SATELLITE NETWORKS

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(No Transcript)
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Why Satellite Networks ?

• Wide geographical area coverage
• From kbps to Gbps communication everywhere
• Faster deployment than terrestrial
  infrastructures
• Bypass clogged terrestrial networks and are
  oblivious to terrestrial disasters
• Supporting both symmetrical and asymmetrical
  architectures
• Seamless integration capability with terrestrial
  networks
• Very flexible bandwidth-on-demand capabilities
• Flexible in terms of network configuration and
  capacity allocation
• Broadcast, Point-to-Point and Multicast
  capabilities
• Scalable

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Orbits

• Defining the altitude where the satellite will
  operate.
• Determining the right orbit depends on proposed
  service characteristics such as coverage,
  applications, delay.

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Orbits (cont.)
GEO (33786 km)
GEO Geosynchronous Earth Orbit MEO Medium Earth
Orbit LEO Low Earth Orbit
Outer Van Allen Belt (13000-20000 km)
MEO ( lt 13K km)
?
LEO ( lt 2K km)
Inner Van Allen Belt (1500-5000 km)
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Types of Satellites

• Geostationary/Geosynchronous Earth Orbit
  Satellites (GSOs) (Propagation Delay 250-280
  ms)
• Medium Earth Orbit Satellites (MEOs) (Propagation
  Delay 110-130 ms)
• Highly Elliptical Satellites (HEOs) (Propagation
  Delay Variable)
• Low Earth Orbit Satellite (LEOs) (Propagation
  Delay 20-25 ms)

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Geostationary/Geosynchronous Earth Orbit
Satellites (GSOs)

• 33786 km equatorial orbit
• Rotation speed equals Earth rotation speed
  (Satellite seems fixed in the horizon)
• Wide coverage area
• Applications (Broadcast/Fixed Satellites, Direct
  Broadcast, Mobile Services)

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Advantages of GSOs

• Wide coverage
• High quality and Wideband communications
• Economic Efficiency
• Tracking process is easier because of its
  synchronization to Earth

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Disadvantages of GSOs

• Long propagation delays (250-280 ms).(e.g.,
  Typical Intern. Tel. Call ? 540 ms round-trip
  delay. Echo cancelers needed. Expensive!)(e.g.,
  Delay may cause errors in data Error correction
  /detection techniques are needed.)
• Large propagation loss. Requirement for high
  power level.(e.g., Future hand-held mobile
  terminals have limited power supply.)Currently
  smallest terminal for a GSO is as large as an A4
  paper and as heavy as 2.5 Kg.

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Disadvantages of GSOs (cont.)

• Lack of coverage at Northern and Southern
  latitudes.
• High cost of launching a satellite.
• Enough spacing between the satellites to avoid
  collisions.
• Existence of hundreds of GSOs belonging to
  different countries.
• Available frequency spectrum assigned to GSOs is
  limited.

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Medium Earth Orbit Satellites (MEOs)

• Positioned in 10-13K km range.
• Delay is 110-130 ms.
• Will orbit the Earth at less than 1 km/s.
• Applications
• Mobile Services/Voice (Intermediate Circular
  Orbit (ICO) Project)
• Fixed Multimedia (Expressway)

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Highly Elliptical Orbit Satellites (HEOs)

• From a few hundreds of km to 10s of thousands ?
  allows to maximize the coverage of specific Earth
  regions.
• Variable field of view and delay.
• Examples MOLNIYA, ARCHIMEDES (Direct Audio
  Broadcast), ELLIPSO.

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Low Earth Orbit Satellites (LEOs)

• Usually less than 2000 km (780-1400 km are
  favored).
• Few ms of delay (20-25 ms).
• They must move quickly to avoid falling into
  Earth ? LEOs circle Earth in 100 minutes at 24K
  km/hour. (5-10 km per second).
• Examples
• Earth resource management (Landsat, Spot,
  Radarsat)
• Paging (Orbcomm)
• Mobile (Iridium)
• Fixed broadband (Teledesic, Celestri, Skybridge)

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Low Earth Orbit Satellites (LEOs) (cont.)

• Little LEOs 800 MHz range
• Big LEOs gt 2 GHz
• Mega LEOs 20-30 GHz

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Comparison of Different Satellite Systems
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Comparison of Satellite Systems According to
their Altitudes (cont.)
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Why Hybrids?

• GSO LEO
• GSO for broadcast and management information
• LEO for real-time, interactive
• LEO or GSO Terrestrial Infrastructure
• Take advantage of the ground infrastructure

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Frequency Bands

• NarrowBand Systems
• L-Band ? 1.535-1.56 GHz DL
  1.635-1.66 GHz UL
• S-Band ? 2.5-2.54 GHz DL
  2.65-2.69 GHz UL
• C-Band ? 3.7-4.2 GHz DL 5.9-6.4
  GHz UL
• X-Band ? 7.25-7.75 GHz DL 7.9-8.4
  GHz UL

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Frequency Bands (cont.)

• WideBand/Broadband Systems
• Ku-Band ? 10-13 GHz DL 14-17
  GHz UL(36 MHz of channel bandwidth enough for
  typical 50-60 Mbps applications)
• Ka-Band ? 18-20 GHz DL 27-31
  GHz UL(500 MHz of channel bandwidth enough for
  Gigabit applications)

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Next Generation Systems Mostly Ka-band

• Ka band usage driven by
• Higher bit rates - 2Mbps to 155 Mbps
• Lack of existing slots in the Ku band
• Features
• Spot beams and smaller terminals
• Switching capabilities on certain systems
• Bandwidth-on-demand
• Drawbacks
• Higher fading
• Manufacturing and availability of Ka band devices
• Little heritage from existing systems (except
  ACTS and Italsat)

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Frequency Bands (cont.)

• New Open Bands (not licensed yet)
• GHz of bandwidth
• Q-Band ? in the 40 GHz
• V-Band ? 60 GHz DL 50 GHz UL

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Space Environment Issues

• Harsh ? hard on materials and electronics (faster
  aging)
• Radiation is high (Solar flares and other solar
  events Van Allen Belts)
• Reduction of lifes of space systems (12-15 years
  maximum).

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Space Environment Issues (cont.)

• Debris (specially for LEO systems) (At 7 Km/s
  impact damage can be important. Debris is going
  to be regulated).
• Atomic oxygen can be a threat to materials and
  electronics at LEO orbits.
• Gravitation pulls the satellite towards earth.
• Limited propulsion to maintain orbit (Limits the
  life of satellites Drags an issue for LEOs).
• Thermal Environment again limits material and
  electronics life.

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Basic Architecture
SIU - Satellite Interworking Unit
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Basic Architecture (cont.)
SIU - Satellite Interworking Unit
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Satellite Interworking Unit (SIU)
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Payload Concepts

• Bent Pipe Processing
• Onboard Processing
• Onboard Switching

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Bent-Pipe Protocol Stack (Internet)
Physical
Satellite
Applications
Applications
TCP
TCP
IP
IP
Network
Network
Medium Access Control Data Link Control
Medium Access Control Data Link Control
Physical
Physical
User Terminal
User Terminal
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Onboard Processing Protocol Stack (Internet)
Satellite
User Terminal
User Terminal
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Onboard Switching Protocol Stack (Internet)
Applications
TCP
IP
Network
Medium Access Control Data Link Control
Physical
User Terminal
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Routing Algorithms for Satellite Networks

• Satellites organized in planes
• User Data Links (UDL)
• Inter-Satellite Links (ISL)
• Short roundtrip delays
• Very dynamic yet predictable network topology
• Satellite positions
• Link availability
• Changing visibility from the Earth

http//www.teledesic.com/tech/mGall.htm
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LEOs at Polar Orbits

• Seam
• Border between counter-rotating satellite planes
• Polar Regions
• Regions where the inter-plane ISLs are turned off

• E. Ekici, I. F. Akyildiz, M. Bender, The
  Datagram Routing Algorithm for Satellite IP
  Networks ,
• IEEE/ACM Transactions on Networking, April 2001.
  
• E. Ekici, I. F. Akyildiz, M. Bender, A New
  Multicast Routing Algorithm for Satellite IP
  Networks,
• IEEE/ACM Transactions on Networking, April 2002.

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Routing in Multi-Layered Satellite Networks
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Iridium Network
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Iridium Network (cont.)
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Iridium Network (cont.)

• 6 orbits
• 11 satellites/orbit
• 48 spotbeams/satellite
• Spotbeam diameter 700 km
• Footprint diameter 4021km
• 59 beams to cover United States
• Satellite speed 26,000 km/h 7 km/s
• Satellite visibility 9 - 10 min
• Spotbeam visibility lt 1 minute
• System period 100 minutes

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Iridium Network (cont.)

• 4.8 kbps voice, 2.4 Kbps data
• TDMA
• 80 channels /beam
• 3168 beams globally (2150 active beams)
• Dual mode user handset
• User-Satellite Link L-Band
• Gateway-Satellite Link Ka-Band
• Inter-Satellite Link Ka-Band

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Operational Systems
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Operational Systems (cont.) Little LEOs
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Proposed and Operational Systems

• ICO Global Communications (New ICO)
• Number of Satellites 10
• Planes 2
• Satellites/Plane 5
• Altitude 10,350 km
• Orbital Inclination 45
• Remarks
• Service Voice _at_ 4.8 kbps, data _at_ 2.4 kbps and
  higher
• Operation anticipated in 2003
• System taken over by private investors due to
  financial difficulties
• Estimated cost 4,000,000,000
• 163 spot beams/satellite, 950,000 km2 coverage
  area/beam, 28 channels/beam
• Service link 1.98-2.01 GHz (downlink), 2.17-2.2
  GHz (uplink) (TDMA)
• Feeder link 3.6 GHz band (downlink), 6.5 GHz
  band (uplink)

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Proposed and Operational Systems (cont.)

• Globalstar
• Number of Satellites 48
• Planes 8
• Satellites/Plane 6
• Altitude 1,414 km
• Orbital Inclination 52
• Remarks
• Service Voice _at_ 4.8 kbps, data _at_ 7.2 kbps
• Operation started in 1999
• Early financial difficulties
• Estimated cost 2,600,000,000
• 16 spot beams/satellite, 2,900,000 km2 coverage
  area/beam,175 channels/beam
• Service link 1.61-1.63 GHz (downlink), 2.48-2.5
  GHz (uplink) (CDMA)
• Feeder link 6.7-7.08 GHz (downlink), 5.09-5.25
  GHz (uplink)

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Proposed and Operational Systems (cont.)

• ORBCOM
• Number of Satellites 36
• Planes 4 2
• Satellites/Plane 2 2
• Altitude 775 km 775 km
• Orbital Inclination 45 70
• Remarks
• Near real-time service
• Operation started in 1998 (first in market)
• Cost 350,000,000
• Service link 137-138 MHz (downlink), 148-149 MHz
  (uplink)
• Spacecraft mass 40 kg

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Proposed and Operational Systems (cont.)

• Starsys
• Number of Satellites 24
• Planes 6
• Satellites/Plane 4
• Altitude 1,000 km
• Orbital Inclination 53
• Remarks
• Service Messaging and positioning
• Global coverage
• Service link 137-138 MHz (downlink), 148-149 MHz
  (uplink)
• Spacecraft mass 150 kg

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Proposed and Operational Systems (cont.)

• Teledesic (original proposal)
• Number of Satellites 840 (original)
• Planes 21
• Satellites/Plane 40
• Altitude 700 km
• Orbital Inclination 98.2
• Remarks
• Service FSS, provision for mobile service
  (16 kbps 2.048 Mbps, including video) for
  2,000,000 users
• Sun-synchronous orbit, earth-fixed cells
• System cost 9,000,000,000 (2000 for terminals)
• Service link 18.8-19.3 GHz (downlink), 28.6-29.1
  GHz (uplink) (Ka band)
• ISL 60 GHz
• Spacecraft mass 795 kg

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Proposed and Operational Systems (cont.)

• Teledesic (final proposal)
• Number of Satellites 288 (scaled down)
• Planes 12
• Satellites/Plane 24
• Altitude 700 km
• Remarks
• Service FSS, provision for mobile service
  (16 kbps 2.048 Mbps, including video) for
  2,000,000 users
• Sun-synchronous orbit, earth-fixed cells
• System cost 9,000,000,000 (2000 for terminals)
• Service link 18.8-19.3 GHz (downlink), 28.6-29.1
  GHz (uplink) (Ka band)
• ISL 60 GHz
• Spacecraft mass 795 kg

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References

• Survey Paper
• Akyildiz, I.F. and Jeong, S., "Satellite ATM
  Networks A Survey," IEEE Communications
  Magazine, Vol. 35, No. 7, pp.30-44, July 1997.