afsar free space optics
TRANSCRIPT
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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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