Basics of SATELLITE COMMUNICATION

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OVERVIEW
OF
SATELLITE COMMUNICATION
AND
SATELITE SYSTEM

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3. Satellite Communication
SATELLITE
CO
M
M
UNICATIO
N

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Transmission System
can be placed under three broad categories
 Radio SystemRadio System
 Co-axial cable systemCo-axial cable system
 Optical fibre systemOptical fibre system
Radio SystemRadio System
Deals with electronic radiation of electromagnetic
energy from one point to another through
atmosphere or free space
It is possible only in certain portion of frequency
spectrum
Frequency from 9Khz to 400Ghz

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Earth
Layers of Atmosphere
Different layers of the atmosphere play a
role in propagating radio waves
18Km
70Km
500Km

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Ionosphere and troposphere are useful
for radio communication in certain
frequency range
Radio communication can be placed
under four categories
Skywave or Ionosphere communicationSkywave or Ionosphere communication
LOS MW CommunicationLOS MW Communication
Troposphere scatter communicationTroposphere scatter communication
Satellite communicationSatellite communication

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Ionosphere communicationIonosphere communication
It deals with frequency range of 3-30Mhz
which are classified as HF band
Altitude(Km)
Electron density
F1
F2
E
D
IONOSPHERE
EarthT R R

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LOS MW CommunicationLOS MW Communication
IS CHARCTERSIED BY
► the useful range of frequencies lie between 150Mhz-
150Ghz
► it is line of sight communication limited by horizon due
to the curvature of the earth
► Signal propagation is affected by free space attenuation
► Frequency / Phase modulation technique are employed
► Spread spectrum or Time sharing techniques are used

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d0 Optical horizon
dr radio horizon
OPTICAL & RADIO HORIZON
A Microwave link
A
B
R R

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Troposphere scatter communicationTroposphere scatter communication
 Are single hop systemAre single hop system
 Operates over length greater than LOS distanceOperates over length greater than LOS distance
Scatter region
Atmospheric turbulence and local variation of
refractive index in the tropospheric region causes
scattering of electromagnetic waves

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50Km
10000Km
750Km
Troposphere
scatter
1500Km
Ionosphere
Reflection
SATELLITE
CO
M
M
UNICATIO
N

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Earth
Global Coverage

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Advantages Of Sat. Com
1. Large Coverage Area
2. High Quality
3. High Reliable
4. High Capacity
5. Flexibility
6. Easy For installation
7. Emergency Communication
8. Point to Multipoint transmission

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Sat. Com Network
1. Space Segment
Uplink
Downlink
2. Ground Segment

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Sat. Com Network
Frequency for space communication depends on
1. Band width required
2. Noise consideration
3. Propagation factor
4. Technology
Most of the sat.Com uses 6/4Ghz frequency band
1. Less Atmospheric Absorption2. Less noise both galactic and manmade3. Less Space loss compared to high frequency

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59000-64000Mhz & 54000-58000Mhz59000-64000Mhz & 54000-58000MhzV BandV Band
Inte.SatInte.Sat
40000-51000Mhz & 40000-41000Mhz40000-51000Mhz & 40000-41000MhzV BandV Band
INSATINSAT6725-7025Mhz & 4500-4800Mhz6725-7025Mhz & 4500-4800MhzExt “C”BandExt “C”Band
27500-30000Mhz & 17700 – 21200Mhz27500-30000Mhz & 17700 – 21200Mhz““K”BandK”Band
14000-14500 & 10950-11200Mhz14000-14500 & 10950-11200Mhz
11450-11700Mhz11450-11700Mhz
““Ku” BandKu” Band
7900-8400Mhz &7250-7750Mhz7900-8400Mhz &7250-7750Mhz““X” BandX” Band
INSATINSAT5925-6425Mhz & 3700-4200Mhz5925-6425Mhz & 3700-4200Mhz““C” BandC” Band
INSATINSAT2500-2700Mhz2500-2700Mhz““S” BandS” Band
1830-2700Mhz1830-2700Mhz““L” BandL” Band
Frequency band for Sat. Com

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Equator
4000miles
A
35786KmB
Geographical Advantage
Time Delay
Uplink35786Km
250msec
D
ow
nlink
35786K
m
250m
sec

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Geostationary Satellite
Altitude:35786Km
Direction :moves in eastern direction as earth
Period of revolution is 23Hr 56min34sec
Equator

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Broadcasting mode of operation

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Kinds of Communication Satellites
depends on type of orbit and freq. band used.
Communication Satellite can be classified by the
orbit used and also by frequency band used.
natural laws that control the movement of satellites.
These are based on Kepler's laws
1.The orbit plane of any earth satellite must bisect
the Earth centrally.
2.The Earth must be at the centre of any orbit.

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The choice of orbit is restricted to three basic types.
1.polar,
2.equatorial
3.inclined

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Communication SystemsCommunication Systems
 Satellite communication systems areSatellite communication systems are
classifiedclassified
1.Communication system
Multiplexed telephone channels with one
(i) carrier frequency system, and
(ii) Single channel per carrier system.
2.Modulation system
Analog modulation (Frequency Modulation system),
and
Digital modulation system

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3.System configuration
Pre–assignment system
Demand assignment system, and
MULTIPLE ACCESS TECHNIQUES
the number of earth stations to be
interconnected is such larger than the number of
transponders
the capacity of a transponder is much more
than what is required between a pair of earth
stations;

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Types of Multiple Access
 Frequency Division Multiple Access (FDMA)
 Time Division Multiple Access (TDMA)
 Code Division Multiple Access (CDMA)

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1. FDMA
36Mghz36Mghz
E/S DE/S DE/S CE/S CE/S BE/S BE/S AE/S A
 Transponder BW is divided into smaller
frequency bands and assigning them to
different E/S
 E/S transmitting the carriers towards the
satellite within the assigned frequency bands
 Retransmitting the carriers from satellite after
frequency translation and amplification by a
common transponder
 E/S receives all the carriers which contain
telephony channels meant for the E/S

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1. FDMA
A-B A-C A-D
Station A
FM
Satellite
ABCD ABCD
FM FM FM
Station C
DA B
A-C

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TDMA
P B C D
PSKTDMA
BUFFER
TIMING
INFORMATION
To UP-Converter
B
C
D

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TDMA
P B C D
PSKTDMA
BUFFER
TIMING
INFORMATION
To Down-Converter
B
C
D
P A B D P A C B

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EQUIPMENT CONFIGURATION
OFCOMMUNICATION

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SPACE SEGMENT
A satellite consists of essentially two parts
 Communication payload
 Support subsystems
Communication payload for communication
satellites comprises
1.communication transponders
2.transmit/receive antennas.

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 Major support subsystems include :
 Structure
 Attitude and orbit control systems
 Electrical power system
 Thermal control system
 Telemetry and Telecommand system

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