Chapter 1 Introduction to Satellite Communication System

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BEE 4243 SATELLITE COMMUNICATION SYSTEMDept. Of Communication Engineering,FacultyOf Electrical And Electronics,

UniversitiTun Hussein OnnMalaysia

The space race, legacy of the

SPUTNIK

Oct 4th 1957, Sputnik 1, launch

from Tyurastam, USSR Means “Friendly Traveller”, weighed

just 184.3 pounds (83.6kg) continue

to send signals for 21 days before

decaying 3 months after launch on

Jan 4th 1958

Spirited the technological

competition in the space race



Next was Explorer 1 on Jan 31st 1958 USA answers to Sputnik

Carried scientific equipment to study the

Earth atmosphere

Found the van Allen belt

Transmitted telemetry for nearly 5 months

SCORE, Signal Communication by Orbiting

Relay Equipment

Dec 18, 1958 by the USA, 150 pounds conical-shaped satellite

The first artificial satellite used for relaying

terrestrial communication

First bent pipe repeater



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1960, ECHO (USA)

First communicating satellite (passive) into space

100 ft diameter plastic balloon with aluminium coating

1962, Telstar

First active communication satellite

1962, Relay (USA)

First comm. satellite to transmit TV signal worldwide

1963, Syncom II (USA)

First geosynchronous communications satellite

Jul 1964, IntelSat formed

1965, INTELSAT 1 (Early Bird) launched

68 kg, 480 telephone channels, annual cost $32,500 perchannel

Caused by launch cost, satellite, short lifetime and lowcapacity

1965, MOLNYA series launched



Important Milestone

1000 AD, Chinese invented the rocket

1903, Konstantin Tsiokovsky, publishes his ideas on space flight

1926, first liquid propellant rocket launched by R.H. Goddard in the USA

1942, first successful launch of V-2 rocket in Germany

1945, Arthur C. Clarke published his ideas on geostationary satellite for

worldwide communications Today, satellite communications is very much a fact of everyday life

Form an essential part of telecommunications systems worldwide carrying

large amount of data and telephone traffic in addition to television signals

Cost is distance insensitive, it cost about the same to provide a satellite

communication link over a short distance as it does over a longer distance

due to its wide coverage

According to the Union of Concerned Scientists, there are around 900

satellites currently in operation (not including the secret/ classified

satellite).



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ARCHITECTURE OF SATELLITE

COMMUNICATION SYSTEM Space segment Satellite

All terrestrial facilities for the control and monitoring of the satellite

Tracking, telemetry and command (TT&C) station

Satellite control centre

Station keeping

Check vital function of the satellite

Satellite can be divided into two parts

Payload

Consists of the receiving and transmitting antennas and all theelectronic equipment which support the transmission of

carriers and information Platform (bus)

All the subsystems which permit the payload to operate such asstructure, electrical power supply, temperature control, attitudeand orbit control, propulsion equipment, TT&C equipment



Ground segment All the earth stations; receive, or both transmit and receive

The simplest is Home TV receive-only (TVRO)

Most complex – Terminal station used for international communicationnetwork

Stations are distinguished by

Size : varied according to volume of traffic to be carried on space

links Type of traffic : telephone, television or data

Satellite can link network of ground station in three ways:

Point-to-point : signal transmitted in one part of the world toanother individual stations

Point-to-multipoint : From one stations to an unlimited number of independent receiving stations (e.g. satellite TV broadcasting

Multipoint-to-point : From many point to a single controllingstation (e.g. environmental data-collection



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The performance of a satellite link is typically specified in terms of itchannel capacity

Definition

A channel is one-way link from transmitting earth station through thesatellite to the receiving earth station

A circuit is full duplex link between two earth station

A half circuit is a two-way link between an earth station and thesatellite only

The capacity of a link is specified by these types and number of channelsand the performance requirement of each channel

the term channel may also apply to televisions and data circuits

The quality of a radio link is specified by it carrier-to-noise ratio (C/N)

The quality of the total link determines the quality of the signals deliveredto the end user in accordance with the type of modulating and coding used



The satellite has dual role

To amplify the received carriers for retransmission downlink

The carrier power input at the satellite receiver is in the order of

100pW to 1nW

The carrier power at the output of the transmission amplifier is of

the order of 10 to 100W The power gain is thus of the order of 100 to 300dB

To change the frequency of the carrier to avoid re-injection of a

fraction of the transmitted power to the receiver

The rejection capability of the input filters at the downlink

frequency combines with the low antenna gains between the

transmitting output and the receiving input to ensure isolation of

the order of 150dB



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Conventional satellite

Regenerative satellite

Figure 1.1 Conventional and regenerative satellite



Definitions Local communications

Communications limited in distance e.g. few tens of kilometres

Regional communications

Communications over a specific region of the world such as groupsof countries or continent

Global communications

World wide established link

Communications can be classified into two main categories

Real time communications

Delayed communications

This distinction is essential for identifying the type of service that canbe performed, since it will affect the system design

Possible mix of the two concept within the constrain of a cost-effectivedesign e.g. LEO satellite systems can well be adopted for providing



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(a) Typical Vista application (b) domestic/regional Vista network with standard Aor B gateway



The design of a satellite communications system present many

interesting alternatives and tradeoffs

Choice of orbits

Method of multiple access

Method of modulation and coding

Trade off between power and bandwidth



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The most favourable orbits for satellite communication LEO (Low Earth Orbit)

Altitude : 300 km – 2,000 km (more common : 600 km – 1,000 km) Either elliptical or (more usual) circular

Many different type, no firm decision as to what constitutes a LEO

Polar (inclination = 90o, circular) Near polar ( inclination ~90o, circular)

Circular inclined

LEqO ( inclination = 0o, circular)

Period : 90 minutes 2 hours

Negligible transmission delay between end-users and satellite

Radius of the footprint varies from 3,000 to 4,000 km

The maximum time during which a satellite above a local horizon for an

observer on the ground is up to 20 minutes Large Doppler shift

Affected by atmospheric drag which cause the orbit to gradually deteriorate



ICO ( Intermediate Circular Orbit) or MEO (Medium Earth Orbit)

Altitude : between 10,000 – 20,000 km

Orbit period depends on altitude, e.g. ~10,000 km altitude period ~ 6hours

Stable orbits, allowing more accurate long term orbital predictions

Large area of coverage

Slower Doppler shift

Some radiation effect (high electron dose)

GEO ( Geostationary Earth Orbit Satellites)

Altitude 35, 786

Circular prograde orbit in the equatorial plane

Orbital period 23 hours 56 minutes

Appear fixed above the surface of the earth

Footprint cover almost 1/3 of the earth surface ( from ~75oS to ~75oN)

Roundtrip delay ~250ms

Doppler shift non or low



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Tomasi

Electronic Communications Systems, 5eCopyright ©2004 byPearson Education, Inc.

Upper Saddle River, New Jersey 07458

Allrights reserved.

Three satellite used to cover the inhabited world



Satellites in geosynchronous earth orbits



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HEO ( Highly Elliptical Orbit)

Have a perigee at about 500 km above the surface of the earth and

apogee as high as 50,000 km

The orbits are inclined at 63.4o in order to provide communications

services to location at high northern latitude

Orbit period varies from 8 to 24 hours

Owing to the high eccentricities of the orbit, a satellite will spend about

two-third of the orbital period near apogee and during that time it

appears to be almost stationary for an observer on the earth

Free space loss and propagation delay is comparable to that of GEO

Large Doppler shift (due to large movement of satellite in HEO)



Example of HEO

Russian Molniya

Employs 3 satellite in three 12 hours orbits separated by 120o

around the earth

Apogee : 39, 354 km, Perigee : 1000 km

Russian Tundra 2 satellites in two 24 hour orbits separated by 180o around the

earth

Apogee : 53, 622 km, Perigee : 17, 951 km

Loopus system

Achimedes System (ESA)



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Highly elliptical orbit

Various type of orbits



The appropriate orbit is often suggested by The nature of the service

The business plan, or

The constraints of the communication link

Example : Satellite Mobile Telephony System

Iridium Inclination 86.4o , 6 plane , 11 per plane

LEO constellation of 66 satellites in polar orbit at an altitude of 780 km The orbital period is 100 minutes and a given satellite is in view for only 10

minutes before handover of a call to a following satellite

Has extensive on-board processing and telephone call is routed throughconstellation via inter-satellite links

The choice of LEO was dictated by the desire to : minimize power on both the satellite and the mobile handset minimize satellite antenna size minimize time delay, or latency for a two-way signal

maximize the angle of elevation





GlobalStar A constellation of 48 satellites ( 8 plane , 6 per plane) in orbit inclined

at 52°at an altitude of 1,414km

Concentrates coverage over the temperature regions of the earth from70°S to 70°N

Employed spatial diversity - signal are combined in the receiver tomitigate losses due to blockage and multipath effects

The inclined, non-polar orbit constellation was chosen to ensure that atleast two satellites are visible at all times

Uses non-processing, or "bent-pipe" satellite

Relay communications between the user and a gateway- the party beingcall will be connected with the gateway. Through the PSTN(maximizing the use of existing, low cost communication service or

back through a satellite if the party is another Globalstar user.



ICO Consists of 10 operational satellites in MEO at an altitude of 10,390km The orbit is an excellent compromise between LEO and GEO The satellite antenna size and power are relatively modest and the

latency is still small The number of satellite required for global coverage is significantly

less than LEO and the dwell time is considerably longer Has a period of revolution of six hours and the time a satellite is visible

is on the order of two hours ECCO

- circular orbit constellation in the equatorial plane, design forcommunication in tropical region

Ellipse elliptical orbit to maximize coverage over northern hemisphere

AceS Asia Cellular Satellite system GEO orbit Serve Pacific rim Satellite antenna ~12m across

Chapter 1 Introduction to Satellite Communication System

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