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DIGITALSATELLITECOMMUNICATIONS

MSCCOURSE

Prepared by :

Nisreen Bashar AL-Madanat

Under supervision of :

Dr.Ibrahm AL-Qatawneh


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OUTLINES Objectives

Introduction

Principle of Satellite Communication

Basics of Satellites

Types of Satellite

Sources of Impairment

Frequency bands

Satellite Network Configurations

Capacity Allocation

Types of satellite categories

Application of satellite communication

Satellite Applications Overview Summary

References


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OBJECTIVES

After completing this lecture the student will be able to :

o Discuss the concept of digital satellite communications and itsmain principle.

o Describe how does a satellite communication works.

o Build the main block diagram of the earth station andfunctioning transponder.

o Discuss the advantages and disadvantage of satellite system.

o Identify satellites main factors , parameters and impairments.

o Identify the basic types of satellites .

o Got awareness of the frequency bands and their applications .

o Distinguish the satellite network configurations .

o Discuss the capacity allocation .

o Identify satellite categories and orbits.

o Mention its applications and how satellites are used .


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INTRODUCTION:-

The use of satellite in communication systems has become very

common now - a- days. This is because the satellite can see a

very large area of the earth.

Hence satellites can form a star point of a communication net, to

link many users together, simultaneously. This will include users

widely separated geographically.

A communication satellite is a station in space that is used for

telecommunication, radio and television signals.

The construction and launch cost of a satellite are extremely high.

These costs are distance insensitive, that means the cost of a

short distance satellite link is approximately same as that of along distance link.

Therefore a satellite communication system is economical only

where the system is used continuously and a large number of

users use it.


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PRINCIPLEOFSATELLITECOMMUNICATION

A geostationary communication satellite is basically a

relay station in space.

It receives signal from one earth station, amplifies it,

improves the signal quality and radiate the signal back to

other earth stations. Such a relay system allows us to communicate with any

corner of the world.

Satellite System: The use of orbiting satellites to relay

transmissions from one satellite dish to another or multiple

dishes.


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BASICS:HOWDOESASATELLITE

COMMUNICATIONWORK?

Two Stations on Earth want to communicate through radio

broadcast but are too far away to use conventional means.

An Earth Station sends message in GHz range. (Uplink)

Satellite Receive and retransmit signals back (Downlink)

Other Earth Stations receive message in useful strengtharea

Main Earth Station is in Delhi, Kolkata, Chennai, Mumbai

and Shilling


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EARTHSTATIONBLOCKDIAGRAM

Functioning of Transponder

TO /FROM EARTH STATION


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BASICS: ADVANTAGESOFSATELLITES

The advantages of satellite communication

over terrestrial communication are:

The coverage area of a satellite greatly exceeds

that of a terrestrial system.

Transmission cost of a satellite is independent of

the distance from the center of the coverage area. Satellite to Satellite communication is very

precise.

Higher Bandwidths are available for use.


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BASICS: DISADVANTAGESOFSATELLITES

The disadvantages of satellite communication:

Launching satellites into orbit is costly. Satellite bandwidth is gradually becoming used up.

There is a larger propagation delay in satellite

communication than in terrestrial communication.


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BASICS: FACTORSINSATELLITE

COMMUNICATION

Elevation Angle: The angle of the horizontal of the earth

surface to the center line of the satellite transmission

beam.

This effects the satellites coverage area. Ideally, you want a

elevation angle of 0 degrees, so the transmission beam

reaches the horizon visible to the satellite in all directions.

However, because of environmental factors like objects

blocking the transmission, atmospheric attenuation, and

the earth electrical background noise, there is a minimum

elevation angle of earth stations.


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COMMUNICATION(CONT.)

Coverage Angle: A measure of the portion of the earth

surface visible to a satellite taking the minimum elevation

angle into account.

R/(R+h) = sin(/2 - - )/sin( + /2)

= cos( + )/cos()

R = 6370 km (earths radius)

h = satellite orbit height = coverage angle

= minimum elevation angle


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COMMUNICATION(CONT.)

Other impairments to satellite communication:

The distance between an earth station and a satellite (free

space loss).

Satellite Footprint: The satellite transmissions strength is

strongest in the center of the transmission, and decreases

farther from the center as free space loss increases.

Atmospheric Attenuation caused by air and water can impair

the transmission. It is particularly bad during rain and fog.


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BASICS: HOWSATELLITESAREUSED

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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TYPESOFSATELLITES

Satellite Orbits

GEO

LEO MEO

Molniya Orbit

HAPs

Frequency Bands


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SATELLITEORBITS

In space, satellites move in

certain specific paths. Thesepaths are called as orbits.

A result stays in an orbit

because the two forces acting on

it namely the centripetal force

and the gravitational force are

equal.

The selection of a particular

orbit depends on the following

factor:

Transmission path loss. Earth coverage area.

Delay time.

Time period for which the

satellite should be visible.


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GEOSTATIONARYEARTHORBIT(GEO)

These satellites are in orbit 35,863 km above the earths

surface along the equator.

Objects in Geostationary orbit revolve around the earth atthe same speed as the earth rotates. This means GEO

satellites remain in the same position relative to the

surface of earth.


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GEO (CONT.)

Advantages

A GEO satellites distance from earth gives it a large coverage area,

almost a fourth of the earths surface.

GEO satellites have a 24 hour view of a particular area.

These factors make it ideal for satellite broadcast and other multipointapplications.

Disadvantages

A GEO satellites distance also cause it to have both a comparatively

weak signal and a time delay in the signal, which is bad for point to

point communication.

GEO satellites, centered above the equator, have difficulty broadcasting

signals to near polar regions


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LOWEARTHORBIT(LEO)

LEO satellites are much closer to the earth than GEO

satellites, ranging from 500 to 1,500 km above the surface.

LEO satellites dont stay in fixed position relative to thesurface, and are only visible for 15 to 20 minutes each pass.

A network of LEO satellites is necessary for LEO satellites

to be useful


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LEO (CONT.)

Advantages

A LEO satellites proximity to earth compared to a GEO satellite

gives it a better signal strength and less of a time delay, which

makes it better for point to point communication.

A LEO satellites smaller area of coverage is less of a waste of

bandwidth.

Disadvantages

A network of LEO satellites is needed, which can be costly

LEO satellites have to compensate for Doppler shifts cause by

their relative movement.

Atmospheric drag effects LEO satellites, causing gradual orbital

deterioration.


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MEDIUMEARTHORBIT(MEO)

A MEO satellite is in orbit somewhere between 8,000 km

and 18,000 km above the earths 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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MEO (CONT.)

Advantage

A MEO satellites longer duration of visibility and wider

footprint means fewer satellites are needed in a MEO

network than a LEO network.

Disadvantage

A MEO satellites distance gives it a longer time delay and

weaker signal than a LEO satellite, though not as bad as a

GEO satellite.


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OTHERORBITS

Molniya Orbit Satellites

Used by Russia for decades.

Molniya Orbit is an elliptical orbit. The satellite remains ina nearly fixed position relative to earth for eight hours.

A series of three Molniya satellites can act like a GEO

satellite.

Useful in near polar regions.


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OTHERORBITS(CONT.)

High Altitude Platform (HAP)

One of the newest ideas in satellite communication.

A blimp or plane around 20 km above the earths surface is

used as a satellite.

HAPs would have very small coverage area, but would have

a comparatively strong signal.

Cheaper to put in position, but would require a lot of themin a network.


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SOURCESOFIMPAIRMENT

Distance between earth and satellite

Atmospheric Attenuation

Terrestrial Distance between the receiving antenna andthe aim point of the satellite (Satellite Footprint)

Distances and Free Space Loss

dB98.21)log(20)log(20LdB d

GEO: Losses at the equator

dB07.173)log(20LdB GEO: Losses at maximum distance (horizon) d=42711 Km)

dB59.174)log(20LdB


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DISTANCESANDFREESPACELOSS

1500 km - LEO

12000 km - MEO


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SATELLITEFOOTPRINT

Satellite Footprint: In geostationary orbit, communications satellites

have direct line-of sight to almost half the earth - a large "footprint"

which is a major advantage. A signal sent via satellite can be

transmitted simultaneously to every U.S. city. Multiple downlinks can be

aimed at one satellite and receive the same program; called point to

multipoint.


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SATELLITENETWORKCONFIGURATIONS

Point to Point

Broadcast


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SATELLITENETWORKCONFIGURATIONS

Sub-Type of Broadcast : VSAT (very

small aperture terminal)

Subscribers use low cost VSAT

antenna. Stations share a satellite

transmission

capacity for transmission to a hub

station

Hub can exchange messages withthe subscribers and relay messages

between the subscribers


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CAPACITYALLOCATION

FDMA

FAMA-FDMA

DAMA-FDMA

TDMA

Advantages over FDMA

CDMA


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FDMA

Satellite frequency is already broken into bands, and isbroken in to smaller channels in Frequency Division

Multiple Access (FDMA).

Overall bandwidth within a frequency band is increased

due to frequency reuse (a frequency is used by two carriers

with orthogonal polarization).

The number of sub-channels is limited by three

factors:

Thermal noise (too weak a signal will be effected by

background noise).

Intermodulation noise (too strong a signal will cause noise).

Crosstalk (cause by excessive frequency reusing).


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FDMA (CONT.)

FDMA can be performed in two ways:

Fixed-assignment multiple access (FAMA): The sub-

channel assignments are of a fixed allotment. Ideal for

broadcast satellite communication.

Demand-assignment multiple access (DAMA): The sub-

channel allotment changes based on demand. Ideal for

point to point communication .


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FREQUENCYDIVISIONMULTIPLEXING

Satellite squeezes 24 channels in 500 MHz using

frequency reuse


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TDMA

TDMA (Time Division Multiple Access) breaks a

transmission into multiple time slots, each one dedicated to

a different transmitter.

TDMA is increasingly becoming more widespread insatellite communication.

TDMA uses the same techniques (FAMA and DAMA) as

FDMA does.


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TDMA (CONT.)

Advantages of TDMA over FDMA.

Digital equipment used in time division multiplexing is

increasingly becoming cheaper.

There are advantages in digital transmission techniques.Ex: error correction.

Lack of intermodulation noise means increased efficiency.


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FAMA-TDMA OPERATION

UPLINK DOWNLINK


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COMMUNICATIONSATELLITE

Geostationary satellites when used for the communication

application are called communication satellite.

They are used in applications such as point to point

communication radio broadcasting, TV transmission,

military application, Commercial application.

Communications satellites are classified based on the

coverage are as global, regional or domestic satellites.

A term INTELSAT is often used in satellite

communication. INTELSAT means International

Telecommunication Satellite.

These are communication satellites which are used for

communication of telephony, computer data, TV signals

etc More than 140 nations are interconnected via the

INTELSAT system.


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WEATHERSATELLITE

These satellites are used for weather prediction, for taking

the photographs of clouds. TIROS-1 was the first weather

satellite. Other weather satellites are Nimbus and

Meteosat.

Indias INSAT satellite is being used for three

application i.e. communications. TV transmission and

meteorology or weather prediction. Thus it is s

multipurpose satellite.


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REMOTE-SENSINGSATELLITES

This type of satellites can be used to find out the

condition of crops , forests or minerals

underground , condition of soil etc. Indian

satellite IRS is a remote sensing satellite.

From the information obtained from the remotesensing satellite detailed maps can be prepared.


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SCIENTIFICSATELLITE

These satellites are relatively simpler and of

short life span.

They are used to carry out various scientific

studies. Indias Aryabhatta was a scientific

satellite.


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APPLICATIONOFSATELLITECOMMUNICATION

The main application of satellite communication is in the

field of communication. The communication of video signals

(TV), audio signals (telephones, satellites phones) and

computer data (internet).

To gain meteorological or weather information. The

photographs taken by the satellites are analyzed for

predicting weather.

To monitor the status of earths resources such as land,

forests and oceans. We can get very important information

about crops, lakes, rivers, forests, fire etc

To spot our mineral resources, polluted areas, sources of

pollution etc.


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SATELLITEAPPLICATIONSOVERVIEW

Systems using geostationary satellites:

Inmarsat (International Maritime Satellite Organization)

used for voice, data, especially for ships worldwide except

Polar Regions.

MSAT (Mobile Satellite) used for voice data, mainly forland mobile western hemisphere.

Systems using low-earth-orbit (LEO) satellite:

Iridium: major uses are voice, paging, low speed data.

Globalstar: major uses are voice paging, low speed date.

Teledesic: major uses high speed data, voice.


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SATELLITEAPPLICATIONSOVERVIEW

(CONT.)

Systems using little LEO satellite:

ORBCOMM: major uses are paging, short messaging, e-mail,

vehicle location.

LEO: one major uses are paging, short messaging, e-mail vehicle

location.

E-sat: major uses are remote meter reading.

Systems using Medium earth orbit (MEO):

Ellipso: major uses are voice communication using portable and

mobile terminals.

ICO (Intermediate Circular Orbit): major uses are satellite to

mobile links.


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SUMMARY


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REFERENCES

Satellite Communications Systems: Systems, Techniques

and Technology (5thedition ) byMichel Bousquet

Satellite communication systems(3rdedition) by B.G.Evans

Fundamentals of Satellite Communications, by Howard

Housman/President-MITEQ, Inc. Hauppauge, NY11788/May 29, 2008

Satellite Communications CSC 490:

Wireless Networking /Author: Michael Charles

Telecommunications Glossary

from "A Technical Guide to Teleconferencing and Distance

Learning," 3rd edition
http://www.amazon.com/s/ref=ntt_athr_dp_sr_2?_encoding=UTF8&field-author=Michel%20Bousquet&search-alias=books&sort=relevancerankhttp://www.amazon.com/s/ref=ntt_athr_dp_sr_2?_encoding=UTF8&field-author=Michel%20Bousquet&search-alias=books&sort=relevancerankhttp://www.amazon.com/s/ref=ntt_athr_dp_sr_2?_encoding=UTF8&field-author=Michel%20Bousquet&search-alias=books&sort=relevancerankhttp://www.amazon.com/s/ref=ntt_athr_dp_sr_2?_encoding=UTF8&field-author=Michel%20Bousquet&search-alias=books&sort=relevancerank


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THANKYOUFORYOURTIME

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