Satcomm

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Satcomm

  1. 1. NATIONAL COLLEGE OF SCIENCE AND TECHNOLOGY Amafel Bldg. Aguinaldo Highway Dasmariñas City, Cavite Assignment 1 SATELLITE COMMUNICATIONSReyes, Ron Henreb C. September 05, 2011Communications 1/BSECE 41A1 Score: Engr. Grace Ramones Instructor
  2. 2. SATELLITE COMMUNICATIONIn telecommunications, the use of artificial satellites to provide communication links betweenvarious points on Earth. Satellite communications play a vital role in the globaltelecommunications system. Approximately 2,000 artificial satellites orbiting Earth relay analogand digital signals carrying voice, video, and data to and from one or many locations worldwideSATELLITE APPLICATIONSTelephoneAn Iridium satelliteThe first and historically most important application for communication satellites was inintercontinental long distance telephony. The fixed Public Switched TelephoneNetwork relaystelephone calls from land line telephones to an earth station, where they are thentransmitted to a geostationary satellite. The downlink follows an analogous path. Improvementsinsubmarine communications cables, through the use of fiber-optics, caused some decline inthe use of satellites for fixed telephony in the late 20th century, but they still serve remoteislands such as Ascension Island, Saint Helena, Diego Garcia, and Easter Island, where nosubmarine cables are in service. There are also regions of some continents and countrieswhere landline telecommunications are rare to nonexistent, for example large regions of SouthAmerica, Africa, Canada, China, Russia, and Australia. Satellite communications also provideconnection to the edges of Antarctica and Greenland.Satellite phones connect directly to a constellation of either geostationary or low-earth-orbitsatellites. Calls are then forwarded to a satellite teleport connected to the Public SwitchedTelephone NetworkSatellite televisionAs television became the main market, its demand for simultaneous delivery of relatively fewsignals of large bandwidthto many receivers being a more precise match for the capabilities of
  3. 3. geosynchronous comsats. Two satellite types are used for North American television andradio: Direct broadcast satellite (DBS), and Fixed Service Satellite (FSS)The definitions of FSS and DBS satellites outside of North America, especially in Europe, are abit more ambiguous. Most satellites used for direct-to-home television in Europe have the samehigh power output as DBS-class satellites in North America, but use the same linear polarizationas FSS-class satellites. Examples of these are the Astra, Eutelsat, and Hotbird spacecraft inorbit over the European continent. Because of this, the terms FSS and DBS are more so usedthroughout the North American continent, and are uncommon in Europe.Fixed Service SatelliteFixed Service Satellites use the C band, and the lower portions of the Ku bands. They arenormally used for broadcast feeds to and from television networks and local affiliate stations(such as program feeds for network and syndicated programming, live shots, and backhauls),as well as being used for distance learning by schools and universities,businesstelevision (BTV), Videoconferencing, and general commercial telecommunications. FSSsatellites are also used to distribute national cable channels to cable television headends.Free-to-air satellite TV channels are also usually distributed on FSS satellites in the Ku band.The Intelsat Americas 5,Galaxy 10R and AMC 3 satellites over North America provide a quitelarge amount of FTA channels on their Ku bandtransponders.The American Dish Network DBS service has also recently utilized FSS technology as well fortheir programming packages requiring their SuperDish antenna, due to Dish Network needingmore capacity to carry local television stations per the FCCs "must-carry" regulations, and formore bandwidth to carry HDTV channels.Direct broadcast satelliteA direct broadcast satellite is a communications satellite that transmits to small DBS satellitedishes (usually 18 to 24 inches or 45 to 60 cm in diameter). Direct broadcast satellites generallyoperate in the upper portion of the microwaveKu band. DBS technology is used for DTH-oriented(Direct-To-Home) satellite TV services, such as DirecTV and DISH Network in the UnitedStates, Bell TV and Shaw Direct in Canada, Freesat and Sky Digital in the UK, the Republic ofIreland, and New Zealand and DSTV in South Africa .Operating at lower frequency and lower power than DBS, FSS satellites require a much largerdish for reception (3 to 8 feet (1 to 2.5m) in diameter for Ku band, and 12 feet (3.6m) or larger forC band). They use linear polarization for each of the transponders RF input and output (as
  4. 4. opposed to circular polarization used by DBS satellites), but this is a minor technical differencethat users do not notice. FSS satellite technology was also originally used for DTH satellite TVfrom the late 1970s to the early 1990s in the United States in the form of TVRO (TeleVisionReceive Only) receivers and dishes. It was also used in its Ku band form for the now-defunct Primestar satellite TV service.Satellites for communication have now[when?] been launched that have transponders inthe Ka band, such as DirecTVsSPACEWAY-1 satellite, and Anik F2. NASA as well haslaunched experimental satellites using the Ka band recently.Mobile satellite technologiesInitially available for broadcast to stationary TV receivers, by 2004 popular mobile directbroadcast applications made their appearance with the arrival of two satellite radio systems inthe United States: Sirius and XM Satellite Radio Holdings. Some manufacturers have alsointroduced special antennas for mobile reception of DBS television. UsingGlobal PositioningSystem (GPS) technology as a reference, these antennas automatically re-aim to the satelliteno matter where or how the vehicle (on which the antenna is mounted) is situated. These mobilesatellite antennas are popular with some recreational vehicle owners. Such mobile DBSantennas are also used by JetBlue Airways for DirecTV (supplied by LiveTV, a subsidiary ofJetBlue), which passengers can view on-board on LCD screens mounted in the seats.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 terrestrial radiosignals.Satellite radio offers a meaningful alternative to ground-based radio services in some countries,notably the United States. Mobile services, such as Sirius, XM, and Worldspace, allow listenersto roam across an entire continent, listening to the same audio programming anywhere they go.Other services, such as Music Choice or Muzaks satellite-delivered content, require a fixed-location receiver and a dish antenna. In all cases, the antenna must have a clear view to thesatellites. In areas where tall buildings, bridges, or even parking garages obscure the signal,repeaters can be placed to make the signal available to listeners.Radio services are usually provided by commercial ventures and are subscription-based. Thevarious services are proprietary signals, requiring specialized hardware for decoding and
  5. 5. playback. Providers usually carry a variety of news, weather, sports, and music channels, withthe music channels generally being commercial-free.In areas with a relatively high population density, it is easier and less expensive to reach thebulk of the population with terrestrial broadcasts. Thus in the UK and some other countries, thecontemporary evolution of radio services is focused on Digital Audio Broadcasting (DAB)services or HD Radio, rather than satellite radio.Amateur radioAmateur radio operators have access to the OSCAR satellites that have been designedspecifically to carry amateur radio traffic. Most such satellites operate as spaceborne repeaters,and are generally accessed by amateurs equipped with UHF or VHF radio equipment and highlydirectional antennas such as Yagis or dish antennas. Due to launch costs, most current amateursatellites are launched into fairly low Earth orbits, and are designed to deal with only a limitednumber of brief contacts at any given time. Some satellites also provide data-forwardingservices using the AX.25 or similar protocols.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 broadbandconnection, or require high availability ofservices.Military usesCommunications satellites are used for military communications applications, such as GlobalCommand and Control Systems. Examples of military systems that use communicationsatellites are the MILSTAR, the DSCS, and theFLTSATCOM of the UnitedStates, NATO satellites, United Kingdom satellites, and satellites of the former Soviet Union.Many military satellites operate in the X-band, and some also use UHF radio links, whileMILSTAR also utilizes Ka band.
  6. 6. SATELLITE SYSTEMS: There are three different types of satellite systems.1. International satellite communication system INTELSAT.2. Domestic satellite system DOMSAT.3. Search and rescue system SARSAT. INTELSAT: The INTELSAT Organization was established in 1964 to handle the myriad of technical and administrative problems associated with a world wide telecommunication system. The international regions served by INTELSAT are divided in to the Atlantic Ocean region (AOR), the Pacific Ocean Region (POR), and the Indian Ocean region (IOR). For each region , satellites are positioned in geo-stationary orbit above the particular Ocean, where they provide a transoceanic telecommunication route. In addition to providing trans oceanic routes, the INTELSAT satellites are used for domestic services within any given country and regional services between countries. Two such services are vista for telephony and Intelnet for data exchange. DOMSAT Domestic satellites are used to provide various telecommunication services, such as voice, data, and video transmission (T.V channels), with in a country. Satellite cell phones allow global travelers and those in remote areas to avoid landlines and terrestrial cell phone services entirely. Satellite cell phones relay your call to a satellite and down through a hub to the end user. This means that most of the earths geographical area is now accessible by a satellite cell phone! Third party providers of satellite cell include Satcom Global, Roadpost Satcom, Online Satellite Communications, and others.
  7. 7. SARSAT SARSAT is one type of Polar orbiting satellites. Polar-orbiting satellites orbit the earth in such a way as to cover the north and south polar-regions. Infinite number of polar polar satellite orbits are possible Polar satellites are used to provide environmental data, and to help locate ships and aircraftsin distress .This service known as SARSAT, for search and rescue satellite. This figure shows polar satellite path and earth rotation

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