Satcom 2

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Satellite Communications
Course: Communication Systems
Dr. Muhammad Saleem Awan

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

History of Satellites
 The First Satellites
The theory of satellites was simple enough - shoot something out into space a...

History of Satellites
 Early Bird (1965)
The world's first commercial communications satellite was Early Bird, built
for ...

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...

How do Satellites Work
Other Earth Stations receive
message in useful strength
area. (Footprint)

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

COMSAT ADVANTAGES
TERRESTRIAL COMMUNICATIONS SATELLITE COMMUNICATIONS

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

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...

Geostationary Earth Orbit (GEO)

Satellites are positioned
every 4-8 degrees.

Approx. 300 GEO
satellites are in orbit.

GEO (cont.)
 Instruments usually have:
 Small telescope or antenna.
A scanning mechanism.
One or more detectors that d...

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

 Altitude (375-1000 miles)
 Revolution time: 90 min - 3
hours.
 Advantages:
Reduces transmission
delay
Eliminates nee...

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...

Middle-Earth-Orbiting (MEO)
MEOs orbits between the altitudes
of 5,600 and 9,500 miles.
These orbits are primarily reser...

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...

Hubble Telescope
 Classification: LEO
 Orbit: 375 miles, 600 km.
 Revolution time: 100 min.
 Speed: 17,000 miles/hr
 ...

Space Debris
 According to the U.S. Space
Command (USSC), there are
more than 8,000 objects
larger than a softball now
ci...

GPS: What is it ?
A constellation of 24 satellites
The Global Positioning System (GPS) is a
worldwide radio-navigation sy...

GPS: How it works
Satellites are reference points for locations on Earth
The whole idea behind GPS is to use
satellites i...

GPS: Problems in the System
 Even though the satellites
positions are constantly
monitored, they can't be watched
every s...

GPS: Who Uses GPS ?
GPS has a variety of applications
 Land: diverse uses; ex. surveying, recreational. Etc
 Sea: naviga...

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
HIGHLY INCLINED,
ELLIPTICAL ORBITS COVER
THE POLES, BUT...
...DO NOT PROVIDE CONTINUOUS
...

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...

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

0 0.5 1.0 1.5 2.0 2.5
+10
-10
-30
-50
Link distance in km
3.0 km
+30
+50 dBm
+40
+20
0
-20
-40
System power figure (virtua...

Frequency Bands
All satellites have some basic elements

A structural subsystem, or bus. The bus
is a metal or composite frame on which
the other elements are mounted. Because
it ...

A power source. Power is often supplied
by arrays of solar cells (“solar
panels”) that generate electricity, which is
stor...

A communications system (TT&C).
Communications form the link between the
satellite and its ground stations or other
satell...

TT&C - Telemetry refers to the information the satellite sends the control
station about the status of its various compone...

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