05_global mobile satellite

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Global Mobile Satellite System Communication

Guided By Submitted By

Mr. Vijay Chavada Patel Krushant R.

07-EC-0

!V Sem "EC-#$

%.&.R.P. ' !.(.R)

G#*&+!*#G#R

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#CK*,%E&GEME*(

! tae this //rtunity t/ than /ur rese1ted

MR. V!2#3 C+#V# 4ith/ut 4h/se su/rt and

en1/ura5ement) this aer 1/uld n/t have been

1/mleted. ! als/ tae this //rtunity t/ than t/

/ur /ther 6a1ulty members and 6riends 4h/ have

heled me in 5atherin5 and /r5aniin5 the re8uired

in6/rmati/n.

#bstra1t9

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To make a satellite phone call today fom a location that does not offe teestial !ie line

o !ieless co"ea#e e$uies the use of a la#e% costly teminal% and entails "ey hi#h peminute cha#es& 'uthe% the $uality of se"ice is elati"ely poo because of annoyin#

echoes% la#e tansmission delays% o"e talk associated !ith satellite communications usin#

#eostationay satellites&

Thee is a tend fo mobile satellite system achitectues aimed at the deployment ofmulti-satellite constellations in (on-Geostationay Eath )bits& This allo!s the use

teminals to be small si*e% lo! cost and ha"in# lo! po!e demand& +n pesent and ne,t

#eneation satellite systems% CM. has been poposed as the multiple access techni$ue foa numbe of mobile satellite communication systems& To enhance the co"ea#e and $uality

of se"ice% /o! Eath )bitin# /E) constellations ae usually selected& ee% !e analy*e

the pefomance of the do!nlink of a /E) satellite channel& The po"ision of such a

se"ice e$uies that the use ha"e sufficient link $uality fo the duation of se"ice& To

ha"e sufficient link $uality% the use must ha"e an ade$uate po!e to o"ecome the pathloss and othe physical impaiments to po"ide acceptable communication and impo"e the

pefomance of the system&

Thus% in many pats of the !old% the demand fo communications mobility can be met

effecti"ely only thou#h #lobal mobile satellite se"ices& andheld satellite phones aetheefoe foecast as the eme#in# mobile communications fontie !ith #o!th that could

paallel ecent #o!th in cellula mobile industy& +n ode to #uaantee the se"ice $uality

and eliability fo mobile satellite communication systems% !e ha"e to take into account

outa#es due to obstuction of the line-of-si#ht path bet!een a satellite and a mobileteminal as !ell as the si#nal fluctuation caused by intefeence fom multipath adio

!a"es& Thus% !e need a #ood chaactei*ation fo the satellite popa#ation channel& +t iscommonly accepted that satellite communications systems in paticula% lo! eath obit/E) systems ae the de facto solution fo po"idin# the eal pesonal communications

se"ices 3CSs to the uses eithe stationay o on the mo"e any!hee% anytime and in any

fomat "oice% data% and multimedia&

The satellite se#ment is a net!ok of GE) o /E) satellites aan#ed in obital planes i&e&

diffeent pats of the sky in such a !ay that they ha"e a communications link !ith end-use e$uipment% #ound #ate!ays and othe satellites& The #ate!ay connects the satellites

to the local telephone net!ok& The #ate!ay also tansmits si#nals to the satellites and

ecei"es tansmission fom the satellites& ue to the hi#h mobility of lo! eath obit /E)

satellites% thee is a si#nificant numbe of hando"e attempts in a /E)-based mobilesatellite communication system% causin# a hi#h hando"e failue ate& This pape poposes

to e,tend the peiod of !hich a hando"e e$uest is "alid% and thus endein# hi#he

pobability of successful hando"e&

Satellite communication se"ice can be po"ided by #eostationay eath obit GE)%

medium eath obit ME) o lo! eath obit /E) satellites& 5ecause of its much shotedistance fom eath% lo!e po!e e$uiement and thus smalle mobile teminal MT si*e%

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/E) satellite system is a pefeable choice& iffeences bet!een satellite and teestial

systems e,ist in spite of common obecti"es fo hi#h $uality se"ices and e,cellent

spectum efficiency& Some diffeences aise because8- use costs ae closely elated tosatellite tansmit po!e the satellite popa#ation channel is hi#hly pedictable satellite paths

intoduce si#nificant popa#ation delays and opple shifts fe$uency co-odination has to

be on a #lobal basis fe$uency e-use options ae moe limited% hence band!idth is a ti#htconstaint satellite beam shapin# and si*in# oppotunities ae limited&

The most si#nificant attibute of any satellite communication system is the !ide aeaco"ea#e that can be po"ided !ith "ey hi#h #uaantees of a"ailability and consistency of

se"ice& Satellite communication systems ae desi#ned to po"ide "oice% data% fa,% pa#in#%

"ideo confeencin# and intenet se"ices to uses !old!ide& Thou#h satellite based

systems% uses !ill be able to make a phone call fom an .fican safai o !hile sailin#aound the !old& (o matte !hee uses ae% they !ill be able to communicate !ith

clients% customes% associates% fiends% and family any!hee in the !old& +n addition%

satellite communications !ill allo! counties to po"ide phone se"ices !ithout la#e

in"estments in landline o !ieless systems& Satellite communications !ill be one of thefastest #o!in# aeas !ithin the communications industy&

!*&E:

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T)3+C 3.GE ()

1& +(T9):CT+)( 07

2& C/.SS+'+C.T+)( )' M)5+/E S.TE//+TE C)MM:(+C.T+)( S;STEMS 10

2&1 GE)ST.T+)(.9; S.TE//+TE&

2&2 E.9T )95+T /E)&

6& S)ME /E) S.TE//+TE S;STEM 14

6&1 TE +9++:M S;STEM

6&2 TE G/)5./ST.9 S;STEM

6&6 TE TE/EES+C S;STEM

4& ME) S.TE//+TE S;STEM 1?

4&1 TE +C) S;STEM

@& )A9EA+E> )' )> . M)5+/E S.TE//+TE S;STEM >)9BS 20

@&1 )> . S.TE//+TE C.// GETS 9):TE

@&2 .()AE9 M.(.GEME(T +( M)5+/E S.TE//+TE S;STEMS

& GE(E9./ .S3ECTS )' M)5+/E S.TE//+TE S;STEMS 2@

7& C.3.5+/+T+ES )' M)5+/E S.TE//+TE S;STEMS 2

?& /+M+T.T+)(S )' M)5+/E S.TE//+TE S;STEMS 2?

D& G9)>T 9+AE9S )' M)5+/E S.TE//+TE C)MM:(+C.T+)( SE9A+CES 2D

10& >) >+// :SE S.TE//+TE C)MM:(+C.T+)(S S;STEMS 61

11& G/)5./ M)5+/E S.TE//+TE C)MM:(+C.T+)(S SE9A+CES 62

12& .33/+C.T+)( )' M)5+/E S.TE//+TE S;STEM 66

16& C)(C/:S+)( 6

14& 5+5/+)G9.3; 6

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1& +(T9):CT+)(

To make a satellite phone call today fom a location that does not offe teestial !ieline

o !ieless co"ea#e e$uies the use of a la#e% costly teminal% and entails "ey hi#h pe

minute cha#es& 'uthe% the $uality of se"ice is elati"ely poo because of annoyin#

echoes% la#e tansmission delays% o"etalk associated !ith satellite communicationsusin# #eostationay satellites& The ne,t #eneation of satellite communication systems

!ill use ad"ances in satellite systems% !ieless technolo#ies% and miniatui*ation% to

po"ide #lobal mobile satellite se"ices that !ill make calls bet!een any t!o locations oneath much easie% much moe affodable and much moe use fiendly&

E"en in the yea 2000% the teestial cellula co"ea#e is a"ailable to less than 0F of the

!olds population and only about 1@F of the eaths total suface& Moe than 6 billion ofthe !olds population ha"e no phone se"ice& The !aitin# list of landline telephone

se"ice has o"e @0 million names !ith the a"ea#e !ait #eate than 1&@ yeas& 9ual

aeas% e#ions% that ae spasely populated in de"eloped counties and la#e pats of thede"elopin# !old ae destined to be undese"ed o to emain out of each of teestial

mobile se"ices alto#ethe& Thus% in many pats of the !old% the demand fo

communications mobility can be met effecti"ely only thou#h #lobal mobile satellitese"ices& andheld satellite phones ae theefoe foecast as the eme#in# mobile

communications fontie !ith #o!th that could paallel ecent #o!th in cellula mobile

industy& 9e#adless of ho! you look at the numbes% thee is a si#nificant amount of

people !ithout phone se"ice thou#hout the !old& Mobile Satellite communicationse"ices !ill sol"e the need of !old!ide ta"eles and po"ide phone se"ices to many

aeas of the !old that cuently do not ha"e phone se"ice& The eme#in# ne,t

#eneatin# mobile systems ae #eneally efeed as GM3CS% fo Global Mobile 3esonalCommunication by Satellites&

:ntil no! Communication Satellites ha"e opeated usin# Geo-Stationey )bits GE)%lyin# abo"e 6%000 kilometes abo"e the eaths suface& 'om this )bit the satelliteappeas to be stationey fi,ed abo"e a specific location fom eath% theeby ensuin#

continuous% uninteupted co"ea#e to that location& The pimay ole of a #eostationay

communications satellite is to act as a !ieless epeate station in space that opeates in aboadcast mode and po"ides a mico!a"e link bet!een t!o emote locations on eath&

The key components of a communication satellite include "aious tanspondes%

tanscei"es% and antennas that ae tuned to the allocated fe$uency channels& .lthou#hthe Geostationay Satellites ha"e a la#e footpint% so that the entie suface of the eath

can be co"eed by fe! such satellites% thei hi#h altitude leads to "ey lon# oundtip

si#nal delays and esultant de#adation in se"ice $uality&

Thee is a tend fo mobile satellite system achitectues aimed at the deploymentof multi-satellite constellations in (on-Geostationay Eath )bits (GE)s&This allo!s

the use teminals to be small si*e% lo! cost and ha"in# lo! po!e demand&To enhancethe co"ea#e and $uality of se"ice% /o! Eath )bitin# /E) constellations ae usually

selected& To suppots a !ide an#e of se"ices and to po"ide supeio se"ice $uality

compaable to that a"ailable fom teestial !ieless and !ieline net!oks%

constellations of satellites opeatin# in /o! Eath )bits /E) o Medium Eath )bitsME) ae consideed moe suitable&

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. numbe of "aious #lobal mobile satellite communications systems ha"e aleady been

in de"elopment sta#es& >ith the fist #lobal mobile satellite se"ices initiated in 1DD?&The fou such systems that ae in ad"anced sta#es of plannin# o ealy implementations

ae +idium% Globalsta% +C) and Teledesic&

The ea of satellite-based mobile communications systems stated !ith the fistM.9+S.T satellite !hich !as launched into a #eostationay obit o"e the 3acific )cean

in 1D7 to po"ide communications bet!een ships and shoe stations& The combination of

hi#h cost and unacceptably la#e e$uipment has kept mobile satellite communicationsMSC systems fom appealin# to the !ide maket of pesonal mobile communications&

o!e"e% the po#ess made o"e the last ten yeas in di#ital "oice pocessin#% satellite

technolo#y% and component miniatui*ation has esulted in the "iability of MSC systems

in espondin# to the #o!in# maket in pesonal mobileCommunications&The system achitectues of each system ae pesented alon# !ith a

desciption of the satellite and use handset desi#ns% the multi-access techni$ues

employed% and an analysis of thei especti"e cost stuctues&+t is concluded that the

technical feasibility of satellite-based mobile communications systems seems to besecue& +t !ill be challen#in# ho!e"e% fo the "endos to actually de"elop and deploy

these systems in a cost effecti"e% timely% and eliable !ay that meets a continuallye"ol"in# set of e$uiements di"en by use e,pectations fueled by a apidly chan#in#

technolo#y base&

+n ode to #uaantee the se"ice $uality and eliability fo mobile satellitecommunication systems% !e ha"e to take into account outa#es due to obstuction of the

line-of-si#ht path bet!een a satellite and a mobile teminal as !ell as the si#nal

fluctuation caused by intefeence fom multipath adio !a"es& Thus% !e need a #oodchaactei*ation fo the satellite popa#ation channel& +t is commonly accepted that

satellite communications systems in paticula%lo! eath obit /E) systems ae the de

facto solution fo po"idin# the eal pesonal communications se"ices 3CSs to theuses eithe stationay o on the mo"e any!hee% anytime and in any fomat "oice%data%and multimedia&Satellite communication systems ha"e po"ided intenational

telecommunications se"ices since the 1D0s& These systems !ee au#mented in the

1D70s and 1D?0s !ith e#ional satellite systems% national systems% and pi"ate net!ok-based "ey small apetue teminals AS.Ts& Thou#hout this peiod% systems ha"e

been based e,clusi"ely on satellites in #eosynchonous obit communicatin# !ith eath

stations usin# hi#h #ain fi,ed antennas& .s the systems ha"e e"ol"ed% the oi#inal 60-m-diamete +ntelsat eath stations ha"e e"ol"ed into 1&2-m -band AS.Ts fo business and

home TA usa#e% but the basic system achitectue e,plainin# a #eosynchonous

spacecaft has not chan#ed duin# this peiod& >ith the launch of the fist +idium

spacecaft in 1DD7 and 1DD?% a si#nificant ne! achitectue has been intoduced into thefield of satellite communications& These systems ae based upon the use of /E) and

medium eath obitin# ME) systems& hese /E) and ME) systems ha"e se"eal

ad"anta#es o"e #eosynchonous systems& The most si#nificant ad"anta#es ae81 The eduction in an#e po"ides a la#e decease in path loss esultin# in much small

ecei"in# antennas and

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i. +i5hly Elliti1 ,rbit "+E,$

1& .ltitude8 about 40%000km

2& )bit8 about @- hous6& (umbe of Satellites8 2-6 as the minimum

4& The system plannin# is in po#ess&

ii. Medium Earth ,rbit "ME,$

1& .ltitude8 se"eal thousand - 20%000km about 10%000km2& )bit8 about @- hous

6& (umbe of Satellites8 ?-10 fo the entie !old

4& The system plannin# is in po#ess&

iii. %/4 Earth ,rbit "%E,$

1& .ltitude8 @00km - se"eal thousand km about 1%000km2& )bit8 about @- hous

6& (umbe of Satellites8 se"eal do*en fo the entie !old

4& 3inciple Satellite System8 Globalsta Mobile Satellite Communication System%)bcomm Mobile Satellite Communication System +9++:M Mobile Satellite

System abolished

Satellites in GSO

GS) satellites obit the Eath in the e$uatoial plane !ith the same an#ula "elocity as theEath at a hei#ht of about 6 000 km abo"e the e$uato& Geostationay satellites theefoe

appea stationay to an eath-bound obse"e and a sin#le satellite can po"ide continuousse"ice to ou#hly one thid of the EathHs suface but e,cludin#

pola e#ions abo"e K 7@ de#ees of latitude& The ma,imum distance the satellite can JseeJ

on the EathHs suface is about 42 000 km and means the popa#ation delay fo a sin#le hop"ia the satellite once up and do!n can be up to 2?0 ms& Geostationay satellites also mo"e

about thei nominal positions causin# a small but noticeable opple shift on both the

feede and mobile links&'o pesonal and "ehicle teminals% hando"e duin# a call bet!eenGS) satellites is unnecessay because the co"ea#e is static and !ide& o!e"e hando"e

mi#ht be contemplated fo aicaft teminals bet!een diffeent spot beams of the same

satellite& +n the latte case thee is pactically no diffeence in path len#th to conside&>ithin Euope% GS) satellites appea at lo! ele"ation an#les& 'o the #eo#aphical latitudeof @0L(oth e&/u,embou#% the satellites each appo,imately 61L ele"ation as a

ma,imum !hen the satellite is due South8 eithe East o >est of this position the ele"ation

slo!ly educes& 'e$uent blockin# of the line-of-si#ht si#nal theefoe occus fom tees%buildin#s and hills& GS) satellites can !ok in such a shado!ed en"ionment but the

satellite E$ui"alent +sotopic 9adiated 3o!e E+93 !ould ha"e to be inceased by 1@ d5

to 20 d5 o moe dependin# on the co"ea#e e$uied&This could be achie"ed but has a

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seious impact on the si*e and cost of the satellite& +n addition% assumin# that the mobile

E+93 is limited% the satellite ecei"e sensiti"ity also has to incease and this can only be

done !ith "ey la#e spacecaft dish antennas& 'o this eason% only "ey lo! bit atese"ices i&e& pa#in#% aletin#% etc& mi#ht be "iable unde such cicumstances until the use

mo"es to a moe fa"ouable position to ecei"e a "oice call&

Satellites in HEO

Satellites in E) constellations obit the Eath in planes that ae inclined nominally 6%4La#ainst the e$uatoial plane&This is necessay in ode to keep the apo#ees in the most

nothen southen positions !ithin thei elliptical obits&Typically E) obital peiods ae

bet!een ? and 24 hous& E) satellites ae nomally acti"e only about thei apo#ees !heethey appea nealy stationay to an eath obse"e fo about ei#ht hous% and then ha"e to

hand o"e to a follo!in# satellite&The satellites belon#in# to one paticula system appea

in time shift in the same celestial e#ion& +n the E) tack is sketched in pofile sho!in# at

e"ey point the tue distance to the EathHs suface& +n this specially depicted case% the

obital peiod is 12 hous and the satellites appeaaltenati"ely at the opposite sides of the otatin# #lobe& Theefoe the illustated E) tack

eaches a ma,imum hei#ht at both ends abo"e the #eo#aphical latitude of 6%4L (oth& .tboth uppe ends solid line% the satellite payloads ae acti"e& The dotted line constitutes the

pat !hee the satellite payloads ae typically s!itched off& 'o compaison% see fi#ue 2%

!hee t!o E) loops ae indicated coespondin#to the t!o ends in pofile in fi#ue 1&:nde the abo"e conditions% the E) apo#ee

ma,imum hei#ht abo"e the EathHs suface can be up to 42 000 km&o!e"e the

ma,imum an#e to the EathHs suface is in the ode of 47 000 km esultin# in a ma,imumpopa#ation delay of the ode of 610 ms& E) satellites each hi#h elati"e speeds duin#

thei acti"e phase ode of ma#nitude82 kms% so that the opple shift 1&6 , 10-@ of

adio fe$uency and bit ate cannot be ne#lected8 the adio fe$uencyshift is mainly due to the mico!a"e feede link and is of the ode of @0 k* fo C-bandfeede links& The satellite motion is mainly adial elati"e to the use community% so that

common compensation of the opple main component is feasible&+especti"e of any use

oamin#% E) systems e$uie hando"e fom the descendin# to the ascendin# satellitetypically e"ey ei#ht hous& ependin# on the specific system desi#n% the distance to the

t!o satellites at hando"e could be si#nificant and a ump in path len#th cannot be

e,cluded& o!e"e% a la#e opple ump !ill al!ays happen&>ithin Euope E)satellites can appea nea the *enith& Theefoe the use can !ok unde "etical line-of-

si#ht condition fo most of the time% !ith blocka#e only bein# e,peienced in tunnels o

unde bid#es% tees% etc& o!e"e "etical popa#ation is not "ey #ood !ithin multi-stoey

buildin#s and hence pa#in#% aletin#% etc& may not be satisfactoy&5ecause "etical popa#ation can be in pinciple multipath-fee% hi#h data ate se"ices ae

possible fo outdoo opeation&. numbe of E) obits ha"e been studied e,tensi"ely and

#i"en names such as JMolnyaJ% JTundaJ% and J/oopusJ&

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Satellites in MEO

ME) satellites ae in pinciple the same as /E) satellites& The diffeences ae that ME)

systems cause moe popa#ation delay ?0 ms to 120 ms% thei opple shift is smalle%

and hando"e happens less fe$uently and is less poblematic& ME)s also need to !ok in amultipath en"ionment as the numbe of satellites is usually smalle than fo /E) but the

a"ea#e ma#ins can be lo!e since many calls !ill be at a continuously hi#h

ele"ation an#le&The typical ME) altitude is bet!een 10 000 km and 20 000 km% ustoutside the Aan .llen belts !ith an obital peiod of aound to 12 hous& . complete

ME) constellation !ould pobably e$uie bet!een 10 to 1@ satellites& ME) satellites ae

used to po"ide cuent #lobal adio na"i#ation se"ices and ae optimum fo such se"ices&

Satellites in LEO

/E)s ae typically cicula obits !hee satellites fly lo! abo"e the EathHs atmosphee

typically 700 to 1 @00 km% bounded by oute atmospheic da# and the Aan .llen adiationbelts !ith an obit time of about D0 minutes& 'o obits nea 1 @00 km% inclinations nea @0

de#ees educe the isk of debis collisions& >heeas pola obits po"ide a !hole Eath

co"ea#e includin# the poles themsel"es% inclined obits can po"ide impo"ed co"ea#e

o"e the populated aeas located bet!een latitudes -7@ to N7@ de#ees& )ne poposedsystem is kno!n to stay 700 km abo"e the suface see fi#ue 1 /E) !hee the co"ea#e

aea at any point in time may measue up to 6 000 km in adius fo about 10 de#ee

ele"ation& This implies a ma,imum popa#ation delay of 20 ms and !hile hi#he altitude/E) systems !ould ha"e hi#he popa#ation delays% they !ill ne"e appoach the "alues

associated !ith GS) o E) systems fo a sin#le satellite hop& o!e"e% on-boad

pocessin# and +nte-Satellite /inks +S/ can incease delays consideably&/E) satellitesmo"e at "ey hi#h speeds elati"e to the EathHs suface 7 kms and poduce la#e opple

fe$uency shifts 4%7,10-@ of adio fe$uency and bit ate& .s the "elocity is tan#ential to

the Eath% opple compensation may need to be applied indi"idually fo each use&/E)

systems% in common !ith E) systems% also e$uie to hando"e bet!een adacentsatellites% but at a much moe fe$uent ate of about ten minutes& .lthou#h the t!o /E)

satellites ae !idely spaced% the indi"idual path len#ths can be simila and it is possible to

minimise any path len#th ump& o!e"e% the opple shift ump !ill still al!ays happen&.s /E) satellites obit "ey close to Eath% they can be consideed as mo"in# base stations&

'o the use the satellites appea most of the time belo! 60 de#ee ele"ation& Theefoe

/E) satellites !ok much of the time in a multipath en"ionment& The additional satelliteE+93 and ecei"e sensiti"ity to compensate fo multipath losses ae achie"ed !itha much

smalle antenna on a /E) spacecaft compaed to GS) because of the much shotean#e ou#hly 112th&

i"esity techni$ues may offset some of these multipath effects&The total numbe ofsatellites e$uied to #i"e total #lobal co"ea#e depends on many factos includin# $uality

of se"ice and system capacity but the total could be as hi#h as 70& /o!e numbes ae

possible usin# special obits o by usin# a mi,tue of /E) and GS) fo e,ample& Thecost fo la#e numbes of /E) satellites is offset to some e,tent by thei lo!e comple,ity

and easie launch e$uiements& o!e"e thei obital life tends to be half that of typical

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GS) satellites 10 - 16 yeas& .nothe facto in /E) desi#n is the e$uied battey

capacity and sola panel si*e to allo! opeation fo nealy @0F of time in eclipse&

A. S,ME %E, S#(E%%!(E S3S(EM

1. THE IRIDIUM SYSTEM

The +idium System is not poposed to be a eplacement fo e,istin# teestialcellula systems% but athe as an e,tension of e,istin# !ieless systems to po"ide mobile

se"ices to emote and spasely populated aeas that ae not co"eed by teestial cellula

se"ices& +t po"ides moe capacity la#e no of channels and bette $uality of se"iceshote tansmission delays to aeas that cuently ecei"e mobile se"ices fom

#eostationay satellites& +t can also po"ide eme#ency se"ice in the e"ent that teestial

cellula se"ices ae disabled in disaste situationseath$uakes%fies%floods%etc&&

The concept of usin# a constellation of lo! eath obit satellites to po"ide #lobaltelecommunication se"ices to mobile uses& 5ecause the initial poposal called fo 77satellites in the constellation% the system !as called +9++:M afte the element% !hich has77 electons in its obit&late studies indicated that only satellite !ould be ade$uate to

po"ide the ta#eted se"ices and pefomance& The satellites ae ae #ouped in si,

obital planes thee ae 11 acti"e satellites in each plane !ith unifom nominal spacin# of62&7O& the satellites ha"e cicula obits at an altitude of 7?6 km% and fo each plane an in-

obit satellite is po"ided&

Satellites in one plane ae placed to ta"el out of phase !ith those in the adacent planes&E,cept fo the fist and last planes% !hich ae counteotatin# !hee they ae adacent% all

emainin# planes ae cootatin#% The distance bet!een cootatin# planes is 61&% and thedistance bet!een the counteotatin# planes is 22& The educed sepeation bet!eencounteotatin# planes is needed to compensate fo the educed co"ea#e po"ided by

satellites on counteotatin# planes& +n the +idium system% each satellite is e$uipped !ith

fou t!o-!ay communication linksintesatellite links% o +S/s% one each !ith itsnei#hbos in the same plane and !ith those in the adacent planes&

Each +idium satellite uses a 4?-beam antenna patten% and each beam% !hich has a

minimum diamete of 00 km% can be indi"idually s!itched& 'o e,ample% only about t!o-thids of the beams !ill be acti"e at any #i"en time because some the beams !ill be

s!itched off !hen the satellites ae in the "icinity of the poles% !hee beam pattens tend to

o"elap% o !hen the satellites ae o"e counties o e#ions in !hich% +idium does not ha"e

e#ulatoy aan#ements to opeate& The s!itched of beams is efeed a cell mana#ement&+n a /E)-based system like +idium% the beams ae e$ui"alent to cells associated !ith

teestial mobile systems& o!e"e% in case of the +idium system% it is the beams that

mo"e apidly elati"e to the subscibe% !ho is consideed to be stationay !ith espect tothe satellite& Thus% s!itchin# of beams o cell mana#ement to po"ide continuity of an

e,istin# call is e$ui"alent to handoff in teestial cellula mobile systems& This e$uiement

fo cell mana#ement is% of couse% and additional comple,ity associated !ith /E)- basedsystems compaed !ith ME) o GE) systems&

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The +idium system suppots links of thee types8up- and do!nlinks fom the space "ehicle

SA to the #ate!ay G> Po to the telemety% tackin#% and contol TT Q C centeR%usin# the ka band up- and do!nlinks bet!een the SA and the +idium subscibe unit

+S:% usin# the / band and t!o-!ay inte-satellite links bet!een the SAs usin# the Ba

band&

;. (+E G%,B#%S(#R S3S(EM

Globalsta is a #lobal mobile satellite system based on a constellation of 4? /E) satellites&

:nlike the +idium system% Globalsta system does not use intesatellite links but athe

depends on a la#e numbe of inteconnected eath stations o #ate!ays fo efficient calloutin# and deli"ey o"e the teestial net!ok& +t is desi#ned to complement the

teestial cellula mobile net!oks to po"ide telephony and messa#in# se"ices to

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subscibes in locations that ae not co"eed% o inade$uately co"eed% by con"entional

!ieline o !ieless net!oks&

Globalstas constellation of 4? /E) satellites is desi#ned t obit at an altitude of 1414 km

abo"e eaths suface in ei#ht obital plans inclined at @2& >ith each plane to be occupied

by si, satellited !ith a po"ision fo one in-obit spae satellite in each plane& The nominal

!ei#ht of each satellite is 4@0 k#% !ith a deployed span of 7 metes and !okin# life of 7&@yeas& Since Globalsta satellites do not employ intesatellite communication% they

essentially po"ide only tansponde functions% makin# thei desi#n and opeation less

comple, and pehaps moe eliable& Each satellite suppots a 1-beam antenna patten !ithan a"ea#e beam diamete of 22@0 km& To miti#ate blockin# and shado!in#% Globalsta

!ill deploy path di"esity% !heeby multiple satellites may be used to complete a call&

+n the absence of intesatellite links% the Globalsta system makes ma,imum use of theintenational teestial net!oks !ieline and !ieless& Calls fom a subscibe ae outed

"ia a satellite to the neaest eath station#ate!ay% and fom thee they !ill be outed o"e

the e,istin# teestial net!ok& To po"ide the inteface bet!een the #ound se#ment

teestial net!oks and space se#ment Globalsta satellites Globalsta desi#n deploys100 o moe #ate!ay stations distibuted aound the !old !ith each station e$uipped !ith

thee o fi"e antennas that can tack the taectoies of the satellites& . Globalsta #ate!ayis desi#ned to se"e an aea 6000 km in diamete and !ill be desi#ned to take into account

the technical and administati"e e$uiements of the co"ea#e aea& These e$uiements

may include such factos as co"ea#e% $uality of se"ice% and satellite "isibility% as !ell ase#ulatoy and contactual factos associated !ith national boundaies&

Globalsta uses t!o types of communication links8 se"ice links in the /S band fo

communication bet!een the teminals and the space "ehicle% and the #ate!ay links in the Cband fo communication bet!een the eath stations and the space "ehicle&

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A. (+E (E%E&ES!C S3S(EM

Cuently the hi#h band!idth% hi#h $uality fibe connecti"ity needed to suppot +ntenet

access% compute intenet!okin#% "ideo confeencin#% and so on is esticted to mao

commecial and population centes& )utside these application aeas% such facilities aeeithe too e,pensi"e o simply not a"ailable& The aim of the Teledesic net!ok is to e,tend

the e,istin# teestial% fibe-based infastuctue to po"ide ad"anced infomation and

communication se"ices any!hee on eath& >heeas the ta#et application fo +idium%Globalsta% and +C) is "oice% !ith suppot of lo! bit ate data fo facsimile and messa#in#

fo mobile subscibes% the pimay ta#et application fo the Teledesic system is the

po"ide !old!ide% seamless% fibe like connecti"ity to suppot multimedia% "ideo% and hi#hbit ate data se"ices& +n a stict sense% Teledesic does not fall in the cate#oy of #lobal

mobile satellite systems o GM3CS because its focus is not on !old!ide teminal

mobility% but athe on po"idin# the so-called +ntenet in the sky function& The planned

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ta#et fo Teledesic se"ice a"ailability is end of yea 2002& 9athe than indi"idual end

uses% pimay customes fo the Teledesic system !ill be se"ice po"ides in counties

aound the !old !ishin# to e,tend thei net!ok capabilities in tems of #eo#aphic scopeand the an#e of se"ices% and also multinational copoations needin# to e,tend the

capabilities of thei entepise net!oks&

The desi#n of the Teledesic system has not been finali*ed& .ccodin# to the oi#inal plans%the Teledesic satellite se#ment !as to use ?40 /E) satellites in 21 planes at altitudes of

700 km& The Teledesic system no! intends to deploy only 2?? acti"e /E) satellites placed

in 12 planes 24 satellites pe plane at altitudes aound 16@0 km& Each satellite in theTeledesic constellation !ill ha"e connections to ei#ht of its nei#hboin# satellites thou#h

intesatellite links opeatin# in the connectionless packet mode% !ith each satellite in this

inteconnected mesh net!ok po"idin# necessay s!itchin# functions& The Teledesicnet!ok is desi#ned fo dual-satellite "isibility !ith at lest one insi#ht satellite at a

minimum ele"ation of 40& This hi#h ele"ation an#le ensues an unobstucted and

omnidiectional "ie! of the sky fom most buildin# tops !hee Teledesic teminals may belocated& 5esides eliminatin# shado!in# effects fom nei#hboin# buildin#s and teain% the

hi#h ele"ation an#el #eatly educes the fadin# effects of ain at hi#h fe$uencies&

. ME, S#(E%%!(E S3S(EM

>. (+E !C, S3S(EM

The +C) is a medium eath obit ME) mobile satellite system% !hich is desi#nedpimaily to po"ide se"ices to handheld phones& +C) !ill use TM. as the adio

tansmission technolo#y& The system is desi#ned to offe di#ital "oice% data% facsimile% and

shot-ta#eted messa#in# se"ices to its subscibes& +C)s pimay ta#et customes ae

uses fom the e,istin# teestial cellula systems !ho e,pect to ta"el to locations in!hich co"ea#e is una"ailable o inade$uate& )the custome #oups potentially se"ed by

+C) include oad tanspot% maitime% and aeonautical uses% as !ell as uses of semifi,ed

teminals in ual aeas and de"elo0pin# counties% !hee con"entions teestial !ieline o

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!ieless mobile satellite communications capability !ith the public land mobile net!oks

like GSM% -.M3S% and 3C and thei 3CS "aiants&

+C) system is desi#ned to use a constellation of 10 ME) satellites in intemediate cicula

obit +C)% at an altitude of 10%6@@ km abo"e the eaths suface& The nominal !ei#ht of

these satellites at launch is less than 2000 k#& The satellites% !ith an e,pected life of 12

yeas% ae aan#ed in t!o planes !ith fi"e satellites and one spae in each plane8 obitalplanes inclined at 4@ elati"e to the e$uato& Each satellite has antennas to po"ide 16

tansmit and ecei"e se"ice link beams& The obital confi#uation po"ides co"ea#e of

eaths entie suface at all times and ensues si#nificant o"elap so that t!o o moesatellites ae "isible to the use and the satellite access node S.( at any time& 'uthe% at

least one of the satellites appeas at the hi#h ele"ation an#le% theeby minimi*in# the

pobability of blockin# due to shado!in# effects&

The #ound se#ment in the +C) system% !hich !ill link the +C) satellites to the teestial

net!oks% !ill consist of the 12 inteconnected S.(s located in "aious pats of the !old&

Each S.( consists of eath stations !ith multiple antennas fo communication !ith the

satellites% s!itchin# e$uipment% and databases to facilitate inteconnection !ith publictelephone% data% and mobile net!oks& The inteconnection to the public net!oks is

thou#h appopiate #ate!ays& >heeas each S.( suppots A/9 functions% the /9function can eside in one o moe of the S.(s& . S.( tacks the satellites !ithin its

si#ht and !ill diect communication taffic to the satellite% !hich can po"ide eliable%

uninteupted link fo a #i"en call% in tems of an#le of ele"ation and duation of satellite"isibility& S.(s also ha"e the capability to e,ecute handoffs fom an aea co"eed by one

satellite to anothe satellites co"ea#e& Such handoffs ae e,pected to be "ey infe$uent in

+C)s ME)-based system& 5esides the S.(s% the +C) system deploys TT Q C stations

connected to a satellite contol cente SCC fo monitoin# and contollin# the satellites% as!ell as one o moe net!ok contol centes (CC fo o"eall mana#ement and contol of

the +C) system& The TT Q C functions ae associated !ith of the 12 inteconnected

S.(s&

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. # br/ad /vervie4 h/4 a m/bile satellite system 4/rs

. satellite system consists of a satellite se#ment% #ound se#ment% and end-use se#ment&

Satellite SegmentThe satellite se#ment is a net!ok of GE) o /E) satellites aan#ed in obital planes i&e&

diffeent pats of the sky in such a !ay that they ha"e a communications link !ith end-

use e$uipment% #ound #ate!ays and othe satellites& The satellites tansmit a continuoussi#nal to eath !hich enables the satellites% end-use e$uipment and#ate!ays to be linked to#ethe& The links allo! end-uses to be tansfeed bet!een

satellites as the satellites mo"e o"ehead /E) systems& )n the #ound% thee is a #ound

contol facility o facilities !hich mana#e the pefomance of the satellites and thetansfe of infomation fom the satellites to the #ate!ays&

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Ground segment - gatewaysThe #ate!ay connects the satellites to the local telephone net!ok& The #ate!ay also

tansmits si#nals to the satellites and ecei"es tansmission fom the satellites& The #ate!aytends to ha"e s!itchin# capabilities alon# !ith soft!ae that allo!s the system po"ide to

keep tack of billin# infomation and oute calls&

End-userThe end use teminals% pa#es and phones communicate !ith the #ate!ay e$uipment%satellites% satellite and cellula phones alon# !ith the cellula base station e$uipment& 'o

the +idium and Globalsta systems% the enduses !ill use a phone sli#htly la#e than the

a"ea#e cellula phone& 5oth +idium and Globalsta plan to offe dual mode handsets!hich !ill allo! uses to connect to the e,istin# cellula systems o thei o!n satellite

system&)the systems fom such companies as .meican Mobile Satellite and +ntelsat% use

phones !hich ae the si*e of a biefcase and must be unpacked befoe use& The pa#in#e$uipment fom +idium% the only satellite company !ho cuently has a pa#in# system in

place% is you nomal un of the mill pa#e& . fe! satellite systems Globalsta includedplan to offe fi,ed satellite teminals !hich ae a telephone booth in ual aeas& The phone

booth !ill include one o moe phones and !ill not look much diffeent than a phone boothyou may find on the steets of (e! ;ok City&

+/4 a satellite 1all 5ets r/utedThee ae t!o types of satellite systems unde de"elopment and each ha"e a diffeentappoach to outin# phone calls& The poposed satellite systems !ill use eithe a bent pipe

o an intesatellite linked system&

Bent ie

+n a bent pipe system Globalsta a call is placed by a satellite use !hich is then beamed

up to the neaest obitin# satellite& The satellite eflects the call to the neaest #ound#ate!ay& )nce at the #ate!ay% the call is outed thou#h the public telephone net!ok to

the intended ecei"e of the call& The #ate!ay must be in the line of si#ht of the satellite% so

the system opeato must ha"e a si#nificant numbe of #ound #ate!ays to po"ide diectsatellite links& 'o the most pat% a bent pipe system is less comple, than an intesatellite

linked system because the bains of the system s!itchin# ae on the #ound and the

satellites ae ust eflectos in the sky& 5ent pipe systems ae easie to opeate because mostof the call is tansfeed o"e the public telephone net!ok% this also educes the cost of the

system& Many of the technical featues !ill be located at the #ate!ay !hich !ill allo!s

most technical poblems to be fi,ed on the #ound&

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!ntersatellite lins

+n an intesatellite linked system +idium a uses call is beamed up to the neaest obitin#satellite& >hen it eaches the satellite% the call entes the onboad satellite s!itchin# system

and is outed bet!een satellites up in space& The call is then do!nlinked to anothe satellite

use o the closest local #ate!ay to the end use& :ponentein# the #ate!ay the call is diected to the intended ecei"e thou#h the public

telephone net!ok& The mao benefit of the intesatellite linked system is that it minimi*es

the cost of the #ound se#ment i&e& - the call is s!itched in the ai theefoe you do notneed a #ound #ate!ay in the line of si#ht of each satellite and it also

minimi*es the lon# distance and inteconnect fees much of !hich is bypassed in the ai&

The intesatellite linked system opeato is able to keep a la#e dolla amount of each call

as compaed to the bent pipe system opeato&o!e"e% thee is added isk and hi#he costsbecause each satellite must ha"e on-boad s!itchin# capabilities&)n-boad s!itchin# also

adds to the comple,ity of the system because epais must be made to satellites&

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+and/ver Mana5ement in M/bile Satellite Systems

ue to the hi#h mobility of lo! eath obit /E) satellites% thee is a si#nificant numbe of

hando"e attempts in a /E)-based mobile satellite communication system% causin# a

hi#h hando"e failue ate& This pape poposes to e,tend the peiod of !hich a hando"ee$uest is "alid% and thus endein# hi#he pobability of successful hando"e& Satellite

communication se"ice can be po"ided by #eostationay eath obit GE)% medium eathobit ME) o lo! eath obit /E) satellites& 5ecause of its much shote distance fom

eath% lo!e po!e e$uiement and thus smalle mobile teminal MT si*e% /E) satellite

system is a pefeable choice& +n this pape% only the /E) satellite system is consideed&The satellite co"ea#e aea% o its footpint% is di"ided into a numbe of aeas% each of !hich

spotted by one of the satelliteHs multiple spotbeams% fomin# a cell& Since a /E) satellite is

not located at a #eosynchonous obit% it is mobile !ith espect to a fi,ed point on eath&

ence an acti"e MT may mo"e fom one cell to anothe and hando"e occus& The #ound"elocity of the MT is i#noed compaed to the

much hi#he satellite "elocity& Suppose the len#th of a cell is 400 km and the satellitemo"es at a "elocity of & kmsec% the time taken fo a MT to coss a cell% Tcell% is about 0seconds& Thus hando"e is e,temely fe$uent in this system& .nd it is pobable that a call

is dopped due to unsuccessful hando"e& ando"e is pone to failue !hen the subse$uent

cell has no unused channel to offe& op call is a phenomenon !hee an on#oin# call hasto be discontinued% !hich the uses find had to toleate !ith% makin# it a mao technical

issue&Thee ha"e been some methods poposed to minimise hando"e failue& +t is !idely

accepted that hando"e e$uests ae to be pioitised o"e ne! call e$uests% eithe by

allocatin# #uad channels to the hando"e e$uests P1R% o by $ueuin# up the hando"ee$uests !hen all the channels in one cell ae occupied P1R P2R& This is because doppin# an

on#oin# call is less desiable than blockin# a ne! call attempt& Thee ae also poposals of

makin# the hando"e e$uest ealie% so that the e$uest has lon#e time to !ait fo a feechannel% thus educin# the hando"e failue ate P6R P4R&

Gead Maal et al& ha"e poposed that a hando"e e$uest is to be made to a cell as ealy as

the MT entes the cell located i#ht befoe the ta#et cell P6R& +n P4R% the time of sendin# outa hando"e e$uest duin# hando"e pocess !as made a"ailable e#adless of the location

of MS in a cell& +n all of these cases% a call someho! has to be teminated !hen the

oi#inatin# MT has cossed into the ta#et cell and yet hando"e is not #anted by the ta#etcell& The temination is done since no se"ice is po"ided by eithe the oi#inal cell o the

ta#et cell& +n this pape it is poposed that in a simila situation% the call be only

tempoaily discontinued fo a specific amount of time% befoe it is pemanently teminated

if thee is still no a"ailable channel& .lthou#h no se"ice is po"ided by both cells to the

MT% its hando"e e$uest !hich has been $ueued is kept in "ie! by the ta#et cell& uin#this idle peiod% thee is a chance that an oi#inally occupied channel in the ta#et cell is

eleased& +f this is the case% this channel is allocated to the suspended call and hando"e iscompleted& .s a esult% the hando"e failue ate is educed&

Mathematical analysis has been caied out to "eify the idea and the esults ae

encoua#in#& 'o a use% heshe only e,peiences a shot peiod of call discontinuity and isnotified about the tempoay discontinuity thou#h a special tone& +n tems of $uality of

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. hando"e mana#ement state#y is poposed to efficiently mana#e the channel

esouce of a cell in a multibeam mobile satellite system MSS and impo"es its se"ice

$uality by educin# the intebeam hando"e failue ate Phf caused by limited numbe ofcommunication channels& The E,tended hen a use teminal :T lea"es fom one cell and entes the adacent one% a hando"epocess must be completed fo the sake of call continuity% !hee a

communication channel must be allocated to the :T by the adacent cell destination cell&

+n a channel esouce limited system% hando"e is subect to failue !hen the destinationcell has no idle channel to offe& +n this case the call is dopped and this is intoleable to

uses& +n ode to po"ide hi#he hando"e $uality% system opeato has to allocate a la#epotion of the channel esouce to the on#oin# call as compaed to the ne! call& . method

in use is by applyin# the blocked-calls-$ueued policy to the callse$uestin# fo hando"e handover calls P1R and on the othe hand sacificin# some ne!

calls thou#h the blocked-call-cleaed policy& The lon#e a hando"e call stays in a $ueue%

the hi#he chance of it bein# handed o"e successfully& )the methods that pioitisehando"e call o"e ne! call ae8 #uad channelallocation P2R% and channel ese"ation in

ad"ance P6R P4R& The compomise of ne! call causes inefficiency in channel utilisation

because channels that ae allocated to hando"e call cannot be taken up by ne! calls e"enthou#h they ae idle&

Etended ?ueuein5 /6 +and/ver "E?+$ S1heme

+n a hando"e pocess% a :T !ith unfulfilled hando"e e$uest !ill ha"e its call

teminated once it lea"es the pesent cell i&e& !hen the si#nal sten#th of the pesent beamdops belo! an acceptable le"el& :nde the poposed E,tended


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and uninfomed dop call& )n theothe hand% if the call is able to be esumed upon the

a"ailability of an idle channel% the shot temdiscontinuity makes it !oth than ha"in# the

call teminated and follo!ed by settin# up a ne! call a#ain%!hich is hade because ne!call is less pi"ile#ed& ence e#adless of the outcome E


25/35


!hee possible& o!e"e it must be eco#nised that most paametes ae inte-dependent

and !ill also "ay !ith achitectue of the #ound infastuctue% the satellite obital

aan#ement% and the use teminal confi#uation&

7. Capabilities of Mobile Satellite Systems (MSS)

The most si#nificant attibute of any satellite communication system is the !ide aeaco"ea#e that can be po"ided !ith "ey hi#h #uaantees of a"ailability and consistency of

se"ice& The satellite component of :MTS can potentially po"ide the teestial se"ice

use !ith a #lobal se"ice !ithout e#ad to incompatible teestial standads usedelse!hee& E,istin# satellite mobile se"ices ha"e po"ed "ey attacti"e to the maitime

and aeonautical sectos and they ha"e also been of #eat benefit to eme#ency se"ices%

elief a#encies% ounalists% and e,peditions o"e ecent yeas&Se"ices ae no! e,tendin# to the land mobile maket !hee hand-potable "oice teminals

ae no! technically feasible& The ne,t subclauses addess the key attibutes of !ide aea

co"ea#e and types of se"ices appopiate fo satellite :MTS&

7.1 Large area coerage

. sin#le satellite can see "ey la#e aeas of the Eath8 a sin#le /E) can illuminate an aea

of 000 km diamete and a GS) can illuminate about 16d of the #lobe& >ithin these

aeas% the spacecaft antenna can be desi#ned to maintain a nea-constant po!e flu,density on the EathHs suface iespecti"e of an#e& o!e"e fo the GS) and E) and

possibly the /E) o ME)% the spacecaft antenna may need to be aan#ed as a cluste of

spot beams 1 000 to 2 000 km diamete in ode to make hand-held teminals feasible and

to achie"e spectum efficiency& Such spot beams e$uie la#e spacecaft antennas foeithe GS) o E) systems& The ad"anta#es of E) and GS) ae that it is possible to

deploy a satellite system to fulfil a e#ional e$uiement athe than a #lobal one% andfe$uency plannin# and co-odination may be elati"ely stai#htfo!ad& 'uthemoe% the

#ound infastuctue to suppot the satellites could follo! taditional /and Eath Station

/ES appoaches&The only satellite system that cannot po"ide pola co"ea#e is GS)&

>ith this estiction% any satellite constellation can po"ide assued line-of-si#ht #lobalco"ea#e unaffected by !eathe& )peation to shado!ed o in-buildin# teminals !ould

e$uie an additional link ma#in in the ode of 20 d5 o moe% dependin# on the co"ea#e

e$uied& (ote that in cities% the teestial :MTS se"ice is likely to be a"ailable andtheefoe in-buildin# and city co"ea#e may not be essential&

The line-of-si#ht case e$uies polaisation matchin# bet!een the satellite and the mobileteminal& To a"oid the need fo polaisation tackin#% mobile communications ha"etaditionally used cicula polaisation&

7.! "le#ible net$or%s an& serices

. featue of most pesent day satellites is the use of Jtanspaent tanspondesJ&

Compaed to con"entional cellula base stations% the satellite tansponde is little moe than

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a fe$uency shiftin# amplifie& This does ha"e da!backs !ith e#ad to some aspects of

system desi#n but it also means that any one satellite is easonably independent of

modulation system o access method% o of se"ice data ate o net!okin#& This has led tosatellites bein# used fo a "aiety of applications% each !ith diffeent teestial

achitectues& 3o"ided the basic satellite paametes ae satisfactoy% these se"ices can be

intoduced lon# afte launch& 'utue satellites may not be $uite so fle,ible as some studiespopose to use on-boad pocessin# to impo"e capacity% spectum efficiency and satellite

payload pefomance& The tanspaency concept has ho!e"e po"ed e,temely

costeffecti"e and any on-boad pocessin# function is likely to be at least e-confi#uableand e-po#ammable& .nothe featue that mi#ht be intoduced fo ME) o /E) is the

inte-satellite link to simplify teestial net!okin# bet!een satellites duin# hando"e&

The tanspaency concept has enabled mobile satellite systems to efficiently suppot a

an#e of se"ices beyond that of "oice telephony8

- hi#h data ate se"ices up to 4 kbits to la#e antenna 0%1@ m 1%0 m% ? d5i 20 d5i

mobile o fi,ed

teminals

- #oup call and boadcastin#- lo! data ate pa#in#% aletin# and t!o-!ay messa#in#

- teminal location findin#&

Some cuent satellite systems ae desi#ned so that e,ta se"ices can be po"ided at "ey

little additional cost& This is paticulaly effecti"e !hen se"ices ae offeed as a packa#e to

pehaps offset the e$uiement fo line-of-si#ht paths fo lo!-cost "oice telephony&

8 Limitations of Mobile Satellite Systems

'.1 elay an& oppler

The delay and opple effects associated !ith satellite links ae due entiely to the

mechanical la!s #o"enin# the satellite obit& .ny system desi#n must take full account of

these effects& 'o e,ample% simple delay has an impact on speech $uality that !ill e$uieecho cancelles to be used at intefaces !ith the analo#ue net!ok& elay also e$uies

allo!ances to be made in si#nallin# potocols and po!e le"el contol&Chan#es in delay ae the esult of inte#ated opple shifts on the bit data ate and ae

si#nificant fo all obits e,cept GS) duin# a call and paticulaly duin# satellitehando"e& Such chan#es ae likely to e$uie a data buffe to maintain the delay at a

constant ma,imum "alue& The data buffe can eside in eithe the /ES o the mobile

teminal bet!een the t!o echo contol de"ices and is e$uied fo both ecei"e andtansmit& opple shift itself complicates si#nal ac$uisition and spectum mana#ement& The

opple shift !ill not be identical fo the in-bound and out-bound links due to the diffeent

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feede and mobile link mico!a"e fe$uencies& 'uthemoe% the shift is in diffeent

diections if coected at the mobile teminal& 'o /E) and ME) obits% the shift may need

to be indi"idually coected fo each mobile fo E)% common opple compensation canbe incopoated in the /ES o onboad the satellite&

'.! Lo$ lin% margins

Emphasis has aleady been made on the impotance of keepin# impaiment ma#ins lo!&

.n illustation can be based on the calculation of Caie-to-(oise C( atios fo uplink%

do!nlink% and the total link& .ssumin# the do!nlink has C(d U 10 d5 and is nea thepefomance theshold% the feede !ill need a 16 d5 ma#in C(u U 26 d5 to maintain

the de#adation to less than 0%2 d5 i&e& C(t U D%? d5& )peation at le"els ust abo"e

theshold ae only feasible fo satellite because of the stable popa#ation path and becausemost impaiments includin# the la#e noise contibution can be consideed to be andom&

These lo! ma#ins% compaed to the teestial en"ionment% esult in lon#e si#nal

ac$uisition times&

.ll impaiments must be caefully analysed and include8 impefect in-band filtein#% #oup

delays% out-of-channel emissions !hich demand "ey ti#ht po!e amplifie lineaity

e$uiements% caie to intefeence atios% etc& Multi-path also e$uies especial attention&+n the teestial en"ionment% multipath popa#ation nomally esults in inte-symbol

intefeence that can be compensated !ith e$ualises& The effects of multipath fadin# itself

ae often ne#li#ible !ithin the main se"ice aeas because the detected si#nal le"el is

sufficiently abo"e theshold& +n the satellite path% multipath delays ae often shot enou#h tobe i#noed e,cept fo aicaft and ships due to the compaati"ely hi#h ele"ation an#le of

the adio path& o!e"e multi-path fadin#% in !hich a multipath si#nal patially cancels the

main si#nal% can educe the final si#nal belo! the modem opeatin# theshold& and-offsbet!een successi"e /E)% ME)% o E) satellites !ill be moe comple, because of the

small opeatin# ma#ins !hich makes it difficult to pomptly detect si#nal disappeaance&

Satellite si#nal $ualities often cannot be assessed fom si#nal le"el !hich is s!amped bythemal noise but ae often estimated fom the acti"ity !ithin the fo!ad eo coection

al#oithm& This e$uies time a"ea#in# and cannot be an instantaneous measuement&

Satellite di"esity eception

mi#ht alle"iate some of these issues& Mobile teminals !ith hi#h #ain diecti"e antennasha"e futhe poblems !ith si#nal ac$uisition as the antenna may need to be mechanically

o electonically steeed to!ads the satellite befoe the si#nal ises abo"e the detection

theshold&

'. Scope for tec*nical &eelopments

'..1 Signal to +oise (S,+) leelsSatellite systems opeate "ey close to theoetical si#nal to noise demodulation thesholds&Thee is "itually no scope fo eduction in ecei"e themal noise le"els at the satellite o at

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the mobile teminal as noise le"els ae dominated by the EathHs back#ound themal noise

2D0 B& The noise pefomance of moden amplifies is almost

insi#nificant a#ainst this back#ound& The only scope to impo"e si#nal to noise ma#insfo e,ample to po"ide shado! o in-buildin# opeation is to impo"e satellite antenna

#ain&

'..! Han&-*el& terminal antennas3esent opeational mobile satellite systems po"ide "oice se"ices !ith medium #ain

steeed antennas in the #ain an#e ? d5i to 1@ d5i& /o! data ate se"ices can use unsteeedlo!e #ain antennas !ith #ains bet!een 0 d5i and 4 d5i&The challen#e fo :MTS is to

po"ide "oice telephony to hand-held teminals usin# unsteeed lo! #ain antennas& The

hand-held ta#et imposes pactical limitations on the fom of antenna and it is unlikely thatantennas !ill ha"e usable #ains #eate than 0 d5i& o!e"e this does not pohibit the use

of hi#he #ain antennas fo paticula applications o cicumstances&

D. Gr/4th drivers /6 m/bile satellite 1/mmuni1ati/n servi1es

DeregulationGo"enments thou#hout the !old ae openin# up thei telecommunications systems

!hethe it be thou#h spectum allocations% pi"ati*ation% competition o access&Go"enments ha"e eali*ed that thee is a ston# coelation bet!een telecommunications

se"ices and economic #o!th& Theefoe they ha"e stated to knock do!n the !alls that

e,isted !ithin thei telecommunications makets and ae encoua#in# in"estment in thelatest technolo#ies so that thei counties do not fall behind in communications&

TechnologyTechnolo#ical de"elopments ha"e impo"ed the po!e and "esatility of satellites% today

they ha"e #eate capacity and lo!e costs& 'o instance% the smalle si*e of many of

todays satellites lo!es the cost of launchin# satellites& .t the same time ecent di#ital

technolo#ies TM. - Time i"ision Multiple .ccess% CM. - Code i"isionMultiple .ccess ae bein# applied to satellite systems !hich a inceases capacity and

lo!es the cost of launchin# a system&

Globalization3eople no lon#e ae isolated fom the !old& 3eople ae affected by tade like ne"e

befoe (ike and Gillette ae no lon#e ust :&S& companies& 5ecause people ae ta"elin#half!ay aound the !old on a moments notice% thee is a demand fo communications

se"ices that allo! people to stay in touch no matte !hee they ae& 3eople !ant

to be able to make a phone call and ecei"e one -- they !ant one telephone numbe that canbe used anytime% any!hee in the !old& Thus% !e feel the de"elopment of the #lobal

economy is a key di"e of the mobile communications business&

Economic growth

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Economic #o!th thou#hout the !old has inceased li"in# standads !hich also di"es

demand fo communications se"ices& .s indi"iduals incease thei economic statue% one

of the fist thin#s they desie is a phone& This is a positi"e fo satellite se"ice po"ides& .sde"elopin# economies continue to #o! and ente the #lobal economy% the demand fo

satellite se"ices !ill incease because people !ill be able to affod it% and the need fo

mobile se"ices !ill incease&

Demand for phone serviceMoe than 6 billion of the !olds people do not ha"e phone se"ice& The !aitin# list fo

landline telephone se"ice has o"e @0 million names !ith the a"ea#e !ait #eate than 1&@

yeas& )n a"ea#e% thee ae sli#htly fe!e than 12 phones lines pe e"ey 100 people in the!old& This is fa lo!e than !hat e,ists in de"eloped counties such as S!eden ? lines

and the :&S& 0 lines& >e belie"e that because the !ait is so lon#% many do

not e"en attempt to #et se"ice -- this could undestate the actual numbe of people!aitin# fo phone se"ices& .tthe same time% +idium thou#h eseach by 5oo* .llen and

Gallup has detemined that the demand fom !old!ide ta"eles fo mobile satellitese"ices !ill be 42 million people by the yea 2002& 9e#adless of ho! youlook at thenumbes% thee is a si#nificant amount of people !ithout phone se"ices thou#hout the

!old& .lso% phone se"ices ae not de"eloped in many counties% so ta"eles ae unable to

access a eliable phone& Satellite communications se"ices !ill sol"e the needs of

!old!ide ta"eles and po"ide phone se"ices to many aeas of the !old that cuentlydo not ha"e phone se"ice&

Mobile communications trendsCellula demand continues to e,plode thou#hout the !old !ith some estimates of @00

million subscibes by the yea 2002& Cellula phone bills in Thid >old counties ae

hi#he than the a"ea#e bill in the :&S& This su##ests that demand fo mobilecommunications se"ices continues to #o! at a "ey fast pace and that de"elopin#

counties ae !illin# to pay fo phone se"ices& .n ubi$uitous phone se"ice offeed by

satellite companies !ill benefit fom these tends in cellula communications&

>0. h/ 4ill use satellite 1/mmuni1ati/ns systems

Global roamerThe fist type of satellite use !ill be the #lobal oame& The #lobal oame consists mainly

of business ta"eles !ho !ant to ha"e the ability to make and ecei"e calls any!hee in

the !old& +idium has conducted e,tensi"e analysis of this maket and concluded that thismaket !ill consist of 42 million people by the yea 2002&

Cellular etensionThe second type of use !ill be indi"iduals !ho !ish to e,tend thei cellula co"ea#e to

aeas !hee no se"ice cuently e,ists& 5oth Globalsta and +idium plan to offe dualmode phones !hich !ill !ok !ith GSMTM.CM. cellula systems and satellite

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communications systems& .n e,ample of a dual mode use !ould be !ould be an

indi"idual !ho li"es in Chica#o and ta"els to upstate Montana fo a huntin# tip& The

peson !ould nomally ha"e cellula se"ice fom .meitech but that co"ea#e does notinclude upstate Montana !hee no cellula co"ea#e e,ists& To be able to ecei"e se"ice on

thei .meitech system same phone numbe in Montana% the indi"idual !ould si#n up

!ith +idium fo dual mode se"ice& Si#nin# up !ould mean that once theindi"idual #ot out of the an#e of thei .meitech systems% they could hit a s!itch on thei

+idium phone and make o ecei"e calls outside of thei .meitech co"ea#e *one outed

thou#h the +idium satellite system& This !ould allo! fo ubi$uitous se"ice fo cellulauses e"en !hen they ae out of an#e of thei cuent cellula system&

!andline etensionThe thid type of satellite use !ill an indi"idual !ho !ants landline e,tension& +n this

instance a satellite company !ould install a fi,ed telephone booth in a ual aea e& in the

outskits of +ndia& This !ould enable a ual to!n% !hich cuently has no means of "oicecommunications% to communicate !ith an uban aea !hee medical% police o othe

se"ices e,ist& The ual to!n could also use the phone to call supplies of staple poducts&

'i,ed satellite se"ice !ould mostly be used !hen a landline system is uneconomical o

technolo#ically incapableo se"in# a paticula location& Aodaphone has been usin# fi,ed!ieless phone booths in South .fica and has a"ea#ed ?00 minutes of use pe booth&

>>. Gl/bal M/bile Satellite 1/mmuni1ati/ns servi1es

Satellite communication systems ae desi#ned to po"ide "oice% data% fa,% pa#in#% "ideoconfeencin# and intenet se"ices to uses !old!ide& Thou#h satellite based systems%

uses !ill be able to make a phone call fom an .fican safai o !hile sailin# aound the

!old& (o matte !hee uses ae% they !ill be able to communicate !ith clients%customes% associates% fiends% and family any!hee in the !old& +n addition% satellite

communications !ill allo! counties to po"ide phone se"ices !ithout la#e in"estments

in landline o !ieless systems& Satellite communications !ill be one of the fastest #o!in#

aeas !ithin the communications industy&

GE) satellite net!oks offe #eat potential fo multimedia applications !ith thei ability

to boadcast and multicast la#e amounts of data o"e a "ey la#e aea thus achie"in#

#lobal connecti"ity& +ntenet "ia satellites% in paticula% GE) satellites% ha"e the follo!in#

meits8

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+i5h band4idth.

. Ba-band 20-60Gh* satellite can deli"e thou#hput of #i#abits pe second ates&

!neensive.

. satellite communications system is elati"ely ine,pensi"e because thee ae no

cable-layin# costs% and one satellite co"es a "ey la#e aea&


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1. Conclsion

Satellite net!oks pomise a ne! ea of #lobal connecti"ity% !hee #eo#aphical isolation!ill no moe be the baie amon# continent& +n this !ok% !e ha"e sho!n that indeed

many popula +ntenet applications pefom to use e,pectation o"e satellite net!oks%

such as "ideo teleconfeencin#% bulk data tansfe% back#ound electonic mail% and non-eal time infomation dissemination& Some othe applications% especially hi#hly inteacti"e

applications such as !eb bo!sin#&

E"en thou#h the systems !ill e"entually be built% conflicts o"e billin# and contol still

emain& )peatos of phone se"ices in Euope donHt like the idea of systems that !ouldbypass thei e$uipment and% pobably% ta,es and fees& Some "ey comple, ne#otiatin# !ill

be needed to calm obections by such bodies% and no doubt some inteestin# compomises

!ill be made& The iidium poectHs futue is still uncetain% but looks athe pomisin# as

fa as space "entues #o& The use of such a system in helpin# pomote the thou#ht of the!old as a J#lobal "illa#eJ dese"es thou#ht and% + think% espect& The #lobal

communications industy has #o!n like no one e"e thou#ht it !ould% and the futue foiidium o an iidium-like system is% in the lon# un% assued

Thus the field mobile satellite communication ha"e bette pospectus in the futue& .s

conditions on mas ae seems to be fa"ouable fo human life&

>. B!B%!,GR#P+3

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