SATELLITE NETWORKSSATELLITE NETWORKS

Ian F. AkyildizIan F. Akyildiz

Broadband & Wireless Networking LaboratoryBroadband & Wireless Networking Laboratory

School of Electrical and Computer EngineeringSchool of Electrical and Computer Engineering

Georgia Institute of TechnologyGeorgia Institute of Technology

Tel: 404-894-5141; Fax: 404-894-7883 Tel: 404-894-5141; Fax: 404-894-7883

Email: ian@ece.gatech.eduEmail: ian@ece.gatech.edu

Web: http://www.ece.gatech.edu/research/labs/bwnWeb: http://www.ece.gatech.edu/research/labs/bwn

2IFA’2004

Why Satellite NetworksWhy 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

3IFA’2004

OrbitsOrbits

Defining the altitude where the satellite Defining the altitude where the satellite will operate.will operate.

Determining the right orbit depends on Determining the right orbit depends on proposed service characteristics such as proposed service characteristics such as coverage, applications, delay.coverage, applications, delay.

4IFA’2004

Orbits (cont.)Orbits (cont.)

Outer Van Allen Belt (13000-20000 km)

MEO ( < 13K km)

GEO (33786 km)

LEO ( < 2K km)

Inner Van Allen Belt (1500-5000 km)

GEO: Geosynchronous Earth OrbitGEO: Geosynchronous Earth Orbit

MEO: Medium Earth OrbitMEO: Medium Earth Orbit

LEO: Low Earth OrbitLEO: Low Earth Orbit

5IFA’2004

Types of SatellitesTypes of Satellites

HEOHEO: : var. (Molniya, Ellipso)var. (Molniya, Ellipso)

LEO: < 2K kmLEO: < 2K km

MEO: < 13K km (Odyssey, Inmarsat-P)MEO: < 13K km (Odyssey, Inmarsat-P)

GEO: 33786 kmGEO: 33786 km

(Globalstar, Iridium, Teledesic)(Globalstar, Iridium, Teledesic)

Geostationary/Geosynchronous Earth Orbit Geostationary/Geosynchronous Earth Orbit Satellites (GSOs) Satellites (GSOs) (Propagation Delay: 250-280 ms)(Propagation Delay: 250-280 ms)

Medium Earth Orbit Satellites (MEOs) Medium Earth Orbit Satellites (MEOs) (Propagation Delay: 110-130 ms)(Propagation Delay: 110-130 ms)

Highly Elliptical Satellites (HEOs) Highly Elliptical Satellites (HEOs) (Propagation Delay: Variable)(Propagation Delay: Variable)

Low Earth Orbit Satellite (LEOs) Low Earth Orbit Satellite (LEOs) (Propagation (Propagation Delay: 20-25 ms)Delay: 20-25 ms)

6IFA’2004

Geostationary/Geosynchronous Geostationary/Geosynchronous Earth Orbit Satellites (GSOs)Earth Orbit Satellites (GSOs)

33786 km equatorial orbit33786 km equatorial orbit Rotation speed equals Earth rotation Rotation speed equals Earth rotation

speed speed (Satellite seems fixed in the horizon)(Satellite seems fixed in the horizon)

Wide coverage areaWide coverage area Applications (Broadcast/Fixed Satellites, Applications (Broadcast/Fixed Satellites,

Direct Broadcast, Mobile Services)Direct Broadcast, Mobile Services)

7IFA’2004

Advantages of GSOsAdvantages of GSOs

Wide coverageWide coverage High quality and Wideband High quality and Wideband

communicationscommunications Economic EfficiencyEconomic Efficiency Tracking process is easier because of its Tracking process is easier because of its

synchronization to Earthsynchronization to Earth

8IFA’2004

Disadvantages of GSOsDisadvantages of GSOs

Long propagation delays (250-280 ms).Long propagation delays (250-280 ms).(e.g., Typical Intern. Tel. Call (e.g., Typical Intern. Tel. Call 540 ms round-trip delay. 540 ms round-trip delay. Echo cancelers needed. Expensive!)Echo cancelers needed. Expensive!)(e.g., Delay may cause errors in data; (e.g., Delay may cause errors in data; Error correction /detection techniques are needed.)Error correction /detection techniques are needed.)

Large propagation loss. Requirement for Large propagation loss. Requirement for high power level.high power level.(e.g., Future hand-held mobile terminals have limited (e.g., Future hand-held mobile terminals have limited power supply.)power supply.)Currently: smallest terminal for a GSO is as large as an Currently: smallest terminal for a GSO is as large as an A4 paper and as heavy as 2.5 Kg.A4 paper and as heavy as 2.5 Kg.

9IFA’2004

Disadvantages of GSOs Disadvantages of GSOs (cont.)(cont.)

Lack of coverage at Northern and Lack of coverage at Northern and Southern latitudes.Southern latitudes.

High cost of launching a satellite.High cost of launching a satellite. Enough spacing between the satellites to Enough spacing between the satellites to

avoid collisions.avoid collisions. Existence of hundreds of GSOs belonging Existence of hundreds of GSOs belonging

to different countries.to different countries. Available frequency spectrum assigned to Available frequency spectrum assigned to

GSOs is limitedGSOs is limited..

10IFA’2004

Medium Earth Orbit Satellites Medium Earth Orbit Satellites (MEOs)(MEOs)

Positioned in 10-13K km range.Positioned in 10-13K km range.Delay is 110-130 ms.Delay is 110-130 ms.Will orbit the Earth at less than 1 Will orbit the Earth at less than 1

km/s.km/s.Applications Applications

– Mobile Services/Voice Mobile Services/Voice (Intermediate (Intermediate Circular OrbitCircular Orbit (ICO) (ICO) Project)Project)

– Fixed Multimedia (Expressway)Fixed Multimedia (Expressway)

11IFA’2004

Highly Elliptical Orbit Satellites Highly Elliptical Orbit Satellites (HEOs)(HEOs)

From a few hundreds of km to 10s From a few hundreds of km to 10s of thousands of thousands allows to maximize allows to maximize the coverage of specific Earth the coverage of specific Earth regions.regions.

Variable field of view and delay.Variable field of view and delay.Examples: Examples: MOLNIYA, ARCHIMEDESMOLNIYA, ARCHIMEDES

(Direct Audio Broadcast)(Direct Audio Broadcast), , ELLIPSOELLIPSO..

12IFA’2004

Low Earth Orbit Satellites Low Earth Orbit Satellites (LEOs)(LEOs)

Usually less than 2000 km Usually less than 2000 km (780-1400 km are (780-1400 km are favored).favored).

Few ms of delay Few ms of delay (20-25 ms).(20-25 ms). They must move quickly to avoid falling into Earth They must move quickly to avoid falling into Earth

LEOs circle Earth in 100 minutes at 24K km/hour. LEOs circle Earth in 100 minutes at 24K km/hour. (5-10 km per second).(5-10 km per second).

Examples: Examples: – Earth resource management (Earth resource management (Landsat, Spot, RadarsatLandsat, Spot, Radarsat))– Paging (Paging (OrbcommOrbcomm))– Mobile (Mobile (IridiumIridium))– Fixed broadband (Fixed broadband (Teledesic, Celestri, SkybridgeTeledesic, Celestri, Skybridge))

13IFA’2004

Low Earth Orbit Satellites Low Earth Orbit Satellites (LEOs) (cont.)(LEOs) (cont.)

Little LEOs: 800 MHz rangeLittle LEOs: 800 MHz range Big LEOs: > 2 GHzBig LEOs: > 2 GHz Mega LEOs: 20-30 GHzMega LEOs: 20-30 GHz

14IFA’2004

Comparison of Different Comparison of Different Satellite SystemsSatellite 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

15IFA’2004

Comparison of Satellite Comparison of Satellite Systems According to their Systems According to their Altitudes (cont.)Altitudes (cont.)

16IFA’2004

Why Hybrids?Why Hybrids?

GSO + LEOGSO + LEO– GSO for broadcast and GSO for broadcast and

management informationmanagement information– LEO for real-time, interactiveLEO for real-time, interactive

LEO or GSO + Terrestrial LEO or GSO + Terrestrial InfrastructureInfrastructure– Take advantage of the ground Take advantage of the ground

infrastructureinfrastructure

17IFA’2004

Frequency BandsFrequency Bands

NarrowBand SystemsNarrowBand Systems L-BandL-Band 1.535-1.56 GHz DL; 1.535-1.56 GHz DL;

1.635-1.66 GHz UL1.635-1.66 GHz UL S-BandS-Band 2.5-2.54 GHz DL; 2.5-2.54 GHz DL;

2.65-2.69 GHz UL2.65-2.69 GHz UL C-BandC-Band 3.7-4.2 GHz DL; 3.7-4.2 GHz DL;

5.9-6.4 GHz UL5.9-6.4 GHz UL X-BandX-Band 7.25-7.75 GHz DL; 7.25-7.75 GHz DL;

7.9-8.4 GHz UL7.9-8.4 GHz UL

18IFA’2004

Frequency Bands Frequency Bands (cont.)(cont.)

WideBand/Broadband SystemsWideBand/Broadband SystemsKu-BandKu-Band 10-13 GHz DL; 10-13 GHz DL;

14-17 GHz UL 14-17 GHz UL(36 MHz of channel bandwidth; enough (36 MHz of channel bandwidth; enough for typical 50-60 Mbps applications)for typical 50-60 Mbps applications)

Ka-BandKa-Band 18-20 GHz DL; 18-20 GHz DL; 27-31 GHz UL 27-31 GHz UL(500 MHz of channel bandwidth; enough (500 MHz of channel bandwidth; enough for Gigabit applications)for Gigabit applications)

19IFA’2004

Next Generation Systems: Next Generation Systems: Mostly Ka-bandMostly Ka-band

Ka band usage driven by:Ka band usage driven by:– Higher bit rates - 2Mbps to 155 MbpsHigher bit rates - 2Mbps to 155 Mbps– Lack of existing slots in the Ku bandLack of existing slots in the Ku band

FeaturesFeatures– Spot beams and smaller terminalsSpot beams and smaller terminals– Switching capabilities on certain systemsSwitching capabilities on certain systems– Bandwidth-on-demandBandwidth-on-demand

DrawbacksDrawbacks– Higher fadingHigher fading– Manufacturing and availability of Ka band devicesManufacturing and availability of Ka band devices– Little heritage from existing systems (except ACTS and Italsat)Little heritage from existing systems (except ACTS and Italsat)

20IFA’2004

Frequency Bands Frequency Bands (cont.)(cont.)

New Open BandsNew Open Bands (not licensed yet)(not licensed yet)

GHz of bandwidthGHz of bandwidthQ-BandQ-Band in the 40 GHz in the 40 GHzV-BandV-Band 60 GHz DL; 60 GHz DL;

50 GHz UL 50 GHz UL

21IFA’2004

Space Environment IssuesSpace Environment Issues

Harsh Harsh hard on materials and hard on materials and electronics electronics (faster aging)(faster aging)

Radiation is high Radiation is high (Solar flares and (Solar flares and other solar events; Van Allen Belts)other solar events; Van Allen Belts)

Reduction of lifes of space systems Reduction of lifes of space systems

(12-15 years maximum).(12-15 years maximum).

22IFA’2004

Space Environment Issues Space Environment Issues (cont.)(cont.)

DebrisDebris (specially for LEO systems) (specially for LEO systems) (At 7 Km/s impact damage can be important. (At 7 Km/s impact damage can be important. Debris is going to be regulated).Debris is going to be regulated).

Atomic oxygenAtomic oxygen can be a threat to can be a threat to materials and electronics at LEO orbits.materials and electronics at LEO orbits.

GravitationGravitation pulls the satellite towards pulls the satellite towards earth.earth.

Limited propulsion to maintain orbit Limited propulsion to maintain orbit (Limits (Limits the life of satellites; Drags an issue for LEOs).the life of satellites; Drags an issue for LEOs).

Thermal EnvironmentThermal Environment again limits material again limits material and electronics life.and electronics life.

23IFA’2004

Basic ArchitectureBasic Architecture

Ring

WirelessTerrestrial

Network

Internet

LAN

EthernetEthernet

Internet

Ethernet

RingMobile Network

Public Network

MAN

SIU- Satellite Interface UnitSIU - Satellite Interworking Unit

24IFA’2004

Basic Architecture Basic Architecture (cont.)(cont.)

SIU - Satellite Interworking Unit

25IFA’2004

Satellite Interworking Unit Satellite Interworking Unit (SIU)(SIU)

26IFA’2004

Payload ConceptsPayload Concepts

Bent Pipe ProcessingBent Pipe ProcessingOnboard ProcessingOnboard ProcessingOnboard SwitchingOnboard Switching

27IFA’2004

Bent-Pipe Protocol Stack Bent-Pipe Protocol Stack (Internet)(Internet)

PhysicalSatelliteSatellite

Applications

IP

Network

Medium Access Control

Data Link Control

Physical

User Terminal

TCP

Applications

IP

Network

Physical

User Terminal

TCP

Medium Access Control

Data Link Control

28IFA’2004

Onboard Processing Onboard Processing Protocol Stack Protocol Stack (Internet)(Internet)

SatelliteSatellite

User Terminal

Applications

IP

Network

Medium Access Control

Data Link Control

Physical

TCP

User Terminal

Applications

IP

Network

Physical

TCP

Medium Access Control

Data Link Control

Physical

Medium Access Control

Data Link Control

29IFA’2004

Onboard Switching Onboard Switching Protocol Stack Protocol Stack (Internet)(Internet)

Applications

IP

Network

Medium Access Control

Data Link Control

Physical

User Terminal

TCP

Applications

IP

Network

Physical

User Terminal

TCP

Medium Access Control

Data Link Control

SatelliteSatellite

Physical

Medium Access Control

Data Link Control

Network

30IFA’2004

Routing Algorithms Routing Algorithms for Satellite Networksfor Satellite Networks

Satellites organized in Satellites organized in planesplanes

User Data Links (UDL)User Data Links (UDL) Inter-Satellite Links (ISL)Inter-Satellite Links (ISL) Short roundtrip delaysShort roundtrip delays Very dynamic yet Very dynamic yet

predictable network predictable network topologytopology– Satellite positionsSatellite positions– Link availabilityLink availability

Changing visibility from the Changing visibility from the EarthEarth

http://www.teledesic.com/tech/mGall.htmhttp://www.teledesic.com/tech/mGall.htm

31IFA’2004

SeamSeam– Border between Border between

counter-rotating counter-rotating satellite planessatellite planes

Polar RegionsPolar Regions– Regions where the Regions where the

inter-plane ISLs inter-plane ISLs are turned offare turned off

LEO’s at Polar OrbitsLEO’s at Polar Orbits

E. Ekici, I. F. Akyildiz, M. Bender, “The Datagram Routing Algorithm for Satellite IP Networks” ,E. Ekici, I. F. Akyildiz, M. Bender, “The Datagram Routing Algorithm for Satellite IP Networks” ,IEEE/ACM Transactions on Networking, April 2001. IEEE/ACM Transactions on Networking, April 2001.

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

32IFA’2004

Routing in Multi-Layered Routing in Multi-Layered Satellite NetworksSatellite Networks

33IFA’2004

Iridium NetworkIridium Network

34IFA’2004

Iridium Network Iridium Network (cont.)(cont.)

35IFA’2004

Iridium Network Iridium Network (cont.)(cont.)

6 orbits6 orbits 11 satellites/orbit11 satellites/orbit 48 spotbeams/satellite48 spotbeams/satellite Spotbeam diameter = 700 kmSpotbeam diameter = 700 km Footprint diameter = 4021kmFootprint diameter = 4021km 59 beams to cover United States59 beams to cover United States Satellite speed = 26,000 km/h = 7 km/sSatellite speed = 26,000 km/h = 7 km/s Satellite visibility = 9 - 10 minSatellite visibility = 9 - 10 min Spotbeam visibility < 1 minuteSpotbeam visibility < 1 minute System period = 100 minutesSystem period = 100 minutes

36IFA’2004

Iridium Network Iridium Network (cont.)(cont.)

4.8 kbps voice, 2.4 Kbps data4.8 kbps voice, 2.4 Kbps data TDMATDMA 80 channels /beam80 channels /beam 3168 beams globally (2150 active beams)3168 beams globally (2150 active beams) Dual mode user handsetDual mode user handset User-Satellite Link = L-BandUser-Satellite Link = L-Band Gateway-Satellite Link = Ka-BandGateway-Satellite Link = Ka-Band Inter-Satellite Link = Ka-BandInter-Satellite Link = Ka-Band

37IFA’2004

Operational SystemsOperational Systems

Reference EUTELSAT INTELSATType Bent Pipe Bent PipeOrbit GSO GSOInvestors Eutelsat IntelsatPrime Various VariousServices Multimedia Voice, Data, Video Conf.Frequencies Ku KuAntennas (cm) 120+ 120+U/ L Rates (Mbps) 0.016-2 0.016-2Number of Satellites 1 26Primary Access FDMA/TDMA FDMA/TDMAMultibeam No NoISLs No NoTransport Protocol IP/ATM IP

38IFA’2004

Operational Systems Operational Systems (cont.) Little LEOs(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 ofSatellites

36 24 24

Mass ofSatellites (kg)

40 150 150

39IFA’2004

Proposed and Proposed and Operational SystemsOperational Systems

1.1. ICO Global Communications (New ICO)ICO Global Communications (New ICO) Number of Satellites:Number of Satellites: 1010 Planes:Planes: 22 Satellites/Plane:Satellites/Plane: 55 Altitude:Altitude: 10,350 km10,350 km Orbital Inclination:Orbital Inclination: 4545°° Remarks:Remarks:

Service:Service: Voice @ 4.8 kbps, data @ 2.4 kbps and higher Voice @ 4.8 kbps, data @ 2.4 kbps and higher Operation anticipated in 2003Operation anticipated in 2003 System taken over by private investors due to financial difficultiesSystem taken over by private investors due to financial difficulties Estimated cost:Estimated cost: $4,000,000,000 $4,000,000,000 163 spot beams/satellite, 950,000 km163 spot beams/satellite, 950,000 km22 coverage area/beam, coverage area/beam,

28 channels/beam28 channels/beam Service link:Service link: 1.98-2.01 GHz (downlink), 2.17-2.2 GHz (uplink); (TDMA)1.98-2.01 GHz (downlink), 2.17-2.2 GHz (uplink); (TDMA) Feeder link:Feeder link: 3.6 GHz band (downlink), 6.5 GHz band (uplink)3.6 GHz band (downlink), 6.5 GHz band (uplink)

40IFA’2004

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

2.2. GlobalstarGlobalstar Number of Satellites:Number of Satellites: 48 48 Planes:Planes: 88 Satellites/Plane:Satellites/Plane: 66 Altitude:Altitude: 1,414 km 1,414 km Orbital Inclination:Orbital Inclination: 52 52°° Remarks:Remarks:

Service:Service: Voice @ 4.8 kbps, data @ 7.2 kbps Voice @ 4.8 kbps, data @ 7.2 kbps Operation started in 1999Operation started in 1999 Early financial difficultiesEarly financial difficulties Estimated cost:Estimated cost: $2,600,000,000 $2,600,000,000 16 spot beams/satellite, 2,900,000 km16 spot beams/satellite, 2,900,000 km22 coverage area/beam, coverage area/beam,

175 channels/beam175 channels/beam Service link:Service link: 1.61-1.63 GHz (downlink), 2.48-2.5 GHz (uplink); (CDMA)1.61-1.63 GHz (downlink), 2.48-2.5 GHz (uplink); (CDMA) Feeder link:Feeder link: 6.7-7.08 GHz (downlink), 5.09-5.25 GHz (uplink)6.7-7.08 GHz (downlink), 5.09-5.25 GHz (uplink)

41IFA’2004

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

3.3. ORBCOMORBCOM Number of Satellites:Number of Satellites: 3636 Planes:Planes: 44 22 Satellites/Plane:Satellites/Plane: 22 22 Altitude:Altitude: 775 km775 km 775 775

kmkm Orbital Inclination:Orbital Inclination: 4545°° 7070°° Remarks:Remarks:

Near real-time serviceNear real-time service Operation started in 1998 Operation started in 1998 (first in market)(first in market) Cost:Cost: $350,000,000 $350,000,000 Service link:Service link: 137-138 MHz (downlink), 148-149 MHz (uplink)137-138 MHz (downlink), 148-149 MHz (uplink) Spacecraft mass: Spacecraft mass: 40 kg40 kg

42IFA’2004

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

4.4. StarsysStarsys Number of Satellites:Number of Satellites: 2424 Planes:Planes: 6 6 Satellites/Plane:Satellites/Plane: 4 4 Altitude:Altitude: 1,000 km1,000 km Orbital Inclination:Orbital Inclination: 5353°° Remarks:Remarks:

Service:Service: Messaging and positioning Messaging and positioning Global coverageGlobal coverage Service link:Service link: 137-138 MHz (downlink), 148-149 MHz (uplink)137-138 MHz (downlink), 148-149 MHz (uplink) Spacecraft mass: Spacecraft mass: 150 kg150 kg

43IFA’2004

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

5.5. Teledesic (original proposal)Teledesic (original proposal) Number of Satellites:Number of Satellites: 840 (original) 840 (original) Planes:Planes: 21 21 Satellites/Plane:Satellites/Plane: 40 40 Altitude:Altitude: 700 km700 km Orbital Inclination:Orbital Inclination: 98.298.2°° Remarks:Remarks:

Service:Service: FSS, provision for mobile service FSS, provision for mobile service (16 kbps – 2.048 Mbps, including video) for 2,000,000 (16 kbps – 2.048 Mbps, including video) for 2,000,000

usersusers Sun-synchronous orbit, earth-fixed cellsSun-synchronous orbit, earth-fixed cells System cost:System cost: $9,000,000,000 ($2000 for terminals) $9,000,000,000 ($2000 for terminals) Service link:Service link: 18.8-19.3 GHz (downlink), 28.6-29.1 GHz (uplink) (K18.8-19.3 GHz (downlink), 28.6-29.1 GHz (uplink) (Kaa band) band) ISL:ISL: 60 GHz60 GHz Spacecraft mass: Spacecraft mass: 795 kg795 kg

44IFA’2004

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

6.6. Teledesic (final proposal)Teledesic (final proposal) Number of Satellites:Number of Satellites: 288 (scaled down)288 (scaled down) Planes:Planes: 12 12 Satellites/Plane:Satellites/Plane: 24 24 Altitude:Altitude: 700 km700 km Remarks:Remarks:

Service:Service: FSS, provision for mobile service FSS, provision for mobile service (16 kbps – 2.048 Mbps, including video) for 2,000,000 (16 kbps – 2.048 Mbps, including video) for 2,000,000

usersusers Sun-synchronous orbit, earth-fixed cellsSun-synchronous orbit, earth-fixed cells System cost:System cost: $9,000,000,000 ($2000 for terminals) $9,000,000,000 ($2000 for terminals) Service link:Service link: 18.8-19.3 GHz (downlink), 28.6-29.1 GHz (uplink) (K18.8-19.3 GHz (downlink), 28.6-29.1 GHz (uplink) (Kaa band) band) ISL:ISL: 60 GHz60 GHz Spacecraft mass: Spacecraft mass: 795 kg795 kg

45IFA’2004

ReferencesReferences

Survey PaperSurvey Paper• Akyildiz, I.F. and Jeong, S., Akyildiz, I.F. and Jeong, S., "Satellite ATM "Satellite ATM

Networks: A Survey,"Networks: A Survey," IEEE Communications IEEE Communications Magazine, Vol. 35, No. 7, pp.30-44, July 1997.Magazine, Vol. 35, No. 7, pp.30-44, July 1997.