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1、通信技术综述Communicationtechnologyreview(2009-12-2010:59:11)Mobilecommunicationtechnologyhasgonethroughthreemajorstagesofdevelopment.Everygenerationofdevelopmentisthebreakthroughoftechnologyandinnovationofideas・Thefirstgenerationoriginatedinthe1980s,mainlyusi
2、nganalogandfrequencydivisionmultipleaccess(FDMA)technology.Thesecondgeneration(2G)originatedintheearly1990s,withtheuseoftimedivisionmultipleaccess(TDMA)andcodedivisionmultipleaccess(CDMA)technology.Thethirdgeneration(3g)mobilecommunicationsystemcanprovid
3、eawiderband,transportnotonlyvoice,alsocantransmithighspeeddata,toprovidequickandconvenientwirelessapplications・However,thethirdgenerationmobilecommunicationsystemisstillbasedonthegroundhavedifferentstandardsofregionalcommunicationsystem,althoughthetransm
4、issionratecanbeupto2Mb/s,butstillcan，tmeettherequirementsofmultimediacommunication,therefore,thefourthgenerationmobilecommunicationsystem(4g)researchthenarisesatthehistoricmoment・Theconceptof4GcommunicationtechnologyThedefinitionof4Ghasyettobedefined,and
5、itstechnicalparameters,internationalstandards,networkstructures,andevenbusinesscontentarenotclearlystated・Wi-fiwasseenas4Gtechnologyduringthewi-fiboominlate2002.Butadvocatesof4Gtechnologysay4Gisdifferentfromwi-fi.InJune2004,analystsatForrester,amarket-re
6、searchfirm,predictedthatthe4Gmobileservicewouldbeacombinationof3GandWiMax・4gwillprovideEthernetaccess(e.g.,10MB/s),andthroughthe3ginamobilephoneandWiMaxtogether,providingintegratedwirelessLANandwanservice・WiMax(or802.16)canprovidewirelessbroadbandservice
7、,whichcanbeasfaras30miles,atarateofabout10Mb/s・Ina2004whitepaperpublishedbyFujitsu,WiMAXwasreferredtoas〃4G〃wirelesstechnology.Inaddition,thereareplentyofexpertswhoareoptimisticthattheLASCDMAsystemwillrepresentthe4Glevel・Whatkindoftechnologyis4G?Thegenera
8、ldescriptionisasfollows:4Gisacombinationof3GandWLAN,andcantransmithigh-qualityvideoimages,whichhavethesamequalityashigh-definitiontelevisions・4gsystemcandownloadatarateofabout100MB/s,2000timesfasterthancurrentdial-upIntern
