会员注册 | 登录 | 微信快捷登录 QQ登录 微博登录 | 帮助中心 人人文库renrendoc.com美如初恋!
站内搜索 百度文库

热门搜索: 直缝焊接机 矿井提升机 循环球式转向器图纸 机器人手爪发展史 管道机器人dwg 动平衡试验台设计

   首页 人人文库网 > 资源分类 > DOC文档下载

外文翻译--全球移动通信系统概要.doc

  • 资源星级:
  • 资源大小:76.00KB   全文页数:11页
  • 资源格式: DOC        下载权限:注册会员/VIP会员
您还没有登陆,请先登录。登陆后即可下载此文档。
  合作网站登录: 微信快捷登录 支付宝快捷登录   QQ登录   微博登录
友情提示
2:本站资源不支持迅雷下载,请使用浏览器直接下载(不支持QQ浏览器)
3:本站资源下载后的文档和图纸-无水印,预览文档经过压缩,下载后原文更清晰   

外文翻译--全球移动通信系统概要.doc

OverviewoftheGlobalSystemforMobileCommunications1HistoryofGSMDuringtheearly1980s,analogcellulartelephonesystemswereexperiencingrapidgrowthinEurope,particularlyinScandinaviaandtheUnitedKingdom,butalsoinFranceandGermany.Eachcountrydevelopeditsownsystem,whichwasincompatiblewitheveryoneelsesinequipmentandoperation.Thiswasanundesirablesituation,becausenotonlywasthemobileequipmentlimitedtooperationwithinnationalboundaries,whichinaunifiedEuropewereincreasinglyunimportant,buttherewasalsoaverylimitedmarketforeachtypeofequipment,soeconomiesofscaleandthesubsequentsavingscouldnotberealized.TheEuropeansrealizedthisearlyon,andin1982theConferenceofEuropeansPostsandTelegraphsCEPTformedastudygroupcalledtheGroupSpecialMobileGSMtostudyanddevelopapanEuropeanpubliclandmobilesystem.TheproposedsystemhastomeetcertaincriteriaGoodsubjectivespeechqualityLowterminalandservicecostSupportforinternationalroamingAbilitytosupporthandheldterminalsSupportforrangeofnewservicesandfacilitiesSpectralefficiencyISDNcompatibilityIn1989,GSMresponsibilitywastransferredtotheEuropeanTelecommunicationStandardsInstituteETSI,andphaseIoftheGSMspecificationswerepublishedin1990.Commercialservicewasstartedinmid1991,andby1993therewere36GSMnetworksin22countries.AlthoughstandardizedinEurope,GSMisnotonlyaEuropeanstandard.Over200GSMnetworksareoperationalin110countriesaroundtheworld.Inthebeginningof1994,therewere1.3millionsubscribersworldwide,whichhadgrowntomorethan55millionbyOctober1997.WithNorthAmericamakingadelayedentryintotheGSMfieldwithaderivativeofGSMcalledPCS1900,GSMsystemsexistoneverycontinent,andtheacronymGSMnowaptlystandsforGlobalSystemforMobilecommunications.ThedevelopersofGSMchoseanunprovenatthetimedigitalsystem,asopposedtothethenstandardanalogcellularsystemslikeAMPSintheUnitedStatesandTACSintheUnitedKingdom.Theyhadfaiththatadvancementsincompressionalgorithmsanddigitalsignalprocessorswouldallowthefulfillmentoftheoriginalcriteriaandthecontinualimprovementofthesystemintermsofqualityandcost.Theover8,000pagesofGSMrecommendationstrytoallowflexibilityandcompetitiveinnovationamongsuppliers,butprovideenoughstandardizationtoguaranteeproperinterworkingbetweenthecomponentsofthesystem.Thisdonebyprovidingfunctionalandinterfacedescriptionsforeachofthefunctionalentitiesdefinedinthesystem.2GeneralConcepts2.1AnalogVersusDigitalTelephonySystemsFirstgenerationsystemswereanalog.Duringtheearly1980stheseunderwentrapiddevelopmentinEurope.AlthoughtheNMTsystemwasusedbyalltheNordiccountries,andtheTACSsystemintheUnitedKingdomandItaly,therewasavarietyofsystemsandnocompatibilityamongthem.Comparedwiththesesystems,themainadvantagesofferedbyGSM,whichisthemostimportantofthesecondgenerationdigitalsystems,areStandardizationCapacityQualitySecurity.Standardizationguaranteescompatibilityamongsystemsofdifferentcountries,allowingsubscriberstousetheirownterminalsinthosecountriesthathaveadoptedthedigitalstandard.Thelackofstandardizationinthefirstgenerationsystemlimitedservicetowithinthebordersofacountry.Mobilityisimproved,sinceroamingisnolongerlimitedtoareascoveredbyacertainsystem.Callscanbechargedandhandledusingthesamepersonalnumberevenwhenthesubscribermovesfromonecountrytoanother.Standardizationalsoallowstheoperatortobuyentitiesofthenetworkfromdifferentvendors,sincethefunctionalelementsofthenetworkandtheinterfacesbetweentheseelementsarestandardized.Thismeansthatamobilephonefromanymanufacturerisabletocommunicatewithanynetwork,evenifthisnetworkisbuiltwithentitiesfromdifferentvendors.Thisleadstoalargeeconomyofscaleandresultsincostreductionforboththeoperatorandthesubscriber.Furthermore,thephonecostisalsoreduced,becauseGSMisaninternationalstandard,producedquantitiesaregreaterandthelevelofcompetitionishigh.Withrespecttocapacity,theuseoftheradioresourceismuchmoreefficientinadigitalsystemsuchasGSMthaninananalogsystem.Thismeansthatmoreuserscanbeallocatedinthesamefrequencybandwidth.Thisispossiblewiththeuseofadvanceddigitaltechniques,suchasvoicecompressionalgorithms,channelcoding,andmultipleaccesstechniques.Notethatcapacitygainsarealsoachievedwithradiofrequencyreuse,whichhadalsousedinanalogsystems.Frequencyreusemeansthatagivencarriercanbeemployedindifferentareas.Thequalityindigitaltransmissionsystemsisbetter,thankstothechannelcodingschemesthatincreasetherobustnessinthefaceofnoiseanddisturbancessuchasinterferencecausedbyotherusersorothersystems.Thequalityimprovementisalsoduetotheimprovedcontroloftheradiolink,andadaptationstopropagationconditions,withadvancedtechniquessuchaspowercontrolorfrequencyhopping.Thiswillbeexplainedingreaterdetailinthenextsection.Intermsofsecurity,powerfulauthenticationandencryptiontechniquesforvoiceanddatacommunicationsareenabledwithGSM,whichguaranteesprotectedaccesstothenetwork,andconfidentiality.2.2CellularTelephonyInmobileradiosystems,oneofthemostimportantfactorsisthefrequencyspectrum.Inordertomakethebestuseofthebandwidth,thesystemisdesignedbymeansofthedivisionoftheserviceareaintoneighboringzones,orcells,whichintheoryhaveahexagonalshape.EachcellhasaBaseTransceiverStationBTS,whichtoavoidinterferenceoperatesonasetofradiochannelsdifferentfromthoseoftheadjacentcells.Thisdivisionallowsfortheuseofthesamefrequenciesinnonadjacentcells.Agroupofcellsthatasawholeusetheentireradiospectrumavailabletotheoperatorisreferredtoasacluster.Theshapeofacellisirregular,dependingontheavailabilityofaspotfortheBTS,thegeographyoftheterrain,thepropagationoftheradiosignalinthepresenceofobstacles,andsoon.Indenseurbanareas,forinstance,wherethemobiletelephonytrafficisimportant,thediameterofthecellsisoftenreducedinordertoincreasecapacity.Thisisallowedsincethesamefrequencychannelsareusedinasmallerarea.Ontheotherhand,reducingthecelldiameterleadstoadecreaseinthedistancenecessarytoreusethefrequenciesthatis,thedistancebetweentwocochannelcells,increasingcochannelinterference.Inordertominimizethelevelofinterference,severaltechniquesareusedontheradiointerface.AbasicexampleofclusterorganizationisshowninFigure1.Inthisexample,weseeareuseatternforsevendifferentfrequencies,f1tof7.Thesefrequenciescorrespondtothebeaconcarrierofeachcell,onwhichsignalinginformationaboutthecellisbroadcastseeSection2.7.Itcanbeseenfromthisfigurethatagivencarriercanbereusedintwoseparategeographicalareas,aslongastheseareasarefarenoughfromeachothertoreducetheeffectofinterference.Withthistechniqueofdividingtheareaincellsandclusters,theoperatorcanincreasetheareaitisabletocoverwithalimitedfrequencybandwidth.Figure1ExampleofaCellPlanning2.3PublicLandMobileNetworkApublicLandMobileNetworkPLMNisanetworkestablishedforthepurposeofprovidinglandmobiletelecommunicationsservicestothepublic.Itmaybeconsideredasanextensionofafixednetwork,suchasthePublicSwitchedTelephoneNetworkPSTN,orasanintegralpartofthePSTN.2.4MultibandMobilePhonesBecauseoftheincreasingdemandonthemobilenetworks,todaythemobilestationsMSstendtobemultiband.Indeed,toavoidnetworksaturationindenselypopulatedregions,mobilephonescapableofsupportingdifferentfrequencybandshavebeenimplemented,toallowfortheusermakingcommunicationsinanyarea,atanytime.Adualbandphonecanoperateintwodifferentfrequencybandsofthesametechnology,forinstanceinthe900MHzand1800MHzfrequencybansoftheGSMsystem.Triplebandmobilephoneshavealsocomeonthemarket,withthesupportofGSM900900MHzGSMband,DCS18001800MHzGSMband,andPCS19001900MHzGSMband,forexample.NotethatDCS1800andPCS1900areneverdeployedinthesamecountry,andthereforethiskindofphonecanbeusedbytravelerswhowanttohaveservicecoverageinalargenumberofcountries.2.5SIMCardOneofthemostinterestinginnovationsofGSMisthatthesubscribersdataisnotmaintainedinthemobilephone.Ratherasmartcard,calledasubscriberidentityf3f2f1f4f7f5f6f3f2f1f4f7f5f6CellCluster

注意事项

本文(外文翻译--全球移动通信系统概要.doc)为本站会员(英文资料库)主动上传,人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对上载内容本身不做任何修改或编辑。 若此文所含内容侵犯了您的版权或隐私,请立即通知人人文库网(发送邮件至[email protected]或直接QQ联系客服),我们立即给予删除!

温馨提示:如果因为网速或其他原因下载失败请重新下载,重复下载不扣分。

[email protected] 2015-2017 人人文库网网站版权所有
苏ICP备12009002号-5