Satellite communication Basics

Satellite Communication

04/12/23 RTTC \ SATCOM 1

OVERVIEWOF

SATELLITE COMMUNICATION AND

SATELITE SYSTEM




SATE

LLIT

E

COM

MUNICATIO

N



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 SystemDeals 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



Earth

Layers of Atmosphere

Different layers of the atmosphere play a

role in propagating radio waves

18K

m

70K

m

500K

m



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 M\W Communication LOS M\W Communication

Troposphere scatter communication Troposphere scatter communication

Satellite communicationSatellite communication



Ionosphere communicationIonosphere communication

It deals with frequency range of 3-30Mhz which are classified as HF band

Alti

tude

(K

m)

Electron density

F1

F2

ED

IONOSPHERE

EarthT R R



LOS M\W CommunicationLOS M\W 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



d0 Optical horizon

dr radio horizon

OPTICAL & RADIO HORIZON

A Microwave link

A B

R R



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



50Km

10000Km

750Km

Troposphere scatter

1500Km

Ionosphere Reflection

SATELLITE

COMMUNICATIO

N



Earth

Global Coverage



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



Sat. Com Network

1. Space Segment

Upl

ink

Downlink

2. Ground Segment



Sat. Com Network

Frequency for space communication depends on

1. Band width required

2. Noise consideration

3. Propagation factor

4. TechnologyMost 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



59000-64000Mhz & 54000-58000Mhz59000-64000Mhz & 54000-58000MhzV Band V 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 – 27500-30000Mhz & 17700 – 21200Mhz21200Mhz

““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



Equator

4000miles

A

35786KmB

Geographical Advantage

Time Delay

Upl

ink

3578

6Km

250m

sec

Downlink 35786Km

250msec



Geostationary Satellite

Altitude:35786KmDirection :moves in eastern direction as earth

Period of revolution is 23Hr 56min34sec

EquatorEquator



Broadcasting mode of operation



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.



The choice of orbit is restricted to three basic types.

1.polar,

2.equatorial

3. inclined



Communication SystemsCommunication Systems Satellite communication systems are Satellite communication systems are

classified classified 1.Communication system

Multiplexed telephone channels with one (i) carrier frequency system, and (ii) Single channel per carrier system.

2.Modulation systemAnalog modulation (Frequency Modulation system),

and Digital modulation system



3.System configurationPre–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;



Types of Multiple Access

Frequency Division Multiple Access (FDMA)

Time Division Multiple Access (TDMA)

Code Division Multiple Access (CDMA)



1. FDMA36Mghz36Mghz

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



1. FDMA

A-B A-C A-D

Station AFM

SatelliteABCD ABCD

FM FM FM

Station C

DA B

A-C



TDMA

P B C D

PSKTDMABUFFER

TIMING INFORMATION

To UP-Converter

B

C

D



TDMA

P B C D

PSKTDMABUFFER

TIMING INFORMATION

To Down-Converter

B

C

D

P A B D P A C B



EQUIPMENT CONFIGURATION OFCOMMUNICATION



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.



Major support subsystems include :

Structure

Attitude and orbit control systems

Electrical power system

Thermal control system

Telemetry and Telecommand system

