




Small, light, compact size, low power consumption. (SWAP)

17

L‐Band Antenna2.35 m

Ka‐Band Antenna2.35 m

Optical TelescopeRx: 25 cmTx: 12.5 cm

ARTEMIS (ESA)



SPOT‐4

What are the disadvantages of FSOC?

Required LOS especially in ourdoor applications.Cone‐shaped laser beam transmissionSolution : Acquisition, Tracking and Pointing Systems

18

Beamwidth FOV

Pointer Laser(Beacon)




Effected by weather conditions.A Rain particle size : 200 ∼ 2000 μm → close to microwaveA Fog particle size : 5 ∼ 15 μm → close to light (laser)

19

Rain : 3‐17 dB/km Snow : 6‐26 dB/km Fog : 20‐300 dB/km

Light Attenuation




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)

20




Solution : Adaptive Optics

21

Transmitter

OriginalWavefront

AtmosfericTurbulance

DistortedWavefront

AO system

TiltMirror

Partial repairedWavefront

RepairedWavefront

High VoltageAmplifier

WavefrontController

High SpeedSensor

DeformableMirror

CableFibre Cable

Optical Signal

Receiver

E/Oconverter

ElectricalBlock




Solution : Adaptive Optics

22




Solution : Error Correcting Coding

Repetition MIMO BI‐LDPC‐coded PAM (a) Transmitter (b) Receiver

23




Solution : Error Correcting Coding

BER performance of BI and MLC LDPC‐coded modulation

24




Effected by Ambient Ligth Sources.

25

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



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


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


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)


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


Mona Lisa

29 A Brief History


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

30


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

31

FSOC and Radio Comparison


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

32

FSOC and FO Comparison


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


Typically grouped into four system configuration.

34

RX

TX TX

RX

TX RX RX

TX

Directed Nondirected

Diffuse Tracked

Link Configurations


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.

35

RX

TX

Link Configurations


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.

36

RX

TX

Link Configurations


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


What about FSOC Application areas…Optical Fibre Backup

In the event of damage or unavailability.

38

Fibre Cable

FSOC Link

Application Areas


What about FSOC Application areas…Cellular backhaul

Traffic between BSs and switching centres in 3G/4G networks.

39

BTSeNB

MSUE

aGWBSC

IP gateway

PDN gateway

?? gateway

Application Areas


What about FSOC Application areas…Disaster recovery Temporary link, Transport HD TV signal

40Application Areas


What about FSOC Application areas…Multicampus communication network

41

Fibre CableInternet

Campus

Application Areas


What about FSOC Application areas…Difficult Terrain

Bridge accross a river, busy street, valley etc.

42Application Areas


What about FSOC Application areas…Convoy Communication in military

43Application Areas


What about FSOC Application areas…Fleet Communication in navy

44Application Areas


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


What about FSOC Application areas…Scout intelligence in army

46

Boundary

RF

Application Areas


What about FSOC Application areas…Intelligence or surveillance transfer

From HAP or LEO satellite.

47

• Aircraft-to-aircraft• Aircraft-to-ground• Aircraft-to-satellite• Aircraft-to-HAP

Application Areas


And at last…

48

mm m km >10000 km

Application Areas


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


What about safety?

Response/absorption of the human eye versus wavelength



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.

51

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


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.



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


What about FSOC Challenges?

54Challenges

Sunlight

Building Motion

Alignment

WindowAttenuationFog

Scintillation

RangeObstructions

Low Clouds

Aerosol& Gases


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


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


The End of The Lesson,Thank you for listening…

57Finish


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