Guide to Satellites

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GlossaryANALOGUE SIGNALUsed of a signal where a continuously varying physicalquantity precisely describes the variation of the infor-mation it represents. This uses a considerable amountof bandwidth. One analogue television channel occu-pies the whole of a 30 to 36 MHz transponder.

BEAMBy analogy with a beam of light, indicates a unidirec-tional flow of radio waves emitted by an antenna andconcentrated in a particular direction. The intersectionof a satellite beam with the earth's surface is referredto as the footprint. A beam is steerable when it can berepointed in orbit towards another coverage zone bymechanical or electrical means.

COLOCATEDDescribes a satellite that occupies the same controlwindow on the geostationary satellite orbit as anothersatellite or satellites, such that the angular separationbetween them is very small when viewed from theground. When a small receive antenna is pointed to-wards colocated satellites, the satellites appear to beat exactly the same position. In reality, they are kept atleast several kilometers apart from one anotherthrough respective orbits that use slightly different va-lues in terms of inclination and eccentricity.

COVERAGEThe geographical area where satellite signals can bereceived with sufficient quality when using appropria-telysized earth stations. Satellite coverages are usuallycommunicated in the form of footprints displaying sa-

tellite G/T, e.i.r.p., or another parameter such as theantenna size required for good quality reception of aparticular service.

DIGITAL SIGNALDescribes a system where information is convertedinto numbers, instead of into a continuously-varyingquantity (as in an analogue system), thereby reducingthe necessary bandwidth. One 36 MHz transpondercan carry a multiplex of eight to ten video channels inMPEG2 compression format.

DVBDigital Video Broadcasting. A set of standards for thetransmission and reception of digital video signals viasatellite, cable or terrestrial means, formalised by theEuropean Telecommunications Standards Institute(ETSI). There are many standards within the DVB fa-mily, including specifications for satellite (DVB-S), cable(DVB-C) and terrestrial (DVB-T) transmission and re-ception.

E.I.R.P.Equivalent Isotropically Radiated Power. Measures thestrength of the signal transmitted by a satellite towardsthe earth or by an earth station towards a satellite. It isexpressed in dBW. The higher the e.i.r.p., the more theG/T can be reduced to obtain the same quality of re-ception (and the smaller the receive antenna can be).

EARTH EQUINOX (SATELLITE ECLIPSE)During the equinoxes of March and September, thesun passes across the plane of the equator, which

means that it is on the same plane as the geostationaryorbit. Due to the rotation of the earth, this alignmentmeans that the earth obstructs the sun for certain pe-riods and the solar panels cannot generate energy. Theduration of the satellite eclipse gradually changes asthe equinox approaches, building up to a maximum of70 minutes on the day itself. During these periods thesatellites storage batteries are used instead of thesolar panels so that the satellite can continue to func-tion normally.

EPGElectronic Programme Guide. A graphical user inter-face generated by a digital satellite receiver and dis-played on the users TV set. It provides informationabout programme times and content carried on the di-gital signals received from the satellite. An EPGs mainfunction is to help the viewer quickly locate and selectprogrammes, but it can also be used for other interac-tive services.

FREQUENCYIdentifies the number of oscillations produced in a spe-cified time, expressed in hertz. A hertz corresponds toone oscillation per second. Satellite transmissions areusually expressed in GHz (billion hertz). The term fre-quency spectrum is used to describe a continuousrange of frequencies. The frequency spectrum of theKu-Band allotted to satellite communications systemsextends from 10.7 GHz to 14.5 GHz.

FREQUENCY RE-USEA technique for using a specified range of frequenciesmore than once within the same satellite system sothat the total capacity of the system is increased wi-thout increasing the allocated bandwidth. Frequencyre-use requires sufficient isolation between signalsusing the same frequencies so that mutual interferencebetween them is controlled and kept below an accep-table level.Frequency re-use is achieved by using separate polari-zations horizontal/vertical for linear or left-hand/right-hand for circular) for transmission and/or by usingsatellite antenna (spot) beams serving geographicalzones which are sufficiently separated from one another.

HIGH DEFINITIONA digital TV pictures definition is expressed in mil-lions of pixels per second and is essentially made up ofthe number of horizontal lines, the number of dots perline and the number of images downloaded per se-cond. By multiplying the number of pixels per secondby a factor of at least five, High Definition renders eachplane extremely sharp, reproducing the 3D effect of theimage originally captured.

LNBThe Low-Noise Block converter (or LNB) is located be-hind the feedhorn of a satellite antenna. Its function isto amplify signals received and to lower their frequency(typically into the 950 to 2150 MHz band) so that theycan be processed by the receiver, DVB-S terminal ordemodulator. A universal LNB enables reception of

the full range of Ku-band downlink frequencies (10.7to 12.75 GHz).

MPEG COMPRESSIONMotion Picture Experts Group. A group established bythe International Organization for Standardization (ISO),which prescribes international standards for compres-sion coding of moving pictures and audio pro-grammes. MPEG2 (in 1995) was the first videocompression format used for television, bringing digi-tal TV to the general consumer by satellite and cable.On average, MPEG2 can carry eight digital channelsin the same space required for a single analogue chan-nel. MPEG4 was already being used to stream videoover the Internet when it was launched commerciallyfor TV broadcasting in 2006. Its role is vital to the de-velopment of HDTV programming because it uses si-gnificantly lower bit-rates. HD in MPEG2 formatrequires at least 18 Mbps whereas MPEG4 needs only8 Mbps. Further gains in the order of 30 to 40% areexpected over the next few years.

PARABOLIC ANTENNAAn antenna whose principal reflector is shaped like a pa-rabola. It can reflect parallel incoming signals by direc-ting them to a single point of focus where the sourceequipped with its LNB is located.

PAYLOADA satellites payload is the element that enables it tofulfil its mission, i.e. for a communications satellite, thereception and processing of signals and their retrans-mission back to earth. The payload includes the satel-

lite antennas and transponders but not the control,propulsion and electrical power equipment, which ispart of the satellite platform (physical structure).

PLATFORMThe platform is where all the satellite pointing control,thermal regulation, propulsion and power supply func-tionality is located. The pointing control equipment hassensors to notify the satellites orientation to the groundin order to maintain it correctly pointed to the earth.Steering usually employs a chemical or sometimes anelectrical propulsion system. In a chemical propulsionsystem, the platform, in addition to the engines (noz-zles), contains tanks of propellant and a pressurisinggas (typically helium) which drives the propellant to-wards the engines.The satellite is powered by photovoltaic cells to convertsunlight into electricity. The solar cells are situated onthe satellites skin (in the case of spin-stabilised sa-tellites) or on deployable solar panels. The energy pro-duced by solar cells is stored in batteries.

POLARISATIONPolarisation characterises the way a radio electric fre-quency propagates. It can be organised in more thanone direction. Linear polarisation can be vertical or ho-rizontal. A frequency can also propagate by turning likea corkscrew. In this case it is circular polarisation, eitherright or left.

2120

GlossaryANALOGUE SIGNALUsed of a signal where a continuously varying physicalquantity precisely describes the variation of the infor-mation it represents. This uses a considerable amountof bandwidth. One analogue television channel occu-pies the whole of a 30 to 36 MHz transponder.

BEAMBy analogy with a beam of light, indicates a unidirec-tional flow of radio waves emitted by an antenna andconcentrated in a particular direction. The intersectionof a satellite beam with the earth's surface is referredto as the footprint. A beam is steerable when it can berepointed in orbit towards another coverage zone bymechanical or electrical means.

COLOCATEDDescribes a satellite that occupies the same controlwindow on the geostationary satellite orbit as anothersatellite or satellites, such that the angular separationbetween them is very small when viewed from theground. When a small receive antenna is pointed to-wards colocated satellites, the satellites appear to beat exactly the same position. In reality, they are kept atleast several kilometers apart from one anotherthrough respective orbits that use slightly different va-lues in terms of inclination and eccentricity.

COVERAGEThe geographical area where satellite signals can bereceived with sufficient quality when using appropria-telysized earth stations. Satellite coverages are usuallycommunicated in the form of footprints displaying sa-

tellite G/T, e.i.r.p., or another parameter such as theantenna size required for good quality reception of aparticular service.

DIGITAL SIGNALDescribes a system where information is convertedinto numbers, instead of into a continuously-varyingquantity (as in an analogue system), thereby reducingthe necessary bandwidth. One 36 MHz transpondercan carry a multiplex of eight to ten video channels inMPEG2 compression format.

DVBDigital Video Broadcasting. A set of standards for thetransmission and reception of digital video signals viasatellite, cable or terrestrial means, formalised by theEuropean Telecommunications Standards Institute(ETSI). There are many standards within the DVB fa-mily, including specifications for satellite (DVB-S), cable(DVB-C) and terrestrial (DVB-T) transmission and re-ception.

E.I.R.P.Equivalent Isotropically Radiated Power. Measures thestrength of the signal transmitted by a satellite towardsthe earth or by an earth station towards a satellite. It isexpressed in dBW. The higher the e.i.r.p., the more theG/T can be reduced to obtain the same quality of re-ception (and the smaller the receive antenna can be).

EARTH EQUINOX (SATELLITE ECLIPSE)During the equinoxes of March and September, thesun passes across the plane of the equator, which

means that it is on the same plane as the geostationaryorbit. Due to the rotation of the earth, this alignmentmeans that the earth obstructs the sun for certain pe-riods and the solar panels cannot generate energy. Theduration of the satellite eclipse gradually changes asthe equinox approaches, building up to a maximum of70 minutes on the day itself. During these periods thesatellites storage batteries are used instead of thesolar panels so that the satellite can continue to func-tion normally.

EPGElectronic Programme Guide. A graphical user inter-face generated by a digital satellite receiver and dis-played on the users TV set. It provides informationabout programme times and content carried on the di-gital signals received from the satellite. An EPGs mainfunction is to help the viewer quickly locate and selectprogrammes, but it can also be used for other interac-tive services.

FREQUENCYIdentifies the number of oscillations produced in a spe-cified time, expressed in hertz. A hertz corresponds toone oscillation per second. Satellite transmissions areusually expressed in GHz (billion hertz). The term fre-quency spectrum is used to describe a continuousrange of frequencies. The frequency spectrum of theKu-Band allotted to satellite communications systemsextends from 10.7 GHz to 14.5 GHz.

FREQUENCY RE-USEA technique for using a specified range of frequenciesmore than once within the same satellite system sothat the total capacity of the system is increased wi-thout increasing the allocated bandwidth. Frequencyre-use requires sufficient isolation between signalsusing the same frequencies so that mutual interferencebetween them is controlled and kept below an accep-table level.Frequency re-use is achieved by using separate polari-zations horizontal/vertical for linear or left-hand/right-hand for circular) for transmission and/or by usingsatellite antenna (spot) beams serving geographicalzones which are sufficiently separated from one another.

HIGH DEFINITIONA digital TV pictures definition is expressed in mil-lions of pixels per second and is essentially made up ofthe number of horizontal lines, the number of dots perline and the number of images downloaded per se-cond. By multiplying the number of pixels per secondby a factor of at least five, High Definition renders eachplane extremely sharp, reproducing the 3D effect of theimage originally captured.

LNBThe Low-Noise Block converter (or LNB) is located be-hind the feedhorn of a satellite antenna. Its function isto amplify signals received and to lower their frequency(typically into the 950 to 2150 MHz band) so that theycan be processed by the receiver, DVB-S terminal ordemodulator. A universal LNB enables reception of

the full range of Ku-band downlink frequencies (10.7to 12.75 GHz).

MPEG COMPRESSIONMotion Picture Experts Group. A group established bythe International Organization for Standardization (ISO),which prescribes international standards for compres-sion coding of moving pictures and audio pro-grammes. MPEG2 (in 1995) was the first videocompression format used for television, bringing digi-tal TV to the general consumer by satellite and cable.On average, MPEG2 can carry eight digital channelsin the same space required for a single analogue chan-nel. MPEG4 was already being used to stream videoover the Internet when it was launched commerciallyfor TV broadcasting in 2006. Its role is vital to the de-velopment of HDTV programming because it uses si-gnificantly lower bit-rates. HD in MPEG2 formatrequires at least 18 Mbps whereas MPEG4 needs only8 Mbps. Further gains in the order of 30 to 40% areexpected over the next few years.

PARABOLIC ANTENNAAn antenna whose principal reflector is shaped like a pa-rabola. It can reflect parallel incoming signals by direc-ting them to a single point of focus where the sourceequipped with its LNB is located.

PAYLOADA satellites payload is the element that enables it tofulfil its mission, i.e. for a communications satellite, thereception and processing of signals and their retrans-mission back to earth. The payload includes the satel-

lite antennas and transponders but not the control,propulsion and electrical power equipment, which ispart of the satellite platform (physical structure).

PLATFORMThe platform is where all the satellite pointing control,thermal regulation, propulsion and power supply func-tionality is located. The pointing control equipment hassensors to notify the satellites orientation to the groundin order to maintain it correctly pointed to the earth.Steering usually employs a chemical or sometimes anelectrical propulsion system. In a chemical propulsionsystem, the platform, in addition to the engines (noz-zles), contains tanks of propellant and a pressurisinggas (typically helium) which drives the propellant to-wards the engines.The satellite is powered by photovoltaic cells to convertsunlight into electricity. The solar cells are situated onthe satellites skin (in the case of spin-stabilised sa-tellites) or on deployable solar panels. The energy pro-duced by solar cells is stored in batteries.

POLARISATIONPolarisation characterises the way a radio electric fre-quency propagates. It can be organised in more thanone direction. Linear polarisation can be vertical or ho-rizontal. A frequency can also propagate by turning likea corkscrew. In this case it is circular polarisation, eitherright or left.

2322

Glossary

POWERThe amount of electrical energy fed into or taken from adevice or system in a specified time, expressed in Watt ordBW. The signal strength on the uplink or downlink of asatellite communications system is quantified by thepower of the radio wave radiated by the transmit antenna.

RECEIVE SENSITIVITY (FIGURE OF MERIT G/T)The sensitivity of a receive system is described by its figure of merit G/T (gain/noise temperature). Sensitivitydepends on the gain of the receive antenna (which increases with the surface area of the antenna and thefrequency of the signal received) and the total noise ofthe electronic equipment used for reception (expressedin noise temperature). The higher the G/T, the more thetransmit power can be reduced. Inversely, the higher thetransmit power, the more the G/T can be reduced (i.e.the smaller the receive antenna required).

SET-TOP BOXUsed generically to describe any adapter that convertsan external signal into content that can be displayedon a television screen. The Set-Top Box is connectedto the TV set in the same way as a VCR, using a Scartsocket, for example, or an HDMIThe first STBs werethe decoders used to receive satellite and cable television.

STEREOSCOPIC IMAGE (3D)Normally both eyes see the same object but from twoslightly different angles, meaning that the two imagesare similar but actually different. Stereoscopic shootingreplicates the vision of both eyes. A pair of camerasrecordsthe same object from two views. Each of theviews is projected to go independently and without in-terference to each eye. Once the left eye receives theleft view and the right eye the right view, the braincreates a tri dimensional, with depth image. Differenttechnologies exist to send the two views separately tothe left and right eye. All make use of glasses based ondifferentiation on colorimetry, polarisation or timing (ac-tive glasses). The function of the glasses is to managethe differentiation between the left/right view.

TRANSPONDERA transmitter-receiver device that transmits signals automatically when it receives certain pre-determined signals. The term satellite transponder is a signal processing unit which uses a single high-power ampli-fication chain. Each transponder handles a particular frequency range (also referred to as "bandwidth") cen-tred on a specific frequency and with a given receive polarisation for the signal. The transponder changes the

frequency and the polarisation between reception of thesignal from the earth station and its amplification and retransmission back to earth. There are multiple trans-ponders on a satellite, each capable of supporting oneor more communication channels.

2322

Glossary

POWERThe amount of electrical energy fed into or taken from adevice or system in a specified time, expressed in Watt ordBW. The signal strength on the uplink or downlink of asatellite communications system is quantified by thepower of the radio wave radiated by the transmit antenna.

RECEIVE SENSITIVITY (FIGURE OF MERIT G/T)The sensitivity of a receive system is described by its figure of merit G/T (gain/noise temperature). Sensitivitydepends on the gain of the receive antenna (which increases with the surface area of the antenna and thefrequency of the signal received) and the total noise ofthe electronic equipment used for reception (expressedin noise temperature). The higher the G/T, the more thetransmit power can be reduced. Inversely, the higher thetransmit power, the more the G/T can be reduced (i.e.the smaller the receive antenna required).

SET-TOP BOXUsed generically to describe any adapter that convertsan external signal into content that can be displayedon a television screen. The Set-Top Box is connectedto the TV set in the same way as a VCR, using a Scartsocket, for example, or an HDMIThe first STBs werethe decoders used to receive satellite and cable television.

STEREOSCOPIC IMAGE (3D)Normally both eyes see the same object but from twoslightly different angles, meaning that the two imagesare similar but actually different. Stereoscopic shootingreplicates the vision of both eyes. A pair of camerasrecordsthe same object from two views. Each of theviews is projected to go independently and without in-terference to each eye. Once the left eye receives theleft view and the right eye the right view, the braincreates a tri dimensional, with depth image. Differenttechnologies exist to send the two views separately tothe left and right eye. All make use of glasses based ondifferentiation on colorimetry, polarisation or timing (ac-tive glasses). The function of the glasses is to managethe differentiation between the left/right view.

TRANSPONDERA transmitter-receiver device that transmits signals automatically when it receives certain pre-determined signals. The term satellite transponder is a signal processing unit which uses a single high-power ampli-fication chain. Each transponder handles a particular frequency range (also referred to as "bandwidth") cen-tred on a specific frequency and with a given receive polarisation for the signal. The transponder changes the

frequency and the polarisation between reception of thesignal from the earth station and its amplification and retransmission back to earth. There are multiple trans-ponders on a satellite, each capable of supporting oneor more communication channels.