Satellite Communication Presentation By

Overview Today’s world become a vast network for global communication. With the help of advanced earth stations & new connectivity services makes the critical transmissions to reach their intended targets efficiently and instantly. A big role is played by Satellite Communication for this advancement. The idea of satellite Communication was first introduced by a British Science Fiction writer Authur C. Clarke in 1945. He has already pointed out that a satellite in a circular equatorial orbit with a radius of about 42,242 km wound have an angular velocity that matched the Earth.

Satellite 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 . A satellite is an object in space that orbits or circles around a bigger object. There are two kinds of satellites: natural (such as the moon orbiting the Earth) or artificial (such as the International Space Station orbiting the Earth).There are dozens upon dozens of natural satellites in the solar system, with almost every planet having at least one moon. Saturn, for example, has at least 53 natural satellites To understand why satellites move this way, we must revisit our friend Newton. Newton proposed that a force -- gravity -- exists between any two objects in the universe. If it weren't for this force, a satellite in motion near a planet would continue in motion at the same speed and in the same direction -- a straight line. This straight-line inertial path of a satellite, however, is balanced by a strong gravitational attraction directed toward the center of the planet.

History Early 1950’s and 1960’s,satellite communication by metalized weather balloons. Moon as an artificial satellite. In 1954, the US Naval Research Laboratory successfully transmitted the first voice message. Disadvantage using moon as a satellite….Communications via the Moon is limited by simultaneous visibility of the Moon by both the transmit and the receive stations  The first satellite with radio transmitter was in 1957. In October 1957, the first artificial satellite Sputnik -I was launched. 1963 Clark’s idea became a reality when the first geosynchronous satellite SYNCOM was successfully launched by NASA. India launched its first satellite Aryabhatta on 19 April 1975.

What is Satellite Communication? In satellite communication, signal transferring between the sender and receiver is done with the help of satellite. In this process, the signal which is basically a beam of modulated microwaves is sent towards the satellite. Then the satellite amplifies the signal and sent it back to the receiver’s antenna present on the earth’s surface. So, all the signal transferring is happening in space. Thus this type of communication is known as space communication. Two satellites which are commonly used in satellite communication are Active and passive satellites.

Passive satellites: It is just a plastic balloon having a metal coated over it. This sphere reflects the coming microwave signals coming from one part of the earth to other part. This is also known as passive sphere. Our earth also has a passive satellite i.e. moon. Active satellites: It basically does the work of amplifying the microwave signals coming. In active satellites an antenna system, transmitter, power supply and a receiver is used. These satellites are also called as transponders. The transmitters fitted on the earth generate the microwaves. These rays are received by the transponders attached to the satellite. Then after amplifying, these signals are transmitted back to earth. This sending can be done at the same time or after some delay. These amplified signals are stored in the memory of the satellites, when earth properly faces the satellite. Then the satellite starts sending the signals to earth. Some active satellites also have programming and recording features. Then these recording can be easily played and watched. The first active satellite was launched by Russia in 1957. The signals coming from the satellite when reach the earth, are of very low intensity. Their amplification is done by the receivers themselves. After amplification these become available for further use.

Features of satellite communications: Satellites used in satellite communications are usually in geostationary orbit. Some of them are placed in highly elliptical orbits. Satellite communications can provide global availability. It can not only land masses but also maritime areas as well. Large distances can thus be covered quiet easily. One of the main advantages provided by satellite communication is the superior reliability unlike other forms of communication. It does not need terrestrial infrastructure for operation. Satellite communication could provide superior performance as uniformity and speed are much more pronounced than other forms of communication. Scalability is higher in case of satellite communications. Deployment cost is higher than most forms of communications in case of satellite communications. As it is less vulnerable than other forms of communication, it is highly used in defense departments. Satellite communications also provide weather information. It can be helpful during times of disasters as the services rarely fail. High amount of data can be transmitted with the help of satellites.

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An earth station transmits information signal to the satellite using a highly directional dish antenna. The satellite receives this signal, processes it and transmits it back at a reduced frequency. The receiving earth stations will receive this signal using parabolic dish antennas pointed towards the satellite. The signal which being transmitted upwards to the satellite is called as the "up-link" and it is normally at a frequency of 6 GHz. The signal which is transmitted back to the receiving earth station is called as the "down-link" and it is normally at a frequency of 4 GHz. Thus a satellite has to receive, process and transmit the signal. All these functions are performed by a unit called satellite transponder. A communication satellite generally has two sets of transponders, each set having 12 transponders making it a total of 24 transponders. Each transponder has a bandwidth of 36 MHz which is sufficient to handle at least one TV channel. The up-link signal received by a transponder is a weak and down-link signal transmitted by the transponder is strong. Therefore to avoid interference between them, the up-link and down-link frequencies are selected to be of different value The operation of satellite takes place at a very high signal frequencies in the microwave range.

Geostationary (GEO) Satellite The satellites orbiting in the geostationary orbit are called geostationary satellites. They travel at the velocity of revolution of earth, hence complete one revolution around the earth in oner day i.e. 24 hours. This is the reason why geostationary satellites appear to be stationary. The geostationary satellites are also called as GEO satellites.They are basically used for communication applications. These satellites are at about 36000 km above the earth's surface. There are certain advantages of such a high altitude such as: The solar cells get the solar radiation for almost 99% of the orbital period. Therefore energy storage is not necessary. The earth's magnetic field is weak at such heights. Therefore the adverse effects of magnetic field are absent. Large coverage area. A geostationary satellite is visible from about 42% of the earth's surface area. Therefore three communication satellites can cover the entire surface area of the earth as shown in the fig.

The elements of satellite communication system Earth Station Terrestrial System User

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