Download satellite networks - BWN-Lab

SATELLITE NETWORKS
Ian F. Akyildiz
Broadband & Wireless Networking Laboratory
School of Electrical and Computer Engineering
Georgia Institute of Technology
Tel: 404-894-5141; Fax: 404-894-7883
Email: [email protected]
Web: http://www.ece.gatech.edu/research/labs/bwn
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
Outer Van Allen Belt (13000-20000 km)
MEO: Medium Earth Orbit
LEO: Low Earth Orbit
MEO ( < 13K km)

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LEO ( < 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)
GEO: 33786 km
 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)
LEO: < 2K km
(Globalstar, Iridium, Teledesic)

MEO: < 13K km (Odyssey, Inmarsat-P)
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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: > 2 GHz
 Mega LEOs: 20-30 GHz
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Comparison of Different Satellite
Systems
LEO
MEO
GEO
Satellite Life
3-7
10-15
10-15
Hand-held Terminal
Possible
Possible
Difficult
Propagation Delay
Short
Medium
Long
Propagation Loss
Low
Medium
High
Network Complexity Complex
Medium
Simple
Hand-off
Very
Medium
None
Visibility of a
Satellite
Short
Medium
Mostly
Always
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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
LAN
Ring
Mobile
Network
Internet
Ring
Public
Network
Internet
MAN
Ethernet
Wireless
Terrestrial
Network
Ethernet
SIU-- Satellite
Unit Unit
SIU
Satellite Interface
Interworking
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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)
Satellite
Applications
Physical
Applications
TCP
TCP
IP
IP
Network
Network
Medium Access Control
Medium Access Control
Data Link Control
Data Link Control
Physical
Physical
User Terminal
User Terminal
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Onboard Processing
Protocol Stack (Internet)
Medium Access Control
Satellite
Data Link Control
Physical
Applications
Applications
TCP
TCP
IP
IP
Network
Network
Medium Access Control
Medium Access Control
Data Link Control
Data Link Control
Physical
Physical
User Terminal
User Terminal
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Onboard Switching
Protocol Stack (Internet)
Network
Satellite
Applications
Medium Access Control
Data Link Control
Physical
Applications
TCP
TCP
IP
IP
Network
Network
Medium Access Control
Medium Access Control
Data Link Control
Data Link Control
Physical
Physical
User Terminal
User Terminal
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Routing Algorithms for
Satellite Networks
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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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LEO’s 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.)
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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 < 1 minute
 System period = 100 minutes
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Iridium Network (cont.)
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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
Reference
Type
Orbit
Investors
Prime
Services
Frequencies
Antennas (cm)
U/L Rates (Mbps)
Number of Satellites
Primary Access
Multibeam
ISLs
Transport Protocol
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EUTELSAT
INTELSAT
Bent Pipe
GSO
Eutelsat
Various
Multimedia
Ku
120+
0.016-2
1
FDMA/TDMA
No
No
IP/ATM
Bent Pipe
GSO
Intelsat
Various
Voice, Data, Video Conf.
Ku
120+
0.016-2
26
FDMA/TDMA
No
No
IP
37
Operational Systems (cont.)
Little LEOs
Reference
ORBCOMM
VITASAT
STARNET
Type
Bent Pipe
Bent Pipe
Bent Pipe
Altitude (km)
775
1000
1000
Coverage
Below 1 GHz
Below 1 GHz
Below 1 GHz
Number of
Satellites
Mass of
Satellites (kg)
36
24
24
40
150
150
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Proposed and Operational
Systems
1.
ICO Global Communications (New ICO)
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Number of Satellites:
Planes:
Satellites/Plane:
Altitude:
Orbital Inclination:
Remarks:
10
2
5
10,350 km
45°
Service: Voice @ 4.8 kbps, data @ 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.)
2. Globalstar
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Number of Satellites:
Planes:
Satellites/Plane:
Altitude:
Orbital Inclination:
Remarks:
48
8
6
1,414 km
52°
Service: Voice @ 4.8 kbps, data @ 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.)
3. ORBCOM
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Number of Satellites:
Planes:
Satellites/Plane:
Altitude:
Orbital Inclination:
Remarks:
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36
4
2
775 km
45°
2
2
775 km
70°
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.)
4. Starsys
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Number of Satellites:
Planes:
Satellites/Plane:
Altitude:
Orbital Inclination:
Remarks:
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24
6
4
1,000 km
53°
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.)
5. Teledesic (original proposal)
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Number of Satellites:
Planes:
Satellites/Plane:
Altitude:
Orbital Inclination:
Remarks:

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840 (original)
21
40
700 km
98.2°
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.)
6. Teledesic (final proposal)

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
Number of Satellites:
Planes:
Satellites/Plane:
Altitude:
Remarks:

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



288 (scaled down)
12
24
700 km
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.
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