Transcript Satellite Applications

Satellite Applications
COMT 391 Wireless
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Overview
• Coverage and Power Consideration
• Regulation/Coordination
• Market Position
• Special Issues in Data Communications
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GEO Coverage
• Altitude is about 6 times the earth’s
radius
• Three satellite can cover the surface of
the earth
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LEOS Coverage
• Altitude is 1/6 of the earth’s radius
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Power Determination
• Antenna can radiate a certain amount of
power (measured in Watts or dBW)
• At a given distance this generates a
measurable power flux (power per area)
• Directional antennas sends their power into a
smaller area and therefore generate more
power flux
• EIRP = Equivalent Isotropic Radiated Power
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Regulation
• Satellite Positioning
– all geostationary satellites are in a single
ring orbit
– Spacing is 2 deg to 9 deg depending in
power levels
• Frequency Coordination
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The ITU-R
• WRC meets
every two years
• Agenda is
outlined 4 years
in advance
• Agenda is set 2
years in advance
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http://www.itu.int
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Satellite Market Positioning
• How do satellite services compare to
other wireless services?
• How do satellite services compare to
terrestrial wired services?
• When would I use satellite services?
• When would I not use satellite services?
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Satellite vs Terrestrial
Wireless
• Both allow mobile or ad-hoc
communications
• Satellites have more complete coverage
• Terrestrial systems can use more
frequency re-use
• Satellites have more power restrictions
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Power Issues
• Satellites are equivalent to terrestrial
base stations, but with limited available
electrical power
• Mobile to Base Station Distances:
–
–
–
–
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PCS: less than 1km
Cellular: several km
LEOS: several 100s of km
GEOS: 35,000 km
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Satellites vs Terrestrial Wired
Network
• Total available bandwidth is much smaller in
wireless systems
• Cost (installation, usage, management) of
wired solutions is usually lower if the wired
network is already in place (but satellite
service is not distance sensitive)
• Satellite solutions are usually cheaper and
faster if the wired network is not in place
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When to use satellite services?
• If we need mobility, including areas
where terrestrial coverage is
unavailable
• If we need global standardized mobility
• If the terrestrial network service is not
available at the site
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What applications may not
make sense?
• GEOS can probably not serve mobile
hand-held stations
• LEOS can serve hand-helds, but
probably cannot compete with existing
cellular/PCS systems
• GEOS can provide high-capacity
service, but probably cannot compete
with installed terrestrial networks
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Where do satellites fit in a
hybrid network?
Regional
Net
End User
Regional
Net
End User
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Backbone
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Special Issues for Datacomm
• GEO satellite links have a 560ms round
trip delay
– Flow/Error control must use large
“windows”
• All wireless links are more error-prone
and may require error-correction
techniques
– e.g., ATM is designed for error-free links
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