• Satellite technology has progressed tremendously over the last 50 years since Arthur C. Clarke first proposed its idea in 1945 in his article in Wireless World.• Today, satellite systems can provide a variety of services including broadband communications, audio/video distribution networks, maritime navigation, worldwide customer service and support as well as military command and control.• Satellite systems are also expected to play an important role in the emerging 4G global infrastructure providing the wide area coverage necessary for the realization of the “Optimally Connected Anywhere, Anytime” vision that drives the growth of modern telecom industry.
• The use of satellite in communication system is very much a fact of everyday in life.• This is evidence by the many homes, which are equipped with antennas and dishes.• These antennas were used for reception of satellite signal for television.• What may not be well known that satellites also form an essential part of communication system worldwide carrying large amount of data, telephone traffic in addition to television signals.
REQUIREMENT FOR SATELLITE COMMUNICATION• The communication between one point to other depends upon frequency of the transmitted signal as well as mode of communication.• The frequency up to appropriately 10 MHz was used for small distance• Satellite & Cable TV communication through Ground Wave Propagation
• As frequency increases, the attenuation of ground wave increases (Earth starts behaving like absorber for high frequency signals) because of which, it is not possible to establish a reliable communication link through ground waves for frequencies more than 10 Mhz. Since Earth is elliptical in shape, thus direct wave which are reaching at receiving antenna are restricted by curvature of Earth (The direct wave communication is not possible beyond Line of Sight).
• The above limitation for long distance communication requires a reflector above the earth surface, which reflects the signal towards receiving antenna.• The Sky Wave Propagation is possible due to Ionosphere present in the atmosphere.• The ionosphere has property that it reflect transmitted signals up to a certain frequency and after that the layer is behaving as transparent medium and signal passes the layer.• This natural reflector present in the atmosphere provides radio broadcasting link to larger area of Earth beyond Line of Sight
• The signals having frequency more than 30 MHz are pass through ionosphere and these are required to reflected back to earth by some artificial medium for establishing reliable communication between transmitter and receiver.• For fulfilling the requirement of high frequency and long distance communication across the globe, the artificial reflector (Satellite) above the ionosphere are required for transmitted signal.
• The satellites were used for reflecting the signals having frequencies more than 30MHz.• The transponders in the satellite receive the signal and after signal conditioning (suppressing noise, amplification) re-transmit back to ground for reception.• The frequency at which signal is transmitted from ground to satellite is known as uplink frequency and signal frequency transmitted from satellite to ground is known as downlink frequency.• It has been decided by international community that uplink frequency is always higher than downlink frequency.• It is to be noted that as frequency of communication increases, the size of transmitting and receiving antenna as well as the size of the electronics components required are decreases drastically (Inversely proportional).
• A communications satellite is an orbiting artificial earth satellite that receives a communications signal from a transmitting ground station, amplifies and possibly processes it, then transmits it back to the earth for reception by one or more receiving ground stations.• Today’ s communications satellites offer extensive capabilities in applications involving data, voice, and video, with services provided to fixed, broadcast, mobile, personal communications, and private networks users.
ADVANTAGES OF SATELLITE COMMUNICATION• Distance Independent Costs: The cost of satellite transmission is basically the same, regardless of the distance between the transmitting and receiving earth stations. Satellite based transmission costs tend to be more stable, particularly for international or intercontinental communications over vast distances.• Fixed Broadcast Costs: The cost of satellite broadcast transmission, that is, transmission from one transmit ground terminal to a number of receiving ground terminals, is independent of the number of ground terminals receiving the transmission.
• High Capacity: Satellite communications links involve high carrier frequencies, with large information bandwidths.• Capacities of typical communications satellites range from 10s to 100s of Mbps (Mega-bits per second), and can provide services for several hundred video channels or several tens of thousands of voice or data links.
• Low Error Rates. Bit errors on a digital satellite link tend to be random, allowing statistical detection and error correction techniques to be used. Error rates of one bit error in 106 bits or better can be routinely achieved efficiently and reliably with standard equipment.• Diverse User Networks. Large areas of the earth are visible from the typical communications satellite, allowing the satellite to link together many users simultaneously. Satellites are particularly useful for accessing remote areas or communities not otherwise accessible by terrestrial means. Satellite terminals can be on the surface, at sea, or in the air, and can be fixed or mobile.
History of satellite communication• How I lost a billon dollar in my spare time was is a partial title of Arthur C. Clark ‘s 1965 essay on why and how he didn’t patent the idea of geostationary satellite which he detailed and publicized in 1945.• Arthur C. Clark wrote the first well-known article on communication satellites. "Extra-Terrestrial Relays" was published in Wireless World in 1945. In the article, Clark discussed geosynchronous earth orbit and the possibility of covering the earth with three satellites.• Marvel is that sir arthur survived to see his concept fulfilled by approximately 250 geo stationary satellites ringing the globe.
• People considered consider Clark to be the father of sat.. Comm. Bt he consider himself the God father of satellite communication and other two scientists as father who gave technical concepts…. Dr. John R Pierce and Dr. Harold Rosen.• As a honour the orbit where satellite seem to be stationary from the surface is called as clark’s orbit.
• The actual journey into space began October 4, 1957, when the Soviet Union launched Sputnik 1, the worlds first orbital spacecraft, which orbited the world for three months.• The first communication satellite was launched on December 18, 1958.• Signal Communication by Orbital Relay (SCORE), which broadcasted a Christmas message from President Eisenhower - "Peace on Earth, Good will toward men" - orbited the earth for 12 days until the batteries failed.• The main purpose of the SCORE project was to prove that an atlas missile could be put into orbit.
Combined, the U.S. and U.S.S.R. launched six satellites in 1958, 14 satellites in 1959, 19 in 1960 and 35 in 1961. In 1962, the United Kingdom and Canada launched satellites of their own, along with the 70 satellites launched by the U.S. and U.S.S.R.• On August 12, 1960, the United States launched Echo 1, a passive reflector satellite with no amplification possibilities.• Echo 1 could only reflect the radiation back to earth. At the time of its launch, it was thought that passive reflector satellites could serve a purpose in communications, but the technology was soon abandoned.
In 19th century a foresighted writer described a satellite that communicated to earth by having people on the satellite jump up and down. The brillient and pioneering German Hermann Oberth wrote of communicating with manned satellite by mirrors and lights in 1923 when radio was still in its infancy.Other writers including a little known Austrian army officernamed Hermann Potonik has proposed a manned name stationin his 1928 book The Problem Of Spaceflight placing it in ageostationary orbit to facilitate radio communication with earth . In 1942 an Engineer writer George .O, Smith proposed a radiorelay satellite in Venus orbit to permit communication betweenthat planet and earth when they were on opposite sides of thesun.
History of satellite communication• 1945 Arthur C. Clarke publishes an essay about “Extra Terrestrial Relays“ Satellite communication began after Second World War. Scientists knew that is was possible to build rockets that could carry radio transmitters into space.• 1957 first satellite SPUTNIK :The satellite was launched by the Soviet Union and the event chocked the Western world.• 1965 first commercial geostationary satellite Satellite “Early Bird“ (INTELSAT I): It weighed 68 kg and offered 240 duplex telephone channels or 1 TV channel, 1.5 years lifetime.• 1982 first mobile satellite telephone system INMARSAT-A• 1998 global satellite systems for small mobile phones• Today more than 250 geostationary satellites orbit the earth!!