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Introduction to SATELLITE COMMUNICATION P.L.Nagaraju :
Introduction to SATELLITE COMMUNICATION P.L.Nagaraju
CONTENTS: INTRODUCTION WHY USE SATELLITES GENERAL STRUCTURE TYPES OF SATELLITES HOW SATELLITE WORKS ADVANTAGES AND DISADVANTAGES
Introduction : In 1962, the American telecommunications giant AT&T launched the world’s first true communications satellite, called TELSTAR. Since then, countless communications satellites have been placed into earth orbit, and the technology being applied to them is forever growing in sophistication
Communication: Communication means conveying or transfer of information from one place to the another place. Communication by using satellite is called satellite communication.
Satellite: A satellite is an object that orbits or revolves around another object. For example, the Moon is a satellite of Earth, and Earth is a satellite of the Sun. They are highly specialized wireless receiver/transmitters that are launched by a rocket and placed in orbit around the Earth.
Satellite communication: Satellite communication is one particular example of wireless communication systems Satellite communication systems differ from terrestrial systems in that the transmitter is not based on the ground but in the sky.
History: The first artificial satellite, called Sputnik, was launched by the Soviet Union in 1957 and was the size of a basketball. Its purpose was simply to transmit a Morse code signal repeatedly. India has launched 60 satellites(as of 26 April 2012) of many types since its first attempt in 1975.
1st artificial satellite SPUTHNIK::
1 st artificial satellite SPUTHNIK:
1st Indian satellite Aryabhatta: :
1 st Indian satellite Aryabhatta:
Why Use Satellite?:
Why Use Satellite? Satellite communication is just one example of wireless communication systems. Familiar examples of wireless systems are all around us, such as radio and television broadcasting and mobile and 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. One major use of satellites familiar to everyone is satellite television broadcasting. Other applications of satellite communications include high speed internet, telephony and corporate networks for multinational businesses. One major use of satellites familiar to everyone is satellite television broadcasting. The
Earth station: :
Earth station: The basic functions of the earth station are, It transmits the information to the satellite It also receives the information from the satellite. It telecommunicates with satellites.
Subsystems of Earth station::
Subsystems of Earth station: Transmitter Receiver Antenna system Ground communication Equipment Power supply subsystem
Types of Earth stations::
Types of Earth stations: Two types: 1. Large Earth station 2.Small Earth station Large Earth stations may use dish antennas in order of 30m diameter. Small Earth stations may use antennas of only 3 to 10m in diameter
Frequency Bands :
Frequency Bands Band Download Bands MHz Uplink Bands MHz UHF (Military) 250-270 292-312 C Band (Commercial) 3700-4200 5925-6425 Ku Band (Commercial) 11700-21200 14000-14500 Ka Band (Commercial) 17,700-21200 27500-30,000 Ka Band (Military) 20200-21200 43500-45500
Uplink & downlinks::
Uplink & downlinks:
Uplink frequency: An uplink is the frequency transmitted by the Earth station transmitter and is Received by the satellite. FREQUENCY BAND UPLINK FREQUENCY C- band 6 GHZ KU-band 14 GHZ
Downlink frequency: The down link is the frequency transmitted by the satellite transmitter and is received by earth station receiver. FREQUENCY BAND DOWN LINK FREQUENCY C-band 4 GHZ KU-band 12 GHZ
Apogee and Perigee::
Apogee and Perigee:
Apogee: When the satellite is in elliptical orbit, the farthest point from the earth of that orbit is called the apogee. The distance between the centre of the earth and apogee is called Apogee distance .
Perigee: When the satellite is in an elliptical orbit, the lowest point from the earth station of that orbit is called perigee. The distance between the centre of the earth and perigee is called perigee distance .
Look angles: The look angles are the angles to which an Earth station antenna must be pointed out to communication with satellite. They are 1.Azimuth angle. 2.Elevation angle. Generally we choose low elevation angle.
Azimuth & Elevation angles: :
Azimuth & Elevation angles:
Transponder: A transponder is a trans receiver. It means combination of transmitter and receiver system. In a communications satellite, a transponder gathers signals over a range of uplink frequencies and re-transmits them on a different set of downlink frequencies to receivers on Earth, often without changing the content of the received signal or signals.
Basic functions of transponder::
Basic functions of transponder: Receives the signal transmitted by Earth station transmitter. Amplifies the received signal. Down converts the amplified signal to downlink frequency. Retransmits the downlink frequency towards the Earth station Receiver.
Types of satellites::
Types of satellites: Based on purpose 1.Communication satellite 2.Observatory satellite. based on the signal processing 1.Active satellites 2.passive satellites
Types: Based on the area of working 1.Domsat 2.Intel sat Based on orbital placed 1.GEO 2.MEO 3.LEO
Communication satellite: Communication satellites are synchronous satellites used for communication purpose. it consists of 1.communication subsystem 2.power supply subsystem 3.TTC subsystem 4.attitude and orbit control subsystem
Advantages of Satellites::
Advantages of Satellites: 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 . International calls done through satellite communication only.
Disadvantages of Satellites:
Disadvantages of Satellites Launching satellites into orbit is costly . repair of satellite is almost impossible. There is a larger propagation delay in satellite communication than in terrestrial communication. Satellite bandwidth is gradually becoming used up.
Applications: Telephone transmission TV broadcasting Electric mail Global positioning system (GPS) Radio program distribution Remote sensing
Three satellites covering earth surface::
Three satellites covering earth surface: Theoretically three geostationary satellites provides 100% earth coverage.