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: ian@ece.gatech.edu
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
2

 Defining the altitude where the satellite will operate.
 Determining the right orbit depends on proposed service characteristics such as coverage, applications, delay.
IFA’2004
3

GEO: Geosynchronous Earth Orbit
MEO: Medium Earth Orbit
LEO: Low Earth Orbit

GEO (33786 km)
Outer Van Allen Belt (13000-20000 km)
MEO ( < 13K km)
LEO ( < 2K km)
Inner Van Allen Belt (1500-5000 km)
IFA’2004
4

GEO: 33786 km
 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)

LEO: < 2K km
(Globalstar, Iridium, Teledesic)
MEO: < 13K km (Odyssey, Inmarsat-P)
IFA’2004
5

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)
IFA’2004
6

 Wide coverage
 High quality and Wideband communications
 Economic Efficiency
 Tracking process is easier because of its synchronization to Earth
IFA’2004
7

 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.
IFA’2004
8

 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.
IFA’2004
9

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)
IFA’2004
10

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:
(Direct Audio Broadcast) ,
.
IFA’2004
11

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 )
IFA’2004
12

Low Earth Orbit Satellites (LEOs)
(cont.)
 Little LEOs: 800 MHz range
 Big LEOs: > 2 GHz
 Mega LEOs: 20-30 GHz
IFA’2004
13

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
IFA’2004
Visibility of a
Satellite
Very
Short
Medium None
Medium Mostly
Always
14

IFA’2004
Comparison of Satellite Systems
According to their Altitudes (cont.)
15


– GSO for broadcast and management information
– LEO for real-time, interactive

– Take advantage of the ground infrastructure
IFA’2004
16

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
IFA’2004
17

WideBand/Broadband Systems

 10-13 GHz DL;
14-17 GHz UL
(36 MHz of channel bandwidth; enough for typical 50-60 Mbps applications)

 18-20 GHz DL;
27-31 GHz UL
(500 MHz of channel bandwidth; enough for
Gigabit applications)
IFA’2004
18

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)
IFA’2004
19

New Open Bands (not licensed yet)
 GHz of bandwidth

 in the 40 GHz

 60 GHz DL;
50 GHz UL
IFA’2004
20

 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).
IFA’2004
21

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.
IFA’2004
22

LAN
Mobile
Network
Internet
Ethernet
Ring
MAN
IFA’2004
Ring
Internet
Ethernet
Wireless
Terrestrial
Network
Public
Network
23

Basic Architecture (cont.)
IFA’2004
SIU - Satellite Interworking Unit
24

IFA’2004
Satellite Interworking Unit (SIU)
25

 Bent Pipe Processing
 Onboard Processing
 Onboard Switching
IFA’2004
26

Physical Satellite
Applications
TCP
IP
Network
Medium Access Control
Data Link Control
Physical
User Terminal
IFA’2004
Applications
TCP
IP
Network
Medium Access Control
Data Link Control
Physical
User Terminal
27

Satellite
Medium Access Control
Data Link Control
Physical
Applications
TCP
IP
Network
Medium Access Control
Data Link Control
Physical
Applications
TCP
IP
Network
Medium Access Control
Data Link Control
Physical
User Terminal
IFA’2004
User Terminal
28

Satellite
Network
Medium Access Control
Data Link Control
Physical
Applications
TCP
IP
Network
Medium Access Control
Data Link Control
Physical
Applications
TCP
IP
Network
Medium Access Control
Data Link Control
Physical
User Terminal
IFA’2004
User Terminal
29

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
IFA’2004
30



 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.
IFA’2004
31

IFA’2004
Routing in Multi-Layered
Satellite Networks
32

IFA’2004
33

IFA’2004
34

 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
IFA’2004
35

 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
IFA’2004
36

Operational Systems
Reference EUTELSAT INTELSAT
Type
Orbit
Investors
Prime
Services
Bent Pipe
GSO
Eutelsat
Various
Bent Pipe
GSO
Intelsat
Various
Multimedia Voice, Data, Video Conf.
Frequencies
Antennas (cm)
Ku
120+
U/L Rates (Mbps) 0.016-2
Number of Satellites 1
Ku
120+
0.016-2
26
Primary Access
Multibeam
FDMA/TDMA FDMA/TDMA
No
ISLs No
Transport Protocol IP/ATM
No
No
IP
IFA’2004
37

Reference
Type
ORBCOMM VITASAT
Bent Pipe
Altitude (km) 775
Bent Pipe
1000
Coverage
Number of
Satellites
Mass of
Satellites (kg)
STARNET
Bent Pipe
1000
Below 1 GHz Below 1 GHz Below 1 GHz
36
40
24
150
24
150
IFA’2004
38

Proposed and Operational
Systems
1.
ICO Global Communications (New ICO)
 Number of Satellites:
 Planes:
 Satellites/Plane:
10
2
5


Altitude:
Orbital Inclination:
10,350 km
45 °
 Remarks:
 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 km 2 coverage area/beam,
28 channels/beam
 Service link: 1.98-2.01 GHz (downlink), 2.17-2.2 GHz (uplink); (TDMA)
IFA’2004
3.6 GHz band (downlink), 6.5 GHz band (uplink)
39

Proposed and Operational
Systems (cont.)
2.
Globalstar
 Number of Satellites:
 Planes:
 Satellites/Plane:
48
8
6


Altitude:
Orbital Inclination:
1,414 km
52 °
 Remarks:
 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 km 2 coverage area/beam,
175 channels/beam
 Service link: 1.61-1.63 GHz (downlink), 2.48-2.5 GHz (uplink); (CDMA)
IFA’2004
6.7-7.08 GHz (downlink), 5.09-5.25 GHz (uplink)
40

Proposed and Operational
Systems (cont.)
3.
ORBCOM
 Number of Satellites:
 Planes:
 Satellites/Plane:
36
4
2


Altitude:
Orbital Inclination:
775 km
45 °
 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
2
2
775 km
70 °
IFA’2004
41

Proposed and Operational
Systems (cont.)
4.
Starsys
 Number of Satellites:
 Planes:
 Satellites/Plane:
24
6
4


Altitude:
Orbital Inclination:
1,000 km
53 °
 Remarks:
 Service: Messaging and positioning
 Global coverage
 Service link: 137-138 MHz (downlink), 148-149 MHz (uplink)
 Spacecraft mass: 150 kg
IFA’2004
42

Proposed and Operational
Systems (cont.)
5.
Teledesic (original proposal)
 Number of Satellites:
 Planes:
 Satellites/Plane:
840 (original)
21
40


Altitude:
Orbital Inclination:
700 km
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) (K a
 ISL: 60 GHz
 Spacecraft mass: 795 kg band)
IFA’2004
43

Proposed and Operational
Systems (cont.)
6.
Teledesic (final proposal)
 Number of Satellites:
 Planes:
 Satellites/Plane:
288 (scaled down)
12
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) (K a
 ISL: 60 GHz
 Spacecraft mass: 795 kg band)
IFA’2004
44

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.
IFA’2004
45