1. SATELLITE COMMUNICATIONS
Topic
SATELLITE COMMUNICATIONS By
Muhammad Zubair Khan Qureshi

2. CONTENTS 9. First Satellite Launchings by Country 1. Introduction
2. Orbit
3. Kepler’s Laws
4. Elements of Satellite Communications
5. Advantages of Satellites
6. Disadvantages of Satellites
7. Applications
9. First Satellite Launchings by Country
10. Conclusion

3. 1.INTRODUCTION Satellite is a microwave repeater in the space
Topic
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 earth’s surface
Transmission delay is about 0.3 sec
Transmission cost is independent of distance
Ref: [1]

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”

5. COMPONENTS OF A SATELLITE
Ref: [3]

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

7. COMMUNICATION SATELLITE
Ref: [4]

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 1940’s)
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]

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)

10. Terrestrial: Refers to things related to land or the planet Earth
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: Refers to things related to land or the planet Earth
Ref: [6]

11. WHY USE SATELLITE? (contd..)
One major use of satellites familiar to everyone is
“Satellite Television Broadcasting”
Ref: [7]

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]

13. I will discuss about “Satellite Transponder” in later slides
HOW DO SATELLITES WORK?
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
I will discuss about “Satellite Transponder” in later slides

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”

15. HOW DO SATELLITES WORK contd..
UPLINK
Ref: [10]

16. HOW DO SATELLITES WORK contd..
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
Ref: [13]

17. HOW DO SATELLITES WORK contd..
UPLINK
DOWNLINK
Ref: [10]

18. EARLY SATELLITES TELSTAR SYNCOM
Allowed live transmission across the Atlantic
SYNCOM
First Geosynchronous Satellite
Ref: [11]
Geosynchronous Satellite: With an orbital period the same as the Earth's rotation period
Ref: [11]
Ref: [12]

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

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]

21. Difference between Geosynchronous and Geostationary Satellites
Features of a Geosynchronous Satellite
The orbit is NOT circular
The orbit is NOT in equatorial plane i.e. directly above the equator, it’s 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
Ref: [26]

22. Difference between Geosynchronous and Geostationary Satellites
Ref: [24]
Ref: [25]

23. v=average speed, a=average acceleration
2.ORBITS
Ref: [15]
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
Ref: [17]
v=average speed, a=average acceleration
Ref: [14]

24. CONCEPT OF ORBITS
Ref: [16]

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]

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]

27. HOW SATELLITE STAYS IN ORBIT?
Centripetal Force:
A center seeking force which means that the force is always directed toward the center of the circle
Ref: [20]

28. 3.ORIGIN OF PLANETRY LAWS
Derived 3 laws based
upon his observations
of planetary motion
Sir. Johannes Kepler

29. KEPLER’S FIRST LAW
“Planets move around the Sun in ellipses, with the Sun at one focus”
Ref: [21]

30. KEPLER’S SECOND LAW
“The line connecting the Sun to a planet sweeps  equal areas in equal times”
Ref: [21]

31. KEPLER’S 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]

32. KEPLER’S THIRD LAW contd…
Near Orbit
Distant Orbit
Distant Orbit 1 revolution = Near Orbit 2 revolutions
Ref: [21]

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

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]

35. SATELLITE ORBIT ALTITUDES
Start Range=35786 km & above
35786 km
Start Range=8000 km End Range=18000 km
18000 km
8000 km
Start Range=500 km End Range=1500 km
1500 km
500 km
Ref: [22]

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

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 earth’s surface
LEO satellites don’t 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

38. ADVANTAGES OF LEO
A LEO satellite’s 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 satellite’s smaller area of coverage wastes less bandwidth

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]

40. MEDIUM EARTH ORBIT (MEO)
MEO satellites are above the LEO satellites and below the GEO satellites
ORBITAL RANGE: Between 8000 KM and KM above the earth’s 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

41. ADVANTAGES OF MEO DISADVANTAGES OF MEO
A MEO satellite’s longer duration of visibility and wider footprint means fewer satellites are needed in a MEO network than a LEO network
DISADVANTAGES OF MEO
A MEO satellite’s distance gives it a longer time delay and weaker signal than a LEO satellite, though not as bad as a GEO satellite

42. GEOSTATIONARY EARTH ORBIT (GEO)
GEO satellites are above LEO and MEO satellites
ORBITAL RANGE: KM above the earth’s 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

43. ADVANTAGES OF GEO
A GEO satellite’s distance from earth gives it a large coverage area, almost a fourth of the earth’s surface
GEO satellites have a 24 hours view of a particular area
These factors make it ideal for satellite broadcast and other multipoint applications

44. DISADVANTAGES OF GEO
GEO satellite’s 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

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

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

47. MAJOR PROBLEMS FOR SATELLITES
Positioning in orbit
Stability
Power
Communications
Harsh Environment

48. 7.APPLICATIONS
Ref: [23]

49. APPLICATIONS contd… TELEPHONY: TELEVISION AND RADIO:
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

50. APPLICATIONS contd… RADIO: INTERNET: MILITARY: Radio Broadcast
Low Earth Orbits
INTERNET:
High Speed
Useful for far away places
MILITARY:
Uses Geostationary Satellites
e.g; The Defense Satellite Communications

51. 9.FIRST SATELLITE LAUNCHINGS BY COUNTRY

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

53. Communication Satellites bring the world to you Anywhere and Any Time

54. REFERENCES [1]- http://www.iconshock.com/networking-icons/
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