Satellite Network

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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 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.) 4

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

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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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 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 Architecture23

Ring

WirelessTerrestrial

Network

Internet

LAN

EthernetEthernet

Internet

Ethernet

RingMobile Network

Public Network

MAN

SIU- Satellite Interface UnitSIU - Satellite Interworking Unit

Basic Architecture (cont.)24

SIU - Satellite Interworking Unit

Satellite Interworking Unit (SIU)25

Payload Concepts

Bent Pipe Processing

Onboard Processing

Onboard Switching

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Bent-Pipe Protocol Stack (Internet)

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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

Onboard Processing Protocol Stack (Internet)

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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

Onboard Switching Protocol Stack (Internet)

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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