(fso)1 (2)

8/7/2019 (fso)1 (2)

http://slidepdf.com/reader/full/fso1-2 1/31

Free Space Optics (FSO)

By:- RAJEEV NAIK

4SH08EC404

8/7/2019 (fso)1 (2)


8/7/2019 (fso)1 (2)


Why Not Just Bury More Fiber?

Cost

Rights of Way

PermitsTrenching

Time

With FSO, especially through theWith FSO, especially through thewindow, no permits, no digging,window, no permits, no digging,no feesno fees

8/7/2019 (fso)1 (2)


Introduction to the concepts of Free

Space Optics (FSO)

FSO is a line-of-sight technologywhich uses LASERS and Photodetectors to provide opticalconnections between twopoints²without the fiber.

FSO can transmit data, voice or video at speeds capable of reaching 2.5 Gbps. Productscapable of speeds upto 10 Gbpsare expected to hit the marketswithin one year.

FSO units consist of an opticaltransceiver with a laser (transmitter) and a Photodetector (receiver) to provide fullduplex (bi-directional) capability.

FSO systems use invisibleinfrared laser light wavelengthsin the 750nm to 1550nm range.

8/7/2019 (fso)1 (2)


HISTORY OF FSO:

8/7/2019 (fso)1 (2)


HISTORY OF FREE SPACE OPTICS(FSO)

Free space optics was first demonstrated by Alexander Graham Bellin late nineteenth century.

Bell's experiment converted voice sounds into telephone signals.

Late 1950¶s~early 1960's, several scientists theorized anddeveloped laser.

In the early 1980's U.S military and NASA made research on FSOfor inter-satellite communication proposes.

Germany, France and Japan made significantadvancements in free space optics for satellitecommunications since 1985 for private sector.

8/7/2019 (fso)1 (2)


FSO Major S ub System

8/7/2019 (fso)1 (2)


SYSTEM DESIGN

Based on connectivity between wireless units,each consisting of an transceiver.

Each unit uses

Optical sourceLens (transmitter and receiver)Optical receiver Transmitter fiber Receiver fiber

Photon detector receiver.Usually FSO uses laser,communication over

short distance will be done using LEDs.

8/7/2019 (fso)1 (2)


SYSTEM DESIGN

8/7/2019 (fso)1 (2)


How FSO Works

1 Network traffic

converted intopulses of narrow& invisiblebeams

2 Transmitter transmits themodulated beams into the air

5 Reverse direction datatransported the same way.

� Full duplex

3 A receiver at the other end of thelink collects those modulatedbeams

4 Received signal

converted back intodata steam andgiven to the network

8/7/2019 (fso)1 (2)


WAVELENGTHS USED

Depending on their robust property againstatmospheric absorption and possibility of their implementation

780nm-850nm

1529nm-1600nm

10,000nm(researches are going on)

8/7/2019 (fso)1 (2)


TECHNOLOGIES USED

VCSEL(780nm-850nm)

Silicon based

receiver(780nm-850nm)

Fabry-perotlaser(1600nm)

Indium galliumarsenidereceiver(1600nm)

8/7/2019 (fso)1 (2)


TYPES OF BEAM USED

Gaussian beam:

EM RADIATION WHOSE

TRANSEVERSE ELECTRIC

FIELD AND RADIATION CAN BEMODELLED BY GAUSSIANFUCTION.

Top hat beam: A LASER BEAM WITH

UNIFORM ENERGY DENSITYWITHIN A CIRCULAR DISK.

TYPICALLY FORMED BYDEFRACTIVE OPICALELEMENTS FROM BY

GAUSSIAN BEAM

8/7/2019 (fso)1 (2)


Why Free Space Optics (FSO)?

The ³Last Mile´ Bottleneck Problem

Only about 5% of commercial

buildings are lit with fiber

Wide Area Networks betweenmajor cities are extremely fast

� Fiber based� >2.5 Gbps

Local Area Networks inbuildings are also fast

� >100Mbps

The connections inbetween are typicallya lot slower

� 0.3-1.5 Mbps

8/7/2019 (fso)1 (2)


Fundamental Concepts

Small Angles - Divergence & Spot

Size

1 mrad

1 km

1 m

Small angle approximation:

Angle (in milliradians) * Range (km)= Spot Size (m)

Divergence Range Spot Diameter

0.5 mrad 1.0 km ~0.5 m (~20 in)

2.0 mrad 1.0 km ~2.0 m (~6.5 ft)

4.0 mrad (~ ¼ deg) 1.0 km ~4.0 m (~13.0 ft)

1° § 17 mrad 1 mrad § 0.0573°

8/7/2019 (fso)1 (2)


Challenges

Environmental factors

Sunlight

Building

Motion

Alignment

Window

AttenuationFog

Each of these factors can ³attenuate´ (reduce) the signal.

However, there are ways to mitigate each environmental

factor .

Scintillation

RangeObstructions

Low Clouds

8/7/2019 (fso)1 (2)


8/7/2019 (fso)1 (2)


Challenges

Low Clouds, Rain, Snow and DustLow Clouds

Very similar to fog

May accompany rain and snow

Rain

Drop sizes larger than fog andwavelength of light

Extremely heavy rain (can¶t see throughit) can take a link down

Water sheeting on windows

Heavy Snow

May cause ice build-up on windows

Whiteout conditions

Sand Storms

Likely only in desert areas; rare in theurban core

8/7/2019 (fso)1 (2)


� Beam spreading and wandering due to propagation throughair pockets of varying temperature, density, and index of refraction.

� Almost mutually exclusive with fog attenuation.

� Results in increased error rate but not complete outage.

Challenges

ScintillationChallenges

Scintillation

8/7/2019 (fso)1 (2)


Challenges

Building Motion ± Thermal Expansion

R esults from SeattleDeployment:

� 15% of buildings movemore than 4 mrad



8/7/2019 (fso)1 (2)


1. Automatic Pointing and Tracking

Allows narrow divergence beams for greater link margin

System is always optimally aligned for maximum link margin

Additional cost and complexity

2.

Large Divergence and Field of View Beam spread is larger than expected building motion

Reduces link margin due to reduced energy density

Low cost

Challenges

Compensating for Building Motion ± Two Methods

0.2 ± 1 mrad divergence

= 0.2 to 1 meter spread at 1 km

2 ± 10 mrad divergence

2 to 10 meter spread

at 1 km

8/7/2019 (fso)1 (2)


FSO SECURITY

FSO is more secure than other wireless-basedtransmission technologies.

FSO laser beams cannot be detected with spectrum

analyzers or RF meters. It requires a matching Free Space Optics FSO

transceiver.

beams generated by FSO systems are narrow

and invisible.Data transmitted over an encrypted connection.

8/7/2019 (fso)1 (2)


APPLICATIONS

TOP 5 APPLICATIONS

Telecommunication Networks

Computer Networks (LAN-to-LAN)

Broadband Internet Access

Disaster Recovery

Temporary Deployment

TYPICAL APPLICATIONS

Short distance LAN extension

Internet/intranet provision

Traffic Grooming in Cell Networks

Airports, Railways

8/7/2019 (fso)1 (2)


...(CONTD)

ENTERPRISE APPLICATIONS

Entreprise Connectivity

Health Care

Engineering & design

Video services Security

8/7/2019 (fso)1 (2)


Limitations

� Unreliable Bandwidth availability : Variations in weather conditions affect available bandwidth

� Requires Line of Sight link

� Limited Range

� Need sophisticated mechanism for alignment of thetransmitter and receiver

� Even slight mechanical disturbances may lead to loss of alignment, and may result in complete link break-down

8/7/2019 (fso)1 (2)


COMPARISON OF FSO WITH OTHERS

AccessMedium

Speed

(Mbps)

Monthlycost ($)

Cost/Mbps/month($)

Dial-up 0.056 20 357

Satellite 0.4 50 125CableModem

1.5 50 33

DSL(min) 0.144 49 340DSL(max) 8 1200 150

RF 155 1250 8

FSO 155 555 4

8/7/2019 (fso)1 (2)


WHY FSO ?

DEMAND OF MORE BANDWIDTH.

OFFER LOWEST COST.

REQUIRES LESS INSTALLATION TIME.

FSO BRINGS NEW POSSIBLE TECHNOLOGY THAT

MAY NOT BE ABLE TO BE FULFILLED BY ANOTHERACCESS TECHNOLOGY

8/7/2019 (fso)1 (2)


FUTURE OF FSO

FSO technology became popular as it was used toenable the Wall Street Stock Exchange back tobusiness after the 9/11 tragedy in less than 48 hours.

Manufacturers of FSO optical products areLightPointer, AirFiber, and Fsona Communications.

It is an alternative to fiber optics technology.

In future FSO will be used everywhere.

like cellular base station, Wi-Fi hotspots, disaster recovery etc.

8/7/2019 (fso)1 (2)


CONCLUSION

Free-space optics technology is a goodalternative, especially compare to fiber optics.

In the future, FSO may be one of the mostimportant access technologies due to itsadvantages.

It will capture big market in the future.

8/7/2019 (fso)1 (2)


8/7/2019 (fso)1 (2)


Documents

(fso)1 (2)