Satellite Communication

Uses of satellites
Communication Surveillance
Monitoring earth
(Meteorological)
Navigation - Global Positioning System
24 satellite uniformly distributed over earth surface 4 are always visible from any point
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Satellite communication applications
• Telecommunication
– global telephone connections* – backbone for global networks* – connections for communication in remote places or underdeveloped areas – global mobile communication * Largely superseded by long-haul fibre optic networks
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Example - Radarsat Constellation Mission *. I
Main Space Segment Parameters N of satellites 3 equally-spaced in a dawn-dusk plane Bus Canadian Smallsat Bus Launcher DNEPR specifications (for design) Total Mass < 1300 kg Antenna 9.45m2 Power < 1600 W (peak); < 220 W (average) Orbit 600 km, 100 m radius orbital tube Polarisation Dual cross selectable pole on all low and medium resolution modes; "experimental" quad pol Imaging Time 12 minutes/orbit (peak 20 minutes every three orbits) 10 minutes continuous imaging Lifetime 7 years (each satellite)
*Canadian Space Agency: Satellites > RADARSAT > Components and specifications http://www.asc-csa.gc.ca/eng/satellites/radarsat/components.asp
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Example - Radarsat Constellation Mission *. II
*Canadian Space Agency: Satellites > RADARSAT > Components and specifications http://www.asc-csa.gc.ca/eng/satellites/radarsat/components.asp
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Example - Radarsat Constellation Mission *. III
Ground segment
RADARSAT Constellation Mission reception stations Constellation Mission Telemetry, Tracking and Control System
*Canadian Space Agency: Satellites > RADARSAT > Components and specifications http://www.asc-csa.gc.ca/eng/satellites/radarsat/components.asp
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What does a Satellite do?
• Some satellites are just active repeaters – receive signal from ES and amplify this signal for retransmission back to Earth using number of transponders that amplify the signal in specific frequency band • More advanced satellites can also demodulate received signal and then remodulate it in various ways for retransmission to the receiving ES. Advantage of such satellites – reduced errors of data transfer
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Link power budget
Retransmitted signal must be received by ES with a given fidelity – so sent information can be extracted Thus main task of comms engineer is to calculate power at various points and establish requirements Uplink is mainly affected by free space path loss -Signal transmitted by the Earth Station will be very weak when reaches the satellite Downlink is restricted by power provided by satellite and affected by free space path loss Indeed – cost of 1 kg of satellite to get to GEO is tens of thousands $, so it places restriction on size and weight – so there is limit on generated power Book C
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