Technical Seminar Report
Submitted in partial fulfilment of the requirements for the award of the degree of Bachelor of Engineering
Electronics and Communication Engineering
Lachu Man Limbu
ELECTRONICS AND COMMUNICATION ENGINEERING
COLLEGE OF SCIENCE AND TECHNOLOGY
RINCHENDHING :: PHUENTSHOLING, BHUTAN
AcknowledgementI really feel that, this is my great opportunity to enhance my knowledge level. In due course of doing this seminar, I was able to acquire valuable information and had consumed huge amount to work, research and dedication. The successful completion of my seminar is solely because of the consistent support and guidance given to me during whole process of my research.
Therefore I would like to thank the department of Electronics and Communication of the college for letting us to work on the seminar. Moreover, my hearty gratitude goes to my seminar guide Mr. Jigme Zangpo for guiding me with the work schedules and providing with relevant documents of seminars and also for his consistent help in the process of doing this seminar.
I also would like to thank each and every individual who directly or indirectly helped me in contributing to the completion of my seminar.
AbstractSatellite communication is one of the most important means of communication. It is regarded as one of the backbones of long distance wireless communication. Satellite communication provides broadband communication along with fiber optic communication. These days due to advancement in technology, the artificial earth satellites have emerged as an essential part of telecommunication infrastructure around the globe. Besides telecommunication, the satellites are also being used for purpose of meteorological data collection and weather forecasting, search and rescue, global positing system, minerals and oil exploration, maritime navigation and so on. The main purpose of communication satellite is to relay the signal around the curve of the Earth allowing communication to happen through wide ranges and distant points. The electromagnetic signals that communication satellites work with, have a large spectrum of wavelengths and frequencies. To keep these waves from interfering with one another, international organizations have certain rules and regulations describing which wavelength a certain company or group can use. By separating out wavelengths, communication satellites will have minimal interference and be able to communicate effectively.
List of AbbreviationsAbbreviation Description Page
TV Television 1
GEO Geostationary Earth Orbit 3
MEO Medium Earth Orbit 4
LEO Low Earth Orbit 8
GHz Giga Hertz 11
MHz Mega Hertz 12
RF Radio Frequency 12
List of Tables TOC h z c “Table” Table 1: Main frequency bands used by satellite communication system (Reddy, n.d.). PAGEREF _Toc527152163 h 11
List of Figures TOC h z c “Figure” Figure 1: Satellite Communication (University of Science and Technology of China, 2018). PAGEREF _Toc527155475 h 2Figure 2: General Block Diagram of the Satellite communication system (DAEnotes, 2018). PAGEREF _Toc527155476 h 3Figure 3: Different types of orbits for satellite communication (Hussaini, 2017). PAGEREF _Toc527155477 h 4Figure 4: Low earth orbit (Reddy, n.d.). PAGEREF _Toc527155478 h 5Figure 5: Medium earth orbit (Reddy, n.d.). PAGEREF _Toc527155479 h 6Figure 6: Geostationary earth orbit (Reddy, n.d.). PAGEREF _Toc527155480 h 7Figure 7: Working of Satellite Communication in brief. PAGEREF _Toc527155481 h 9Figure 8: Basic Elements of Satellite Communications System (Visahli, 2014). PAGEREF _Toc527155482 h 10Figure 9: Block diagram of the Transponder (Vamsiram’s Jyothi Celestia, n.d.). PAGEREF _Toc527155483 h 12
Contents TOC o “1-3” h z u Acknowledgement PAGEREF _Toc527878680 h iAbstract PAGEREF _Toc527878681 h iiList of Abbreviations PAGEREF _Toc527878682 h iiiList of Tables PAGEREF _Toc527878683 h ivList of Figures PAGEREF _Toc527878684 h vContents PAGEREF _Toc527878685 h vi1 INTRODUCTION PAGEREF _Toc527878686 h 12 SATELITE COMMUNICATION PAGEREF _Toc527878687 h 22.1 Types of Satellite PAGEREF _Toc527878688 h 32.1.1 Active satellite PAGEREF _Toc527878689 h 42.1.2 Passive satellite PAGEREF _Toc527878690 h 4 2.2 Different Types of Orbit PAGEREF _Toc527878691 h 42.2.1 Low Earth Orbit (LEO): 500-2000 km above the earth PAGEREF _Toc527878692 h 52.2.2 Medium Earth Orbit (MEO): 8,000-20,000 km above the earth PAGEREF _Toc527878693 h 62.2.3 Geostationary Earth Orbit (GEO) Beyond 36,000 km above the earth PAGEREF _Toc527878694 h 73WORKING OF SATELLITE COMMUNICATION PAGEREF _Toc527878695 h 93.1 Working of Uplink and Downlink PAGEREF _Toc527878696 h 103.2 The Transponder PAGEREF _Toc527878697 h 124 APPLICATIONS OF SATELLITE COMMUNICATION PAGEREF _Toc527878698 h 134.1 Weather Forecasting PAGEREF _Toc527878699 h 134.2 TV and Radio Broadcast PAGEREF _Toc527878700 h 134.3 Military Satellites PAGEREF _Toc527878701 h 134.4 Navigation Satellites PAGEREF _Toc527878702 h 134.5 Global Telephone PAGEREF _Toc527878703 h 144.6 Global Mobile Communication PAGEREF _Toc527878704 h 145 ADVANTAGES AND DISADVANTAGES OF SATELLITE COMMUNICATION PAGEREF _Toc527878705 h 155.1 Advantages PAGEREF _Toc527878706 h 155.2 Disadvantages PAGEREF _Toc527878707 h 156 CONCLUSION PAGEREF _Toc527878708 h 16References PAGEREF _Toc527878709 h 17
1 INTRODUCTIONA satellite is a self-contained communication system with the ability to receive signals from the Earth, amplify it and retransmit those amplified signals back with the use of transponder – an integrated receiver and transmitter of radio signals. A satellite is an object that orbits or revolves around another object. And if a satellite is man-made and place around the earth for communication purpose at microwave frequency level then it is called as a satellite communication. Most communications satellites use geosynchronous orbits or near geostationary orbits, although some recent systems use low Earth-orbiting satellites CITATION Bru08 l 1033 (R.Elbert, 2008).
Communications satellites provide a technology that is complementary to that of fiber optic submarine communication cables. But unlike fiber optic communication, satellite communication has a propagation delay of at least 270 milliseconds, which is the time it takes by the radio signal to travel 35,800 km from earth to a satellite and then back to earth. Therefore satellite internet connections has an average delay of 600-800 millisecond i.e., about ten times more than that of a terrestrial Internet link. This delay is more of a challenge to deployment of Virtual private networks over satellite internet connections all over the world.
The main idea of satellite communication was first proposed by Arthur C. Clarke, based on Herman Poto?nik’s pseudonymous work from 1929. After 16 years later in the year 1945 Clarke published an article titled “Extra-terrestrial Relays” in the magazine Wireless World. The article described the fundamentals behind the deployment of artificial satellites in geostationary orbits for the purpose of relaying radio-wave signals. Thus Arthur C. Clarke is often quoted as the inventor of the communications satellite.
Using satellite communication, people all over the world can share their information through telephone, exchange e-mails or messages from anywhere in the world and have access to Internet and receive hundreds of TV channels in their homes. Unlike fiber optic technology it can it can be used in providing communication in difficult terrains, high mountain regions, oceans, etc.
2 SATELITE COMMUNICATIONcenter151130
Figure SEQ Figure * ARABIC 1: Satellite Communication CITATION Uni18 l 1033 (University of Science and Technology of China, 2018).Satellite communication is one of the most important means of communication. It is regarded as one of the backbones of long distance wireless communication. Satellite communication provides broadband communication along with fiber optic communication. These days the artificial earth satellites have emerged as an essential part of telecommunication infrastructure around the world. Besides telecommunication, the satellites are also being used for purpose of meteorological data collection and weather forecasting, search and rescue, global positing system, minerals and oil exploration, maritime navigation and so on.
All the communication system must have a medium for operation. Likewise satellite communication system also uses a satellite as a repeater between two points that exchange information. So probably here the medium will be air and information is being passed as electromagnetic waves. Satellite communication is important where installation of cable is difficult and as a whole from the cost analysis point of view satellite communication is more effective than using cables and optical fibre. Therefore satellite communication has emerged fruitful in wideband communication systems like TV Broadcasting, Defence, Weather forecasting, space navigation and telemetry CITATION Den95 l 1033 (Roddy, 1995).
However general block diagram of the Satellite communication consists of the following components.
Uplink signal 5.9 t0 6.4 GHz
2.2 GHz local Oscillator
6 GHz Amplifier
Downlink Signal 3.7 to 4.2 GHz
4 GHz Amplifier
Figure SEQ Figure * ARABIC 2: General Block Diagram of the Satellite communication system CITATION DAE18 l 1041 (DAEnotes, 2018).The ground station also known as earth segment consists of a base band processor, an up-converter, high Powered amplifier and a parabolic dish antenna and are mainly used to transmit the terrestrial data to an orbiting satellite. In the case of downlink, the ultimate reverse operation happens whereby the up-linked signals are recaptured through parabolic antenna.
The transponder comprises of a receiving antenna that receives signals from the ground station, a broad band receiver, an input multiplexer and a frequency converter that is used to reroute the received signals through a high powered amplifier for downlink. The key function of satellite is to reflect electromagnetic signals. Like in case of a telecom satellite, the primary role of the satellite is to pick up signals from a ground station that might be located at certain distant.
2.1 Types of Satellite
The satellite can be classified into two categories:
2.1.1 Active satelliteAn active satellite is one which has transmitting equipment abroad such as a transponder. It is a device which receives a signal from earth, amplifies it and retransmits it back to earth. Its advantages are requirement of lower power earth station, cheaper, not open to random use and directly controlled by operators from ground.
2.1.2 Passive satellite
Passive satellite is one that doesn’t reflect or scatter the incident radiation from ground station. Passive satellite relays would require surface transmitters of greater power than that of an active satellite relay, however the active satellite relays must carry abroad receiving and transmitting equipment and the necessary power sources. Some of the disadvantages of the Passive satellites are:
Earth Stations require high power (10 kW) to transmit signals strong enough to produce an adequate return echo.
Large Earth Stations with tracking facilities were expensive.
A global system would have required a large number of passive satellites accessed randomly by different users.
Control of satellites not possible from ground
center40830500 2.2 Different Types of Orbit
Figure SEQ Figure * ARABIC 3: Different types of orbits for satellite communication CITATION Uma17 l 1033 (Hussaini, 2017).The most unique thing about satellites is the way they orbit or rotate along the different paths they follow at very different heights above Earth. A satellite fired into space might fall back to Earth just like a stone tossed into the air due to gravitational force. To stop that happening, satellites have to keep on moving all the time so, even though the force of gravity is pulling them towards the center of the earth, they will never actually crash back to Earth.
Some turn at the same rotational rate as Earth so they’re effectively fixed in one position above our head, while others go much faster. Although there are many different types of satellite orbits, they come in three basic varieties, low, medium, and high—which are short, medium, and long distances above Earth, respectively.
2.2.1 Low Earth Orbit (LEO): 500-2000 km above the earth590550-5715
Figure SEQ Figure * ARABIC 4: Low earth orbit CITATION BIM l 1033 (Reddy, n.d.).Some Satellites tend to be quite close to Earth—often just a few hundred kilometers up—and follow an almost circular path called a low-Earth orbit (LEO). The distance of the Low Earth Orbit extends from 160km above Earth and ends at 2000km. Satellites in this orbit have an orbital period in the range of 90-120 minutes. It is impossible to achieve an orbit below 160km without artificial thrusters because of the atmospheric drag at that altitude.
The mean orbital velocity of any satellite that needs to reach LEO should be 7.5km/s (27,000km/h). The satellites have to move very fast in order to overcome Earth’s gravity, and since they have a relatively small orbit as they are close to the earth, they cover large areas of the planet quite quickly and never stay over one part of Earth for more than a few minutes. The low earth orbit is the most crowded and accessible realm of all other orbits. More than 800 satellites are currently available in orbit within the Low-Earth Orbit region. The most popular of these is the International Space Station and the Iridium network of communication satellites.
Advantages and disadvantages
Due to shorter distance range the Low-Earth orbit is chosen as communication and imaging satellite. Due to the low altitude, communication signals require less power and time to travel between the different Earth stations and the satellites. Moreover the imaging satellites can capture very detailed pictures and views as per our wish.
Satellites for the Low-Earth orbit are easier to build and can be cheaper than their counterparts in higher orbits. It is a very popular orbital choice for hobbyists who wish to launch CubeSats. CubeSats are incredibly tiny satellites used for small amounts of data collection and other experiments.
However, with the advantage of easy launching of a satellite into this orbit has inadvertently contributed to the issue of space debris. Perhaps, the International Space Station uses layers of shields to protect itself from space debris which is not good for satellite. Also, Satellites in this orbit have to deal with atmospheric drag therefore they usually have a shorter lifespan compared to the geostationary satellites CITATION LRo l 1033 (L.Ronga, 2003). These orbits are much closer to the Earth (500-2000 Km) only, and requires the satellites to travel at a very high speed in order to avoid being pulled out of orbit by Earth’s gravity. At LEO, a satellite can encircle around the Earth in approximately one and a half hours.
2.2.2 Medium Earth Orbit (MEO): 8,000-20,000 km above the earth
Figure SEQ Figure * ARABIC 5: Medium earth orbitCITATION BIM l 1033 (Reddy, n.d.).The Medium Earth Orbit is also known as the Intermediate Circular Orbit. All orbits above low-earth orbit and below geostationary orbit are said to be in medium-earth orbit. To be precise, MEO extends from 2000km and ends right below 35,786km. Satellites in this region have an orbital period ranging from 2-24 hours.
A medium-Earth orbit (MEO) is about 10 times higher up than a LEO. For an example the GPS navstar satellites are in MEO orbits roughly 20,000 km (12,000 miles) above our heads and take 12 hours to “loop” the planet. Their orbits are semi-synchronous, which means that, while they’re not always exactly in the same place above our heads, they pass above the same points on the equator at the same times each day.
Advantages and disadvantages
The medium earth orbit is very useful for providing information about the connectivity and navigation to the polar region because an orbital period of 12 hours can be achieved by the satellites in this region. That is a unique period that allows the satellites to rotate around the Earth two times in a day. The main purpose of all the satellites in the MEO are for communication, navigation, and to provide a gravity-less environment for scientific experiments to carry out peacefully.
However, with the increase in altitude compared to LEO, propagation delay will also begin to creep into the transmission of signals. As a result the power required to transmit these signals will also increase. Thus, satellites in this region are more expensive as compared to the satellites in the low-earth orbit. Also similar to the LEO, the satellites in this orbit also have to consider atmospheric drag too. The interference from the upper layers of the atmosphere reduces the lifespan of these satellites in comparison with satellites in the GEO. The charged particles in this region can hurt the performance of satellites.
center3981452.2.3 Geostationary Earth Orbit (GEO) Beyond 36,000 km above the earthFigure SEQ Figure * ARABIC 6: Geostationary earth orbitCITATION BIM l 1033 (Reddy, n.d.).Geostationary or Geosynchronous earth orbit is also sometimes called as High Earth Orbit due to large distance between the earth and its orbit. Most of the satellites have orbits at a carefully chosen distance of about 36,000 km (22,000 miles) from the surface of the earth. This distance ensures that they take exactly one day to orbit Earth and always return to the same position above it, at the same time of day. Such a high-Earth orbit satellite is sometimes called as geosynchronous (because it’s synchronized with Earth’s rotation) or geostationary (if the satellite stays over the same point on Earth all the time). Any orbit beyond the geostationary orbit is known as high earth orbit. High earth orbit is loosely attributed to any orbit beyond 35,786km.
Usually, the satellites in this orbit have an orbital period longer than a day i.e., 24 hours. Due to this, all satellites in this orbit appear to be retrograded. Communications satellites are usually parked in geostationary orbits so their signals always reach the satellite dishes pointing up at them. Weather satellites often use geostationary orbits because they need to keep gathering cloud or rainfall images from the same broad part of Earth from hour to hour and day to day (unlike LEO scientific satellites, which gather data from many different places over a relatively short period of time, geostationary weather satellites gather their data from a smaller area over a longer period of time).
Advantages and disadvantages
Satellites falling in HEO or GEO regions are useful to study about our planet’s magnetosphere and for other astronomical observations and research. These satellites face less exposure to atmospheric drag as compared to satellites in the LEO/MEO orbits. Communication delays and high costs of manufacturing and launching a satellite into this orbit are some of the areas of concern as it has quite far from earth.
Orbiting at the height of 22,282 miles above the equator (35,786 km), the satellite travels in the same direction and at the same speed as the Earth’s rotation on its axis taking 24 hours to complete a full trip around the globe. Thus, as long as a satellite is positioned over the equator in an assigned orbital location, it will appear to be stationary with respect to a specific location on the Earth.
A single geostationary satellite can view approximately one third of the Earth’s surface. If three satellites are placed at the proper longitude, the height of this orbit allows almost all of the Earth’s surface to be covered by the satellites.
3WORKING OF SATELLITE COMMUNICATIONcenter127635
Figure SEQ Figure * ARABIC 7: Working of Satellite Communication in brief.The above diagram depicts a brief description about how the satellite communication happens. Firstly from the ground stations, the transmitter will transmit the desired signals to the satellite and the satellite in the space will detect or receive that particular signal and amplifies it. Then the amplified version of the signal will be retransmitted back to the earth and again the converted and the original signal will be received.
Firstly the users are connected to the earth station through a terrestrial network such as telephone switch or a dedicated link to the earth station. Then the user generates a baseband signal which will be processed through a terrestrial network and will be transmitted to a satellite.
The satellite which consists of a large number of repeaters in space receives the modulated RF carrier in its uplink frequency spectrum from all the earth stations in the network and it will amplify these carriers signals and also retransmits all the signals back to the earth stations in the down link frequency spectrum CITATION Jos98 l 1033 (Joseph N Pelton, 1998).
center310515000To avoid interference of the frequency signals, the downlink frequency spectrum should be different from the uplink frequency spectrum. Therefore the signal at the receiving earth station is processed to get back the baseband signal, it is sent to the user through a terrestrial network. There are many frequency bands utilized by satellites but the mostly used bands are the uplink frequency of 6GHz and the downlink frequency of 4 GHz. Actually the uplink frequency band is 5.725 to 7.075 GHz and the actual downlink frequency band is from 3.4 to 4.8 GHz.
Figure SEQ Figure * ARABIC 8: Basic Elements of Satellite Communications System CITATION Vis14 l 1033 (Visahli, 2014).
3.1 Working of Uplink and DownlinkFor an instance you want to send something like a TV broadcast from one side of Earth to the other, there are three stages involved. Firstly, there will be an uplink, where data is beamed up to the satellite from a ground station from the Earth. Then the satellite processes the data using a number of onboard transponders (radio receivers, amplifiers, and transmitters). These boost the incoming signals and change their frequency, so incoming signals do not interfere with outgoing signals.
Different transponders in the same satellite are used to handle different TV stations carried on different frequencies. Finally there will be the downlink, where data is sent back down to another ground station which can be anywhere on Earth. Although for a single uplink, there may be millions of downlinks, for example, if many people are receiving the same satellite TV signal at once. Therefore a communications satellite might relay a signal between one sender and receiver (fired up into space and back down again, with one uplink and one downlink), satellite broadcasts typically involve one or more uplinks (for one or more TV channels) and multiple downlinks (to ground stations or individual satellite TV subscribers) CITATION ELu00 l 1033 (E.Lutz, 2000).
The following table shows the main frequency bands used for satellite links.
Table SEQ Table * ARABIC 1: Main frequency bands used by satellite communication system CITATION BIM l 1033 (Reddy, n.d.).Frequency Band Downlink Uplink
C 3,700-4,200 MHz5,925-6,425 MHz
Ku 11.7-12.2 GHz 14.0-14.5 GHz
Ka 17.7-21.2 GHz 27.5-31.0 GHz
The band’s reception on Earth is subject to an inverse relationship between frequency and wavelength. When frequency increases, wavelength decreases and vice versa. The larger the wavelength, the bigger the antenna necessary to receive. The two frequently bands that are used mostly are the C-band and the Ku-band. The C-band has an uplink frequency of 6 GHz and a downlink frequency of 4 GHz. The minimum site of an average C-band antenna is approximately 2 to 3 meters in diameter.
Another type of frequency band is called as Ku-band which has an uplink frequency of 14 GHz and a downlink frequency of 11 GHz. Ku-bands can have much smaller antennas as higher frequency means shorter wavelength. The smallest of these antennas can be 18 inches in diameter. This is the type of antenna used with home entertainment satellite dishes. Ku-Band Satellite Antenna.3.2 The TransponderSatellite Antenna
Low Noise Amplifier
Figure SEQ Figure * ARABIC 9: Block diagram of the TransponderCITATION 3rd l 1033 (Vamsiram’s Jyothi Celestia, n.d.).A wireless communications device usually attached to a satellite. A transponder receives and transmits radio signals at a prescribed frequency range. After receiving the signal a transponder will at the same time broadcast the signal at a different frequency. The term is a combination of the words transmitter and responder. Transponders are used in satellite communications and in location, identification and navigation systems.
In a transponder for amplification of a received signal into an antenna to a signal for retransmission, and where the retransmitted signal possibly may have information superimposed, a quenched oscillator is incorporated as amplifying element. The oscillator is preferably of super regenerative type and exhibits negative resistance for the received signal. Transponders according to the present invention may be introduced as system elements in a wireless or wire based network to work as intelligent or unintelligent connections in the network. The transponders can also be used in positioning systems CITATION DKP92 l 1033 (D.K.Paul F. Faris, 1992).
4 APPLICATIONS OF SATELLITE COMMUNICATION4.1 Weather Forecasting
Certain satellites are particularly designed to monitor the climatic conditions of earth i.e., weather forecasting. They continuously monitor the assigned areas of earth and predict the weather conditions of that region. This is done by taking images of earth from the satellite. These images are transferred using assigned radio frequency a particular earth station. These satellites are also exceptionally useful in predicting disasters like hurricanes, and monitor the changes in the Earth’s vegetation, ocean color, and ice fields.
4.2 TV and Radio BroadcastThese dedicated satellites are responsible for making hundreds of channels across the globe available for everyone. They are also responsible for broadcasting live news, matches, world-wide radio services. These satellites require at least 30-40 cm sized dish to make the channels available globally.
4.3 Military Satellites
These satellites are often used for gathering intelligence, as a communications satellite used for military purposes, or as a military weapon during war time. A satellite by itself is neither military nor civil. It is the kind of payload it carries that enables one to take a correct decision regarding its military or civilian character.
4.4 Navigation Satellites
The system allows for precise localization and tracking all over the world, and with some additional techniques, the precision is in the range of some meters distance. Ships and aircraft also rely on GPS as an addition traditional navigation systems. Nowadays many vehicles come with installed GPS receivers which helps to track the accidents and lost vehicles. This system is also used, e.g., for fleet management of trucks or for vehicle localization in case of theft.
4.5 Global Telephone
The first applications of satellites for communication was the establishment of international telephone systems during early days. Instead of using cables it was sometimes faster to launch a new satellite. However, fiber optic cables are still replacing satellite communication across long distance as in fiber optic cable, light is used as a source instead of radio frequency, hence making the communication much faster and more efficient (and of course, reducing the delay caused due to the amount of distance a signal needs to travel before reaching the destination) CITATION BIE96 l 1033 (B.I.Edelson, 1996).
Using satellites, to typically reach a distance approximately about 10,000 km away, the signal needs to travel almost 72,000 km, i.e., sending data from ground to satellite and (mostly) from satellite to another location on earth. This cause substantial amount of delay and this delay becomes more prominent for users during voice calls or other communication process.
4.6 Global Mobile CommunicationThe basic purpose of satellites for mobile communication is to extend the area of network coverage. Cellular phone systems, such as AMPS and GSM and their successors do not cover all parts of a country. The some of areas that are not covered usually have low population where it is too expensive to install a base station. With the integration of satellite communication, however, the mobile phone can switch to satellites offering world-wide connectivity to a customer. Satellites cover a certain area on the earth and has many advantages for communication process.
5 ADVANTAGES AND DISADVANTAGES OF SATELLITE COMMUNICATIONSatellite Communication is one of the most impressive spin-off from space programs, and made a major contribution to the international communication. Satellite plays a very important role in telephone communication, TV and radio program distribution and other certain communications CITATION DKP92 l 1033 (D.K.Paul F. Faris, 1992).
1. Point to multipoint communication is possible whereas terrestrial relay are point to point, this is why satellite relay are wide area broadcast
2. Circuits for the satellite can be installed rapidly. Once the satellite is in Position, Earth Station can be installed and communication may be established within some day or even hours.
3. Mobile communication cab be easily achieved by satellite communication because of its flexibility in interconnecting mobile vehicles.
4. As compared to fiber cable, the satellite communication has the advantage of the quality of transmitted signals and the location of Earth Stations. The sending and receiving information independent of distance.
1. With the Satellite in position the communication path between the terrestrial transmitter and receiver is approximately 75000 km long.
2. There is a delay of ¼ sec between the transmission and reception of a signal because the velocity of electromagnetic wave is 3* 10^5 Km/second.
3. The time delay reduces the efficiency of satellite in data transmission and long file transfer, which carried out over the satellites.
4. Over-crowding of available bandwidth due to low antenna gains is occurred.
5. High atmosphere losses above 30 GHz limit the carrier frequency.
6 CONCLUSIONThe satellite communication in telecommunications, uses the artificial satellites to provide communication links between various points on Earth stations. The Satellite communications play an important role in the telecommunications system all over the world. Approximately about 2,000 artificial satellites orbiting around the Earth and relay analog and digital signals carrying voice, video, and data to and from one or many locations worldwide CITATION LRo l 1033 (L.Ronga, 2003). Satellite communication has two main components: the ground station, which consists of fixed or mobile transmission, reception, and ancillary equipment, and next the space segment, which primarily is the satellite itself.
The typical satellite link involves the transmission or up-linking of a signal from a ground station to a satellite. The satellite then at the space receives the signal and amplifies the original signal and retransmits it back to Earth, where it is received and re-amplified by Earth stations and different terminals. Satellite receivers on the ground or the earth station includes direct-to-home satellite equipment, mobile reception instruments in aircraft, satellite telephones, and handheld devices.
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