Afsar Free Space Optics

8/9/2019 Afsar Free Space Optics

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Free Space Optics

AFSAR HAMEED


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Presentation Overview

What Is Free Space Optics?What Is Free Space Optics?

History Of FSOHistory Of FSO

TechnologyTechnology

WorkingWorking

Why FSO?Why FSO?

Applications & Network IntegrationApplications & Network Integration

The Future of FSOThe Future of FSO


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What is Free Space Optics ?

The transmission of modulated visible

or infrared (IR) beams through the

atmosphere to obtain opticalcommunications.

Transmission of data is via Lasers.

Similar to fiber, but the data stream is

transmitted through the air.


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History of FSO

The first optical wireless communications was

demonstrated by Alexander Graham Bell in

the late nineteenth century via an

experimental device called 'photophone'.

Originally developed in the 1960s for the US

Military and NASA.


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Technology used in FSO

Requires light which can be focused b/w

transceivers for communication.

LASER is used for this purpose.

LASER generates focused light either visible

or infrared.

Can be designed to be eye-safe.


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How Fiber Optic Cable

Works

Light Source

Glass Fiber Strands

Detector

Network

Device

Pulses of light communicate the data

ON = 1 OFF = 0

Capable of more than 40 Gbps

>7 CDs a second

Light Source

Detector

Network

Device


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How LASER works?

It undergoes through two process:

1. Pumping:

The process of injection of energy into

cavity to excite the atom.

2. Emission:

The process of taking the atom from higher

state to ground state releasing the photon.


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How FSO works?

1 Network trafficconverted into

pulses of invisible

light representing

1s and 0s

2 Transmitter 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

or mirrors

4 Received signal

converted back into

fiber or copper and

connected to the

network

Anything that can be done in fiber

can be done with FSO


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Why Free Space Optics?

Why Not Just Bury More Fiber?

Cost

Rights of Way

Permits

Trenching

Time

With FSO, especially throughWith FSO, especially through

the window, no permits, nothe window, no permits, no

digging, no feesdigging, no fees


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Beams only a few meters in diameter at a

kilometer.

Allows VERY close spacing of links without

interference. Efficient use of energy.

License free.

No side lobes. Highly secure.

Ranges of 20m to more than 8km possible.

Why Free Space Optics?Why Free Space Optics?


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Security Aspect of FSO

It transmits a narrow n invisible laser beam inspecific direction so that beam tapping isdifficult.

FSO laser beams cannot be detected withspectrum analyzers or RF meters.

It requires a matching FSO transceiver carefully aligned to complete the transmission

making Interception difficult. Data can be transmitted over an encrypted

connection adding to the degree of security.


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Applications of FSO

A number of applications of Free-Space-

Optics (FSO) has been purposed, such

as:

1. Enterprise Network

2. Service Providers

3. Broadcast & Cctv


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Enterprise Network

A. Campus connectivity solution:

Commn links required b/w buildings

separated by obstacles.

Traditional connectivity requires fiber optics,

copper cables which requires digging.

Provides B.W upto 1500Mbps

Cost effective n easy to deploy.


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B. Disaster recovery and emergency services:

Vehicles are needed to be connected to a

number of other centers, observation points.

Computer n telecom n/w may need to set up

in short space of time.

No risk of ignition in inflammable region.

No interference.


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Service Providers

A. Cable-free solves network problem:

Telecom operators are connected from a

backbone n/w using fiber or copper wires.

Cable digging, increasingly unpopular incities.

Copper wires give 2Mbps access/pair.

Point-to-point Microwave or radio solutionsfor 'wireless local loop' may require licensing

and often suffer from interference.


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Service Providers (Contd..)

B. Cablefree Virtual-Point-to-Multipoint:

Local Multipoint Distribution Service (LMDS)

networks which include high-speed Internet

access, LAN extensions, video-on-demand,video conferencing,etc.

High bandwidths up to 1.5Gbps per

subscriber.

Can be combined to create high

performance cellular n/w.


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Broadcast & Cctv

A. Outside broadcast application:

Connecting remote cameras to OB vans may

not be suited to traditional solutions.

M-wave links are limited to 34Mbps whereas

FSO offers 270Mbps with a range of 2km.

Copper wires are limited to 270Mbps with a

range of 300mt.


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Broadcast & Cctv (Contd..)

B. Cablefree connects to Satellite Uplinks:

Satellite uplinks and downlinks are frequently

used for telecom n broadcast TV .

FSO helps when high B.W connections are

unavailable locally.

FSO offers upto 622Mbps as compared to m-

wave link.


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Challenges

Low Clouds, Rain, Snow and Dust Low Clouds

Very similar to fog

May accompany rain and snow

Rain

Drop sizes larger than fog andwavelength of light

Extremely heavy rain (cant seethrough it) 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 inthe urban core


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Beam spreading and wandering due to propagation through

air 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

Scintillation

Challenges

Scintillation


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Uncoated glass attenuates 4% per surface due to reflection

Tinted or insulated windows can have much greater attenuation

Possible to trade high altitude rooftop weather losses vs. window

attenuation

Challenges

Window Attenuation

Challenges

Window Attenuation

WAM


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Challenges

Building Motion

Type Cause(s) Magnitude Frequency

Tip/tilt Thermal

expansion

High Once per day

Sway Wind Medium Once every

several

seconds

Vibration Equipment

(e.g., HVAC),

door slamming,

etc.

Low Many times

per second


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1. Automatic Pointingand 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 Fieldof 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 1mraddivergence

= 0.2to1meter spreadat1 km

2 10mraddivergence

=2to10meter spreadat1 km


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a enges

Building Motion Thermal

ExpansionResults from SeattleDeployment:

15% of buildings move

more than 4 mrad

5% of buildings movemore than 6 mrad

1% of buildings movemore than 10 mrad


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Performance

Reliability

FOM

Cost

Wavelength.

Security

CHARACTERISTICS


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Conclusion

Most useful to connect organizations to highspeed backbone metro ethernet points due tothe speed of deployment and high speeds.

If the parameters and installation conditionswere fulfilled, a very fast method to install ahigh speed link especially between adjacentbuildings.

Very fast return on investment as well.Generally no recurring costs.


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Afsar Free Space Optics