2013年设计-温湿度检测设计-(外文)翻译

GUANGXIUNIVERSITYOFSCIENCEANDTECHNOLOGY毕业设计（论文）外文翻译外文题目GSM移动通信系统综述院系计算机学院专业通信工程班级学号200900402022姓名指导教师2013年5月20日原文OVERVIEWOFTHEGLOBALSYSTEMFORMOBILECOMMUNICATIONSHISTORYOFGSMDURINGTHEEARLY1980S,ANALOGCELLULARTELEPHONESYSTEMSWEREEXPERIENCINGRAPIDGROWTHINEUROPE,PARTICULARLYINSCANDINAVIAANDTHEUNITEDKINGDOM,BUTALSOINFRANCEANDGERMANYEACHCOUNTRYDEVELOPEDITSOWNSYSTEM,WHICHWASINCOMEPAIBLEWITHEVERYONEELSESINEQUIPMENTANDOPERATION（INTERMSOFEQUIPMENTANDOPERATIONANDOTHERCOUNTRIESARENOTIDENTICAL）THISWASANUNDESIRABLESITUTION,BECAUSENOTONLYWASTHEMOBILEEQUIPMENTLIMITEDTOOPERATIONWITHINNATIONALBOUNDARIES,WHICHINAUNIFIEDEUROPEWEREINCREASINGLYUNIMPORTANT,BUTTHEREWASALSOAVERYLIMITEDMARKETFOREACHTYPEOFEQUIPMENT,SOECONOMIESOFSCALEANDTHESUBSEQUENTSAVINGSCOULDNOTBEREALIZEDTHEEUROPEANSREALIZEDTHISEARLYON,ANDIN1982THECONFERENCEOFEUROPEANPOSTSANDTELEGRAPHSCEPTFORMEDASTUDYGROUPCALLEDTHEGROUPESPECIALMOBILEGSMTOSTUDYANDDEVELOPAPANEUROPEANPUBLICLANDMOBILESYSTEMTHEPROPOSEDSYSTEMHADTOMEETCERTAINCRITERIAGOODSUBJECTIVESPEECHQUALITYLOWTERMINALANDSERVICECOSTSUPPORTFORINTERNATIONALROAMINGABILITYTOSUPPORTHANDHELDTERMINALSSUPPORTFORRANGEOFNEWSERVICESANDFACILITIESSPECTRALEFFICIENCYISDNCOMPATIBILITYIN1989,GSMRESPONSIBILITYWASTRANSFERREDTOTHEEUROPEATELECOMMUNICATIONSTANDARDSINSTITUTEETSI,ANDPHASEIOFTHEGSMSPECIFICATIONSWEREPUBLISHEDIN1990COMMERCIALSERVICEWASSTARTEDINMID1991,ANDBY1993THEREWERE36GSMNETWORKSIN22COUNTRIESALTHOUGHSTANDARDIZEDINEUROPE,GSMISNOTONLYAEUROPEANSTANDARDOVER200GSMNETWORKSINCLUDINGDCS1800ANDPCS1900AREOPERATIONALIN110COUNTRIESAROUNDTHEWORLDINTHEBEGINNINGOF1994,THEREWERE13MILLIONSUBSCRIBERSWORLDWIDEWHICHHADGROWNTOMORETHAN55MILLIONBYOCTOBER1997WITHNORTHAMERICAMAKINGADELAYEDENTRYINTOTHEGSMFIELDWITHDERIVATIVEOFGSMCALLEDPCS1900,GSMSYSTEMSEXISTONEVERYCONTINENT,ANDTHEACRONYMGSMNOWAPTLYSTANDSFORGLOBALSYSTEMFORMOBILECOMMUNICATIONSTHEDEVELOPERSOFGSMCHOSEANUNPROVENATTHETIMEDIGITALSYSTEM,ASOPPOSEDTOTHETHENSTANDARDANALOGCELLULARSYSTEMSLIKEAMPSINTHEUNITEDSTATESTACSINTHEUNITEDKINGDOMTHEYHADFAITHTHATADVANCEMENTSINCOMPRESSIONALGORITHMANDDIGITALSIGNALPROCESSORSWOULDALLOWTHEFULFILLMENTOFTHEORIGINALCRITERIAANDTHECONTINUALIMPROVEMENTOFTHESYSTEMINTERMSOFQUALITYANDCOSTTHEOVER8000PAGESOFGSMRECOMMENDATIONSTRYTOALLOWFLEXIBILITYANDCOMETITIVEINNOVATIONAMONGSUPPLIERSBUTPROVIDEENOUGHSTANDARDIZATIONTOGUARANTEEPROPERINTERWORKBETWEENTHECOMPONENTSOFTHESYSTEMTHISISDONEBYPROVIDINGFUNCTIONAANDINTERFACEDESCRIPTIONSFOREACHOFTHEFUNCTIONALENTITIESDEFINEDINTHESYSTEMSERVICESPROVIDEDBYGSMFROMTHEBEGINNING,THEPLANNERSOFGSMWANTEDISDNCOMPATIBILITYINTERMSOFTHESERVICESOFFEREDANDTHECONTROLSIGNALLINGUSEDHOWEVER,RADIOTRANSMISSIONLIMITATIONS,INTERMSOFBANDWIDTHANDCOST,DONOTALLOWTHESTANDARDISDNBCHANNELBITRATEOF64KBPSTOBEPRACTICALLYACHIEVEDUSINGTHEITUTDEFINITIONS,TELECOMMUNICATIONSERVICESBEDIVIDEDINTOBEARERSERVICES,TELESERVICES,ANDSUPPLEMENTARYSERVICESTHEBASICTELESERVICESUPPORTEDBYGSMISTELEPHONYASWITHANOTHERRCOMMUNICATIONS,SPEECHISDIGITALLYENCODEDANDTRANSMITTEDTHROUGHTHEGSMNETWORKASADIGITALSTREAMTHEREISEMERGENCYSERVICE,WHERETHENARESTEMERGENCYSERVICEPROVIDERISNOTIFIEDBYDIALINGTHREEDIGITSSIMILARTO911AVARIETYOFDATASERVICESISOFFEREDGSMUSERSCANSENDANDRECEIVEDATA,ATRATESUPTO9600BPS,TOUSERSONPOTSISDN,PACKETSWITCHEDPUBLICDATANETWORKS,ANDCIRCUITSWITCHEDPUBLICDATANETWORKSUSINGAVARIETYOFACCESSMETHODSANDPROTOCOLS,SUCHASX25ORX32SINCEGSMISADIGITALNETWORK,AMODEMISNOTREQUIREDBETWEENTHEUSERANDGSMNETWORK,ALTHOUGHANAUDIOMODEMISREQUIREDINSIDETHEGSMNETWORKTOINTERWORKWITHPOTSOTHERDATASERVICESINCLUDEGROUP3FACSIMILE,ASDESCRIBEDINITUTRECOMMENDDATIONT30,WHICHISSUPPORTEDBYUSEOFANAPPROPRIATEFAXADAPTORAUNIQUEFEATUREOFGSM,NOTFOUNDINOLDERANALOGSYSTEMS,ISTHESHORTMESSAGESERVICESMSSMSISABIDIRECTIONALSERVICEFORSHORTALPHANUMERICMESSAGESMESSAGESARETRANSPORTEDINASTOREANDFORWARDFASHIONFORPOINTTOPOINTSMS,AMESSAGECANBESENTTOANOTHERSUBSCRIBERTOTHESERVICEANDANACKNOWLEDGEMENTOFRECEIPTISPROVIDEDTOTHESENDERSMSCANALSOBEUSEDINACELLBROADCASTMODE,FORSENDINGMESSAGESSUCHASTRAFFICUPDATESORNEWSUPDATESMESSAGESCANALSOBESTOREDINTHESIMCARDFORLATERRETRIEVALSUPPLEMENTARYSERVICESAREPROVIDEDONTOPOFTELESERVICESORBEARERSERVICESINTHECURRENTPHASEISPECIFICATIONS,THEYINCLUDESEVERALFORMSOFCALLFORWARDSUCHASCALLFORWARDINGWHENTHEMOBILESUBSCRIBERISUNREACHABLEBYTHENETWORK,ANDCALLBARRINGOFOUTGOINGORINCOMINGCALLS,FOREXAMPLE,WHENROAMINGINANOTHERCOUNTRYMANYADDITIONALSUPPLEMENTARYSERVICESWILLBEPROVIDEDINTHEPHASE2SPECIFICATIONS,SUCHASCALLERIDENTIFICATION,CALLWAITING,MULTIPARTYCONVERSATIONSCONTROLCHANNELSCOMMONCHANNELSCANBEACCESSEDBOTHBYIDLEMODEANDDEDICATEDMODEMOBILESTHECOMMONCHANNELSAREUSEDBYIDLEMODEMOBILESTOEXCHANGETHESIGNALINGINFORMATIONREQUIREDTOCHANGETODEDICATEDMODEMOBILESALREADYINDEDICATEDMODEMONITORTHESURROUNDINGBASESTATIONSFORHANDOVERANDOTHERINFORMATIONTHECOMMONCHANNELSAREDEFINEDWITHINA51FRAMEMULTIFRAME,SOTHATDEDICATEDMOBILEUSINGTHE26FRAMEMULTIFRAMETCHSTRUCTURECANSTILLMONITORCONTROLCHANNELSTHECOMMONCHANNELSINCLUDEBROADCASTCONTROLCHANNELBCCHCONTINUALLYBROADCASTS,ONTHEDOWNLINK,INFORMATIONINCLUDINGBASESTATIONIDENTITY,FREQUENCYALLOCATIONS,ANDFREQUENCYHOPPINGSEQUENCESFREQUENCYCORRECTIONCHANNELFCCHANDSYNCHRONISATIONCHANNELSCHUSEDTOSYNCHRONISETHEMOBILETOTHETIMESLOTSTRUCTUREOFACELLBYDEFININGTHEBOUNDARIESOFBURSTPERIODS,ANDTHETIMESLOTNUMBERINGEVERYCELLINAGSMNETWORKBROADCASTSEXACTLYONEFCCHANDONESCH,WHICHAREBYDEFINITIONONTIMESLOTNUMBER0WITHINATDMAFRAMERANDOMACCESSCHANNELRACHSLOTTEDALOHACHANNELUSEDBYTHEMOBILETOREQUESTACCESSTOTHENETWORKPAGINGCHANNELPCHUSEDTOALERTTHEMOBILESTATIONOFANINCOMINGCALLACCESSGRANTCHANNELAGCHUSEDTOALLOCATEANSDCCHTOAMOBILEFORSIGNALLINGINORDERTOOBTAINADEDICATEDCHANNEL,FOLLOWINGAREQUESTONTHERACHCHANNELCODINGANDMODULATIONBECAUSEOFNATURALANDMANMADEELECTROMAGNETICINTERFERENCE,THEENCODEDSPEECHORDATASIGNALTRANSMITTEDOVERTHERADIOINTERFACEMUSTBEPROTECTEDFROMERRORSGSMUSESCONVOLUTIONALENCODINGANDBLOCKINTERLEAVINGTOACHIEVETHISPROTECTIONTHEEXACTALGORITHMSUSEDDIFFERFORSPEECHANDFORDIFFERENTDATARATESTHEMETHODUSEDFORSPEECHBLOCKSWILLBEDESCRIBEDBELOWRECALLTHATTHESPEECHCODECPRODUCESA260BITBLOCKFOREVERY20MSSPEECHSAMPLEFROMSUBJECTIVETESTING,ITWASFOUNDTHATSOMEBITSOFTHISBLOCKWEREMOREIMPORTANTFORPERCEIVEDSPEECHQUALITYTHANOTHERSTHEBITSAREDIVIDEDINTOTHREECLASSESCLASSIA50BITSMOSTSENSITIVETOBITERRORSCLASSIB132BITSMODERATELYSENSITIVETOBITERRORSCLASSII78BITSLEASTSENSITIVETOBITERRORSCLASSIABITSHAVEA3BITCYCLICREDUNDANCYCODEADDEDFORERRORDETECTIONIFANERRORISDETECTED,THEFRAMEISJUDGEDTOODAMAGEDTOBECOMPREHENSIBLEANDITISDISCARDEDITISREPLACEDBYASLIGHTLYATTENUATEDVERSIONOFTHEPREVIOUSCORRECTLYRECEIVEDFRAMETHESE53BITS,TOGETHERWITHTHE132CLASSIBBITSANDA4BITTAILSEQUENCEATOTALOF189BITS,AREINPUTINTOA1/2RATECONVOLUTIONALENCODEROFCONSTRAINTLENGTH4EACHINPUTBITISENCODEDASTWOOUTPUTBITS,BASEDONACOMBINATIONOFTHEPREVIOUS4INPUTBITSTHECONVOLUTIONALENCODERTHUSOUTPUTS378BITS,TOWHICHAREADDEDTHE78REMAININGCLASSIIBITS,WHICHAREUNPROTECTEDTHUSEVERY20MSSPEECHSAMPLEISENCODEDAS456BITSFURTHERINORDERTOAVOIDEMERGENCYRADIOINTERFACEERROR,EACHSAMPLEWASINTERLACEDTHE456BITSOUTPUTBYTHECONVOLUTIONALENCODERAREDIVIDEDINTO8BLOCKSOF57BITS,ANDTHESEBLOCKSARETRANSMITTEDINEIGHTCONSECUTIVETIMESLOTBURSTSSINCEEACHTIMESLOTBURSTCANCARRYTWO57BITBLOCKS,EACHBURSTCARRIESTRAFFICFROMTWODIFFERENTSPEECHSAMPLESSPEECHCODINGGSMISADIGITALSYSTEM,SOSPEECHWHICHISINHERENTLYANALOG,HASTOBEDIGITIZEDTHEMETHODEMPLOYEDBYISDN,ANDBYCURRENTTELEPHONESYSTEMSFORMULTIPLEXINGVOICELINESOVERHIGHSPEEDTRUNKSANDOPTICALFIBERLINES,ISPULSECODEDMODULATIONPCMTHEOUTPUTSTREAMFROMPCMIS64KBPS,TOOHIGHARATETOBEFEASIBLEOVERARADIOLINKTHE64KBPSSIGNAL,ALTHOUGHSIMPLETOIMPLEMENTCONTAINSMUCHREDUNDANCYTHEGSMGROUPSTUDIEDSEVERALSPEECHCODINGALGORITHMSONTHEBASISOFSUBJECTIVESPEECHQUALITYANDCOMPLEXITYWHICHISRELATEDTOCOST,PROCESSINGDELAY,ANDPOWERCONSUMPTIONONCEIMPLEMENTEDBEFOREARRIVINGATTHECHOICEOFAREGULARPULSEEXCITEDLINEARPREDICTIVECODERRPELPCWITHALONGTERMPREDICTORLOOPBASICALLY,INFORMATIONFROMPREVIOUSSAMPLES,WHICHDOESNOTCHANGEVERYQUICKLY,ISUSEDTOPREDICTTHECURRENTSAMPLETHECOEFFICIENTSOFTHELINEARCOMBINATIONOFTHEPREVIOUSSAMPLES,PLUSANENCODEDFORMOFTHERESIDUAL,THEDIFFERENCEBETWEENTHEPREDICTEDANDACTUALSAMPLE,REPRESENTTHESIGNALSPEECHISDIVIDEDINTO20MILLISECONDSAMPLES,EACHOFWHICHISENCODEDAS260BITS,GIVINGATOTALBITRATEOF13KBPSTHISISTHESOCALLEDFULLRATESPEECHCODINGRECENTLY,ANENHANCEDFULLRATEEFRSPEECHCODINGALGORITHMHASBEENIMPLEMENTEDBYSOMENORTHAMERICANGSM1900OPERATORSTHISISSAIDTOPROVIDEIMPROVEDSPEECHQUALITYUSINGTHEEXISTING13KBPSBITRATEPOWERCONTROLTHEREAREFIVECLASSESOFMOBILESTATIONSDEFINED,ACCORDINTOTHEIRPEAKTRANSMITTERPOWER,RATEDAT20,8,5AND2WATTSTOMINIMIZECOCHANNELINTERFERENCEANDTOCONSERVEPOWER,BOTHTHEMOBILESANDTHEBASETRANSCEIVERSTATIONSOPERATEATTHELOWESTPOWERLEVELTHATWILLMAINTAINANACCEPTABLESIGNALQUALITYPOWERLEVELSCANBESTEPPEDUPORDOWNINSTEPSOF2DBFROMTHEPEAKPOWERFORTHECLASSDOWNTOAMINIMUMOF13DBM。THEMOBILESTATIONMEASURESTHESIGNALSTRENGTHORSIGNALQUALITYBASEDONTHEBITERRORRATIO,ANDPASSESTHEINFORMATIONTOTHEBASESTATIONCONTROLLER,WHICHULTIMATELYDECIDESIFANDWHENTHEPOWERLEVELSHOULDBECHANGEDPOWERCONTROLSHOULDBEHANDLEDCAREFULLY,SINCETHEREISTHEPOSSIBILITYOFINSTABILITYTHISARISESFROMHAVINGMOBILESINCOCHANNELCELLSALTERNATINGLYINCREASETHEIRPOWERINRESPONSETOINCREASEDCOCHANNELINTERFERENCECAUSEDBYTHEOTHERMOBILEINCREASINGITSPOWERTHISINUNLIKELYTOOCCURINPRACTICEBUTITISUNDERSTUDYFREQUENCYHOPPINGTHEMOBILESTATIONALREADYHASTOBEFREQUENCYAGILE,MEANINGITCANMOVEBETWEENATRANSMIT,RECEIVE,ANDMONITORTIMESLOTWITHINONETDMAFRAME,WHICHNORMALLYAREONDIFFERENTFREQUENCIESGSMMAKESUSEOFTHISINHERENTFREQUENCYAGILITYTOIMPLEMENTSLOWFREQUENCYHOPPING,WHERETHEMOBILEANDBTSTRANSMITEACHTDMAFRAMEONADIFFERENTCARRIERFREQUENCYTHEFREQUENCYHOPPINGALGORITHMISBROADCASTONTHEBROADCASTCONTROLCHANNELSINCEMULTIPATHFADINGIDEPENDENTONCARRIERFREQUENCY,SLOWFREQUENCYHOPPINGHELPSALLEVIATETHEPROBLEM,INADDITION,COCHANNELINTERFERENCEISINEFFECTRANDOMIZEDMULTIPATHEQUALIZATIONATTHE900MHZRANGE,RADIOWAVESBOUNCEOFFEVERYTHINGBUILDINGS,HILLS,CARS,AIRPLANES,ETCTHUSMANYREFLECTEDSIGNALS,EACHWITHADIFFERENTPHASE,CANREACHANANTENNAEQUALIZATIONISUSEDTOEXTRACTTHEDESIREDSIGNALFROMTHEUNWANTEDREFLECTIONSITWORKSBYFINDINGOUTHOWAKNOWNTRANSMITTEDSIGNALISMODIFIEDBYMULTIPATHFADING,ANDCONSTRUCTINGANINVERSEFILTERTOEXTRACTTHERESTOFTHEDESIREDSIGNALTHISKNOWNSIGNALISTHE26BITTRAININGSEQUENCETRANSMITTEDINTHEMIDDLEOFEVERYTIMESLOTBURSTTHEACTUALIMPLEMENTATIONOFTHEEQUALIZERISNOTSPECIFIEDINTHEGSMSPECIFICATIONSDISCONTINUOUSTRANSMISSIONMINIMIZINGCOCHANNELINTERFERENCEISAGOALINANYCELLULARSYSTEM,SINCEITALLOWSBETTERSERVICEFORAGIVENCELLSIZE,ORTHEUSEOFSMALLERCELLS,THUSINCREASINGTHEOVERALLCAPACITYOFTHESYSTEMDISCONTINUOUSTRANSMISSIONDTXISAMETHODTHATTAKESADVANTAGEOFTHEFACTTHATAPERSONSPEAKSLESSTHAT40PERCENTOFTHETIMEINNORMALCONVERSATION,BYTURNINGTHETRANSMITTEROFFDURINGSILENCEPERIODSANADDEDBENEFITOFDTXISTHATPOWERISCONSERVEDATTHEMOBILEUNITTHEMOSTIMPORTANTCOMPONENTOFDTXIS,OFCOURSE,VOICEACTIVITYDETECTIONITMUSTDISTINGUISHBETWEENVOICEANDNOISEINPUTS,ATASKTHATISNOTASTRIVIALASITAPPEARS,CONSIDERINGBACKGROUNDNOISEIFACOUSTICALSIGNALISMISINTERPRETEDASNOISE,THETRANSMITTERISTURNEDOFFANDAVERYANNOYINGEFFECTCALLEDCLIPPINGISHEARDATTHERECEIVINGENDIF,ONTHEOTHERHAND,NOISEISMISINTERPRETEDASAVOICESIGNALTOOOFTEN,THEEFFICIENCYOFDTXISDRAMATICALLYDECREASEDANOTHERFACTORTOCONSIDERISTHATWHENTHETRANSMITTERISTURNEDOFF,THEREISTOTALSILENCEHEARDATTHERECEIVINGEND,DUETOTHEDIGITALNATUREOFGSMTOASSURETHERECEIVERTHATTHECONNECTIONISNOTDEAD,COMFORTNOISEISCREATEDATTHERECEIVINGENDBYTRYINGTOMATCHTHECHARACTERISTICSOFTHETRANSMITTINGENDSBACKGROUNDNOISEDISCONTINUOUSRECEPTIONANOTHERMETHODUSEDTOCONSERVEPOWERATTHEMOBILESTATIONISDISCONTINUOUSRECEPTIONTHEPAGINGCHANNEL,USEDBYTHEBASESTATIONTOSIGNALANINCOMINGCALL,ISSTRUCTUREDINTOSUBCHANNELSEACHMOBILESTATIONNEEDSTOLISTENONLYTOITSOWNSUBCHANNELINTHETIMEBETWEENSUCCESSIVEPAGINGSUBCHANNELS,THEMOBILECANGOTOSLEEPMODE,WHENALMOSTNOPOWERISUSEDSIGNALLINGPROTOCOLSTRUCTUREINGSMTHESIGNALLINGPROTOCOLINGSMISSTRUCTUREDINTOTHREEGENERALLAYERS,DEPENDINGONTHEINTERFACE,ASSHOWNINFIGURE3LAYER1ISTHEPHYSICALLAYER,WHICHUSESTHECHANNELSTRUCTURESDISCUSSEDABOVEOVERTHEAIRINTERFACELAYER2ISTHEDATALINKLAYERACROSSTHEUMINTERFACE,THEDATALINKLAYERISAMODIFIEDVERSIONOFTHELAPDPROTOCOLUSEDINISDN,CALLEDLAPDMACROSSTHEAINTERFACE,THEMESSAGETRANSFERPARTLAYER2OFSIGNALLINGSYSTEMNUMBER7ISUSEDLAYER3OFTHEGSMSIGNALLINGPROTOCOLISITSELFDIVIDEDINTO3SUBLAYERSRADIORESOURCESMANAGEMENTCONTROLSTHESETUP,MAINTENANCE,ANDTERMINATIONOFRADIOANDFIXEDCHANNELS,INCLUDINGHANDOVERSMOBILITYMANAGEMENTMANAGESTHELOCATIONUPDATINGANDREGISTRATIONPROCEDURES,ASWELLASSECURITYANDAUTHENTICATIONCONNECTIONMANAGEMENTHANDLESGENERALCALLCONTROL,SIMILARTOCCITTRECOMMENDATIONQ931,ANDMANAGESSUPPLEMENTARYSERVICESANDTHESHORTMESSAGESERVICESIGNALLINGBETWEENTHEDIFFERENTENTITIESINTHEFIXEDPARTOFTHENETWORK,SUCHASBETWEENTHEHLRANDVLR,ISACCOMPLISHEDTHROUGHTTHEMOBILEAPPLICATIONMAPPARTMAPISBUILTONTOPOFTHETRANSACTIONCAPABILITIESAPPLICATIONPARTTCAP,THETOPLAYEROFSIGNALLINGSYSTEMNUMBER7THESPECIFICATIONOFTHEMAPISQUITECOMPLEX,ANDATOVER500PAGES,ITISONEOFTHELONGESTDOCUMENTSINTHEGSMPROTOCOLRADIORESOURCESMANAGEMENTTHERADIORESOURCESMANAGEMENTRRLAYEROVERSEESTHEESTABLISHMENTOFALINK,BOTHRADIOANDFIXED,BETWEENTHEMOBILESTATIONANDTHEMSCTHEMAINFUNCTIONALCOMPONENTSINVOLVEDARETHEMOBILESTATION,ANDTHEBASESTATIONSUBSYSTEM,ASWELLASTHEMSCTHERRLAYERISCONCERNEDWITHTHEMANAGEMENTOFANRRSESSIONWHICHISTHETIMETHATAMOBILEISINDEDICATEDMODE,ASWELLASTHECONFIGURATIONOFRADIOCHANNELSINCLUDINGTHEALLOCATIONOFDEDICATEDCHANNELSANRRSESSIONISALWAYSINITIATEDBYAMOBILESTATIONTHROUGHTHEACCESSPROCEDURE,EITHERFORANOUTGOINGCALL,ORINRESPONSETOAPAGINGMESSAGETHEDETAILSOFTHEACCESSANDPAGINGPROCEDURES,SUCHASWHENADEDICATEDCHANNELISACTUALLYASSIGNEDTOTHEMOBILE,ANDTHEPAGINGSUBCHANNELSTRUCTURE,AREHANDLEDINTHERRLAYERINADDITION,ITHANDLESTHEMANAGEMENTOFRADIOFEATURESSUCHASPOWERCONTROL,DISCONTINUOUSTRANSMISSIONANDRECEPTION,ANDTIMINGADVANCEHANDOVERINACELLULARNETWORK,THERADIOANDFIXEDLINKSREQUIREDARENOTPERMANENTLYALLOCATEDFORTHEDURATIONOFACALLHANDOVER,ORHANDOFFASITISCALLEDINNORTHAMERICA,ISTHESWITCHINGOFANONGOINGCALLTOADIFFERENTCHANNELORCELLTHEEXECUTIONANDMEASUREMENTSREQUIREDFORHANDOVERFORMONEOFBASICFUNCTIONSOFTHERRLAYERTHEREAREFOURDIFFERENTTYPESOFHANDOVERINTHEGSMSYSTEM,WHICHINVOLVETRANSFERRINGACALLBETWEENCHANNELSTIMESLOTSINTHESAMECELLCELLSBASETRANSCEIVERSTATIONSUNDERTHECONTROLOFTHESAMEBASESTATIONCONTROLLERBSCCELLSUNDERTHECONTROLOFDIFFERENTBSCS,BUTBELONGINGTOTHESAMEMOBILESERVICESSWITCHINGCENTERMSCCELLSUNDERTHECONTROLOFDIFFERENTMSCSTHEFIRSTTWOTYPESOFHANDOVER,CALLEDINTERNALHANDOVERS,INVOLVEONLYONEBASESTATIONCONTROLLERBSCTOSAVESIGNALINGBANDWIDTH,THEYAREMANAGEDBYTHEBSCWITHOUTINVOLVINGTHEMOBILESERVICES,SWITCHINGCENTERMSC,EXCEPTTONOTIFYITATTHECOMPLETIONOFTHEHANDOVERTHELASTTWOTYPESOFHANDOVER,CALLEDEXTERNALHANDOVERS,AREHANDLEDBYTHEMSCSINVOLVEDANIMPORTANTASPECTOFGSMISTHATTHEORIGINALMSC,THEANCHORMSC,REMAINSRESPONSIBLEFORMOSTCALLRELATEDFUNCTIONS,WITHTHEEXCEPTIONOFSUBSEQUENTINTERBSCHANDOVERSUNDERTHECONTROLOFTHENEWMSC,CALLEDTHERELAYMSCHANDOVERSCANBEINITIATEDBYEITHERTHEMOBILEORTHEMSCASAMEANSOFTRAFFICLOADBALANCINGDURINGITSIDLETIMESLOTS,THEMOBILESCANSTHEBROADCASTCONTROLCHANNELOFUPTO16NEIGHBORINGCELLS,ANDFORMSALISTOFTHESIXBESTCANDIDATESFORPOSSIBLEHANDOVER,BASEDONTHERECEIVEDSIGNALSTRENGTHTHISINFORMATIONISPASSEDTOTHEBSCANDMSC,ATLEASTONCEPERSECOND,ANDISUSEDBYTHEHANDOVERALGORITHMTHEALGORITHMFORWHENAHANDOVERDECISIONSHOULDBETAKENISNOTSPECIFIEDINTHEGSMPROTOCOLTHEREARETWOBASICALGORITHMSUSE,BOTHCLOSELYTIEDINWITHPOWERCONTROLTHISISBECAUSETHEBSCUSUALLYDOESNOTKNOWWHETHERTHEPOORSIGNALQUALITYISDUETOMULTIPATHFADINGORTOTHEMOBILEHAVINGMOVEDTOANOTHERCELL，THISISESPECIALLYTRUEINSMALLURBANCELLSTHEMINIMUMACCEPTABLEPERFORMANCEALGORITHMGIVESPRECEDENCETOPOWERCONTROLOVERHANDOVER,SOTHATWHENTHESIGNALDEGRADESBEYONDACERTAINPOINT,THEPOWERLEVELOFTHEMOBILEISINCREASEDIFFURTHERPOWERINCREASESDONOTIMPROVETHESIGNAL,THENAHANDOVERISCONSIDEREDTHISISTHESIMPLERANDMORECOMMONMETHOD,BUTITCREATESSMEAREDCELLBOUNDARIESWHENAMOBILETRANSMITTINGATPEAKPOWERGOESSOMEDISTANCEBEYONDITSORIGINALCELLBOUNDARIESINTOANOTHERCELLTHEPOWERBUDGETMETHODUSESHANDOVERTOTRYTOMAINTAINORIMPROVEACERTAINLEVELOFSIGNALQUALITYATTHESAMEORLOWERPOWERLEVELITTHUSGIVESPRECEDENCETOHANDOVEROVERPOWERCONTROLITAVOIDSTHESMEAREDCELLBOUNDARYPROBLEMANDREDUCESCOCHANNELINTERFERENCE,BUTITISQUITECOMPLICATEDMOBILITYMANAGEMENTTHEMOBILITYMANAGEMENTLAYERMMISBUILTONTOPOFTHERRLAYER,ANDHANDLESTHEFUNCTIONSTHATARISEFROMTHEMOBILITYOFTHESUBSCRIBER,ASWELLASTHEAUTHENTICATIONANDSECURITYASPECTSLOCATIONMANAGEMENTISCONCERNEDWITHTHEPROCEDURESTHATENABLETHESYSTEMTOKNOWTHECURRENTLOCATIONOFAPOWEREDONMOBILESTATIONSOTHATINCOMINGCALLROUTINGCANBECOMPLETEDLOCATIONUPDATINGAPOWEREDONMOBILEISINFORMEDOFANINCOMINGCALLBYAPAGINGMESSAGESENTOVERTHEPAGCHCHANNELOFACELLONEEXTREMEWOULDBETOPAGEEVERYCELLINTHENETWORKFOREACHCALL,WHICHISOBVIOUSLYAWASTEOFRADIOBANDWIDTHTHEOTHEREXTREMEWOULDBEFORTHEMOBILETONOTIFYTHESYSTEM,VIALOCATIONUPDATINGMESSAGES,OFITSCURRENTLOCATIONATTHEINDIVIDUALCELLLEVELTHISWOULDREQUIREPAGINGMESSAGESTOBESENTTOEXACTLYONECELL,BUTWOULDBEVERYWASTEFULDUETOTHELARGENUMBEROFLOCATIONUPDATINGMESSAGESACOMPROMISESOLUTIONUSEDINGSMISTOGROUPCELLSINTOLOCATIONAREASUPDATINGMESSAGESAREREQUIREDWHENMOVINGBETWEENLOCATIONAREAS,ANDMOBILESTATIONSAREPAGEDINTHECELLSOFTHEIRCURRENTLOCATIONAREATHELOCATIONUPDATINGPROCEDURES,ANDSUBSEQUENTCALLROUTING,USETHEMSCANDTWOLOCATIONREGISTERSTHEHOMELOCATIONREGISTERHLRANDTHEVISITORLOCATIONREGISTERVLRWHENAMOBILESTATIONISSWITCHEDONINANEWLOCATIONAREA,ORITMOVESTOANEWLOCATIONAREAORDIFFERENTOPERATORSPLMN,ITMUSTREGISTERWITHTHENETWORKTOINDICATEITSCURRENTLOCATIONINTHENORMALCASE,ALOCATIONUPDATEMESSAGEISSENTTOTHENEWMSC/VLR,WHICHRECORDSTHELOCATIONAREAINFORMATION,ANDTHENSENDSTHELOCATIONINFORMATIONTOTHESUBSCRIBERSHLRTHEINFORMATIONSENTTOTHEHLRNORMALLYTHESS7ADDRESSOFTHENEWVLR,ALTHOUGHITMAYBEAROUTINGNUMBERTHEREASONAROUTINGNUMBERISNOTNORMALLYASSIGNED,EVENTHOUGHITWOULDREDUCESIGNALING,ISTHATTHEREISONLYALIMITEDNUMBEROFROUTINGNUMBERSAVAILABLEINTHENEWMSC/VLRANDTHEYAREALLOCATEDONDEMANDFORINCOMINGCALLSIFTHESUBSCRIBERISENTITLEDTOSERVICE,THEHLRSENDSASUBSETOFTHESUBSCRIBERINFORMATION,NEEDEDFORCALLCONTROL,TOTHENEWMSC/VLR,ANDSENDSAMESSAGETOTHEOLDMSC/VLRTOCANCELTHEOLDREGISTRATIONFORRELIABILITYREASONS,GSMALSOHASAPERIODICLOCATIONUPDATINGPROCEDUREIFANHLRORMSC/VLRFAILS,TOHAVEEACHMOBILEREGISTERSIMULTANEOUSLYTOBRINGTHEDA