Fibre optic communication vs satellite communication (1)

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ALTTC OFC V/S SATELLITE 1

OFT V/S SATELLITE COMMUNICATION

Presented by:- Ramakant Tyagi

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• 1790: OPTICAL TELEGRAPH DEVISED BY CLAUDE CHAPPE. • 1880: ALEXANDER GRAHEM BELL INVENTED THE PHOTOPHONE. • 1940’s: OPTICAL GUIDES WITH REFLECTIVE COATING TO CARRY

VISIBLE LIGHT.• 1960: INVENTION OF “LASER”-THE FIRST MAJOR BREAK

THROUGH IN FIBER OPTIC TECHNOLOGY.• UNGUIDED (NON FIBER) COMMNS. SYSTEMS WERE DEVELOPED

AFTER LASER DISCOVERY.• 1966 onwards: DEVELOPMENT OF OPTICL FIBERS BY COMPANIES

LIKE CORNING GLASS (VERY HIGH LOSS).• IN 1970, LOW LOSS FIBER WAS DEVELOPED AND FIBER OPTICAL

COMMNS. SYSTEM BECAME PRACTICAL. IT WAS OPERATED AT WAVE-LENGTH AROUND 820 nm AND ATTENUATION OF 1db/km.

• NOW FIBERS WITH LOSSES OF ONLY A FRACTION OF A db/km ARE AVAILABLE (0.15-0.35 db/km).

“HISTORICAL PERSEPECTIVE”(1)

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Ray Theory:• A number of optic phenomena are adequately explained by considering

light as narrow rays.• The theory based on this approach is called geometrical optics.• These rays obey a few simple rules:1. In a vacuum, rays travel at a velocity of c =3x108m/s. In any other

medium, rays travel at a slower speed, given byv = c/n n =refractive index of the medium.

2. Rays travel straight paths, unless deflected by some change in medium.3. If any power crosses the boundary, the transmitted ray direction is given

by Snell’s law:n1 sin Øi = n2 sin Ør

Optic review

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INCIDENT RAYS 1 REFLECTED RAYS

REFRACTED RAYS

1

1

3

2

2

3

n2¢r

¢i

Principal Of Total Internal Reflection

n1 = 1.48n2 = 1.46

n1

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The Optical Fibre

Cladding

125 mCore 6-10 m

Refractive index

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Light Propagation in fibre

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321

3

2

1


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321

3

2

1


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Air 1.0Carbon dioxide 1.0Water 1.33Ethyl alcohol 1.36Magnesium fluoride 1.38Fused silica 1.46Polymethyl methacrylate polymer 1.5Glass 1.54Sodium chloride 1.59Zinc sulfide 2.3Gallium arsenide 3.35 Silicon 3.5 Indium gallium arsenide phoshide 3.51 Aluminium gallium arsenide 3.6 Germanium 4.0

Index of Refraction materials

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Basic Fibre• core with RI n1

supported by concentric cladding layer with RI n2.

• RI of core is greater than cladding (n1 > n2).

• The cladding layer is surrounded by one or more protective coating.

• Change in RI is achieved by selectively doping the glass perform.

Construction of Optical Fibre Cable

CORE

CLADDING

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• Cabling is to protect the fiber during transportation, installation & operation.

• Cabling protects the optical fibres from mechanical damage and environmental degradation.

• Resembles conventional metal cables externally.• There are a variety of cable design available and irrespective of their

design fibre optic cables have the following parts in common :• Buffer : to protect fibre from outside stress; materials used - nylon, or

plastic.• Strength member ; to reduce stress due to pulling, shearing, and

bending; materials used-textile fiibres (kevlar), or steel.• Cable filling compound: to prevent moisture intrusion and migration in the

cable.• Cable jacket : to protect the fibre against cut and abrasion; material

used-polyethylene polyurethane, polyvinyl chloride or teflon.

Cabling of Optical Fibre :

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Material Classification • Allfused-silica-glass fibre: have silica-core and silica-cladding.• Plasti-clad-silica (PCS) fibre: have silica core and plastic cladding.• All-plastic fibre : have both core and cladding made up of plastic.• Compound glass fibre such as fluride glass fibre.Modal classification :• Similar to metallic wave guides, there are stable propagation states of

electromagnetic waves in an optical fibre called modes.• Fibers can be classified based on number of modes available for

propagation : - single-mode (SM) fibre.- Multi-mode (MM) fibre.

Classification based on refractive index profile :• step index (SI)• Graded index (GRIN) fibre.

CLASSIFICATION OF OPTICAL FIBRE

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2a

2a

2a 8 - 12 m 125 m

50 - 100m 125-400m

50 m 100-400m

C) Multi mode GRIN fiber

b) Multi mode step-index fiber

a) Single mode step-index fiber

Classification of Optical Fibre

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soil categorization : ( for depth of trench )(A) Rocky : Cable trench, where can not be dug without

blasting and/or chiseling. (B) Non Rocky : Other than ‘A’ above, soil mixed with stone and

soft rock.Pipes for cable layingAdvantage for using pipes -1.It gives mechanical protection 2.Pipes can be laid in advance so that the cable laying is faster (1) HDPE pipe 75 mm (diameter) length 5m. (approx 18 to 20’ ) (2) HDPE pipe 50 mm (diameter) length 5m. (approx 18 to 20’ ) (3) PLP pipe (40 mm. outer diameter ) length 1km/200m

Laying of cable

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• Now manual laying method is discoursed due to expensive , time consuming and due to safety consideration.

• Now for digging JCB machines are preferred.• Air blowing method by using Pressure machine is used for cable laying.

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• There are several points in an optic system where losses occur.• These are: coupler, splices, connectors and the fiber itself.• Losses associated within the fiber classified as under:• Losses due to absorption. Even the purest glass will absorb heavily

within specific wavelength regions. Other major source of loss is impurities like, metal ions and OH ions.

• Losses due to scattering: caused due to localized variations in density, called Rayleigh scattering and the loss is:

L = 1.7(0.85/)4 dB/km is in micrometers

• Losses due to geometric effect: – micro-bending.– macro-bending.

Losses in Optical Fiber

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ALTTC OFC faculty 18

• OTDR is used for measurement of splice loss/ fiber loss in a section.• Optical power meter is used to know total loss of terminated cable section.

(General Analysis of OTDR Plot)

FRESNEL REFLECTIONSLOSS

(db)

SPLICE CONNECTOR

DISTANCE (KM)

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A basic comm. System consists of : a transmitter, a receiver, & a medium.

• Optical Transmitters:– convert electrical signals to optical.

• Receivers:– convert optical signal to electrical.

• The basic elements in transmitters: Electronic interfaces, Electronics processing circuitry, Drive circuitry, light source, optical interfaces, output sensing and stabilization, Temperature sensing and control.

• The basic elements in an optical receiver: Detector, Amplifier, Decision circuits.

Basic Fibre Optic Communications

Ligh t source

ELECTRICAL

SIGNALSIGNAL

ELECTRICAL

TRANSMITTER MEDIUM RECIEVER

Ligh t sansor

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• The device which actually converts electrical signals to its optical equipment.

• Most common light sources:– light-emitting diodes (LEDs) – Light Amplification by Stimulated Emission of Radiation (laser)

diodes.• It is particularly required in lasers to maintain stable output power

by way of feedback mechanism.• Laser is very sensitive to temperature. Operating characteristics

of a semiconductor laser-notably threshold, current, output power, and wavelength change with temperature. Hence temperature sensing and control is required to maintain stable temperature.

Optical Sources

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• The detectors used in fibre optic communications are semiconductor photodiodes or photodetectors.

• It converts the received optical signal into electrical form.– Pin photodiode; cheaper, less temperature

sensitive, and requires lower reverse bias voltage.– Aavalanche photodiode APD); used where

receiver is to detect lower power,

DETECTORS

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ADVANTAGES OF FIBRE COMMUNICATIONS (1)

• High information carrying capacity:A valid comparison would be on the basis of cost per meter per telephone channel, rather than just cost per meter.

• Resource plentiful:The basic materials are either silicon dioxide for glass fibers or transparent plastic which are plentiful

• Less attenuation:A typical fibre attenuation is 0.3 dB/km. Whereas a coaxial cable (RG-19/U) will attenuate a 100-Mz signal by 22.6 dB/km.

• Greater safety:Optic fibers glass/plastic, are insulators. No electric current flows through them.


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Advantages of fibre communications

(2)

• Immunity to RFI:Fibers have excellent rejection of radio-frequency interference (RFI) caused by radio and television stations, radar, and other electronics equipment.

• Immunity to EMI:Fibres have excellent rejection of electromagnetic interference (EMI caused by natural phenomena such as lighting, sparking, etc).

• No cross-talk:The optic wave within the fiber is trapped; none leaks out during transmission to interfere with signals in other fibers.

• Higher Security:fibers offer higher degre


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Advantages of fibre communications (3)

• Small size and light weight:typical optical cable; fiber dia. 125m, cable dia. 2.5 mm and weight 6 kg/km. A coaxial cable (RG-19/U), outer dia. 28.4 mm, and weight 1110 kg/km.

• Corrosion : Corrosion caused by water/chemicals is less severe for glass than for copper.

• Less temperatures sensitive:Glass fibers can with stand extreme temperatures before deteriorating Temperatures up to 800 C leave glass fiber unaffected.


BSNLDisadvantages of optical fibre

• Cost - Cables are expensive to install but last longer than copper cables. Transmission - transmission on optical fibre requires repeating at distance intervals.

• Fragile - Fibres can be broken or have transmission loses when wrapped around curves of only a few centimetres radius. However by encasing fibres in a plastic sheath, it is difficult to bend the cable into a small enough radius to break the fibre.

• Protection - Optical fibres require more protection around the cable compared to copper.


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Application of fibre optic communications

• Telecommunications:Long-Distance Telecommunications:Inter-exchange junction:Fibre in the loop (FITL):

• Video Transmission:Television broadcast, cable television (CATV), remote monitoring, etc.

• Broadband Services:provisioning of broadband services, such as video request service, home study courses, medical facilities, train timetables, etc.

• High EMI areas:Along railway track, through power substations can be suspended directly from power line towers, or poles.

• Military applications:• Non-communication fiber optic:

eg.fiber sensors.


BSNLSatellite Communication overview

• Satellite is a microwave repeater in the space.

• There are about 750 satellite in the space, most of them are used for communication.

• They are:– Wide area coverage of the earth’s surface.– Transmission delay is about 0.3 sec.– Transmission cost is independent of distance.


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Satellite communication overview

• The word satellite originated from the Latin word “Satellit”- meaning an attendant, one who is constantly hovering around & attending to a “master” or big man.


BSNLComponents of Satellites

ALTTC OFC V/S SATELITE 29

BSNLHow do Satellites Work

• Two Stations on Earth want to communicate through radio broadcast but are too far away to use conventional means.

• The two stations can use a satellite as a relay station for their communication

• One Earth Station sends a transmission to the satellite. This is called a Uplink.

• The satellite Transponder converts the signal and sends it down to the second earth station. This is called a Downlink.


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BSNLHow Satellites are used

• Service Types:- Fixed Service Satellites (FSS)

• Example: Point to Point Communication Broadcast Service Satellites (BSS)

• Example: Satellite Television/Radio• Also called Direct Broadcast Service (DBS).

Mobile Service Satellites (MSS)• Example: Satellite Phones


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Types of Satellite (Based On Orbit):-

• Satellite Orbits LEO(Low Earth Orbit) MEO(Medium Earth Orbit) GEO(Geostationary Earth

Orbit) Molniya Orbit HAPs

• Frequency Bands


BSNLLow Earth Orbit (LEO)

• LEO satellites are much closer to the earth than GEO satellites, ranging from 500 to 1,500 km above the surface.

• LEO satellites don’t stay in fixed position relative to the surface, and are only visible for 15 to 20 minutes each pass.

• A network of LEO satellites is necessary for LEO satellites to be useful


BSNLMedium Earth Orbit (MEO)

A MEO satellite is in orbit somewhere between 8,000 km and 18,000 km above the earth’s surface.

MEO satellites are similar to LEO satellites in functionality.

MEO satellites are visible for much longer periods of time than LEO satellites, usually between 2 to 8 hours.

MEO satellites have a larger coverage area than LEO satellites.


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Geostationary Earth Orbit (GEO)Geostationary Earth Orbit (GEO)

These satellites are in orbit 35,863 km above the earth’s surface along the equator.

Objects in Geostationary orbit revolve around the earth at the same speed as the earth rotates. This means GEO satellites remain in the same position relative to the surface of earth. A GEO satellite’s distance from earth gives it a large

coverage area, almost a fourth of the earth’s surface. GEO satellites have a 24 hour view of a particular area. These factors make it ideal for satellite broadcast and

other multipoint applications


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Advantages of Satellite Advantages of Satellite communicationcommunication

• Mobile communication can be easily established by satellite communication.

• Satellite communication is economical compared with terrestrial communication particularly where long distances are involved.

• Compared to the optical fibre communication,satellite communication has the advantages that,quality of transmitted signal and location of sending and receiving stations are independent of distance.

• User has control over their own network.• For thin traffic remote areas,satellite communication is most

economical.•


BSNLAPPLICATIONS

Location

Mapping

Tracking

Navigation

Marine

Timings synchronizing

Search and Rescue

Airways and military

OFC V/S SATELLITE

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Comparison b/w Satellite and Optical Fibre

• OFT:- • . Cost of fiber optics communications

depends on:a. Number of channels required. b. Point-to-point link distance.c. Type of installation for example cable laying in ducts or onoverheadPower lines etc .

• Unlimited bandwidth is available (50 THz) for opticalfibers.

• Optical fibre can not use for the marine and airways and also in navigation saytem .

• Oft has the direct ratio with the cost as distance will increase the cost will also increase.

• SATALLITE :-• . Cost of the satellite is independent of

the distancefor example 1 km toA 5000 km cost remains same. Satellitecommunication is viable onlyWhen distances> 500 kilometres .

• Bandwidth is Limited for satellite communicationfor example 75MHz for each transponder.

• Satalite communication is useful in marine and also in the airways and navigation.

• Satalite have the constant relationship cost as distance will increase cost will not increase.


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Thank You

Engineering

Fibre optic communication vs satellite communication (1)