Sat com

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Satellite Communications
Communication System
Dr. Muhammad Saleem Awan

Satellites
 Satellites are man-made objects or vehicles
intended to orbit the Earth, the moon, or
another celestial body....

Overview
 Basics of Satellites
 Types of Satellites
 Capacity Allocation

Basics: How do Satellites Work
 Two Stations on Earth want to communicate through
radio broadcast but are too far away to...

Basics: Advantages of Satellites
 The advantages of satellite communication
over terrestrial communication are:
 The cov...

Basics: Disadvantages of Satellites
 The disadvantages of satellite communication:
 Launching satellites into orbit is c...

Basics: Factors in satellite
communication
 Elevation Angle: The angle of the horizontal of the
earth surface to the cent...

Basics: Factors in satellite
communication (cont.)
 Coverage Angle: A measure of the portion of
the earth surface visible...

Satellites & Probes
Satellites and probes can be classified into
three groups, as follows:
 1. those that observe the Ear...

Types of Satellites
 Communications satellite - provides fast
radio, telephone and TV communications
 Weather satellite ...

 mapping satellite - takes pictures of the Earth
and make exact maps (in the absence of
clouds)
 surveillance satellite ...

Basics: Factors in satellite
communication (cont.)
 Other impairments to satellite communication:
 The distance between ...

Basics: How Satellites are used
 Service Types
 Fixed Service Satellites (FSS)
• Example: Point to Point Communication
...

Types of Satellites
 Satellite Orbits
 GEO
 LEO
 MEO
 Molniya Orbit
 HAPs
 Frequency Bands

Geostationary Earth Orbit (GEO)
 These satellites are in orbit 35,863 km above
the earth’s surface along the equator.
 O...

GEO (cont.)
 Advantages
 A GEO satellite’s distance from earth gives it a
large coverage area, almost a fourth of the ea...

GEO (cont.)
 Disadvantages
 A GEO satellite’s distance also cause it to have
both a comparatively weak signal and a time...

Low Earth Orbit (LEO)
 LEO satellites are much closer to the earth than GEO
satellites, ranging from 500 to 1,500 km abov...

LEO (cont.)
 Advantages
 A LEO satellite’s proximity to earth compared to a
GEO satellite gives it a better signal stren...

LEO (cont.)
 Disadvantages
 A network of LEO satellites is needed, which can
be costly
 LEO satellites have to compensa...

Medium Earth Orbit (MEO)
 A MEO satellite is in orbit somewhere between 8,000
km and 18,000 km above the earth’s surface....

MEO (cont.)
 Advantage
 A MEO satellite’s longer duration of visibility and
wider footprint means fewer satellites are n...

Other Orbits
 Molniya Orbit Satellites
 Used by Russia for decades.
 Molniya Orbit is an elliptical orbit. The satellit...

Other Orbits (cont.)
 High Altitude Platform (HAP)
 One of the newest ideas in satellite
communication.
 A blimp or pla...

COMMUNICATION SYSTEM
APPLICATIONS
 COMPONENTS
– USER/TRANSMITTER SEGMENT
– TRANSMISSION MEDIUM
– USER/RECEIVER SEGMENT
 ...

COMMUNICATION SYSTEM
LINKS
POINT A
POINT A
POINT A
POINT B
POINT B
POINT B
SIMPLEX
(one way only)
HALF DUPLEX
(one way or ...

GEO-SYNCHRONOUS ORBIT
THREE SATELLITES IN NEAR-EQUATORIAL ORBITS CAN PROVIDE
CONTINUOUS GLOBAL COVERAGE...
...EXCEPT FOR T...

HIGHLY INCLINED, ELLIPTICAL ORBIT
...DO NOT PROVIDE CONTINUOUS
GLOBAL COVERAGE
HIGHLY INCLINED,
ELLIPTICAL ORBITS
COVER TH...

NEAR-EARTH ORBIT
NEAR-EARTH SATCOM SYSTEMS USE
MANY SMALL, CHEAP SATELLITES TO
PROVIDE WIDE AREA COVERAGE
NEAR-EARTH ORBITS

SATCOM VS TERRESTRIAL COMM.
GENERAL ADVANTAGES
 LINE OF SIGHT NOT REQUIRED BETWEEN USERS
 COMMUNICATION COST & QUALITY L...

COMSAT ADVANTAGES
TERRESTRIAL COMMUNICATIONS SATELLITE COMMUNICATIONS

Frequency Bands
 Different kinds of satellites use different frequency
bands.
 L–Band: 1 to 2 GHz, used by MSS
 S-Band:...

Satellite Frequency Bands and
Antennas (Dishes)
 The size of Satellite Dishes (antennas) are
related to the transmission ...

Satellite Frequency Bands and
Antennas (Dishes)
C-Band Ku-Band
 Most commonly used bands: C-bandC-band (4 to 8 GHz) , Ku-...

Capacity Allocation
 FDMA
 FAMA-FDMA
 DAMA-FDMA
 TDMA
 Advantages over FDMA

FDMA
 Satellite frequency is already broken into
bands, and is broken in to smaller channels in
Frequency Division Multip...

FDMA (cont.)
 The number of sub-channels is limited by
three factors:
 Thermal noise (too weak a signal will be effected...

FDMA (cont.)
 FDMA can be performed in two ways:
 Fixed-assignment multiple access (FAMA):
The sub-channel assignments a...

TDMA
 TDMA (Time Division Multiple Access)
breaks a transmission into multiple time
slots, each one dedicated to a differ...

TDMA (cont.)
 Advantages of TDMA over FDMA.
 Digital equipment used in time division
multiplexing is increasingly becomi...

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