Examples of wireless communication systems

Examples of wireless communication systems, paging systems, cordless telephone systems, cellular telephone systems,evolution of mobile phone, MSC, MTSO, PSTN, Mobile communication, wireless link, subscriber,

1. By,
Dr. D. Veera Vanitha,
Asso. Prof. /ECE,
School of Engineering,
Avinashilingam Institute for Home Science and Higher
Education for Women, Coimbatore

2. Pagingsystemsarecommunicationsystemsthatsendbriefmessages
toasubscriber
Dependingonthetypeofservice,themessagemaybeeithera
numericmessage,analphanumericmessageoravoicemessage
Pagingsystemsaretypicallyusedtonotifyasubscriberoftheneed
tocallaparticulartelephonenumberortraveltoaknownlocationto
receivefurtherinstruction
Inmodernpagingsystem,newsheadlines,stockquotationandfaxes
maybesent
Amessageissentapagingsubscriberviathepagingsystemaccess
number(usuallyatoll-freetelephonenumber)withatelephone
keypadormodem.Theissuedmessageiscalledapage

3. Thepagingsystemthentransmitsthepagethroughouttheservice
areausingbasestationwhichbroadcastthepageonaradiocarrier
Pagingsystemvarywidelyintheircomplexityandcoveragearea
Whilesimplepagingsystemsmaycoveralimitedrangeof2kmto
5km,ormayevenbeconfinedtowithinindividualbuildings,wide
areapagingsystemscanprovideworldwidecoverage
Thoughpagingreceiversaresimpleandinexpensive,the
transmissionsystemrequiredisquitesophisticated.
Wideareapagingsystemsconsistsofanetworkoftelephonelines,
manybasestationtransmittersandlargeradiotowersthat
simultaneouslybroadcastapagefromeachbasestationthisiscalled
simulcasting.

4. Simulcasttransmittersmaybe
locatedwithinthesameservice
areaorindifferentcitiesor
countries.
Pagingsystemsaredesignedto
providereliablecommunications
tosubscriberswherevertheare;
whetherinsideabuilding,driving
inahighway,orflyinginan
airplane.
Thisnecessitateslargetransmitter
power(ontheorderofkilowatts)
andlowdatarates(acoupleof
thousandbitspersecond)for
maximumcoveragefromeach
basestation.

5. Cordlesstelephonesystemsarefullduplexcommunicationsystems
thatuseradiotoconnectaportablehandsettoadedicatedbase
station,whichistheconnectedtoadedicatedtelephonelinewitha
specifictelephonenumberonthepublicswitchedtelephonenetwork
(PSTN)
Infirstgenerationcordlesstelephonesystem(manufacturedin
1980s),theportableunitcommunicatesonlytothededicatedbase
unitandonlyoverdistanceofafewtensofmeters
Earlycordlesstelephonesoperatesolelyasextensiontelephonestoa
transceiverconnectedtoasubscriberlineonthePSTNandare
primarilyforinhomeuse
Secondgenerationcordlesstelephoneshaverecentlybeenintroduced
whichallowsubscriberstousetheirhandsetsatmanyoutdoor
locationswithinurbancenters

6. Moderncordlesstelephonearesometimescombinedwithpaging
receiverssothatasubscribermayfirstbepagedandthenrespondto
thepageusingthecordlesstelephone
Cordlesstelephonesystemsprovidetheuserwithlimitedrangeand
mobility,asitisusuallynotpossibletomaintainacalliftheuser
travelsoutsidetherangeofthebasestation
Typicalsecondgenerationbasestationprovidecoveragerangesupto
afewhundredmeters

7. Acellulartelephonesystemprovidesawirelessconnectionstothe
PSTNforanyuserlocationwithintheradiorangeofthesystem
Cellularsystemsaccommodatealargenumberofusersoveralarge
geographicarea,withinalimitedfrequencyspectrum
Cellularradiosystemsprovidehighqualityservicethatisoften
comparabletothatofthelandlinetelephonesystems
Highcapacityisachievedbylimitingthecoverageofeachbase
stationtransmittertoasmallgeographicareacalledacellsothatthe
sameradiochannelsmaybereusedbyanotherbasestationlocated
somedistanceaway
Asophisticatedswitchingtechniquecalledahandoffenablesacallto
proceeduninterruptedwhentheusermovesfromonecelltoanother

8. Thediagramshowsabasiccellularsystemwhichconsistsofmobile
stations,basestationandamobileswitchingcenter(MSC)
Themobileswitchingcenterissometimescalledamobiletelephone
switchingoffice(MTSO)sinceitisresponsibleforconnectingall
mobilestothePSTNinacellularsystem

9. Eachmobilecommunicationsviaradiowithoneofthebasestation
andmaybehanded-offtoanynumberofbasestationthroughoutthe
durationofacall
Themobilestationcontainsatransceiver,anantenna,andcontrol
circuitry,andmaybemountedinavehicleorusedasaportable
hand-heldunit
Thebasestationsconsistsofseveraltransmittersandreceiverswhich
simultaneouslyhandlefullduplexcommunicationandgenerallyhave
towerswhichsupportsseveraltransmittingandreceivingantennas
Thebasestationservesasabridgebetweenallmobileusersinthe
cellandconnectsthesimultaneousmobilecallsviatelephonelinesor
microwavelinkstotheMSC
TheMSCcoordinatestheactivitiesofallofthebasestationsand
connectstheentirecellularsystemtothePSTN

10. AtypicalMSChandles100,000cellularsubscribersand5,000
simultaneousconversationsatatime,andaccommodatesallbilling
andsystemmaintenancefunctions,aswell
Inlargecities,severalMSCsareusedbyasinglecarrier
Communicationbetweenthebasestationandthemobilesisdefined
byastandardcommonairinterface(CAI)thatspecifiesfourdifferent
channels
Thechannelsusedforvoicetransmissionfromthebasestationtothe
mobilesarecalledforwardvoicechannel(FVC)andthechannels
usedforvoicetransmissionsfrommobilestothebasestationare
calledreversevoicechannel(RVC)

11. Thetwochannelsresponsibleforinitiatingmobilecallsarethe
forwardcontrolchannels(FCC)andreversecontrolchannels(RCC)
Controlchannelsareoftencalledsetupchannelsbecausetheyare
involvedinsettingupacallandmovingittoanunusedvoice
channel
Controlchannelstransmitandreceivedatamessagesthatcarrycall
initiationsandservicesrequest,andaremonitoredbymobileswhen
theydonothaveacallinprogress
Forwardcontrolchannelsalsoserveasbeaconswhichcontinually
broadcastallofthetrafficrequestsforallmobilesinthesystem
Thetowersrepresentsbasestationswhichprovideradioaccess
betweenmobileusersandthemobileswitchingcenter(MSC)
(Ref.:T.S.Rappaport,“WirelessCommunicationsPrinciplesand
Practice”,2
nd
Edition,)