communication satellite. references joe montana, “introduction to satellite communication,”...
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Communication Satellite
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References
Joe Montana, “Introduction to Satellite Communication,” George Mason University, http://classweb.gmu.edu/jmontana/lecture01.ppt
Tanenbaum, Computer Networks, 4th edition, Prentice Hall.
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Important Milestones (1950’s)Putting the pieces together
1957 First man-made satellite launched by
former USSR (Sputnik, LEO).
1958 First US satellite launched (SCORE). First
voice communication established via satellite
(LEO, lasted 35 days in orbit after batteries
failed).
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Sputnik - I
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Important Milestones (1960’s)First satellite communications
1960 First passive communication satellite launched into space (Large
balloons, Echo I and II).
1962: First non-government active communication satellite launched
Telstar I (MEO).
1963: First satellite launched into geostationary orbit Syncom 1 (comms.
failed).
1964: International Telecomm. Satellite Organization (INTELSAT) created.
1965 First communications satellite launched into geostationary orbit for
commercial use Early Bird (re-named INTELSAT 1).
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ECHO I
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Telstar I
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Intelsat I
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Important Milestones (1970’s)GEO applications development
1972 First domestic satellite system operational (Canada).
INTERSPUTNIK founded.
1975 First successful direct broadcast experiment (one year duration;
USA-India).
1977 A plan for direct-to-home satellite broadcasting assigned by the
ITU in regions 1 and 3 (most of the world except the Americas).
1979 International Mobile Satellite Organization (Inmarsat) established.
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Important Milestones (1980’s)GEO applications expanded
1981 First reusable launch vehicle flight.
1982 International maritime communications made
operational.
1983 ITU direct broadcast plan extended to region 2.
1984 First direct-to-home broadcast system operational
(Japan).
1987 Successful trials of land-mobile communications
(Inmarsat).
1989-90 Global mobile communication service extended to
land mobile and aeronautical use (Inmarsat)http://classweb.gmu.edu/jmontana/lecture01.ppt
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Important Milestones (1990’s) 1990-95:
- Several organizations propose the use of non-geostationary (NGSO) satellite systems for mobile communications.
- Continuing growth of VSATs* around the world.- Spectrum allocation for non-GEO systems. - Continuing growth of direct broadcast systems. DirectTV created.
1997:
- Launch of first batch of LEO for hand-held terminals (Iridium).- Voice service telephone-sized desktop and paging service pocket size mobile terminals launched (Inmarsat).
1998: Iridium initiates services. 1999: Globalstar Initiates Service. 2000: ICO initiates Service. Iridium fails and system is sold to Boeing.
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* VSAT - Very Small Aperture Terminal - small, software-driven earth stations (typically 3-6 feet) used for the transmission of data, video, or voice via satellite.
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Iridium
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Communication Satellites Classified Based on Main orbit types
• Geostationary Satellites• Medium-Earth Orbit Satellites• Low-Earth Orbit Satellites
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Main orbit types
LEO 500 -1000 km
GEO 36,000 km
MEO 5,000 – 15,000 km
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Communication Satellites
Communication satellites and some of their properties, including altitude above the earth, round-trip delay time and number of
satellites needed for global coverage.
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Coverage vs. Altitude
Satellite Altitude (km)
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LEO, MEO and GEO Orbit Periods
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0 5000 10000 15000 20000 25000 30000 35000 40000
Altitude [km]
Ho
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Minimum Delay for two hops
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0 5000 10000 15000 20000 25000 30000 35000 40000
Altitude [km]
De
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[ms
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GEO (GEOSTATIONARY ORBIT) In the equatorial plane Orbital Period = 23 h 56 min. 4.091 s
= one Sidereal Day (defined as one complete rotation relative to the fixed stars)
Satellite appears to be stationary over a point on the equator to an observer
Radius of orbit, r, = 42,164.57 km
NOTE: Radius = orbital height + radius of the earth
Average radius of earth = 6,378.14 km
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Characteristic of Communication Satellite on the GEO Synchronize to the earth's rotation period.
T=23h 56min 4.091s
Orbit altitude H=36,000km
One satellite can cover 40% of the earth All the surface of the earth can be covered by three
satellites.
Fixed propagation delay D=250msec~270ms
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Current GEO Satellite Applications
Broadcasting - mainly TV at present DirecTV, PrimeStar, etc.
Point to Multi-point communications VSAT, Video distribution for Cable TV
Mobile Services Motient (former American Mobile Satellite),
INMARSAT, etc.
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GPS is a medium earth orbit (MEO) satellite system
GPS satellites broadcast pulse trains with very accurate
time signals A receiver able to “see” four GPS satellites can calculate
its position within 30 m anywhere in world “You never need be lost again”
Every automobile and cellular phone will eventually have a GPS location read-out
Satellite Navigation: GPS by MEO Satellite System
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LEO (Low-Earth Orbit) SatellitesIridium
(a) The Iridium satellites from six necklaces around the earth.
(b) 1628 moving cells cover the earth.
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LEO Satellites in year 2000 Several new systems are just starting service
Circular or inclined orbit with < 1400 km altitude
Satellite travels across sky from horizon to horizon in 5
- 15 minutes
Earth stations must track satellite or have omni-directional
antennas
Constellation of satellites is needed for continuous
communication.
Handoff needed.
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Space Segment
Satellite
TT&C Ground Station
Satellite System Elements
Ground Segment
Earth Stations
Coverage Region
SCC
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Space Segment– Satellite Launching Phase– Transfer Orbit Phase– Deployment– Operation
TT&C - Tracking Telemetry and Command Station: Establishes a control and monitoring link with satellite. Tracks orbit distortions and allows correction planning. Distortions caused by irregular gravitational forces from non-spherical Earth and due to the influence of Sun and Moon forces.
SSC - Satellite Control Center, a.k.a.:– OCC - Operations Control Center– SCF - Satellite Control Facility
Provides link signal monitoring for Link Maintenance and Interference monitoring.
– Retirement Phase
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Ground Segment
Earth Station = Satellite Communication Station (air, ground or sea, fixed or mobile).
FSS – Fixed Satellite Service MSS – Mobile Satellite Service
Collection of facilities, users and applications.
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Communication Satellites (2)
The principal satellite bands.
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Bigger, heavier, GEO satellites with multiple roles
More direct broadcast TV and Radio satellites
Expansion into Ka, Q, V bands (20/30, 30/50, 46/56 GHz)
Massive growth in data services fueled by Internet
Mobile services: May be broadcast services rather than point to point Make mobile services a successful business?
Current Trends in Satellite Communications
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