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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
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Chapter 9
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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
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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
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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,)
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#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
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+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 $y the earth2s heat nearits surface adersely affects reception
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#E, ,r$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
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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
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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
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+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$le time is a few hours
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&re.uency *ands 0aila$le for Satellite
Communications
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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 $y o'y!en% water% an!le of eleation% and hi!herfre.uencies
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Satellite &ootprint
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Satellite 6etwork Confi!urations
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Capacity 0llocation Strate!ies
&re.uency diision multiple access (&D+0)
Time diision multiple access (TD+0)
Code diision multiple access (CD+0)
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&re.uency-Diision +ultiple'in!
0lternatie uses of channels in point-to-point
confi!uration
<;44 oice-fre.uency (B&) oice channels
,ne 4-+$ps data stream
<? channels of <= +$ps each
44 channels of ? k$ps each
?44 channels of 4 k$ps each ,ne analo! ideo si!nal
Si' to nine di!ital ideo si!nals
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&re.uency-Diision +ultiple 0ccess
&actors which limit the num$er of su$channels
proided within a satellite channel ia &D+0
Thermal noise
ntermodulation noise
Crosstalk
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&orms of &D+0
&i'ed-assi!nment multiple access (&0+0)
The assi!nment of capacity is distri$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
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&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
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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 $yearth station usin! CSC
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Reasons for ncreasin! Use of TD+
Techni.ues Cost of di!ital components continues to drop
0danta!es of di!ital components
Use of error correction ncreased efficiency of TD+
1ack of intermodulation noise
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&0+0-TD+0 ,peration
Transmission in the form of repetitie se.uence offrames Each frame is diided into a num$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
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&0+0-TD+0 Uplink
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&0+0-TD+0 Downlink
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