BY –

DIGISHA SINGHAL 13BEC026

RITIKA BISWAS 13BEC088

GUIDED BY -PROF. DHAVAL SHAH

FREE SPACE OPTICAL COMMUNICATION

Motivation

FSO involves communication through free space ie vacuum and finds extensive application in interstellar space.

FSO is an upcoming technique used for broadband communication as we face RF spectrum scarcity with respect to increasing throughput requirements.

Useful in places where physical connections are impossible.

Free space optical spectrum is license free and nearly unlimited.

[1][2]

Objectives

FSO is a line-of-sight (LOS) technology that transmits amodulated beam of visible or infrared light through theatmosphere for broadband communications.

FSO technology delivers cost-effective optical wirelessconnectivity, power efficient, and a faster return oninvestment (ROI) for Enterprises and Mobile Carriers.

Of high usage where physical connections are impracticaldue to high costs and other considerations.

Outline

Introduction

Working

Challenges

Advantages-disadvantages

Applications

Conclusions

References

Introduction

Line of Sight “Fiber-less” laser driven technology.

Operating wavelength range :

1) 780-900 nm

2) 1500-1600nm

Up to 1 Gbps Ethernet

Distances – up to 5km.

[3]

History

In 1880, Alexander Graham Bell invented the ‘photophone’ .

The invention of lasers In the 1960s, revolutionized free

space optics.

Germany, France and Japan made significant advancements

in free space optics for satellite communications.

Military organizations especially were interested and forced

some developments.

Why FSO??

Increasing

demand for high

bandwidth in

metro networks

Last mile bottleneck

:Copper-based

connections limits

speed to an average of

around 12Mbps–

generally the slowest

link in the chain.

Digging, delays and associated costs to lay fiber often make it economically prohibitive.

RF-based networks require immense capital investments to acquire spectrum license. Also bandwidth is limited to 622 Mbps

So FSO is

used as an

alternative!!

Working

1 Network traffic converted into pulses of invisible lightrepresenting 1’s and 0’s.

2 Transmitter projects thecarefully aimed lightpulses into the air.

5 Reverse directiondata transportedthe same way.

3 A receiver at the other end of the link collects the light using lenses and/or mirrors.

4 Received signal convertedback into fiber or copperand connected to thenetwork.

Anything that can be done in fiber can be done with

FSO.

[5]

Block Diagram

SOURCE

DESTINATION DEMODULATOR AMPLIFIERPHOTO

DETECTOR

RECEIVE OPTICS

TRANSMIT OPTICS

DRIVERLASER DIODE

MODULATOR

ATMOSPHERIC CHANNEL

Receiver

Transmitter

Working

Based on Connectivity between FSO based optical wireless units, each consists of

an optical transceiver to provide bi-directional capability.

The modulated light source(laser/LED) provides the transmitted optical signal,

determines all the transmitter capabilities of the system which is then

transmitted through the atmosphere.

On the receiving end, once the signal is received, after undergoing the influences

of the time-dispersive channel and ambient light, the optical signal is directly

translated into a photocurrent at the detector.

The electrical SNR in optical links depends on the square of the optical power,

which has a deep impact on both design and performance of OW systems.

[6]

Working (Cont.)

TRANSMITTER : One or more laser diodes (LD) or light

emitting diodes (LED) are used. The choice between LED and

LD is determined by standard factors.

RECIEVER:

LED LASER

LED v/s LASER

Non coherent

Few MHz

Eye safe

Preferred for indoor

applications.

Optical power output.

Coherent Beam

Up to 10 GHz

Harmful eye

Can be used in all practical

outdoor applications

FSO systems require LASER.

Range of Wavelengths Used

780–850 nm: These wavelengths are suitable for FSOoperation and several vendors provide high power lasersin this region.

1520–1600 nm : high quality transmitter and detectorcomponents are readily available, but more expensive anddetectors are less sensitive. 50-65 times much power canbe transmitted.

10,000nm (10 mm): relatively new to the commercial FSOarena, being developed because of claims of better fogtransmission characteristics. Fewer components availableat 10,1000 nm

Challenges facedEnvironmental factors: Sunlight

Building Motion

Alignment

WindowAttenuation

Fog

These factors can “attenuate” (reduce) the signal.

Scintillation

RangeObstructions

Low Clouds

[8]

• Significant reduction in beam

intensity

• Causes a decrease in the power density

• Modifies light characteristics or hinders the

passage of lightFOG ABSORPTION

SCATTERINGSCINTILLATION

Challenges(Cont.)

•Fluctuations in signal amplitude leading to image distortion

Advantages

[9]

Installation cost is very low as compared to laying Fiber

Highly secure transmission possible

Unregulated Spectrum

Low Power Consumption

Ease of installation

License-free long-range operation

Immunity to electromagnetic interference

Speed: high bit rates and low bit error rates

[10]

Disadvantages

High Launch Power represents eye hazard.

Physical obstruction

Atmospheric barriers

SNR can vary significantly with the distance and the ambient noise

Low Power Source requires high sensitive receivers.

If the sun goes exactly behind the transmitter, it can swamp the

signal.

Applications

Metro Area Network (MAN)

Last Mile Access

Enterprise connectivity

Fiber backup

Backhaul

Service acceleration

Space Applications/Extraterrestrial(esp. in military)

CCTV

Video conferencing

[11]

Fso and Other Technologies

Coaxial cable Satellite Optical Fibre Free Space optics

Transmission speed

500Mbps 90Mbps 100Mbps to 100Gbps

Varies

Ease of installation

Moderate Difficult Difficult Moderate

Cost Moderate Moderate (not including cost of satellite)

High Moderate

Maintenance difficulty

Moderate Low Low Low

Skills Required to install

Moderate High High Moderate

Applications Computer networks long distances Point-to-point Between buildings

Advantages Less susceptible to interference

Speed, availability Not susceptible to EMI

Price/ performance

Disadvantages Bulky, difficult to work with

Propagation delay Difficult to terminate

Can be intercepted

Future Of FSO

The FSO industry shows some strength, and the FSO market is growing, though with much less speed as compared to required speed.

Perhaps the best overall prospects are in space, where progress is being made in improving acquisition and tracking.

The FSO industry consists of mostly established vendors that manufacture equipment for various distances and speeds of transmission. The highest speed of 2.5 Gb/s promises to be increased to 10 Gb/s in future.

Conclusion

For future short-range applications, optical wirelesscommunications present a viable and promising supplementaltechnology to radio wireless systems and optical fiber.

It provides a low cost, rapidly deployable method of gaining accessto fiber-quality connections and provides the lowest costtransmission capacity in the broadband industry saving substantialup-front capital investments.

Can be installed for as little as one-tenth of the cost of laying fibercable, and about half as much as comparable microwave/RFwireless systems thus eliminating the need to buy expensivespectrum (it requires no FCC), which further distinguishes it fromfixed wireless technologies.

References

1. http://www.fsona.com/

2. http://en.wikipedia.org/wiki/Free_Space_Optics

3. http://www.slideshare.net/

4. http://www.ieeexplore.ieee.org.proxy.library.carleton.ca/stamp/stamp.jsp?tp=&arnumber=4446618

5. http://web.mst.edu/~mobildat/Free%20Space%20Optics/index.html

6. http://freespaceoptics.org

7. http://www.freespaceoptic.com

8. http://www.free-space-optics.org/

References

[1] www.opticsinfobase.orgoefulltext.cfmuri=oe-19-26-B56&id=224428

[2] www.pi-usa.us/products/images/300x250_images/S-334-Red-Beams.jpg

[3] www.pi-usa.us/products/images/300x250_images/S-334-Red-Beams.jpg

[4] image.slidesharecdn.com/introductiontofsotechnology-1216024918992120-8/95/introduction-to-fso-technology-3-728.jpg?cb=1360750423

[5] image.slidesharecdn.com/freespaceoptics-140721105157-phpapp02/95/free-space-optics-communication-9-638.jpg?cb=1405957976

[6]www.optica.ru/EN/lant3a.jpg.

[7] http://cictr.ee.psu.edu/research/pcs/index_files/image010.jpg

References

[8] image.slidesharescdn.com/freespaceoptics-140721105157-phpapp

02/95/free-space-optics-communication-19-638.jpg?cb=1405957976/

[9] http://www.gigapackets.com/images/ManRunningUpArrow250.jpg

[10] termistron.com/ilginc-devre/guc-tasarrufu-devresi/Power%20Saver

%20circuit.jpg

[11] etutorials.org/shared/images/tutorials/tutorial_63/F02tk06.jpg

[12] http://www.yugatech.com/blog/wp-content/uploads/2010/03/wimax.

gif

[13] beyondthescores.files.wordpress.com/2013/07/edu627-blog-3-2.jpg

FURTHER QUERIES?????

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