Satellite communication; a realistic alternative

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Satellite comm as remains a realistic alternative in comms.
this short note discussed brief history of satellite, as well as types, components, locations and lots more......enjoy!

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Satellite communication; a realistic alternative

  1. 1. UNIVERSITY OF NIGERIA, NSUKKA FACULTY OF ENGINEERING Department of Electronic Engineering TOPICSATELLITE COMMUNICATION – A REALISTIC ALTERNATIVEA TECHNICAL WRITING PREPARED IN FULFILLMENT FOR THE REQUIREMENT OF THE COURSE ECE 491 (TECHNICAL WRITING AND SEMINAR) BY EZEONYIDO KINGSLEY LOTANNA REG NO 2007/147192 SEMINAR SUPERVISOR ENGR M.A. AHANEKU NOVEMBER, 2011.
  2. 2. TITLE PAGESATELLITE COMMUNICATION – A REALISTIC ALTERNATIVE
  3. 3. DEDICATIONThis work is dedicated to my parents Mr. and Mrs. Anthony Ezeonyido and to my belovedsiblings, who stood solidly behind me during the period of my research. ii
  4. 4. ACKNOWLEDGEMENTSI wish to acknowledge GOD ALMIGHTY for His love and kindness towards me and myfamily, His uncountable favors and blessings, and His perfect peace. Without Him, this termpaper would have been impossible. I am also eternally indebted to my friend Precious BonyiLinus who helped me so much during the time of arrangement of this term paper. I wouldalso like to recognize the arduous help that was freely and generously given to me by friends.And finally, I would like to thank my parents for their supports and encouragements duringthis research work. iii
  5. 5. PREFACEChapter one of this term paper gives an overall introduction, important features and briefhistory of Satellite Communication.Chapter two of this work invariably revealed the basic components and requirements that aidthe operations of Satellite Communication.In chapter three, we see the Technological Overview of Satellite communication such as theirCharacteristics and Error Correction for certain short comings associated with its constructionas well as Hybrid Network as an alternative method of signal Transmission without muchloss in energy.Chapter four discussed the various applications and impacts of Satellite Communication inmodern technology, as well as conclusion based on the content of this work. iv
  6. 6. ABSTRACTThis research work consequently addresses as well as explains the components and basicworking principles of satellite communication. It also describes the frequency and functionalrequirements for the operation of communication satellites as well as their orbits in space.Finally, this research work enumerated and explained some well-known applications andimpacts of satellite communication in the modern technology as they all are known provesthat makes Satellite Communication a REALISTIC ALTERNATIVE. v
  7. 7. TABLE OF CONTENTS TITLE PAGE……………………………………………...………………………………….. i DEDICATION……………………………………………………………………………….. ii ACKNOWEDGEMENT…………………………………………………………………….. iii PREFACE…………..……………………………………………………………………….. iv ABSTRACT…………………..……………………………………………………………… v TABLE OF CONTENT…..………………………………………………………………………………. viCHAPTER ONE: INTRODUCTION………………………………………………………... 1 1.1 BRIEF HISTORY OF SATELLITE COMMUNICATION............................................... 1CHAPTER TWO: BASICS OF SATELLITE COMMUNICATION………………... 3 2.1: BASIC COMPONENTS (ELEMENTS) OF COMMUNICATION SATELLITE............ 3 2.1.1 The Satellite……………………………….....……………………………………….. 3 2.1.2: Ground Station……………………....………………………………..………………. 3 2.2 BASIC REQUIREMENTS FOR SATELLITE COMMUNICATION..………….…. 3 2.2.1 Functional Requirements ………………….………………………………………..... 3 2.2.2 Frequency Requirements…………………………………………………….…….…. 4 2.3 ORBITS OF SATELLITE……………………...……...……………………………... 6CHAPTER THREE: TECHNOLOGICAL OVERVIEW………………………………….. 7 3.1 CHARACTERISTICS……………..……………………………………...………….. 7 3.2 ERROR CORRECTION TECHNIQUES……………………………………...…….. 7 3.3 HYBRID NETWORKS…………………………………………………..………….. 8CHAPTER FOUR: SATELLITE COMMUNICATION AS A REALISTIC ALTERNATIVE…………………………………………………… 10 4.1 APPLICATIONS OF SATELLITE COMMUNICATION……………………....….10 4.2 IMPACTS OF SATELLITE COMMUNCATION………………….………..…….. 12 4.3 CONCLUSION………………………………………………………………….….. 12REFERENCES vi
  8. 8. 1 CHAPTER ONE INTRODUCTIONA communications satellite is an artificial satellite stationed in space for the purpose oftelecommunications. The use of satellite in communication system is very much a fact ofeveryday in life. This is evidenced by many homes, which are equipped with antennas anddishes. These antennas were used for reception of satellite signal for television. Satellites alsoform an essential part of communication system worldwide carrying large amount of data andtelephone traffic in addition to television signals.Satellites offer a number of important features, which are not readily available with othersmeans of communication. Some of them are enumerated below. • Very large area of earth is visible from satellite (about 42%) i.e. communication is possible beyond earth curvature (beyond line of sight) • Satellite offers communication with remote communities in sparsely populated area, which are difficult to access by other means of communication. • ‘Satellite communication ignores political boundaries as well as geographical boundaries’1. • Satellite provides communication with moving aircraft from ground control station across the country. • ‘Satellite provides remote sensing i.e. detection of water pollution, oil field, monitoring and reporting of weather conditions etc’2. • For fixed (point-to-point) services, communications satellites provide a microwave radio relay technology complementary to that of communication cables. ‘They are also used for mobile applications such as communications to ships, vehicles, planes and hand-held terminals’3, and for TV and radio broadcasting, for which application of other technologies, such as cable television, is impractical or impossible.1.1 BRIEF HISTORY OF SATELLITE COMMUNICATIONSince the primary role of a satellite is to reflect electronic signal, the first artificial satellitewas the Soviet Sputnik 1, launched on October 4, 1957, and equipped with an on-board radio-transmitter that worked on two frequencies, 20.005 and 40.002 MHz .The first Americansatellite to relay communications was Project SCORE in 1958, which used a tape recorder tostore and forward voice messages. It was used to send a Christmas greeting to the world fromU.S. President Dwight D. Eisenhower. NASA launched an Echo satellite in 1960; the 100-foot (30m) aluminized PET film balloon served as a passive reflector for radio
  9. 9. 2communications. Courier 1B, built by Philco, also launched in 1960, was the world’s firstactive repeater satellite. With the launch of Alouette 1 in 1962 Canada became the thirdcountry to put a man-made satellite into space. Because Canada did not have any domesticlaunch capabilities of its own, Alouette 1, which was entirely built and funded by Canada,was launched by the American National Aeronautics and Space Administration (NASA) fromVandenberg AFB in California.‘In 1962, the American telecommunications giant AT&T launched the worlds first truecommunications satellite, called Telstar. Since then, countless communications satellites havebeen placed into earth orbit, and the technology being applied to them is forever growing insophistication.’4
  10. 10. 3 CHAPTER TWO BASICS OF SATELLITE COMMUNICATION2.1 BASIC COMPONENTS (ELEMENTS) OF COMMUNICATION SATELLITEEvery communications satellite in its simplest form (whether low earth or Geostationary)involves the transmission of information from an originating ground station to the satellite(the uplink), followed by a retransmission of the information from the satellite back to theground station (the downlink). Therefore satellite communications are comprised of 2 maincomponents: 2.1.1 The Satellite The satellite itself is also known as the space segment, and is composed of three separate units, namely the fuel system, the satellite and telemetry controls, and the transponder. ‘The transponder includes the receiving antenna to pick-up signals from the ground station, a broad band receiver, an input multiplexer, and a frequency converter which is used to reroute the received signals through a high powered amplifier for downlink.’5 2.1.2 The Ground Station This is the earth segment. ‘The ground stations job is two-fold. In the case of an uplink, or transmitting station, terrestrial data in the form of baseband signals, is passed through a baseband processor, an up converter, a high powered amplifier, and through a parabolic dish antenna up to an orbiting satellite. In the case of a downlink, or receiving station, it works in the reverse fashion as the uplink, ultimately converting signals received through the parabolic antenna to baseband signal.’6 2.2 BASIC REQUIREMENTS FOR SATELLITE COMMUNICATION 2.2.1 FUNCTIONAL REQUIREMENTS: These are core requirements for satellite communication. In the absence any of the following functional requirements, communication satellite would be as good as non-existing. i. Power Supply: The primary electrical power for operating Satellite electronic equipment is obtained from solar cells. Individual cells can generate small amounts of power, and therefore array of cells in series-parallel connection are required. ii. Attitude Control: The attitude of a satellite refers to its Orientation in space. Much of equipment carried abroad a satellite is there for the purpose of
  11. 11. 4 controlling its attitude. ‘Attitude control is necessary, for example, to ensure that directional antennas point in the proper directions.’7 In the case of earth environmental satellites the earth-sensing instrument must cover the required regions of the earth, which also requires attitude control. iii. Thermal control: Equipment in the satellite also generates heat which has to be removed, and satellites equipment should operate as near as possible in a stable temperature environment. ‘Therefore to achieve this, Thermal blankets and shields may be used to provide insulation while radiation mirrors are often used to remove heat from communication payload (transponders, antenna, and switching systems)’8 iv. TT&C subsystem: The Telemetry, Tracking, and Command (TT&C) subsystem performs several routine functions abroad a spacecraft. • Telemetry: The telemetry or "telemetering" function could be interpreted as "measurement at a distance". Specifically, it refers to the overall operation of generating an electrical signal proportional to the quantity being measured, and encoding and transmitting this to a distant station. ‘Data that are transmitted as telemetry signals includes attribute information (sun earth sensors), environmental information (magnetic field intensity and direction), and spacecraft information (temperatures and power supply voltages)’9. • Tracking: Tracking is obviously important during the transmitter and drift orbital phases of the satellite launch and it is necessary to be able to track the satellites movements and send correction signals as well as know the satellite range as required from time to time. This can be determined by measurement of propagation delay of signals specially transmitted for ranging purposes. • Command Systems: Command system receives instructions from ground system of satellite and decodes the instruction and sends suitable commends to other systems. v. Transponders: A transponder is the series of interconnected units which forms a single communication channel between the receiving and transmitting antennas in a communication satellite. They perform the major functions of receiving signals, conditioning the signals (suppressing noise, amplification), and re- transmitting them back to the ground station.2.2.2 FREQUENCY REQUIREMENTS: The communication between one point and another depends upon frequency of the transmitted signal as well as mode of
  12. 12. 5 communication. This is to say that frequency requirement greatly depends upon the mode of communication which are: a) Small distance Communication b) Long Distance CommunicationSmall Distance Communication: Frequencies up to approximately 10MHz can be usedfor small distance communication through Ground Wave Propagation. As frequencyincreases, the attenuation of ground wave increases (Earth starts behaving like absorber forhigh frequency signals) because of which, it is not possible to establish a reliablecommunication link through ground waves for frequencies more than 10MHz.Long Distance Communication: The signals having frequency more than 30MHz arepassed through ionosphere and these are required to reflect back to earth by some artificialmedium for establishing reliable communication between transmitter and receiver. Forfulfilling the requirement of high frequency and long distance communication across theglobe, the artificial reflector (Satellite) above the ionosphere are required for transmittedsignal. TO TV Transmitted signals FIGURE 1: Sky Wave Propagation OR Long Distance CommunicationThe table below shows the frequency allocation/ranges for Satellite Communication Band Designation Nominal Frequency Range Principal uses HF 3 -30 M Hz Short-wave Broadcast VHF 30 -300 M Hz FM, TV UHF 300 -3000 MHz TV, LAN, cellular, GPS L 1 -2 GHz Radar, GSO satellites TABLE 1: FREQUENCY ALLOCATION FOR SATELLITE COMMUNICATION
  13. 13. 62.3 ORBITS OF SATELLITE 1. Polar Orbits: The polar orbiting satellites orbit the earth in such a way as to cover the north and south Polar Regions. The altitude of polar orbiting satellite is constant over the polar region and it is approximately 1000 Km. The period of orbiting is about 1.5Hrs and at 90°inclination to ensure that satellite passes every region of earth. Example: IRIDIUM, GLOBAL STAR etc. 2. Equatorial Orbit: The equatorial orbit has 0° inclination from Equator. The most popular orbit is geostationary orbits which is present at 35786 Km from the Earth surface. The satellite in geostationary orbit appears to be stationary with respect to earth and period of satellite is 23Hrs, 56 minutes, 4 second means solar time (ordinary clock time). One disadvantage (for some purposes) of the geosynchronous orbit is that the time to transmit a signal from earth to the satellite and back is approximately percentage of a second, that is the time required to travel 35786 Km up and 35786 Km back down at the speed of light. For telephone conversations, this delay can sometimes be annoying but for data transmission and other uses it is not much significant.
  14. 14. 7 CHAPTER THREE TECHNOLOGICAL OVERVIEW 3.1 CHARACTERISTICS OF COMMUNICATION SATELLITE Incorporating satellites into terrestrial networks is often hindered by three characteristics possessed by satellite communication. 1. Latency (propagation delay): Due to the high altitudes of satellite orbits, the time required for a transmission to navigate a satellite link (more than 2/10ths of a second from earth station to earth station) could cause a variety of problems on a high speed terrestrial network that is waiting for the packets. 2. Poor Bandwidth: Due to radio spectrum limitations, there is a fixed amount of bandwidth allocable to satellite transmission. 3. Noise: Radio signals strength is in proportion to the square of the distance travelled. Due to the distance between ground station and satellite, the signal ultimately gets very weak. However this problem can be solved by using appropriate error correction techniques. 3.2 ERROR CORRECTION TECHNIQUES Due to the high noise present on a satellite link, numerous error correction techniques have been devised, and they are;1. Forward-error-correction (FEC): In this method a certain number of information symbols are mapped to new information symbols, but in such a way as to get more symbols than were original had. When these new symbols are checked on the receiving end, the redundant symbols are used to decipher the original symbols, as well as to check for data integrity. ‘The more redundant symbols that are included in the mapping, the better the reliability of the error correction.’10 Disadvantage(s) of Forward-error-Correction a. Waste of Bandwidth: The more redundant symbols that are used to achieve better integrity, the more bandwidth that is wasted, this is to say that this error correction technique uses relatively a large amount of redundant data and therefore may not be the most efficient choice on a clear channel. ‘But when noise levels are high, FEC can more reliably ensure the integrity of the data.’102. Automatic-repeat-request (ARR): In this method, data is broken into packets. Within each packet is included an error checking key. This key is often of the cyclic redundancy check (CRC) sort. If the error code reflects a loss of integrity in a packet, the receiver can request the sender to resend that packet. ARR is not very good in a channel with high noise, since
  15. 15. 8many retransmissions will be required, and the noise levels that corrupted the initial packetwill be likely to cause corruption in subsequent packets. ARR is more suitable to relativelynoise free channels.’10ARR could be achieved using varieties of method as seen below; i. Stop and Wait (SW):With this form of ARR, the sender must wait for an acknowledgement of each packet before it can send a new one. This can take upwards of 4/10ths of a second per packet since it takes 2/10ths seconds for the receiver to get the packet an another 2/10th seconds for the sender to receive the acknowledgement. ii. Go-back-N (GBN): This method of ARR is an improvement over “stop and wait” in that it allows the sender to keep sending packets until it gets a request for a resend. When the sender gets such a request, it sends packets starting at the requested packet over again. It can again send packets until it receives another retransmit request, and so on. iii. Selective-repeat (SR): This ARR protocol is an improvement over GBN in that it allows the receiver to request a retransmit of only that packet that it needs, instead of that packet and all that follows it. The receiver, after receiving a bad packet and requesting a retransmit, can continue to accept any good packets that are coming. This method is the most efficient method for satellite transmissions of the three ARR methods discussed.Disadvantage(s) of Automatic-repeat-request (ARR) a. Cost Effective: ARR methods can be demonstrated to provide a usable error correction scheme, but it is also the most expensive, in terms of hardware. This is in part due to the buffering memory that is required, but more importantly to the cost of the receiver, which needs to be able to transmit re-requests. ‘Systems such as the Digital Broadcast Satellites used for television signal distribution would become inordinately expensive if they had to make use of ARR, since the home based receiver would now need to be a transmitter, and the 18 inch dish would be inadequate for the requirements of transmitting back to a satellite.’103.3 HYBRID NETWORKSIn todays global networking landscape, there are many ways to transmit data from one placeto another and one way to get around the need in ARR for the receiver to have to requestretransmit via an expensive and slow satellite link is to use a form of hybrid network.‘A hybrid network is one that allows data to flow across a network, using satellite, wireless orterrestrial, transparently.’10
  16. 16. 9‘In one form of hybrid network, the receiver transmits its requests back to the sender via aterrestrial link. Terrestrial link allows for quicker, more economical and less error pronetransmission from the receiver, and the costs associated with the receivers hardware aregreatly reduced when compared to the costs involved if it had to transmit back over thesatellite link.’11 ‘There are products on the market today that allow a home user to get internetaccess at around 400MB via digital satellite, while its retransmit signals are sent via aninexpensive modem or ISDN line.’12
  17. 17. 10 CHAPTER FOUR SATELLITE COMMUNICATION AS A REALISTIC ALTERNATIVE Satellite Communication has replaced other means of communication that were in existence before its grand arrival. To prove this fact, applications and impacts of satellite communication has been adopted as seen below:4.1 APPLICATIONS OF SATELLITE COMMUNICATION I. TRADITIONAL TELECOMMUNICATION (TELEPHONY) The first and historically most important application for communication satellites was in intercontinental long distance telephony. Since the beginnings of the long distance telephone network, there has been a need to connect the telecommunications networks of one country to another, and this has been accomplished in several ways. The fixed Public Switched Telephone Network relays telephone calls from land line telephones to an earth station, where they are then transmitted to a geostationary satellite, and then the downlink follows an analogous path. ‘Improvements in submarine communications cables, through the use of fibre-optics, caused some decline in the use of satellites for fixed telephony in the late 20th century, but they still serve remote islands.’13 II. SATELLITE TELEVISION (TELEVISION SIGNALS) Satellites have been used since the 1960s to transmit broadcast television signals between the network hubs of television companies and their network affiliates. This free viewing of corporate content by individuals led to scrambling and subsequent resale of the descrambling codes to individual customers, which started the direct-to-home industry. The direct-to-home industry has gathered even greater momentum since the introduction of digital direct broadcast service. • Direct Broadcast Satellite: A direct broadcast satellite is a communications satellite that transmits to small DBS satellite dishes (usually 18 to 24 inches or 45 to 60 cm in diameter). ‘Direct broadcast satellites generally operate in the upper portion of the microwave Ku band. DBS technology is used for DTH-oriented (Direct-To-Home) satellite TV services. DBS is commonly used in United States, United Kingdom, New Zealand, South Africa etc.’14 • Fixed Service Satellites: FSS uses the C band, and the lower portions of the Ku bands. ‘They are normally used for broadcast feeds to and from television networks and local affiliate stations, as well as being used for distance learning by schools and universities, business television (BTV), Videoconferencing, and general commercial
  18. 18. 11 telecommunications.’13 FSS satellites are also used to distribute national cable channels to cable television head endsIII. MOBILE SATELLITE TECHNOLOGIESSome manufacturers have introduced special antennas for mobile reception of DBStelevision. Using Global Positioning System (GPS) technology as a reference, these antennasautomatically re-aim to the satellite no matter where or how the vehicle (on which theantenna is mounted) is situated.IV. GLOBAL POSITIONING SERVICESAnother Very Small Aperture Terminal (VSAT) oriented service, in which a small apparatuscontaining the ability to determine navigational coordinates by calculating a triangulating ofthe signals from multiple geosynchronous.V. MARINE COMMUNICATIONSIn the maritime community, satellite communication systems provide good communicationlinks to ships at sea. These links use a VSAT type device to connect to geosynchronoussatellites, which in turn link the ship to a land based point of presence to the respective nationtelecommunications system.VI. SATELLITE MESSAGING FOR COMMERCIAL JETSAnother service provided by geosynchronous satellites is the ability for a passenger on anairborne aircraft to connect directly to a land based telecom network.VII. SATELLITE RADIOSatellite radio offers audio services in some countries, notably the United States. Mobileservices allow listeners to roam a continent, listening to the same audio programminganywhere.A satellite radio or subscription radio (SR) is a digital radio signal that is broadcast by acommunications satellite, which covers a much wider geographical range than terrestrialradio signals.VIII. SATELLITE INTERNETAfter the 1990s, satellite communication technology has been used as a means to connect tothe Internet via broadband data connections. This can be very useful for users who are locatedin remote areas, and cannot access a broadband connection, or require high availability ofservices.
  19. 19. 124.2 IMPACTS OF SATELLITE COMMUNCATION i. Very large area of earth is visible from satellite (about 42%) i.e. communication is possible beyond earth curvature (beyond line of sight) ii. Satellite offers communication with remote communities in sparsely populated area, which are difficult to access by other means of communication. iii. Satellite communication ignores political boundaries as well as geographical boundaries. iv. Satellite provides communication with moving aircraft from ground control station across the country. v. Satellite provides remote sensing i.e. detection of water pollution, oil field, monitoring and reporting of weather conditions etc. vi. For fixed (point-to-point) services, communications satellites provide a microwave radio relay technology complementary to that of communication cables. They are also used for mobile applications such as communications to ships, vehicles, planes and hand-held terminals, and for TV and radio broadcasting, for which application of other technologies, such as cable television, is impractical or impossible.4.3 CONCLUSION: The discovery of Satellite Communication has significantly changed our communication modes for better. Although the use of fibre-optics in submarine communication cables has substantially leaped satellite communication of its initial glory, communication satellite remains the best and easiest means of communication since its use and services have inevitably filled communication gap globally. Hence it is a REALISTIC ALTERNATIVE.
  20. 20. REFERENCES1. Gerard Maral,Michel Bousquet, "Satellite Communication System: Systems, Techniques & Technology", John Wiley & Sons, Incorporated, 1993.2. Cochetti, Roger, "Mobile Satellite Communications Handbook", Quantum Publishing, Incorporated 1995.3. Dennis Roddy, "Satellite Communications", McGraw Hill Text, 1995.4. Tom Logsdon, "Mobile Communication Satellites", McGraw Hill Text, February 1995.5. Deepak Ayyagari and Anthony Ephremides, "Enhancement of Cellular Service via the use of Satellite Capacity," University of Maryland, 1995.6. Elbert, Bruce R, The satellite communication applications handbook, Boston, MA: Artech House, 1997.7. Feldman, Phillip M., An overview and comparison of demand assignment multiple access (DAMA) concepts for satellite communications networks Santa Monica, CA: RAND, 1996.8. International journal of satellite communications, Chichester, Sussex: Wiley, c1983.9. Satellite communications systems and technology--Europe, Japan, Russia / Burton I. Edelson ... [et al.], Park Ridge, N.J., U.S.A. : Noyes Data Corp., c1995.10. Daniel E. Friedman, Master’s Thesis: "Error Control for Satellite and Hybrid Communication Networks", directed by Daniel E. Friedman, 1995.11. Vivek Arora, Narin Suphasindhu, John S. Baras, Douglas Dillon, "Effective Extensions of Internet in Hybrid Satellite-Terrestrial Networks", University of Maryland at College Park & Hughes Network Systems, Inc., 1996.12. John S. Baras, ATM in Hybrid Networks, Center for Satellite and Hybrid Communication Networks, 1996.13. Michael J. Miller (Editor),Branka Vucetic (Editor),Les Berry (Editor) , "Satellite Communications: Mobile & Fixed Services" Kluwer Academic Publishers, 1993.14. Wood, James, Satellite communications and DBS systems. Boston: Focal Press, 1992.15. Lindberg, Bertil C., Digital broadband networks and services, New York : McGraw-Hill, 199516. Http://www.tutorialsweb.com/fundamentals-of-satellite-communications.htm17. Http://www.wikipedia.com/Communications_satellite.htm18. Litva, J. (John), Digital beamforming in wireless communications, Boston : Artech House, c1996.

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