Chap 1 Introduction to Satellite Communications

7/28/2019 Chap 1 Introduction to Satellite Communications

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SATELLITECOMMUNICATION

CHAPTER I

INTRODUCTION


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Picture Gallery


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Satellite

What is satellite ??

Why we need satellite ??


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History Sat comm began in Oct 1957.

- launch by USSR

- called as Sputnik I

- 1st artificial earth satellite

- carries only transmitter

Explorer 1

- launch by US from Cape Canaveral

on Jan 31, 1958.

ECHO I and II- launch by AT&T on Aug 12, 1960

and Jan 25, 1964.

- Orbiting balloons 100 ft in diameter

- Operate like radar reflector

- very low orbit


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Telstar I and II

- launched by Bell on July 10,1962 and May

7,1973.- low orbit

- broadband real time transponder.

On July 24, 1961, US President JFK defined thegeneral guideline ofUS policy in regard to satcomm.

On Dec 20, 1961, US congress recommended theInternational Telecommunication Union (ITU)

The 1st successful geosynchronous comm satdeveloped by Comsat for Intelsat.

- launched inApr 6, 1965 remain until 1969.

- routine operation betn US and Europe.- weighed mere 36 kg.

- with 25 MHz bandwidth for each transponder.

- using 6/4 GHz frequency.


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Canada was the 1st country to build thenational telecomm syst using GEO satellite

(Anik 1A launched in May 1974).

1970 and 1980s there was rapiddevelopment of GEO satellite syst forinternational, regional and domestic

telephone traffic and video distribution

Inmarsat (International Maritime satelliteOrganization) had been recognized to

provide service to ship and aircraft.

With these spacecraft, the modern era ofsatellite communication had begun.


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See attachment GEO satellite

system
http://localhost/var/www/apps/conversion/tmp/scratch_5/list%20of%20satellite%20in%20geo.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_5/list%20of%20satellite%20in%20geo.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_5/list%20of%20satellite%20in%20geo.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_5/list%20of%20satellite%20in%20geo.docx


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Satellites in Malaysia


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MEASAT

Since 1996, MEASAT has provided reliable satellitesolutions to customers across the Asia-Pacific region.

MEASAT today owns and operates three satellites,

MEASAT-1 (91.5E), MEASAT-2 (148E) and MEASAT-3 also at (91.5E).

providing high quality C-band coverage across SouthEast Asia, into Greater China, South Asia, Australia andthe United States.

With satellites designed to cut through the high tropicalrainfall, these satellites also provide DTH quality Ku-band coverage into Malaysia, IndoChina, Taiwan,Indonesia, the Philippines and Australia.


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MEASAT SATELITE FLEET

MEASAT 1-C-BAND

MEASAT 1-Ku-BAND

MEASAT 2-C-BAND

MEASAT 2-Ku-BAND MEASAT 3-C-BAND

MEASAT 3-Ku-BAND

For Further details go to:

http://www.measat.com.my
http://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT%20c%20band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT%20ku%20band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-2%20C-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-2%20Ku-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-3%20C-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-3%20Ku-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-3%20Ku-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-3%20Ku-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-3%20Ku-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-3%20Ku-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-3%20Ku-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-3%20C-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-3%20C-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-3%20C-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-3%20C-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-3%20C-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-2%20Ku-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-2%20Ku-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-2%20Ku-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-2%20Ku-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-2%20Ku-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-2%20C-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-2%20C-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-2%20C-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-2%20C-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT-2%20C-Band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT%20ku%20band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT%20ku%20band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT%20ku%20band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT%20ku%20band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT%20ku%20band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT%20c%20band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT%20c%20band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT%20c%20band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT%20c%20band.dochttp://localhost/var/www/apps/conversion/tmp/scratch_5/MEASAT%20c%20band.doc


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Others

Tiungsat 1 by ATSB

Tiungsat

RazakSat
http://localhost/var/www/apps/conversion/tmp/scratch_5/AMSAT%20-%20TiungSat-1.htmhttp://localhost/var/www/apps/conversion/tmp/scratch_5/Tiungsat%20pic.htmhttp://localhost/var/www/apps/conversion/tmp/scratch_5/RazakSat.htmhttp://localhost/var/www/apps/conversion/tmp/scratch_5/RazakSat.htmhttp://localhost/var/www/apps/conversion/tmp/scratch_5/Tiungsat%20pic.htmhttp://localhost/var/www/apps/conversion/tmp/scratch_5/AMSAT%20-%20TiungSat-1.htm


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INTRODUCTION

What is satellite comm??

is a syst in which an e/s transmitradio waves via antenna to a comm

sat that has been put into orbit~35800 km above the equator.

How it operates??

sat rx radio signal then convert the

freq, amplify the signal by on-boardtransponder and then send themback to an e/s in another country.


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What is satellite??- is a celestial body that orbit around planet.- space vehicle launched by human and orbits

earth Act as relay station in space, enabling comm

to take place betn countries separated from each

other by vast distance.

There are three main operation by the satellite:

1. receive signal

2. amplify

3. retransmit back the signal

Sat comm operate in wide range of freq ranging

from 1 GHz to 50 GHz.


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Satellite Frequency Band

L Band 1 & 2 GHz

S Band 2 & 3 GHz

C Band 3.5 & 7.5 GHz Ku Band 11 & 14 GHz

Ka Band 20 & 30 GHz


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Satellite Positioning In GEO

Orbit

The signal emitted by a satellite can coverabout 1/3 of the earth surface

Therefore it is possible to cover the wholeearth by positioning satellite in 3 regions.

Atlantic

Ocean

Pacific Ocean

Indian

Ocean


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Basic Terms

Apogee the point in an orbit that is located farthest fromearth.

Perigee the point in an orbit that located closest to theearth

Major axis the line joining the perigee n apogee throughthe center of earth

Minor axis the line perpendicular to the major axis halfwaybetween the perigee and apogee.

Angle of inclinationthe angle betn the earths equatorialplane and the orbital plane

Ascending node - measured ccw at the point in the orbit

where it crosses the equatorial plane traveling from S to N. Descending node - the point where an inclined orbit crosses

the equatorial plane traveling from N to S.

Lines of nodes line joining the ascending and descendingnodes.


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Satellite Orbits

There are 3 types of orbital paths:

i. Equatorial (0)

ii. Polar (90)

iii. Inclined (0- 180)

2 types of orbit rotations

i. Prograde/ posigrade orbit sat orbit same direction

with earth n angular velocity greater than earth

(s> e)

ii. Retrograde orbit sat orbit opposite direction asearths rotation n angular velocity less than earth

(s< e).


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The orbits that basically used

for communication are:

i. LEO Low Earth Orbit

ii. MEO Medium Earth Orbit

iii. GEO Geostationary Orbit

iv. HEO Highly Elliptical Orbit

Satellite Elevation Categories


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Orbits Pros and Cons

LEO

World wide homogeneous with high elevation

angle. High no. of sat.

Low launch cost per sat.

Large inbuilt syst reliability

Small propagation delay (5 -15 ms gtg). Frequent handover (one every 5 10 min)

Orbital height: less than 2000 km.


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MEO

World wide homogeneous with minimum

elevation angle.

Limited no. of sat.

High launch cost per sat. Higher propagation delay (75 -100 ms gtg).

Frequent handover (one every 1 2 hours)

Orbital height: 10300 km.


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GEO

World wide coverage except polar region with

3 sat only.

Low elevation angle.

High launch cost per sat. small inbuilt syst reliability.

Large propagation delay (250 ms gtg).

Require large sat antenna.

Orbital height: 35780 km.


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Orbits Coverage

GEO

MEO

LEO


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Satellite System

Consists of:

i. Uplinkii. Downlink

iii. Transponder (satellite)


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Satellite System Uplink

Model

Modulator BPFBasebandsignal

Mixer

Generator

BPF HPA

Up- converter

IF RF

RF

At (e/s) transmitter


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Satellite System

Transponder Model

LNABPF Mixer

Oscillator

BPF TWT

Frequency Translator

RF RF

RF

At transponder in the satellite


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Satellite System

Downlink Model

At (e/s) receiver

LNABPF DemodulatorMixer

Generator

BPF

Down-converter

RF IF

RF Baseband

out


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Satellite Communication

Architecture

Control Segment

1. Interface station

Intersatellite link

2. User station

3. Service station

4. TTC station

5. Network management

station

Ground Segment

Gateway vsat Hub

Terrestrial

Network

User

Terminal

User

Terminal

To/from

service

provider

2 3 4

5 6

Space Segment

1


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The satellite communication architecture is composed of

space segment, a control segment and a ground

segment.

Space segment- contains one or several active and

spare sat organized in a constellation.

Control segment consists of all ground facilities for

the control n monitoring of the sat for management of the

traffic n resource onboard the sat.

Ground segment consists of all traffic e/s dependingon the type of service considered.

CONTINUED


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Space Segment

Include the sat and also the ground facilities.

Consists of - payload equipment used to provide the

service.

- bus - vehicle carries the payload and

other systems.

- power, altitude control, orbital

control, thermal control and

TT&C.

Transponder equipment for communications satellite

- main section of payload


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SatelliteSubsystem

Power supply

Altitude Control

Station Keeping Thermal Control

TT&C

Communication Subsystem- transponder Antenna subsystem


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Power Supply

Primary electrical power foroperating the electronic

equipment.

Obtained from solar panel.

Used array cells in series parallel connection togenerate more power.

Rectangular solar sails developed by HughesSpace (HS 601) designed to provide dc power from

2 to 6 kW. Nickel-Cadmium (Ni-Cd) and nickel-hydrogen (Ni-

H2)batteries used as backup power supply.


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Altitude Control

Orientation in space.

To ensure that directional antennas point in the

proper directions.

The altitude control take place aboard the satbut it also possible for control signals to be

transmitted from earth based on the data

obtained from the sat.


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Station Keeping

For GEO sat be kept in its correctorbital slot.

The equatorial ellipticity of theearth causes GEO sat to driftslowly along the orbit.

to counter the drift, an oppositelydirected velocity component isimparted to the sat by jets whichare pulsed once every 2 or 3weeks.


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Thermal Control

The sats equipment should operate as

nearly as possible in the stable

temperature environment.

The radiation mirrors are used to remove

heat from the comm payload.

Used thermal blankets and shields to

provide insulation.

Heaters may be switched on to make up

for the heat reduction which occurs whentransponder are switched off.


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TT&C

Telemetry, Tracking, Command andMonitoring (TT&C).

Partly on sat and partly at the controlling e/s.

The telemetry sends data derived from many

sensors on the sat, which monitor the satshealth (telemetry links).

Tracking system at the e/s provides info onthe range, the elevation and azimuth anglesof the orbital elements.

Based on the data from the telemetry, thecontrol system is used to correct the positionand altitude of the sat.


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Antenna Subsystem

Antennas carried onboard provide dual fxns: rx

the uplink signals and tx the downlink signals.

Normally used dipole type where

omnidirectionals characteristics are required for

TV relays and broadcast.

Paraboloidal reflector antenna is the most

common used


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Communication

Subsystem

Composed of 1 or more antennas which rx and

tx over wide range of freq.

Rx and tx amplify and retransmit the incomingsignal.

Rx and tx units on the sat are known as

transponder- main part of the comm subsystem.


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CONTINUED - Transponder is the series interconnected units which

forms a single comm channel between the rx and tx antennas in acomm sat.

Example:

The 500 MHz bw is divided up into channels, often 36 MHz wide,which are each handled by a separate transponder. (12transponders).

By making use of polarization isolation, this number can be doubled.

Polarization isolation refers to the fact that the carries, which may be

on the same freq but with opposite senses of polarization. It can beisolated from one another by rx antennas matched to the incomingpolarization.


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Example:Linear Polarization => carriers are separated

vertically and horizontally polarized.

Circular Polarization => carriers are separated

left hand circular and right hand circular

polarization.

Bcos the carriers with opposite senses of

polarization can be overlap in freq, the use of bwcan be doubled.

This is called as frequency reuse.

CONTINUED - Transponder


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Frequency reuse


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From figure 7.13 in the handout, the uplink

freq range is 5.925 to 6.425 GHz.

The i/p filter passes the full 500MHz bandto common rx while rejecting out noise and

interference.

Then passes through wideband rx b4 it isdemultiplex into 12 channel transponder.

EXAMPLE

Fi S t llit


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Figure Satellite

Transponder Channel

Figure 7.13 in handout


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Wideband Receiver

All the carriers within 500 MHz will be amplified and freqconverted in the common receiver.

The freq conversions shift the carriers to the downlink

freq band which is also 500 MHz wide extending from3.7 to 4.2 GHz.

The amp adds little noise an in the same time providessufficient amplification for the carriers to override thehigher noise level present in the following mixer stage.

The LNA feeds into mixer stage which also requires localoscillator to the mixer.

The oscillator freq must be highly stable and low phasenoise.

The 2nd amp will amplify the carriers again and send the

carrier to input demultiplexer.

Fi Wid b d


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Figure Wideband

Receiver

Figure 7.14 in handout

Chap 1 Introduction to Satellite Communications

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