Satellite communications
- 2. CONTENTS Introduction Defination of Satellite Need of Satellite Communication How a Satellite works Types of Satellites Basic Satellites First Satellite in INDIA Satellite Communication in INDIA Earth Orbit Satellites Types of Earth Orbit Satellites Elements of Satellite Communication Satellite Communication Services Advantages and Disadvantages Applications Conclusion
- 3. INTRODUCTION • The never ending quest of communication engineer is to transmit maximum information in short time to the largest possible distance, this gave raise to many systems of communications. • A satellite is a smaller object that revolves around a larger object in space. For example, moon is a natural satellite of earth. • We know that Communication refers to the exchange (sharing) of information between two or more entities, through any medium or channel. In other words, it is nothing but sending, receiving and processing of information. • If the communication takes place between any two earth stations through a satellite, then it is called as satellite communication. In this communication, electromagnetic waves are used as carrier signals. These signals carry the information such as voice, audio, video or any other data between ground and space and vice-versa.
- 4. Defination of Satellite • Satellite can be defined as a heavy object which goes around object in space due to the effect of mutual gravitational forces, used for broadband communication.
- 5. Need of Satellite Communication • When using a satellite for long distance communications, the satellite acts as a repeater. • An earth station transmits the signal up to the satellite(uplink), which in turn retransmits it to receiving earth station(downlink). • Different frequencies are used for uplink/downlink. • Satellite systems offer more flexibility than submarine cables, buried underground cables, line-of- sight microwave radio or optical fiber systems.
- 6. How a Satellite works • A satellite is a body that moves around another body in a particular path. A communication satellite is nothing but a microwave repeater station in space. • A repeater is a circuit, which increases the strength of the received signal and then transmits it. But, this repeater works as a transponder. That means, it changes the frequency band of the transmitted signal from the received one. • The frequency with which, the signal is sent into the space is called as Uplink frequency. Similarly, the frequency with which, the signal is sent by the transponder is called as Downlink frequency. • The transmission of signal from first earth station to satellite through a channel is called as uplink. Similarly, the transmission of signal from satellite to second earth station through a channel is called as downlink. • The process of satellite communication begins at an earth station. Here, an installation is designed to transmit and receive signals from a satellite in an orbit around the earth. Earth stations send the information to satellites in the form of high powered, high frequency (GHz range) signals. • The satellites receive and retransmit the signals back to earth where they are received by other earth stations in the coverage area of the satellite. •
- 7. Types of Satellites • Satellite communication uses two types of artificial satellites to transmit the signals: • Passive Satellites: If you put a hydrogen balloon that has a metallic coating over it, up in the air, it technically becomes a passive satellite. Such a balloon can reflect microwaves signals from one place to another. The passive satellites in space are similar. These satellites just reflect the signal back towards the Earth without amplification. Since the satellite orbit height can range from 2000 to 35786 km, attenuation due to the atmosphere also comes into play and due to this, the received signal is often very weak. • Active Satellites: Active Satellites, unlike passive satellites, amplify the transmitted signals before re-transmitting it back to Earth, ensuring excellent signal strength. • Passive satellites were the earliest communication satellite but now almost all the new ones are active satellites.
- 8. Basic Satellites Oct. 4, 1957 The first artificial satellite was Sputnik, a Russian beach-ball-size space probe that lifted off on Oct. 4, 1957. Telstar NASA launched Telstar in June 1962, the world's first active communications satellite, into low-Earth orbit. Project Echo was the first passive communications satellite experiment. Each of the two American spacecraft, launched in 1960 and 1964, were metalized balloon satellites acting as passive reflectors of microwave signals.
- 9. First Satellite In INDIA ARYABHATA SPACECRAFT • The Aryabhata spacecraft, named after the famous Indian astronomer, was India's first satellite; it was completely designed and fabricated in India and launched by a Soviet Kosmos-3M rocket from Kapustin Yar on April 19, 1975. • Aryabhata was built by the Indian Space Research Organization (ISRO) to conduct experiments in X-ray astronomy, aeronomics, and solar physics. • The satellite weighed 360 kilograms.
- 10. Satellite Communications in INDIA • It’s interesting to know that the Indian National Satellite (INSAT) system is one of the largest domestic communication systems that is placed in the geo-stational orbit. There are more than 200 transponders in the INSAT system and are used for various purposes such as telecommunications, weather forecasting, television broadcasting, disaster warning, search and rescue operations, and satellite newsgathering. Satellite name Launch date Application GSAT-30 Jan 17, 2020 Communication GSAT-31 Feb 06, 2020 Communication GSAT-15 Nov 11, 2015 Communication and navigation GSAT-10 Sep 29, 2012 Communication and navigation INSAT-3A Apr 10, 2003 Communication and climate and environment KALPANA-1 Sep 12, 2002 Communication and climate and environment List of Communication satellites along with their applications:
- 11. Earth Orbit Satellites • Satellite should be properly placed in the corresponding orbit after leaving it in the space. It revolves in a particular way and serves its purpose for scientific, military or commercial. The orbits, which are assigned to satellites with respect to earth are called as Earth Orbits. The satellites present in those orbits are called as Earth Orbit Satellites. • We should choose an orbit properly for a satellite based on the requirement. For example, if the satellite is placed in lower orbit, then it takes less time to travel around the earth and there will be better resolution in an onboard camera. Similarly, if the satellite is placed in higher orbit, then it takes more time to travel around the earth and it covers more earth’s surface at one time. • Following are the three important types of Earth Orbit satellites − Geosynchronous Earth Orbit Satellites Medium Earth Orbit Satellites Low Earth Orbit Satellites
- 12. Types of Earth Orbit Satellites GEO MEO LEO These are very far from the earth. These are little far from earth. These are much closer to earth. These are placed at the height of 35,786km from the earth surface. These are placed at the height in between 8000 km to 18000 km from the earth surface These are placed at the height in between 500 to 1500 km from the earth surface. Here satellite revolves with same angular velocity as the earth rotation. In this orbit satellite revolves faster than earth. LEO satellites don’t stay in fixed position relative to the surface. Maximum time taken to complete one revolution is around 23H:56M:4S. MEO satellites are visible for particular period of time, usually between 2 to 8 hours. These are only visible for 15 to 20 minutes each pass. Larger coverage area, a single satellite can cover 42% of earth. Not as much as GEO satellite. Not as much as GEO, MEO satellites. It has larger delay compared to other orbits. Delay is less compared to GEO orbit. Delay is lesser than GEO and MEO orbits.
- 13. Elements of Satellite Communications • Two major elements of Satellite Communication are 1. Ground segment 2. Space segment GROUND SEGMENT: It is a network of earth stations and user terminals that provides applications and services to end users. SPACE SEGMENT: Satellite itself is known as space segment and comprised of complex structure. It has major subsystem like TTC system, Transponder, Fuel Tank called thrusters tank Antenna and Control system etc.
- 14. Satellite Communication Services • One-way satellite communication • In one-way satellite communication, the communication usually takes place between either one or multiple earth stations through the help of a satellite. • The communication takes place between the transmitter on the first earth satellite to the receiver which is the second earth satellite. The transmission of the signal is unidirectional. There are two categories in which the satellite communication services can be classified: •One-way satellite communication •Two- way satellite communication
- 15. Satellite Communication Services Two-way Satellite Communication • In two-way satellite communication, the information is exchanged between any two earth stations. It can be said that there is a point to point connectivity. • The signal is transmitted from the first earth station to the second earth station such that there are two uplinks and two downlinks happening between the earth stations and the satellite.
- 16. ADVANTAGES AND DISADVANTAGES ADVANTAGES: • Area of coverage is more than that of terrestrial systems • Each and every corner of the earth can be covered • Transmission cost is independent of coverage area • More bandwidth and broadcasting possibilities DISADVANTAGES: • Launching of satellites into orbits is a costly process. • Propagation delay of satellite systems is more than that of conventional terrestrial systems. • Difficult to provide repairing activities if any problem occurs in a satellite system. • Free space loss is more • There can be congestion of frequencies.
- 17. APPLICATIONS • Radio broadcasting and voice communications • TV broadcasting such as Direct To Home (DTH) • Internet applications such as providing Internet connection for data transfer, GPS applications, Internet surfing, etc. • Military applications and navigations • Remote sensing applications • Weather condition monitoring & Forecasting
- 18. Conclusion • Satellite Communication technologies have achieved remarkable breakthrough efficiencies and increase in performance. • Satellite Communications have the ability to rapidly communicate between a number of widely dispersed locations. • Satellites remain the best utilization used for communications due to their speed and other advantages.