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COMMUNICATIONS SATELLITES (GEO (Geostationary Earth Orbit) (Cons (Great…
COMMUNICATIONS SATELLITES
Definition
Uplink signal (conversion)
Earth signal reception
Downlink signal (amplification)
Signal retransmission ("bent pipe")
Specialized wireless receiver/transimtter
Purposes
Television broadcasting
Radio communications
Weather forecasting
Internet access
Wide-area network communications
GPS
Components
Satellite transponder
Signal conversion (Uplink to downlink)
Antenna subsystems
Transmission and reception signals
Solar panels and battery backup
Rechargeable by sun
GEO (Geostationary Earth Orbit)
Orbital distance: 35 400 km
Orbital time: 24 h
Seemingly fixed position in the sky
Cons
Great distance --> weak signal
Huge delay
Partial coverage
Pros
3 satellites
All of the Earth's surface covering
Fixed antennas
No tracking activities
10-15 years of lifespan
Reliable and secure
1/3 of Earth's surface viewing
MEO (Medium Earth Orbit)
Orbital distance: 5000÷12000 km
GPS (Global Positioning System)
Elliptical orbit
Pros
Less handoff
Ground stations transferring
No service interruption
LEO (Low Earth Orbit)
Orbital distance: 200÷1400 km
One location for 90 minutes
Pros
Never out of orbit
Shorter delays
Less expensive
Cons
Lots of satellites required
Less powerful
Shorter lifespan
Transponder
Storage capacity: 155 million bits
24÷72 on a satellite
Useful for the all the communications
Band
Radio frequency wavelength
Ku
Used for VSAT
Ka
Smallest wavelength and antenna
C
Larger antenna required