By Muhammad Zubair Khan Qureshi. CONTENTS 1. Introduction 2. Orbit 3. Kepler’s Laws 4. Elements of...
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SATELLITE COMMUNICATIONS By Muhammad Zubair Khan Qureshi
By Muhammad Zubair Khan Qureshi. CONTENTS 1. Introduction 2. Orbit 3. Kepler’s Laws 4. Elements of Satellite Communications 5. Advantages of Satellites
CONTENTS 1. Introduction 2. Orbit 3. Keplers Laws 4. Elements
of Satellite Communications 5. Advantages of Satellites 6.
Disadvantages of Satellites 7. Applications 9. First Satellite
Launchings by Country 10. Conclusion
Slide 3
1.INTRODUCTION Satellite is a microwave repeater in the space
There are about 750 satellites in space, most of them are used for
communication They are used for wide area coverage of earths
surface Transmission delay is about 0.3 sec Transmission cost is
independent of distance Ref: [1]
Slide 4
MEANING OF SATELLITE The word Satellite is originated from the
Latin word Satellit meaning an attendant, one who is constantly
hovering around and attending to a master or a big man For our own
purposes however a satellite is simply any body that moves around
another (usually much larger) one in a mathematically predictable
path called an Orbit
Slide 5
COMPONENTS OF A SATELLITE Ref: [3]
Slide 6
COMMUNICATION SATELLITE? A satellite is an object that orbits
another large object like planet A communication satellite is a
station in space that is used for telecommunication, radio and
television signals The first satellite with radio transmitter was
sent to space in 1957
Slide 7
COMMUNICATION SATELLITE Ref: [4]
Slide 8
THE ORIGIN OF SATELLITE The concept of using object in space to
reflect signals for communication was proved by Naval Research Lab
in Washington D.C. when it use the Moon to establish a very low
data rate link between Washington and Hawaii (in late 1940s) Russia
also started to enter the space age by successfully launching
SPUTNIK the first spacecraft to orbit the earth (in Oct, 1957) Data
Rate: Number of bits that are conveyed or processed per unit of
time Ref: [5]
Slide 9
THE ORIGIN OF SATELLITE (contd..) The American followed by
launching an experimental satellite EXPLORER in 1958 In 1960 two
satellite were deployed ECHO and COURIER In 1963 SYNCOM In 1965
INTELSAT & MOLNYA which provides video (Television) and voice
(Telephone)
Slide 10
WHY USE SATELLITE? Satellite communication is just one example
of wireless communication systems Familiar examples of wireless
systems are all around us i.e; radio, television-broadcasting,
mobile & cordless telephones These systems rely on a network of
ground-based transmitters and receivers and for this reason they
are often referred to as Terrestrial systems Terrestrial:
Terrestrial: Refers to things related to land or the planet Earth
Ref: [6]
Slide 11
WHY USE SATELLITE? (contd..) One major use of satellites
familiar to everyone is Satellite Television Broadcasting Ref:
[7]
Slide 12
WHY USE SATELLITE? (contd..) Other applications of satellite
communications include; 1-High Speed Internet 2-Telephony
3-Networks for multinational businesses The working or use of
telephones Ref: [8] Ref: [9]
Slide 13
A Satellite is basically a self-contained communication system
with the ability to receive signals from Earth and to retransmit
those signals back with the use of a Transponder HOW DO SATELLITES
WORK? I will discuss about Satellite Transponder in later
slides
Slide 14
HOW DO SATELLITES WORK? Two stations on Earth want to
communicate through radio broadcast but are too far away to use
conventional means The two stations can use a satellite as a relay
station for their communication One Earth Station sends a
transmission to the satellite This is called UPLINK
Slide 15
HOW DO SATELLITES WORK contd.. Ref: [10] UPLINK
Slide 16
The Satellite Transponder converts the signal and sends it down
to the second earth station. This is called DOWNLINK Satellite
Transponder: The series of interconnected units that form a
communications channel between the receiving and the transmitting
antennas Transponder (short for Transmitter-Responder) Also called
Brain of Satellite Purpose: It is mainly used in satellite
communication to transfer the received signals HOW DO SATELLITES
WORK contd.. Ref: [13]
Slide 17
HOW DO SATELLITES WORK contd.. Ref: [10] DOWNLINK UPLINK
Slide 18
EARLY SATELLITES TELSTAR Allowed live transmission across the
Atlantic SYNCOM First Geosynchronous Satellite Geosynchronous
Satellite: With an orbital period the same as the Earth's rotation
period Ref: [11] Ref: [12]Ref: [11]
Slide 19
EARLY SATELLITES (contd...) Top view animation of Earth
satellite in a geostationary orbit I will discuss about Difference
between Geosynchronous and Geostationary Satellites in later
slides
Slide 20
Difference between Geosynchronous and Geostationary Satellites
Features of Geostationary Satellite The orbit is circular The orbit
is in equatorial plane i.e. directly above the equator and thus
inclination is zero The angular velocity of the satellite is equal
to angular velocity of earth Period of revolution is equal to
period of rotation of earth. Finish one revolution around the earth
in exactly one day i.e. 23 hours, 56 Minutes and 4.1 seconds There
is ONLY one geostationary orbit. Ref: [26]
Slide 21
Features of a Geosynchronous Satellite The orbit is NOT
circular The orbit is NOT in equatorial plane i.e. directly above
the equator, its in inclined orbit The angular velocity of the
satellite is equal to angular velocity of earth Period of
revolution is equal to period of rotation of earth Finish one
revolution around the earth in exactly one day i.e. 23 hours, 56
Minutes and 4.1 seconds There are many geosynchronous orbits
Difference between Geosynchronous and Geostationary Satellites Ref:
[26]
Slide 22
Difference between Geosynchronous and Geostationary Satellites
Ref: [24] Ref: [25]
Slide 23
2.ORBITS o A satellite orbits the Earth in one of two basic
types of orbit Circular Satellite Orbit: Distance from the Earth
remains the same at all times Elliptical Satellite Orbit: The
elliptical orbit changes the distance to the Earth v=average speed,
a=average acceleration Ref: [14] Ref: [15] Ref: [17]
Slide 24
CONCEPT OF ORBITS Ref: [16]
Slide 25
SATELLITE ORBITS DEFINITIONS Geocentre : When satellites orbit
the Earth, either in a circular or elliptical orbit, the satellite
orbit forms a plane that passes through the centre of gravity or
geocentre of the Earth Direction of Rotation around the Earth:
There are two ways in which a satellite orbit may be categorized:
POSIGRADE: The rotation around the earth is said to be posigrade
when it rotates in the same direction as the rotation of the Earth.
RETROGRADE: The rotation around the earth is said to be retrograde
when it rotates in the opposite direction to the rotation of the
Earth Ref: [16]
Slide 26
HOW SATELLITE STAYS IN ORBIT? A satellite stays in orbit
because the gravitational pull of the earth is balanced by the
centripetal force of the revolving satellite Ref: [18] Ref:
[19]
Slide 27
Centripetal Force: A center seeking force which means that the
force is always directed toward the center of the circle HOW
SATELLITE STAYS IN ORBIT? Ref: [20]
Slide 28
3.ORIGIN OF PLANETRY LAWS Sir. Johannes Kepler Derived 3 laws
based upon his observations of planetary motion
Slide 29
Planets move around the Sun in ellipses, with the Sun at one
focus KEPLERS FIRST LAW Ref: [21]
Slide 30
KEPLERS SECOND LAW The line connecting the Sun to a planet
sweeps equal areas in equal times Ref: [21]
Slide 31
KEPLERS THIRD LAW Kepler's third law quantifies the observation
that more distant orbits have longer periods. Unlike Kepler's first
and second laws that describe the motion characteristics of a
single planet, the third law makes a comparison between the motion
characteristics of different planets. STATEMENT SAYS: The square of
the orbital period of a planet is proportional to the cube of the
mean distance from the Sun Ref: [21]
Slide 32
KEPLERS THIRD LAW contd Ref: [21] Near Orbit Distant Orbit
Distant Orbit 1 revolution = Near Orbit 2 revolutions
Slide 33
4.ELEMENTS OF SATELLITE COMMUNICATIONS The basic elements of a
communication satellite service are divided between; 1. Space
Segment 2. Ground Segment The space segment consists of the
spacecraft and launch mechanism The ground segment comprises the
earth station and network control center of entire satellite
system
Slide 34
SPACE SEGMENT Space segment consist of a satellite in suitable
orbit Space segment classified on the basis of orbit LEO (Low Earth
Orbit) MEO (Medium Earth Orbit) GEO (Geostationary or
Geosynchronous Earth Orbit) Ref: [22]
Slide 35
SATELLITE ORBIT ALTITUDES Ref: [22] Start Range=500 km End
Range=1500 km Start Range=8000 km End Range=18000 km 35786 km 18000
km 8000 km 1500 km 500 km Start Range=35786 km & above
Slide 36
GROUND SEGMENT The ground segment of each service has distinct
characteristics Services are; FSS (Fixed Service Satellite)
Example: Point-to-Point Communication BSS (Broadcast Service
Satellite) Example: Satellite Television/Radio Also called Direct
Broadcast Service (DBS) MSS (Mobile Service Satellite) Example:
Satellite Phones
Slide 37
LOW EARTH ORBIT (LEO) LEO satellites are much closer to the
earth then GEO satellites ORBITAL RANGE: From 500 to 1500 KM above
the earths surface LEO satellites dont stay in fixed position
relative to the surface, and are only visible for 15 to 20 minutes
each pass A network of LEO satellite is necessary for LEO
satellites to be useful
Slide 38
ADVANTAGES OF LEO A LEO satellites communication to earth
compared to a GEO satellite gives it a better signal strength and
less of a time delay, which makes it better for POINT-TO- POINT
communication A LEO satellites smaller area of coverage wastes less
bandwidth
Slide 39
DISADVANTAGES OF LEO As network of LEO satellites is needed for
making it useful, which can be costly LEO satellites have to
compensate for Doppler shifts cause by their relative movement
Atmospheric drag (i.e; air-resistance) effects LEO satellites,
causing gradual orbital decay (i.e; decrease in altitude) The
Doppler effect (or Doppler shift) is the change in frequency of a
wave (or other periodic event) for an observer moving relative to
its source. Ref: [27]
Slide 40
MEDIUM EARTH ORBIT (MEO) MEO satellites are above the LEO
satellites and below the GEO satellites ORBITAL RANGE: Between 8000
KM and 18000 KM above the earths surface Similar to LEO satellites
in functionality MEO satellites are visible for much longer periods
of time than LEO satellites, usually between 2 to 8 hours MEO
satellites have larger coverage area then LEO satellites
Slide 41
ADVANTAGES OF MEO A MEO satellites longer duration of
visibility and wider footprint means fewer satellites are needed in
a MEO network than a LEO network A MEO satellites distance gives it
a longer time delay and weaker signal than a LEO satellite, though
not as bad as a GEO satellite DISADVANTAGES OF MEO
Slide 42
GEOSTATIONARY EARTH ORBIT (GEO) GEO satellites are above LEO
and MEO satellites ORBITAL RANGE: 35786 KM above the earths surface
Objects in Geostationary Orbit revolve around the earth at the same
speed as the earth rotates. This means GEO satellites remain in the
same position relative to the surface of the earth
Slide 43
ADVANTAGES OF GEO A GEO satellites distance from earth gives it
a large coverage area, almost a fourth of the earths surface GEO
satellites have a 24 hours view of a particular area These factors
make it ideal for satellite broadcast and other multipoint
applications
Slide 44
DISADVANTAGES OF GEO GEO satellites distance also cause it to
have both a comparatively weak signal and a time delay in the
signal, which is bad for point-to-point communication GEO
satellites, centered above the equator, have difficulty
broadcasting signals to near polar regions
Slide 45
5.ADVANTAGES OF SATELLITES OVER TERRESTRIAL COMMUNICATION The
coverage area of a satellite greatly exceeds that of a terrestrial
system Transmission cost of a satellite is independent of the
distance from the center of the coverage area Satellite to
Satellite communication is very precise Higher Bandwidths are
available for use
Slide 46
6.DISADVANTAGES OF SATELLITE COMMUNICATION Launching satellites
into orbit is costly Satellite Bandwidth is gradually becoming used
up (i.e; weak) There is a larger propagation delay in satellite
communication than in terrestrial communication
Slide 47
MAJOR PROBLEMS FOR SATELLITES 1. Positioning in orbit 2.
Stability 3. Power 4. Communications 5. Harsh Environment
Slide 48
7.APPLICATIONS Ref: [23]
Slide 49
TELEPHONY: Fixed points -> earth station -> satellite
-> earth stations -> fixed points TELEVISION AND RADIO: e.g;
Direct Broadcast Satellite (DBS) & Fixed Service Satellite
(FSS) MOBILE SATELLITE TECHNOLOGY: Special antenna called Mobile
Satellite Antenna No matter where or how this antenna is mounted on
APPLICATIONS contd
Slide 50
RADIO: Radio Broadcast Low Earth Orbits INTERNET: High Speed
Useful for far away places MILITARY: Uses Geostationary Satellites
e.g; The Defense Satellite Communications APPLICATIONS contd
Slide 51
9.FIRST SATELLITE LAUNCHINGS BY COUNTRY
Slide 52
CONCLUSION Every thing has advantages and disadvantages but as
a whole, satellites remain the best utilization used for
communications due to their speed and other advantages mentioned in
this presentation
Slide 53
Communication Satellites bring the world to you Anywhere and
Any Time
