通信專業(yè)外文翻譯中英文對照：WPF概述

通信專業(yè)外文翻譯中英文對照：WPF概述附件1:外文資料翻譯譯文WPF概述蜂窩無線電通信行業(yè)在過去十年中目睹了全球擁有了超過四十億無線用戶這一巨大發(fā)展,第一代(1G)模擬蜂窩系統(tǒng)只支持有限的漫游語音通信,而第二代(2G)數(shù)字系統(tǒng)比第一代有更高的容量和更好的語音質(zhì)量。此外,由于在各個國家特別是在歐洲國家對漫游有相同的標(biāo)準(zhǔn)和共同的頻譜分配,因此使之變得更為普遍。在第二代(2G)蜂窩系統(tǒng)中,有兩個是比較廣泛部署的,他們分別是GSM(全球移動通信系統(tǒng))和CDMA(碼分多址)。相比于1G的模擬系統(tǒng),2G系統(tǒng)主要支持語音通信。在后來發(fā)布2G版本的標(biāo)準(zhǔn)中,主要介紹了其支持?jǐn)?shù)據(jù)傳輸?shù)哪芰?。然?2G的數(shù)據(jù)傳輸速率普遍低于撥號連接支持,因此有了3G系統(tǒng)的出現(xiàn),而ITU-R倡議的IMT-2000(國際移動電信2000年)為向3G的演進鋪平了道路。根據(jù)IMT-2000的倡議,相關(guān)部門發(fā)表了一系列要求,如2Mb/s的峰值數(shù)據(jù)率和車輛的流動性支持。GSM和CDMA形成了自己獨立的3G合作伙伴項目(3GPP和3GPP2),使IMT-2000標(biāo)準(zhǔn)發(fā)展成基于CDMA技術(shù)的標(biāo)準(zhǔn)。3GPP的3G標(biāo)準(zhǔn)被稱為寬帶CDMA(WCDMA),因為它使用了相比3GPP2的CDMA2000系統(tǒng)中1.25兆赫帶寬來說更大的5兆赫帶寬。3GPP2還制定了一個5兆赫茲的版本,支持三個1.25兆赫到副載波,其被稱為CDMA2000-3X。為了分化從5兆赫茲的CDMA2000-3X的標(biāo)準(zhǔn),1.25兆赫茲的系統(tǒng)被稱為CDMA2000-1X或者干脆稱為3G-1X。首次發(fā)布的3G標(biāo)準(zhǔn)并沒有履行其所說的承諾,使高速數(shù)據(jù)傳輸?shù)臄?shù)據(jù)在實踐中的支持率遠遠低于當(dāng)時聲稱的標(biāo)準(zhǔn)。因此其需要作出一系列認(rèn)真努力來提高有效地數(shù)據(jù)來支持3G系統(tǒng)。3GPP2中首先介紹了HRPD系統(tǒng)(高速率分組數(shù)據(jù))系統(tǒng)使用的數(shù)據(jù)流量,如通道敏感的調(diào)度,快速鏈路自適應(yīng)和混合ARQ等HRPD系統(tǒng)。系統(tǒng)優(yōu)化的各種先進技術(shù),需要一個獨立的1.25兆赫茲載波和只支持沒有語音的服務(wù)。正因為如此,HRPD系統(tǒng)最初被稱為CDMA2000-1xEVDO(演進數(shù)據(jù))系統(tǒng)。3GPP沿襲一種與之類似路徑,并介紹HSPA(高速分組接入)技術(shù)提高對WCDMA系統(tǒng)的訪問。HSPA的標(biāo)準(zhǔn)重復(fù)使用許多相同的數(shù)據(jù)優(yōu)化技術(shù)為HRPD系統(tǒng)。然而,一個相對于HRPD系統(tǒng)來說的的差異是,在HSPA上相同的兩個5MHz載波可以同時進行語音和數(shù)據(jù)傳輸。平行于HRPD系統(tǒng),3GPP2同時也制定了一個聯(lián)合的語音數(shù)據(jù)標(biāo)準(zhǔn),被稱為CDMA2000-1xEVDV(演進數(shù)據(jù)語音)。像HSPA一樣,CDMA2000-1xEVDV系統(tǒng)支持同一載波上語音和數(shù)據(jù),但是它從不商業(yè)化。在以后公布的HRPD,VoIP(互聯(lián)網(wǎng)協(xié)議語音),介紹了其提供語音和數(shù)據(jù)服務(wù)在同一載體的能力?，F(xiàn)在,兩個3G標(biāo)準(zhǔn),即HSPA和HRPD系統(tǒng)終于能夠?qū)崿F(xiàn)3G的承諾,并已被廣泛部署在主要的蜂窩市場提供無線數(shù)據(jù)接入。1.1超越3G系統(tǒng)當(dāng)HSPAHRPD系統(tǒng)得到了開發(fā)和部署,IEEE802LMSC(局域網(wǎng)/城域網(wǎng)標(biāo)準(zhǔn)委員會)也推出了IEEE802.16e移動寬帶無線接入的標(biāo)準(zhǔn)。這個標(biāo)準(zhǔn)作為一種增強被引入到一個較早的IEEE802.16的標(biāo)準(zhǔn)固定寬帶無線接入中去。以802.16e標(biāo)準(zhǔn)命名的OFDMA(正交頻分多址接入)采用不同的接入技術(shù),并聲稱比HSPA和HRPD系統(tǒng)提供、更好的數(shù)據(jù)傳輸速率和頻譜效率。IEEE802.16系列標(biāo)準(zhǔn)被正式稱為IEEE無線都會網(wǎng)路,它被稱為名為Wi論壇的一個產(chǎn)業(yè)群的Wi(全球微波接入互操作性)。Wi論壇的使命是促進和認(rèn)證寬帶無線接入產(chǎn)品的兼容性和互操作性。支持在IEEE802.16e標(biāo)準(zhǔn)的移動Wi系統(tǒng)被稱為移動Wi。除了無線電技術(shù)的優(yōu)勢,移動Wi還雇用了一個簡單的基于IP協(xié)議的網(wǎng)絡(luò)架構(gòu)。引入移動Wi,3GPP和3GPP2超越基于OFDMA技術(shù)和網(wǎng)絡(luò)架構(gòu),在類似的移動Wi的3G系統(tǒng)上開發(fā)自己的版本。在3GPP的3G系統(tǒng)之外,也被叫做進化的通用無線電臺訪問(進化UTRA),也被廣泛稱為LTE(長期演進),或被稱為3GPP2版本的UMB(超移動寬帶)如圖1.1。應(yīng)當(dāng)指出的是,這三個3G系統(tǒng)即超越移動Wi,LET,IMT-2000要求的UMB滿足,因此它們可以滿足IMT-2000標(biāo)準(zhǔn)。圖1.1蜂窩系統(tǒng)演化。表1.1LTE系統(tǒng)的屬性。1.2長期演進(LTE)LTE的目標(biāo)是提供一個高數(shù)據(jù)速率,低延遲技術(shù)支持和分組優(yōu)化的無線接入技術(shù),并支持靈活的帶寬部署。與此同時,新的網(wǎng)絡(luò)架構(gòu)的設(shè)計目標(biāo)是,支持與分組交換通信的無縫移動性,優(yōu)質(zhì)的服務(wù)服和最低限度的延遲。空中接口相關(guān)的屬性總結(jié)在表1.1中。系統(tǒng)支持靈活的帶寬OFDMA和SC-FDMA的訪問,此外,FDD(頻分雙工)和TDD(時分雙工),半雙工FDD支持低成本的UE。不像軟驅(qū),它在半雙工FDD在同一時間內(nèi)操作的問題上是不需要發(fā)送和接收的,這樣就避免了為UE而需要的昂貴的雙工器。該系統(tǒng)主要是優(yōu)化低轉(zhuǎn)速可達15公里/小時。然而,系統(tǒng)規(guī)范允許一些性能下降超過350公里/小時的流動性支持?；趩屋d波頻分多址的接入(SC-FDMA),由于低峰均值功率比(PAPR)相對的OFDMA上行接入,因此要增加上行覆蓋。該系統(tǒng)支持4×4MIMO(多輸入多輸出)在20MHz帶寬326Mb/s的下行峰值數(shù)據(jù)傳輸速率。由于上行MIMO未受聘在首次發(fā)布的LTE標(biāo)準(zhǔn),因此上行峰值數(shù)據(jù)傳輸速率被限制在86Mb/s的20兆赫帶寬。除了峰值數(shù)據(jù)傳輸速率的改善外,LTE系統(tǒng)提供兩到四倍較高的細胞相對推出6HSPA系統(tǒng)的頻譜效率。在小區(qū)邊緣的吞吐量為HSPA的部署,同時保持同一站點的位置觀察到類似的改進。在延遲方面,LTE無線接口和網(wǎng)絡(luò)提供了一個數(shù)據(jù)包從網(wǎng)絡(luò)到UE的傳輸延遲小于10毫秒的能力。1.3演進到4G移動Wi和UMB無線電接口屬性表和表1.1給出的LTE屬性表是非常相似。這三個系統(tǒng)都是支持靈活的帶寬,下行的OFDMA和MIMO方案,FDD/TDD的雙工。有如一些分歧,就是在LTE上行SC-FDMA的基于OFDMA技術(shù)在移動Wi和UMB上。三個系統(tǒng)的性能有所不同,因此預(yù)計將有微小的差別。類似于IMT-2000的主動性,ITU-R的5D工作組指出的IMT-Advanced系統(tǒng)的要求。其中,這些要求包括平均下行100Mbit/s的廣域網(wǎng)數(shù)據(jù)傳輸速率,最高可達1Gbit/s的本地訪問和低流動性的情景。此外,在世界無線電通信大會上(WRC-2007),最大的428兆赫的新頻譜被確定為IMT系統(tǒng),其中還包括一個在全球性的基礎(chǔ)上分配136兆赫的頻譜。3GPP和IEEE802LMSC正在積極發(fā)展自己的標(biāo)準(zhǔn),以提交IMT-Advanced為目標(biāo),LTE和IEEE802.16的標(biāo)準(zhǔn)是要進一步提高系統(tǒng)的頻譜效率和數(shù)據(jù)傳輸速率,同時支持各自的早期版本的向后兼容性。其中幾個增強,包括支持一個大于20MHz的帶寬和較高階MIMO的LTE-Advanced和IEEE802.16標(biāo)準(zhǔn)發(fā)展的一部分,目前正在討論中,以滿足IMT-Advanced的要求。2網(wǎng)絡(luò)架構(gòu)和協(xié)議LTE的網(wǎng)絡(luò)結(jié)構(gòu)設(shè)計與無縫移動性,質(zhì)量和服務(wù)質(zhì)量(QoS)的最小延遲支持分組交換流量的目標(biāo)。分組交換的方式,允許所有服務(wù),包括對語音通過數(shù)據(jù)包連接的支持。結(jié)果一個高度簡化的平坦架構(gòu)只有兩個節(jié)點,即演變節(jié)點B(ENB)和移動性管理實體/網(wǎng)關(guān)(MME/毛重)。相反的,在目前的3G系統(tǒng)的分層網(wǎng)絡(luò)架構(gòu)有更多的網(wǎng)絡(luò)節(jié)點。一個重大變化是,從數(shù)據(jù)路徑和無線網(wǎng)絡(luò)控制器(RNC)被淘汰,到現(xiàn)在在ENB納入其職能。在單個節(jié)點接入網(wǎng)絡(luò)的好處是減少延遲和多個eNB到RNC的處理負荷分布。消除在接入網(wǎng)絡(luò)的RNC是可能的,一方面是因為LTE系統(tǒng)不支持宏多樣性或軟切換。在這一章中,我們討論了單播和廣播流量,QoS架構(gòu)和接入網(wǎng)絡(luò)的移動性管理的網(wǎng)絡(luò)體系結(jié)構(gòu)設(shè)計。此外我們還簡要討論2層結(jié)構(gòu)和不同的邏輯,運輸和物理信道,隨著它們的映射問題。2.1網(wǎng)絡(luò)架構(gòu)所有的網(wǎng)絡(luò)接口都基于IP協(xié)議。通過S1接口的互連,如在圖2.1所示的eNBs通過X2接口和MME/毛重實體。S1接口支持MME的/毛重和eNBs的[1]之間的一對多的關(guān)系。eNB和MME之間的功能分割關(guān)系圖如圖2.2所示。兩個實體的邏輯網(wǎng)關(guān)即服務(wù)網(wǎng)關(guān)(GW)和分組數(shù)據(jù)網(wǎng)網(wǎng)關(guān)(GW)。S-GW作為本地移動錨轉(zhuǎn)發(fā)和接收數(shù)據(jù)包,并服從ENB-UE的服務(wù)。與外部分組數(shù)據(jù)網(wǎng)絡(luò)(如Internet)和IMS(PDNS)的P-GW的接口。在P-GW還執(zhí)行了多個IP地址分配,執(zhí)行政策,包過濾和路由等功能。MME是一個信號的唯一實體,因此,用戶的IP數(shù)據(jù)包是不通過MME的。一個優(yōu)勢是一個單獨的網(wǎng)絡(luò)實體的信令信號和交通網(wǎng)絡(luò)容量可以獨立成長。MME的主要職能是包括控制和執(zhí)行尋呼轉(zhuǎn)播的空閑模式UE的可達性,跟蹤區(qū)列表管理,漫游,認(rèn)證,授權(quán),P-GW/S-GW選擇,承載管理,包括專用的承載建立,安全談判NAS信令等。進化節(jié)點B實現(xiàn)節(jié)點B的功能,以及傳統(tǒng)上RNC中實現(xiàn)的協(xié)議。eNB的主要功能是報頭壓縮,加密和數(shù)據(jù)包的可靠傳遞。在控制方面,ENB采用,如admissioncontrol和無線資源管理的職能。在單個節(jié)點接入網(wǎng)絡(luò)的好處是減少延遲和RNC的處理負載分布到多個eNB。圖2.1網(wǎng)絡(luò)架構(gòu)。圖2.2eNB和MME/毛重之間的功能分割。在圖2.3的用戶平面協(xié)議中,我們注意到,分組數(shù)據(jù)匯聚協(xié)議(PDCP)和無線鏈路控制(RLC)傳統(tǒng)RNC的網(wǎng)絡(luò)側(cè)終止層。圖2.3用戶平面協(xié)議。附件2:外文原文(復(fù)印件)IntroducingWPFThecellularwirelesscommunicationsindustrywitnessedtremendousgrowthinthepastdecadewithoverfourbillionwirelesssubscribersworldwide.Thefirstgeneration1Ganalogcellularsystemssupportedvoicecommunicationwithlimitedroaming.Thesecondgeneration2Gdigitalsystemspromisedhighercapacityandbettervoicequalitythandidtheiranalogcounterparts.Moreover,roamingbecamemoreprevalentthankstofewerstandardsandcommonspectrumallocationsacrosscountriesparticularlyinEurope.Thetwowidelydeployedsecond-generation2GcellularsystemsareGSMglobalsystemformobilecommunicationsandCDMAcodedivisionmultipleaccess.Asforthe1Ganalogsystems,2Gsystemswereprimarilydesignedtosupportvoicecommunication.HInlaterreleasesofthesestandards,capabilitieswereintroducedtosupportdatatransmission.However,thedataratesweregenerallylowerthanthatsupportedbydial-upconnections.TheITU-RinitiativeonIMT-2000internationalmobiletelecommunications2000pavedthewayforevolutionto3G.Asetofrequirementssuchasapeakdatarateof2Mb/sandsupportforvehicularmobilitywerepublishedunderIMT-2000initiative.BoththeGSMandCDMAcampsformedtheirownseparate3Gpartnershipprojects3GPPand3GPP2,respectivelytodevelopIMT-2000compliantstandardsbasedontheCDMAtechnology.The3Gstandardin3GPPisreferredtoaswidebandCDMAWCDMAbecauseitusesalarger5MHzbandwidthrelativeto1.25MHzbandwidthusedin3GPP2’scdma2000system.The3GPP2alsodevelopeda5MHzversionsupportingthree1.25MHzsubcarriersreferredtoascdma2000-3x.Inordertodifferentiatefromthe5MHzcdma2000-3xstandard,the1.25MHzsystemisreferredtoascdma2000-1xorsimply3G-1x.Thefirstreleaseofthe3Gstandardsdidnotfulfillitspromiseofhigh-speeddatatransmissionsasthedataratessupportedinpracticeweremuchlowerthanthatclaimedinthestandards.Aseriouseffortwasthenmadetoenhancethe3Gsystemsforefficientdatasupport.The3GPP2firstintroducedtheHRPDhighratepacketdata[1]systemthatusedvariousadvancedtechniquesoptimizedfordatatrafficsuchaschannelsensitivescheduling,fastlinkadaptationandhybridARQ,etc.TheHRPDsystemrequiredaseparate1.25MHzcarrierandsupportednovoiceservice.ThiswasthereasonthatHRPDwasinitiallyreferredtoascdma2000-1xEVDOevolutiondataonlysystem.The3GPPfollowedasimilarpathandintroducedHSPAhighspeedpacketaccess[2]enhancementtotheWCDMAsystem.TheHSPAstandardreusedmanyofthesamedata-optimizedtechniquesastheHRPDsystem.AdifferencerelativetoHRPD,however,isthatbothvoiceanddatacanbecarriedonthesame5MHzcarrierinHSPA.InparalleltoHRPD,3GPP2alsodevelopedajointvoicedatastandardthatwasreferredtoascdma2000-1xEVDVevolutiondatavoice[3].LikeHSPA,thecdma2000-1xEVDVsystemsupportedbothvoiceanddataonthesamecarrierbutitwasnevercommercialized.InthelaterreleaseofHRPD,VoIPVoiceoverInternetProtocolcapabilitieswereintroducedtoprovidebothvoiceanddataserviceonthesamecarrier.Thetwo3GstandardsnamelyHSPAandHRPDwerefinallyabletofulfillthe3Gpromiseandhavebeenwidelydeployedinmajorcellularmarketstoprovidewirelessdataaccess.1.1Beyond3GsystemsWhileHSPAandHRPDsystemswerebeingdevelopedanddeployed,IEEE802LMSCLAN/MANStandardCommitteeintroducedtheIEEE802.16estandard[4]formobilebroadbandwirelessaccess.ThisstandardwasintroducedasanenhancementtoanearlierIEEE802.16standardforfixedbroadbandwirelessaccess.The802.16estandardemployedadifferentaccesstechnologynamedOFDMAorthogonalfrequencydivisionmultipleaccessandclaimedbetterdataratesandspectralefficiencythanthatprovidedbyHSPAandHRPD.AlthoughtheIEEE802.16familyofstandardsisofficiallycalledWirelessMANinIEEE,ithasbeendubbedWiworldwideinteroperabilityformicrowaveaccessbyanindustrygroupnamedtheWiForum.ThemissionoftheWiForumistopromoteandcertifythecompatibilityandinteroperabilityofbroadbandwirelessaccessproducts.TheWisystemsupportingmobilityasinIEEE802.16estandardisreferredtoasMobileWi.Inadditiontotheradiotechnologyadvantage,MobileWialsoemployedasimplernetworkarchitecturebasedonIPprotocolsTheintroductionofMobileWiledboth3GPPand3GPP2todeveloptheirownversionofbeyond3GsystemsbasedontheOFDMAtechnologyandnetworkarchitecturesimilartothatinMobileWi.Thebeyond3Gsystemin3GPPiscalledevolveduniversalterrestrialradioaccessevolvedUTRA[5]andisalsowidelyreferredtoasLTELong-TermEvolutionwhile3GPP2’sversioniscalledUMBultramobilebroadband[6]asdepictedinFigure1.1.Itshouldbenotedthatallthreebeyond3GsystemsnamelyMobileWi,LTEandUMBmeetIMT-2000requirementsandhencetheyarealsoFigure1.1.Cellularsystemsevolution.Table1.1.LTEsystemattributes.partofIMT-2000familyofstandards.1.2Long-TermEvolutionLTEThegoalofLTEistoprovideahigh-data-rate,low-latencyandpacket-optimizedradio-accesstechnologysupportingflexiblebandwidthdeployments[7].Inparallel,newnetworkarchitectureisdesignedwiththegoaltosupportpacket-switchedtrafficwithseamlessmobility,qualityofserviceandminimallatency[8]Theair-interfacerelatedattributesoftheLTEsystemaresummarizedinTable1.1.ThesystemsupportsflexiblebandwidthsthankstoOFDMAandSC-FDMAaccessschemes.InadditiontoFDDfrequencydivisionduplexingandTDDtimedivisionduplexing,half-duplexFDDisallowedtosupportlowcostUEs.UnlikeFDD,inhalf-duplexFDDoperationaUEisnotrequiredtotransmitandreceiveatthesametime.ThisavoidstheneedforacostlyduplexerintheUE.Thesystemisprimarilyoptimizedforlowspeedsupto15km/h.However,thesystemspecificationsallowmobilitysupportinexcessof350km/hwithsomeperformancedegradation.TheuplinkaccessisbasedonsinglecarrierfrequencydivisionmultipleaccessSC-FDMAthatpromisesincreaseduplinkcoverageduetolowpeak-to-averagepowerratioPAPRrelativetoOFDMA.Thesystemsupportsdownlinkpeakdataratesof326Mb/swith4×4MIMOmultipleinputmultipleoutputwithin20MHzbandwidth.SinceuplinkMIMOisnotemployedinthefirstreleaseoftheLTEstandard,theuplinkpeakdataratesarelimitedto86Mb/swithin20MHzbandwidth.Inadditiontopeakdatarateimprovements,theLTEsystemprovidestwotofourtimeshighercellspectralefficiencyrelativetotheRelease6HSPAsystem.Similarimprovementsareobservedincell-edgethroughputwhilemaintainingsame-sitelocationsasdeployedforHSPA.Intermsoflatency,theLTEradio-interfaceandnetworkprovidescapabilitiesforlessthan10mslatencyforthetransmissionofapacketfromthenetworktotheUE.1.3Evolutionto4GTheradio-interfaceattributesforMobileWiandUMBareverysimilartothoseofLTEgiveninTable1.1.Allthreesystemssupportflexiblebandwidths,FDD/TDDduplexing,OFDMAinthedownlinkandMIMOschemes.ThereareafewdifferencessuchasuplinkinLTEisbasedonSC-FDMAcomparedtoOFDMAinMobileWiandUMB.TheperformanceofthethreesystemsisthereforeexpectedtobesimilarwithsmalldifferencesSimilartotheIMT-2000initiative,ITU-RWorkingParty5DhasstatedrequirementsforIMT-advancedsystems.Amongothers,theserequirementsincludeaveragedownlinkdataratesof100Mbit/sinthewideareanetwork,andupto1Gbit/sforlocalaccessorlow-mobilityscenarios.Also,attheWorldRadiocommunicationConference2007WRC-2007,aimumofa428MHznewspectrumisidentifiedforIMTsystemsthatalsoincludea136MHzspectrumallocatedonaglobalbasis.Both3GPPandIEEE802LMSCareactivelydevelopingtheirownstandardsforsubmissiontoIMT-advanced.ThegoalforbothLTE-advanced[9]andIEEE802.16m[10]standardsistofurtherenhancesystemspectralefficiencyanddatarateswhilesupportingbackwardcompatibilitywiththeirrespectiveearlierreleases.AspartoftheLTE-advancedandIEEE802.16standardsdevelopments,severalenhancementsincludingsupportforalargerthan20MHzbandwidthandhigher-orderMIMOarebeingdiscussedtomeettheIMT-advancedrequirements.2NetworkarchitectureandprotocolsTheLTEnetworkarchitectureisdesignedwiththegoalofsupportingpacket-switchedtrafficwithseamlessmobility,qualityofserviceQoSandminimallatency.Apacket-switchedapproachallowsforthesupportingofallservicesincludingvoicethroughpacketconnections.TheresultinahighlysimplifiedflatterarchitecturewithonlytwotypesofnodenamelyevolvedNode-BeNBandmobilitymanagemententity/gatewayMME/GW.Thisisincontrasttomanymorenetworknodesinthecurrenthierarchicalnetworkarchitectureofthe3Gsystem.OnemajorchangeisthattheradionetworkcontrollerRNCiseliminatedfromthedatapathanditsfunctionsarenowincorporatedineNB.SomeofthebenefitsofasinglenodeintheaccessnetworkarereducedlatencyandthedistributionoftheRNCprocessingloadintomultipleeNBs.TheeliminationoftheRNCintheaccessnetworkwaspossiblepartlybecausetheLTEsystemdoesnotsupportmacro-diversityorsoft-handoff.Inthischapter,wediscussnetworkarchitecturedesignsforbothunicastandbroadcasttraffic,QoSarchitectureandmobilitymanagementintheaccessnetwork.Wealsobrieflydiscusslayer2structureanddifferentlogical,transportandphysicalchannelsalongwiththeirmapping.2.1NetworkarchitectureAllthenetworkinterfacesarebasedonIPprotocols.TheeNBsareinterconnectedbymeansofanX2interfaceandtotheMME/GWentitybymeansofanS1interfaceasshowninFigure2.1.TheS1interfacesupportsamany-to-manyrelationshipbetweenMME/GWandeNBs[1]ThefunctionalsplitbetweeneNBandMME/GWisshowninFigure2.2.TwologicalgatewayentitiesnamelytheservinggatewayS-GWandthepacketdatanetworkgatewayP-GWaredefined.TheS-GWactsasalocalmobilityanchorforward