lec 9 - satellite communication

7/24/2019 Lec 9 - Satellite Communication

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Background of Wireless

Communication

StudentPresentations andProjects

Wireless Communication

Technology

Wireless Networking and

Mobile IP

Wireless Local Area

Networks

Wireless Communication

Satellite CommunicationsSatellite Communications



Chapter 9



Satellite-Related Terms

Earth Stations – antenna systems on or near earth

Uplink – transmission from an earth station to a

satellite

Downlink – transmission from a satellite to an earth

station

Transponder – electronics in the satellite that conert

uplink si!nals to downlink si!nals



Ways to Cate!ori"e

Communications Satellites Coera!e area

#lo$al% re!ional% national

Serice type

&i'ed serice satellite (&SS)

*roadcast serice satellite (*SS)

+o$ile serice satellite (+SS)

#eneral usa!e Commercial% military% amateur% e'perimental



Classification of Satellite ,r$its

Circular or elliptical or$it Circular with center at earths center

Elliptical with one foci at earths center

,r$it around earth in different planes E.uatorial or$it a$oe earths e.uator

/olar or$it passes oer $oth poles

,ther or$its referred to as inclined or$its

0ltitude of satellites #eostationary or$it (#E,)

+edium earth or$it (+E,)

1ow earth or$it (1E,)



#eometry Terms

Eleation an!le - the an!le from the hori"ontal to the

point on the center of the main $eam of the antenna

when the antenna is pointed directly at the satellite

+inimum eleation an!le

Coera!e an!le - the measure of the portion of the

earth2s surface isi$le to the satellite



+inimum Eleation 0n!le

Reasons affectin! minimum eleation an!le of earth

stations antenna (34o)

*uildin!s% trees% and other terrestrial o$5ects $lock

the line of si!ht

0tmospheric attenuation is !reater at low eleation

an!les

Electrical noise !enerated $y the earth2s heat nearits surface adersely affects reception



#E, ,r$it

0danta!es of the the #E, or$it

6o pro$lem with fre.uency chan!es

Trackin! of the satellite is simplified

7i!h coera!e area

Disadanta!es of the #E, or$it

Weak si!nal after traelin! oer 8%444 km

/olar re!ions are poorly sered Si!nal sendin! delay is su$stantial



1E, Satellite Characteristics

Circular:sli!htly elliptical or$it under ;444 km

,r$it period ran!es from <= to ; hours

Diameter of coera!e is a$out >444 km Round-trip si!nal propa!ation delay less than ;4 ms

+a'imum satellite isi$le time up to ;4 min

System must cope with lar!e Doppler shifts 0tmospheric dra! results in or$ital deterioration



1E, Cate!ories

1ittle 1E,s &re.uencies $elow < #7"

+7" of $andwidth

Data rates up to <4 k$ps 0imed at pa!in!% trackin!% and low-rate messa!in!

*i! 1E,s &re.uencies a$oe < #7"

Support data rates up to a few me!a$its per sec

,ffer same serices as little 1E,s in addition to oice and positionin! serices



+E, Satellite Characteristics

Circular or$it at an altitude in the ran!e of 444 to

<;%444 km

,r$it period of ? hours

Diameter of coera!e is <4%444 to <%444 km

Round trip si!nal propa!ation delay less than 4 ms

+a'imum satellite isi$le time is a few hours



&re.uency *ands 0aila$le for Satellite

Communications



Satellite 1ink /erformance &actors

Distance $etween earth station antenna and satellite

antenna

&or downlink% terrestrial distance $etween earth

station antenna and @aim pointA of satellite

Displayed as a satellite footprint (&i!ure 9=?)

0tmospheric attenuation

0ffected $y o'y!en% water% an!le of eleation% and hi!herfre.uencies



Satellite &ootprint



Satellite 6etwork Confi!urations



Capacity 0llocation Strate!ies

&re.uency diision multiple access (&D+0)

Time diision multiple access (TD+0)

Code diision multiple access (CD+0)



&re.uency-Diision +ultiple'in!

0lternatie uses of channels in point-to-point

confi!uration

<;44 oice-fre.uency (B&) oice channels

,ne 4-+$ps data stream

<? channels of <= +$ps each

44 channels of ? k$ps each

?44 channels of 4 k$ps each ,ne analo! ideo si!nal

Si' to nine di!ital ideo si!nals



&re.uency-Diision +ultiple 0ccess

&actors which limit the num$er of su$channels

proided within a satellite channel ia &D+0

Thermal noise

ntermodulation noise

Crosstalk



&orms of &D+0

&i'ed-assi!nment multiple access (&0+0)

The assi!nment of capacity is distri$uted in a fi'ed manner

amon! multiple stations

Demand may fluctuate

Results in the si!nificant underuse of capacity

Demand-assi!nment multiple access (D0+0)

Capacity assi!nment is chan!ed as needed to respondoptimally to demand chan!es amon! the multiple stations



&0+0-&D+0

&0+0 – lo!ical links $etween stations are

preassi!ned

&0+0 – multiple stations access the satellite $y

usin! different fre.uency $ands

Uses considera$le $andwidth



D0+0-&D+0

Sin!le channel per carrier (SC/C) – $andwidthdiided into indiidual B& channels 0ttractie for remote areas with few user stations near each

site Suffers from inefficiency of fi'ed assi!nment

D0+0 – set of su$channels in a channel is treated asa pool of aaila$le links

&or full-duple' $etween two earth stations% a pair ofsu$channels is dynamically assi!ned on demand

Demand assi!nment performed in a distri$uted fashion $yearth station usin! CSC



Reasons for ncreasin! Use of TD+

Techni.ues Cost of di!ital components continues to drop

0danta!es of di!ital components

Use of error correction ncreased efficiency of TD+

1ack of intermodulation noise



&0+0-TD+0 ,peration

Transmission in the form of repetitie se.uence offrames Each frame is diided into a num$er of time slots

Each slot is dedicated to a particular transmitter

Earth stations take turns usin! uplink channel Sends data in assi!ned time slot

Satellite repeats incomin! transmissions *roadcast to all stations

Stations must know which slot to use fortransmission and which to use for reception



&0+0-TD+0 Uplink



&0+0-TD+0 Downlink



F0

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lec 9 - satellite communication

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