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1、通信技术综述(Overviewofcommunicationtechnology)Overviewofcommunicationtechnology(2009-12-2010:59:11)Mobilecommunicationtechnologyhasgonethroughthreemainstagesofdevelopment.Thedevelopmentofeachgenerationisthebreakthroughoftechnologyandtheinnovationofideas・Thefirstgenerationorigi
2、natedin1980s,mainlyusinganalogandfrequencydivisionmultipleaccess(卩DMA)technology.Thesecondgeneration(2G)originatedintheearly90s,mainlyusingtimedivisionmultipleaccess(TDMA)andcodedivisionmultipleaccess(CDMA)technology.Thethirdgenerationmobilecommunicationsystem(3G)canprovi
3、deawiderbandwidth,notonlytotransmitvoice,butalsototransmithigh-speeddata,soastoprovidefastandconvenientwirelessapplications・However,thirdgenerationmobilecommunicationsystemisstillnotaregionalcommunicationsystembasedonthestandardground,althoughitstransmissionratecanbeashig
4、has2Mb/s,butstillcannotmeettherequirementofmultimediacommunication,therefore,thefourthgenerationmobilecommunicationsystem(4G)researchcameintobeing・First,theconceptof4GcommunicationtechnologyThedefinitionof4Ghasyettobeclarified,anditstechnicalparameters,internationalstanda
5、rds,networkstructure,andevenbusinesscontentarenotclearlystated・IntheWi-Fiboominthelate2002,Wi-Fiwasseenas4Gtechnology.Butadvocatesof4Gtechnologyarguethat4GisdifferentfromWi-Fi・InJune2004,analystsatForrester,amarketresearchfirm,predictedthat4Gmobileserviceswou1dbeacombinat
6、ionof3GandWiMax・4GwillprovideEthernetaccessspeed(suchaslOMb/s),andbycombining3GandWiMaxtechnologyinamobilephone,providingintegratedwirelessLANandWanservices・WiMax(orthe802・16standard)canprovidewirelessbroadbandnetworkservices,thelongestdistanceof30miles,thespeedisabout10M
7、b/s・InthewhitepaperreleasedbyFujitsuin2004,WiMAXreferstothe〃4G〃wirelesstechnology.Inaddition,manyexpertsareveryoptimisticaboutLAS-CDMA,thinkLAS-CDMArepresentsthelevelof4G・Whatkindoftechnologyis4G?Itisgenerallydescribedasfollows:4Gisasetof3GandWLANinone,andcantransmithigh-
8、quality-videoimages,theimagequalityofitstransmissionandhigh-definitiontelevisioncomparable・4Gsys
