SATELLITE COMMUNICATIONS Topic SATELLITE COMMUNICATIONS By Muhammad Zubair Khan Qureshi

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

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]

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”

COMPONENTS OF A SATELLITE Ref: [3]

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

COMMUNICATION SATELLITE Ref: [4]

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]

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)

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]

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

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]

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

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”

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

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]

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

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]

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

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]

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]

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

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]

CONCEPT OF ORBITS Ref: [16]

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]

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]

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]

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

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

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

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]

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

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

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]

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]

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

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

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

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]

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 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

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

GEOSTATIONARY EARTH ORBIT (GEO) GEO satellites are above LEO and MEO satellites ORBITAL RANGE: 35786 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

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

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

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

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

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

7.APPLICATIONS Ref: [23]

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

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

9.FIRST SATELLITE LAUNCHINGS BY COUNTRY

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

Communication Satellites bring the world to you Anywhere and Any Time

REFERENCES [1]- http://www.iconshock.com/networking-icons/ [2]- http://www.integ-europe.com/ [3]- http://www.gma.org/surfing/sats.html [4]- http://www.intelsatgeneral.com/resources/satellite-basics [5]- http://en.wikipedia.org/wiki/Bit_rate [6]- http://en.wikipedia.org/wiki/Terrestrial [7]- http://electronics.howstuffworks.com/satellite-tv1.htm [8]- http://en.wikipedia.org/wiki/Telephony [9]- http://business.hughesnet.com/business-broadband [10]- http://www.radio-electronics.com/info/satellite/communications_satellite/communications-satellite-technology.php [11]- http://en.wikipedia.org/wiki/Geosynchronous_satellite [12]- http://cryptome.org/echelon-ep-fin.htm [13]- http://en.wikipedia.org/wiki/Transponder_%28satellite_communications%29 [14]- http://www.physicsclassroom.com/calcpad/circgrav [15]- http://blogs.discovermagazine.com/badastronomy/2012/10/16/space-leap-of-faith/#.VTuwJJP-nQJ [16]- http://www.radio-electronics.com/info/satellite/satellite-orbits/satellites-orbit-definitions.php [17]- http://imgarcade.com/1/elliptical-orbit-animation/ [18]- http://www.slideshare.net/gupshupcornercomm/pakistani-chat-roomschatroomgupshupcornersatellitelec1 [19]- http://quest.nasa.gov/space/teachers/rockets/principles.html [20]- http://www.regentsprep.org/regents/physics/phys06/bcentrif/lrsmlv.gif [21]- http://www.phy6.org/stargaze/Kep3laws.htm [22]- http://en.wikipedia.org/wiki/List_of_orbits [23]- https://www.viasat.com/enterprise-satellite-networks/linkstar-system [24] - http://www.sccs.swarthmore.edu/users/05/shupe/orbits.html [25] - http://www.mpoweruk.com/satellites.htm [26] - http://www.gktoday.in/geostationary-and-geosynchronous-orbits/ [27] - http://en.wikipedia.org/wiki/Doppler_effect