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Note for Satellite Communication System - SCS By srikant vas

  • Satellite Communication System - SCS
  • Note
  • Biju Patnaik University of Technology Rourkela Odisha - BPUT
  • Electronics and Communication Engineering
  • 2 Topics
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Srikant Vas
Srikant Vas
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VIGNAN INSTITUTE OF TECHNOLOGY AND MANAGEMENT SATELLITE COMMUNICATION SYSTEMS Introduction to the satellite communication systems SATELLITE: - A Satellite can be defined as a heavy object which revolves around another object in space due to the effect of mutual gravitational forces. Satellite communication:-Satellite communication is a process in which transmission of signals takes place from one earth station to the other earth station with the help of a satellite. • • The satellite communication acts as big Microwave repeater that is the signal which comes from the earth station is received, amplified and transmitted back to the earth station. In satellite communication the transmission of signal takes place in space due to which it covers the maximum area. BASIC SATELLITE SYSTEM The basic satellite system contains of a 1. Earth station / Ground station. 2. Satellite. Earth station: - Earth station plays an important role in satellite communication for transmission and receiving of the RF signals. Earth station consists of antennas and control unit. Transmission of any information is taken place using earth station only. Satellite:- Satellite acts as trans-receiver which receives the RF signal, amplifies and retransmits it back. SATELLITE RF transmitting signal RF Receiving signal EARTH STATION EARTH STATION BLOCK DIAGRAM OF BASIC SATELLITE SYSTEM 1

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VIGNAN INSTITUTE OF TECHNOLOGY AND MANAGEMENT SATELLITE COMMUNICATION SYSTEMS TYPES OF SATELLITE • • Active satellite. Passive satellite. Active satellite Active satellites are those satellites which are used for linking, transmitting and processing of signals. Ex: - All the communication satellites. Passive Satellite:Passive satellites are those satellites which are only used for linking of two stations through space. In this process, the loss of power is more. Ex: -TIROS-1. SATELLITE SYSTEMS:There are two types of satellite systems 1. Ground to ground. 2. Ground to cross-link Ground. Ground to Ground In Ground to Ground satellite systems the earth station “A” sends signal to the satellite, which after processing retransmits to another earth station “B”. Ground to cross-link Ground If the earth stations are situated such that they are not in the line of sight of a common satellite, then a link between the two satellites in space will be devolved, and the signal is send to the earth station. For example: - If two satellites S1, S2 covers area x1, x2 respectively and 2

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VIGNAN INSTITUTE OF TECHNOLOGY AND MANAGEMENT SATELLITE COMMUNICATION SYSTEMS Advantages of satellite communication • • • • • The long distance communication can be done. It helps in Mobile communication. In Television Broadcasts. In Internet communications. Global positioning system. Disadvantages of satellite communication • • • For maintains of a satellite in its orbit is very costlier. Time delay is more in satellite communication which increases the efficiency of the satellite. High atmospheric losses will be added in the transmitting of a signal. History • • • In 1975 ISRO has launched the first satellite names as aryabhattya on April 19th. In 1957 Sputnik-1 was launched by USSR. In 1965 First communication satellite was launched named as INTELSAT-1. ➢ Why the uplink frequency must be higher than the downlink frequency? Ans. The uplink frequency must be higher than the downlink frequency because 1. At higher frequency the beam width of an antenna will be narrow so that a fine beam width can be aimed at the satellite which is located at the fixed point where as for downlink due to low frequency the beam width will be larger so that it can cover the larger area in earth station. 2. At higher frequency the path loss is more which can be overcome by transmitting with more power from the earth station where as the power is limited in the satellite transponder. ➢ What is different frequency bands used in the satellite communication? Ans. The different frequency bands used in satellite communication are SL.NO FREQUENCY BAND FREQUENCY RANGE 1 L 1-2 GHz 2 S 2-4 GHz 3 C 4-8 GHz 4 X 8-12 GHz 5 Ku 12-18 GHz 6 K 18-27 GHz 7 Ka 27-40 GHz 3

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VIGNAN INSTITUTE OF TECHNOLOGY AND MANAGEMENT SATELLITE COMMUNICATION SYSTEMS ➢ Why 6/4 GHz frequency link OR C-Band is widely used in satellite communication? Ans. 1. The effect of noise in the sky and the rain attenuation is low in 6/4 GHz. 2. It is easier to generate the high power at this frequency. 3. The polarization effect is less at this frequency. ➢ What is the advantage of Ku-Band over C-Band? Ans. In Ku–Band the wavelength is small due to which the size of the antenna decreases so that it will be more compact where in C-Band the wavelength is large due to which the size of the antenna increases. ➢ What are the advantages and disadvantages of C, Ka, and Ku-band? Ans. BAND Advantages Disadvantages C 1. Broad Footprint. 2. Not effected to rain. 3. Less atmospheric losses. 1. Weak signals 2. Interference 3. large antenna sizes. Ka 1. Focused Foot prints 2. Bandwidth arre used less. 3. Small antenna size. 1. Interference to rain. 2. More costly Ku 1. No interference. 2. Small antenna size. 1. Interference to rain. 2. More costly 4

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