Overview Basics of Satellites Types of Satellites Components of Satellites Overview Basics of Satellites Types of Satellites Components of Satellites How do Satellites Work ? Two Stations on Earth want to communicate through radio broadcast but are too far away to use conventional means. The two stations can use a satellite as a relay station for their communication One Earth Station sends a transmission to the satellite. This is called a Uplink. The satellite Transponder converts the signal and sends it down to the second earth station. This is called a Downlink. TransponderEarth Station AEarth Station BUplink Downlink Multiple access capability, point-to-point, point-to-multipoint multipoint-to-multipoint A few reasons of satellite revolution:point-to-point,point-to-multipointmultipoint-to-multipointA few reasons of satellite revolution: Distribution capability (a particular case of point-to-multipoint transmission), including: TV program broadcasting and other video and multimedia applications. Data distribution, e.g. for business services, Internet wideband services, etc.; A single satellite can provide coverage to over 30% of Earths surface. It is ideal for broadcast applications. Wide bandwidths (155 Mbps) are available now. A few reasons of satellite revolution: Flexibility for changes in traffic and in network architecture and also ease of operation and putting into service. It is scalable. It can be rapidly deployed. Depending on application, there is no need for the local loop. Advantages of Satellites The coverage area of a satellite greatly exceeds that of a terrestrial system. Transmission cost of a satellite is independent of the distance from the center of the coverage area. Satellite to Satellite communication is very precise. Higher Bandwidths are available for use. Coverage of SatelliteDisadvantages of Satellites Launching satellites into orbit is costly. Satellite bandwidth is gradually becoming used up. There is a larger propagation delay in satellite communication than in terrestrial communication. Overview Basics of Satellites Types of Satellites Components of Satellites Due to Massmass ClassMore than 1000kg500 to 1000 kg100 to 500 kg10 to 100 kgLess than 10 kgLarge satelliteSmall satelliteMini satelliteMicro satelliteNano satellite Due to Orbit AltitudeA) low earth orbits (LEO), B) Medium earth orbits (MEO), C) geostationary earth orbits (GEO). Due to Missions Telecommunication Relay for telephone, TV, Internet Visibility from everywhere in a country Constellations for global earth coverage Usually GEO orbits Molniya orbits for high latitudes high RF power Earth observation Imaging, topographic mapping intensity measurements images with good resolution good optical payloads civil and military applications Usually LEO polar orbits Weather global coverage of a country visible and IR Atmosphere sounding GEO or LEO Navigation (GPS, GNSS) Ranging, navigation signals Global coverage LEO Constellations Space Science Astronomy, Space telescopes All wavelength range (X to radio) Usually far away orbits (minimise earth perturbation), high eccentricity Complex payload high data rate Space station, shuttle mission Microgravity experiments Presence of human, safety Pressurised spacecrafts Environment control Due to Service Types Fixed Service Satellites (FSS) Example: Point to Point Communication Broadcast Service Satellites (BSS) Example: Satellite Television/Radio Also called Direct Broadcast Service (DBS). Mobile Service Satellites (MSS) Example: Satellite Phones Fixed-satellite services FSSBroadcasting-satellite service (BSS)Mobile-satellite service (MSS)Overview Basics of Satellites Types of Satellites Components of Satellites Components of a Satellite SystemSatellites Ground stations Launcher Satellite: Launcher: Used to bring the satellite on the desired orbit Ground station (s) Commissioning of the satellite Communication with the satellite Prepare & Send telecommands Receive Telemetry process data Distribute data to end users Archive data Satellite bus Space segment Collect and redistribute data 1ModemPoolDispatchSubsystemRoutersSwitchboard1Manager WS3Printers12 2FaxCheckingInformationAnalysis andDisplay WSPlanning and Ballistics Team Server Room Control Room1 - Air-conditioner2 - Talk-Back Equipment3 - Telephone22 2Shift FlightDirectorWSOn-lineControl WSServerClusterUniversalTime System22Ballistic andNavigationSupport WS2MissionPlanning WSPayloadWS22MissionPlanning WSChecking InformationAnalysis and Display WS(Flight Director WS)2General EngineeringSystems Specialist3Cabinet2MathematicalSimulation WSExchangeComputers1SimulatorCheckingInformationAnalysis andDisplay WSExchangeComputerManager WS,ServerMissionPlanning WSBallistic andNavigationSupport WSChecking InformationMathematicalSimulationPayloadWSBallistic andNavigationSupport WSGround Station Components:A Futuristic Network Operations Center Earth StationGround StationsMain Subsystems of the satelliteSatellitePayload ModuleSatellite Bus (SM)StructureMechanismsAttitude &orbit control(AOCS) Propulsion Thermalcontrol Power Telemetry/Telecommand(TM/TC)Data Handling(OBDH)InstrumentsElectronicsTelescopes AntennasCatia: Typical command breakdown Catia: Typical command breakdown Arabsat III-A Arabsat III-APayloadSM (Service Module)Central tube(Main structural element, carbon fibre sandwich)RadiatorArabsat III-APropellant Tanks (2 x 860 l)Helium pressurisation Tanks (50 l)14 x 10 N ThrustersCentral tube400 N Engine Propulsion Module (UPS): Arabsat III-A One telecommunication panel on the Payload: Honeycomb Panel (Radiator)Heat pipesComponentsWave-guidesHarness (not shown)Interface for solar arrayArabsat III-A Telecommunication payload: Repeater accommodation Arabsat III-A Exploded view Transmission AntennaRadiatorReceptionAntennaArabsat III-A Stowed configuration Arabsat III-A Deployed ConfigurationArabsat III-A Antenna deployment Arabsat III-A Preparation for TV test Usage of Satellites Public PublicLibrary/School Library/SchoolTelemedicine TelemedicineDistance DistanceLearning Learning Video VideoConferencing ConferencingVoice VoiceLAN LANExtension ExtensionBusiness Access Business AccessPSTN Gateway PSTN GatewayInternet InternetBackbone BackboneAccess AccessCollaborative CollaborativeComputing ComputingCellular CellularBackhaul BackhaulAviation Aviation Maritime MaritimeCorporate Enterprise Corporate EnterpriseTerrestrial NetworksTerrestrial NetworksTeledesic: Internet-in-the-SkyTeledesic Proprietary Slide 2 of 91What Is a Link Budget? The carrier level received at the end of the link is a straightforward addition of the losses and gains in the path between transmitting and receiving Earth stations. Why we use Link Budget? A link budget is used to predict performance before the link is established. Show in advance if it will be acceptable Show if one option is better than another Provide a criterion to evaluate actual performance Link Budget Components A satellite link budget should include the following parts: 1. Uplink 2. Downlink 3. Combine 1 & 2 4. Define Performance Limit(s) 5. Compare calculated and actual performance. Link Budget Basic QuestionIs the operating margin large enough?It must be positive to account for the items listed in the budget Link Budget Evaluation Important Factors are: Satellite non-linearity (NPR) Satellite transmit power for your signal Interference (including CDMA if implemented) Allowance for future (worse) conditions Lifetime of the system under evaluation How closely can it be maintained at the parameters used in the budget Link Budget Evaluation Performance objectives for digital links consist of: BER for normal operating conditions Link Availability, or percentage of time that the link has a BER better than a specified threshold level Link Budget CalculationsThe link equation in its general form is: ( ) ( ) ( ) + =|.|

\| ) log( 10 kTB Gains Losses EIRPNCdB dB dBWdBEffective Isotropic Radiated PowerFree Space LossWaveguide LossAtmospheric LossRain AttenuationTracking Errorsk= Boltzman const. 1.38*10-23 W/K/Hz B= Noise B/W (Hz) T=Abs. temp in K (Sometimes Equivalent temp) Equivalent Isotropically Radiated Power (EIRP):The gain of a directive antenna results in a more economic use of the RF power supplied by the source. Thus, the EIRP is expressed as a function of the antenna transmit gain GT and the transmitted power PT fed to the antenna. EIRPdBW = 10 log PT dBw + GT dBi e.g., transmit power of 6 W & antenna gain of 48.2 dB: EIRP = 10 log 6 + 48.2 = 56 dBW Equivalent Isotropically Radiated Power (EIRP):Maximum power flux density at distance r from a transmitting antenna of gain G: 2 24 4 rP GrEIRP T TMt t = = +Receiver Power Equation22224 4 44||.|

\|= = + = + =rP G G GrP GG A PT R T RT TR M eff M Rtttt( ) |.|

\| + + =t rP G G P T R TdBR 4log 20Receiver Antenna GainFreeSpace LossAntenna GainThe antenna gain, referred to an isotropic radiator, is defined by: GdBi = 10log()+20log(f)+20log(d)+20.4 dB Where: = antenna efficiency (Typical values are 0.55 - 0.75) d = antenna diameter in m f = operating frequency in GHz Antenna Gain Antenna GainDiameter Gain Increases with DiameterGain Increases with Frequency!Lossesgenerally consist of four components: L = Lo + Latm + Lrain + Ltrack Where: Lo = free Space Loss Latm = atmospheric losses Lrain = attenuation due to rain effects Ltrack = losses due to antenna tracking errors Free Space LossThe expression [4D/]2 is known as the basic free space loss Lo. The basic free space loss is expressed in decibels as: Lo = 20log(D) + 20log(f) + 92.5 dB Where: D = distance in km between transmitter and receiver, f = frequency in GHz 92.5 dB = 20 log {(4*109*103)/c} Free Space Loss Example: ES to satellite is 42,000 km, is 6 GHz, what is Lo? Lo = 92.5 + 20 log 42000 + 20 log 6 = 200.5 dB Very large loss!! Assume EIRP = 56 dBW, Rx antenna gain 50 dB PR = 56 + 50 - 200.4 = -94.4 dBW = 355 pW Depends on: Distance and frequency About 200 dB at C-band About 206 dB at Ku-band Table shows an example of the mean value of atmospheric losses for a 10-degree elevation angle. Atmospheric Losses Due to Freq.Atmospheric Loss(dB) Freq. (GHz.) 0.25 2 < f < 5 0.33 5 < f < 10 0.53 10 < f < 13 0.73 13 < f Atmospheric Losses Due to ElevationAtmospheric Losses Due to ElevationAtmospheric Losses Contributing Factors: Molecular oxygen Constant Uncondensed water vapor Rain Fog and clouds Depend on weather Snow and hail Effects are frequency dependent: Molecular oxygen absorption peaks at 60 GHz Water molecules peak at 21 GHz Decreasing elevation angle will also increase absorption loss Typical Losses (4/6 GHz) A station which is located near the center of a satellite beam (footprint), will have an advantage in the received signal compared to another located at the edge of the same beam of the satellite. The satellite antenna pattern has a defined beam edge to which the values of the satellite Equivalent Isotropically Radiated Power (EIRP), Gain-to-Noise Temperature ratio (G/T), and flux density are referenced. Geographical Advantage7/04/0515MBeam Peak 48. 7 dBWe. i. r. p. Levels 47. 7 dBW 46. 7 dBW 45. 7 dBW 44. 7 dBW 43. 7 dBW 42. 7 dBW 41. 7 dBW 40. 7 dBWGeographical Advantage Thank You For Attention Any Questions?