Category:Satellite Communications

From Eurêka

Jump to: navigation, search

Contents

Satellite Communications

Satellite communications Use of satellites to relay signals between ground stations.

  1. Satellite link Radio link between a transmitting Earth station and a receiving Earth station through one satellite.

Communication satellite (Telecommunication satellites) Space-based vehicle containing electronic equipment that relays messages between earth-based transmitter and earth-based receiver. Usually the communication satellite is in a geostationary orbit with a period of twenty-four hours.

Direct readout Capability that allows a ground station to collect and interpret the data messages that are transmitted from satellites.

Fixed-satellite service Radio-communication service between Earth stations at specified fixed points when one or more satellites are used. In some cases this service includes satellite-to-satellite links which may also be effected by the intersatellite service. The fixed-satellite service may also include feeder links for other space radio-communication services.

Broadcasting-satellite service Radio-communication service in which signals transmitted or retransmitted by space stations are intended for direct reception by the general public.

Frequency of observation Normal period, usually measured in days, elapsing between tow sequential times at which a point on Earth falls within the field of view of one of the spacecraft of the system.

Receive-only earth station (ROES) Receive only earth station for reception of satellite telecommunications.

A priori planning of radio frequencies Procedure by which frequencies and orbital locations are allotted to individual countries according to a plan negotiated by member nations and implemented by the ITU.

DirecDuo® Combined TV and high-speed internet system involving four tightly clustered satellites in geosynchronous orbit, that require only one receiving dish, introduced July 1997.

  1. Direct broadcast satellite TV segment of the service, utilizing 3 satellites.
  2. High-speed Internet service Internet segment utilizing one satellite, downloads at 400,000 bits per second, but uploads at only 28,800 bits per second.

Satellite Earth Stations

Earth station Term used to describe the combination or antenna, low-noise amplifier (LNA), down-converter, and receiver electronics. used to receive a signal transmitted by a satellite. Earth Station antennas vary in size from the 65cm x 3.7m (2 foot x 12 foot) diameter size used for TV reception to as large as 30m1 (00 feet) in diameter sometimes used for international communications. The typical antenna used for INTELSAT communication is today 13 x 18 m (40 to 60 feet).

  1. Very small aperture terminal (VSAT). Refers to small earth stations with a very small antenna, usually in the 1.2 to 2.4m range.
    1. Ultra small aperture terminals (USAT) Small aperture with terminals under 0.5m.
  2. Polar mount Antenna mechanism permitting steering in both elevation and azimuth through rotation about a single axis. While an astronomer’s polar mount has its axis parallel to that of the earth, satellite earth stations utilize a modified polar mount geometry that incorporates a declination offset.
  3. Effective isotropic radiated power (EIRP) Strength of the signal leaving the satellite antenna or the transmitting earth station antenna, and is used in determining the C/N and S/N. The transmit power value in units of dBW is expressed by the product of the transponder output power and the gain of the satellite transmit antenna.

Uplink Unidirectional communications link from an earth station (antenna) to a satellite.

Downlink Unidirectional communications link from a satellite to an earth station (antenna).

Hub Master station through which all communications to, from and between micro terminals must flow, in the future satellites with on-board processing will allow hubs to be eliminated as MESH networks are able to connect all points in a network together.

Slant range Length of the path between a communications satellite and an associated earth station.

Receiver (Rx) Electronic device which enables a particular satellite signal to be separated from all others being received by an earth station, and converts the signal format into a format for video, voice or data.

  1. Receiver sensitivity Expressed in dBm this tells how much power the detector must receive to achieve a specific baseband performance, such as a specified bit error rate or signal to noise ratio.

Low noise amplifier (LNA) Preamplifier between the antenna and the earth station receiver. For maximum effectiveness, it must be located as near the antenna as possible, and is usually attached directly to the antenna receive port. The LNA is especially designed to contribute the least amount of thermal noise to the received signal.

  1. Low noise block down converter (LNB) Combination Low Noise Amplifier and downconverter built into one device attached to the feed.
  2. G/T Figure of merit of an antenna and low noise amplifier combination expressed in dB. “G” is the net gain of the system and “T” is the noise temperature of the system. The higher the number, the better the system.

Satellite Signals

Spot beam Focused antenna pattern sent to a limited geographical area. Spot beams are used by domestic satellites to deliver certain transponder signals to geographically well defined areas such as Hawaii, Alaska and Puerto Rico.

  1. Global beam Antenna down-link pattern used by the Intelsat satellites, which effectively covers one-third of the globe. Global beams are aimed at the center of the Atlantic, Pacific and Indian Oceans by the respective Intelsat satellites, enabling all nations on each side of the ocean to receive the signal. Because they transmit to such a wide area, global beam transponders have significantly lower EIRP outputs at the surface of the Earth as compared to a US domestic satellite system which covers just the continental US. Therefore, earth stations receiving global beam signals need antennas much larger in size (typically 10 meters and above (i.e. 30 feet and up).

Spread spectrum Transmission of a signal using a much wider bandwidth and power than would normally be required. Spread spectrum also involves the use of narrower signals that are frequency hopped through various parts of the transponder. Both techniques produce low levels of interference Between the users. They also provide security in that the signals appear as though they were random noise to unauthorized earth stations. Both military and civil satellite applications have developed for spread spectrum transmissions.

Frequency coordination Process to eliminate frequency interference between different satellite systems or between terrestrial microwave systems and satellites. In the US this activity relies upon a computerized service utilizing an extensive database to analyze potential microwave interference problems that arise between organizations using the same microwave band. As the same C-band frequency spectrum is used by telephone networks and CATV companies when they are contemplating the installation of an earth station, they will often obtain a frequency coordination study to determine if any problems will exist.

Spillover Satellite signal that falls on locations outside the beam pattern’s defined edge of coverage.

Skew Adjustment that compensates for slight variance in angle between identical senses of polarity generated by two or more satellites.

Footprint Map of the signal strength showing the EIRP contours of equal signal strengths as they cover the earth’s surface. Different satellite transponders on the same satellite will often have different footprints of the signal strength. The accuracy of EIRP footprints or contour data can improve with the operational age of the satellite. The actual EIRP levels of the satellite, however, tends to decrease slowly as the spacecraft ages.

Margin Amount of signal in dB by which the satellite system exceeds the minimum levels required for operation.

Edge of coverage (EOC) Limit of a satellite’s defined service area. In many cases, the EOC is defined as being 3 dB down from the signal level at beam center. However, reception may still be possible beyond the -3dB point.

Solid state power amplifier (SSPA) VSLI solid state device that is gradually replacing Traveling Wave Tubes in satellite communications systems because they are lighter weight and are more reliable.

  1. Traveling wave tube amplifier (TWTA)

Transponder Combination receiver, frequency converter, and transmitter package, physically part of a communications satellite. Transponders have a typical output of five to ten watts, operate over a frequency band with a 36 to 72 megahertz bandwidth in the L, C, Ku, and sometimes Ka Bands or in effect typically in the microwave spectrum, except for mobile satellite communications. Communications satellites typically have between 12 and 24 onboard transponders although the INTELSAT VI at the extreme end has 50.

  1. Half transponder Method of transmitting two TV signals through a single transponder through the reduction of each TV signal’s deviation and power level. Half-transponder TV carriers each operate typically 4 dB to 7 dB below single-carrier saturation power.
  2. Single-channel-per-carrier (SCPC) Method used to transmit a large number of signals over a single satellite transponder.
  3. Frequency division multiple access (FDMA) Refers to the use of multiple carriers within the same transponder where each uplink has been assigned frequency slot and bandwidth. This is usually employed in conjunction with Frequency Modulation.

Polarization Technique used by the satellite designer to increase the capacity of the satellite transmission channels by reusing the satellite transponder frequencies. In linear cross polarization schemes, half of the transponders beam their signals to earth in a vertically polarized mode; the other half horizontally polarize their down links. Although the two sets of frequencies overlap, they are 90 degree out of phase, and will not interfere with each other. To successfully receive and decode these signals on earth, the earth station must be outfitted with a properly polarized feedhorn to select the vertically or horizontally polarized signals as desired. In some installations, the feedhorn has the capability of receiving the vertical and horizontal transponder signals simultaneously, and routing them into separate LNAs for delivery to two or more satellite television receivers. Unlike most domestic satellites, the Intelsat series use a technique known as left-hand and right-hand circular polarization.

  1. Circular polarization Unlike many domestic satellites which utilize vertical or horizontal polarization, the international Intelsat satellites transmit their signals in a rotating corkscrew-like pattern as they are down-linked to earth. On some satellites, both right-hand rotating and left-hand rotating signals can be transmitted simultaneously on the same frequency; thereby doubling the capacity of the satellite to carry communications channels.

Polarization rotator Device that can be manually or automatically adjusted to select one of two orthogonal polarizations.

Delay Time it takes for a signal to go from the sending station through the satellite to the receiving station. This transmission delay for a single hop satellite connection is very close on one-quarter of a second.

Quadrature phase shift keying (QPSK) System of modulating a satellite signal.

Phase-locked loop (PLL) Type of electronic circuit used to demodulate satellite signals.


Satellite Communications Industry

Satellite Communications Industry Communications satellite business is dominated by a handful of large companies, but there are smaller companies that operate only one or two satellites.

Global personal communications Satellite-based personal communications creating a global telephone network designed for globe-trotting executives who have to reach their offices from anywhere in the world, especially those places with poorly developed telecommunication’s services.

Echo 1 Passive communications satellite consisting of a 30-meter diameter, inflated orbiting balloon launched into low Earth orbit , 12 August 1960.

ATS-6 First experimental communications satellite with capability for direct broadcasts to small domestic antennae.

Telstar First privately constructed active communications satellite by AT&T, that had an active transponder (transmitter/responder). A half-ton satellite carries 12 such devices and a one-ton satellite carries 24 to 32 transponders, launched 10 July 1962. Relayed the first live transatlantic TV on 23 July 1962.

Syncom II First geosynchronous communications satellite, launched 26 July 1963.

Anik (Eskimo, = brother) Series of Canadian communication satellites, launched from early 1970s.

Inmarsat (International Maritime Satellite Organization) Regulates the world’s satellites for marine purposes, set up in London 1975, became a private company 1999.

Eutel Consortium formed by European PTTs to coordinate interests of the main users of European communications satellites, like OTS and ECS, to provide competition to Intelsat, based in Paris, 1970s. Became a private company with 19 working satellites, 2001.

  1. European Communications Satellite (ECS) Communications satellite program run by ESA, which provides Europe with a satellite system similar to that of the US.
  2. Deutscher Fernmeldesatellit (DFS) German telecommunications satellite.
  3. CCTS (= Comité de coordination pour les télécommunications par satellites) Coordination Committee for Satellite Telecommunications

Westar Series of communications satellites owned by the Western Union Corporation for communication in the US.

Iridium (orig, Satellite Cellular Voice and Data Communication System) Global wireless telephone (PCS) system and one-way data transmission that cost over $5 billion, that was described as outdated, outmoded and unpopular with consumers. Developed by Motorola in the late 1980s and established as a business in 1990, Iridium picks up a call from a hand-held telephone, passes it digitally from satellite to satellite, and then switches it to a landline where the call is completed. Network of 66 satellites rotating around the Earth at an altitude of about 500 miles was created within a year with launchings from US, Baikonur Cosmodrome in Kazakhstan and China, the final launchings were a Boeing Delta II rocket and a Chinese Long March 2C/SD rocket, May 1998, commercial service began 1 November 1998.

Note Originally they planned to have 77 satellites, hence the name iridium with its 77 electrons ringing the nucleus, but they did not change the name to dysprosium when the number of satellites dropped to 66.

  1. Iridium LLC Global communication system, the world’s first truly pan-national company operating seamlessly across national boundaries in which profits were to be repatriated to the investors’ home countries to be taxed and invested locally. Service was able to muster only 55,000 subscribers, not enough to pay interest on its startup costs, and it filed for Chapter 11 bankruptcy August 1999.
    1. Iridium Italia SpA Independent company with its own CEO and governing board.
    2. Iridium Middle East Corporation Independent company with its own CEO and governing board.
  2. Iridiots Employee parlance for those who held on to their jobs to the closure, playing solitaire on their computers.
  3. Iridium Satellite Company takes over assets of Iridium LLC for $25 million, having obtained a Pentagon contract, with Boeing operating the system, reported 8 December 2000.

Teledesic Global communication system focusing on data communication rather than voice, backed by Teleglobe Inc. of Canada, William H. Gates of Microsoft, Craig O. McCaw, and joined in May 1997 by Boeing Corporation as the prime contractor. The Earth is surrounded by 288 low-Earth orbit satellites (LEOS) handling all kind of communications from voice calls to interactive multimedia, the network being designed by Hans-Werner Braun. Unveiled in 1994, first satellite launched in May 1997, and due to be in full operation by 2005.

  1. Internet in the sky Phrase used by Craig O. McCaw when he originally launched Teledesic project with 840 satellites orbiting at 435 miles, 1994.
  2. Teledesic/ICO Craig O. McCaw takes over bankrupt ICO Global Space Communications and merges it into Teledesic, June 2000.
    1. ICO Global Space Communications Private company to provide a global telephone system based on a 12-satellite network built by Hughes Electronics, started by Inmarsat, the international organization that offers marine-telephone service. Filed for bankruptcy 27 August 1999.
    2. ICO Global Communications (ICO) renamed, 19 May 2000.

Loral Global (Loral Space and Communications) Manufactured 52 satellites for Globalstar and is the managing partner and largest shareholder of Globalstar Telecommunications. 10 working satellites (2001).

  1. Globalstar International consortium that created a PCS system to bounce calls back from satellite to ground station, where it is fed into a long-distance landline. The system requires the collection of up to 140 ground stations working in perfect synchronization with 48 low-orbiting satellites launched in 1998, but the project was set back when the Zenit 2 rocket carrying 12 of them crashed in Kazakhstan, 9 September 1998. Began phone service 2000 with full operation projected, 2002. By January 2001, it had only 31,200 subscribers, a fraction of the 1.5 million to cover operating expenses, and was on the brink of bankruptcy.
    1. Globalstar LLC Owner and operator of Globalstar network.
    2. Globalstar Telecommunications Publicly traded holding company based in Bermuda, that is the general partner in Globalstar LLC, whose largest shareholder is Loral Space and Communications with $1.3 billion in the venture. Qualcomm, which makes telephones for Globalstar, is another major investor, with $610 million in the venture.
  2. Skynet network Lorel’s network.

Odyssey PCS system by TRW Inc. offering global coverage with only 12 satellites orbiting much further out, and a smaller number of ground stations.

PanAmSat Corp. Largest owner/operator of 21 commercial satellites used by paging and telephone companies, and television and data services, such as AOL, Time Warmer, Walt Disney and Viacom, owned by Hughes Electronics, based in Wilton, Conn.

  1. Hughes Electronics/PanAmSat Hughes Electronics merges it satellite operation with PanAmSat, 20 September 1996.
  2. Galaxy IIIR Satellite used to supply direct-to-home video as part of Hugh’s DirectTV service in Latin America, launched 1995.
  3. Galaxy X Satellite made by Hughes Electronics for PanAmSat, lost 24 August 1998.
  4. NET/36 PanAmSat high-speed Internet network.

SES Global (Société Européenne des Satelittes SA) Market leader with 28 working satellites and access to 13 others (AsiaSat; Brasilsat) formed by a merger of GE American Communications, a unit of General Electric, and SES Astra, based in Luxembourg, 2001.

  1. Astra Satellite network.

Other Satellites

Experimental Communications Satellite Series of Japanese communications satellites.

Broadcast Satellite Experiment Japanese communications satellite particularly intended to investigate direct television transmission.

AsiaSat

Solidaridad I Mexican telecommunications satellite built by Hughes Space and Communications Company whose principal central processor broke down in 1999, and gave up totally late-August 2000.

  1. Satmex Mexico’s only satellite operating company that had 4 satellites

Brasilsat

Eutelsat

Eutelsat European satellite operator managing a system of satellites in geostationary orbit, 12 fully stabilized satellites: five Hot Birds™, Eurobird™, W1, W2, W3, W4, Sesat and Atlantic Bird 2. The system covers the entire European continent, as well as Africa and the Middle East, south-west Asia, eastern North America, and South America, for broadcasting and video network services, corporate network solutions, Internet services and mobile communications. Headquartered in Paris.

  1. Eutelsat do Brasil Eutelsat subsidiary in Brazil.
  2. Skylogic Italia Eutelsat subsidiary in Italy.

Eutelsat II Satellites designed as multi-purpose satellites for international communications. Between 1990 and 1992 five satellites were successfully launched, designated EUTELSAT II-F1, II-F2, II-F3, II-F4 and II-F6.

  1. II-F6 Last of the series is of a different design and is included the Hot Bird™ satellite family (Hot Bird™ 1).

W satellites replacement for Eutelsat II series.

SESAT (= Siberia - Europe SATellite) Satellite provides a wide range of telecommunications services over a very large geographical coverage area extending from the Atlantic Ocean to Eastern Russia, including a large part of Siberia. Launched 18 April 2000.

Hot Bird™ Seven satellites at 13 degrees East forming one of the largest broadcasting systems in the world, delivering nearly 700 analogue and digital television channels to satellite and cable homes in Europe, North Africa and large parts of the Middle East. The system also provides over 560 radio and multimedia services over the same wide coverage area.

Eurobird™ Satellite provides broadcasting and telecommunication services primarily to the Western and Central European region from an orbital position of 28.5° E., designed for 24-channel operation over its minimum lifetime of 12 years, launched 8 March 2001.

Atlantic Bird 2™ Satellite to broadcast radio and television signals across Europe, North Africa and Asia, launched by Lockheed Martin Atlas 5 rocket, 29 August 2002.

Intelsat

Intelsat (formerly, International Telecommunications Satellite Organization) International consortium that has been described as the “gold standard for operating a fleet” of satellites. The name refers both to a communications satellite organization and to the satellite organization and the satellites it launches. The organization was established in 1964 by eleven nations, and now has 146 member countries. Headquartered in Washington DC with a marketing subsidiary in London.

  1. Colino affair Intelstat’s director general, Richard R. Colino, for most of the 1980s was sentenced to six years in prison for organizing the theft of $5.4 million from Intelstat, mostly in connection with construction of its Washington DC headquarters and Jose L. Alegrett, his deputy, was also convicted for his role in the illegal activities, 1988.

IBS (= Intelsat Business Services)

Intelsat I (pop, Early Bird) Intelsat’s first satellite launched in 1965.

Intelsat V Satellite with a capacity 100 times that of Intelsat I in terms of channels available. Several satellites are kept in geostationary orbit simultaneously, and handle both telephone and television channels.

  1. Communication Satellite Corporation (Comsat) Based in the US, it provides technical and operational support services for the transglobal satellite communications systems using the Intelsat satellite services.
    1. Lockheed Martin/Comsat Acquired by Lockheed Martin from which it got its equity in Intelsat, 1999.
  2. New Skies Satellites Intelsat spun off 5 satellites into a start-up in the Netherlands, 1998.

Intelsat privatization Privatized into a Bermuda-based holding company with 20 satellites working, largest shareholder is Lockheed Martin, July 2001.

Proposed Satellite Systems

Celestri Satellite network based on low-orbit satellites, proposed by Motorola providing voice, data and video communications to large companies that operate around the world, announced June 1997, and projected to begin operations in 2002. Never appeared.

Final Analysis Global wireless data system based in Lanham, Md, that is launching 30 low-orbit satellites from pads in Russia to provide coverage for wireless data customers in North America.

  1. BellSouth Wireless Data Unit of BellSouth research and marketing partner to Final Analysis, announced 12 December 2000.

Satellite Radio

Satellite radio (Subscription radio) (SR) Digital radio signal that is broadcast by a communications satellite, which covers a much wider geographical range than terrestrial radio signals. SR functions any place there is line of sight between the antenna and the satellite, as long as there are no major obstructions, such as tunnels or buildings. SR audiences can follow a single channel regardless of location within a given range. Satellite radio faces new challenges from the rapid growth of HD Radio, Internet radio and next generation wireless technologies. All are proprietary and non-compatible signals, requiring proprietary hardware for decoding and playback.

XM Satellite Radio/SIRIUS Satellite Radio Companies combined in a tax-free, all-stock merger of equals with a combined enterprise value of approximately $13 billion, which includes net debt of approximately $1.6 billion, and the companies have approximately 14 million combined subscribers, 20 February 2007.

  1. SIRIUS Operating from its corporate headquarters in New York City's Rockefeller Center, SIRIUS broadcasts over 130 digital-quality channels, including 69 channels of 100% commercial-free music, plus exclusive channels of sports, news, talk, entertainment, traffic, weather and data.This unique listening experience is available to subscribers from coast-to-coast in the United States. The service can be used in cars, trucks, RVs, homes, offices, stores, and even outdoors. Boaters around the country, and up to 200 miles offshore, can also hear SIRIUS. SIRIUS provides premium quality programming delivered by three dedicated satellites orbiting directly over the US.
Retrieved from "http://www.ultralingua.com/eureka/index.php/Category:Satellite_Communications"
Views
Personal tools