Handbook of Wireless Networks and Mobile Computing

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1、11DataBroadcastJIANLIANGXUandDIK-LUNLEEDepartmentofComputerScienceHongKongUniversityofScienceandTechnologyClearWaterBay,HongKongxujl,dlee
@cs.ust.hkQINGLONGHUIBMSiliconValleyLabSanJose,CA,USAqhu@us.ibm.comWANG-CHIENLEEVerizonLaboratoriesWaltham,MA,USAwan

2、g-chien.lee@verizon.com11.1INTRODUCTIONWehavebeenwitnessinginthepastfewyearstherapidgrowthofwirelessdataapplicationsinthecommercialmarketthankstotheadventofwirelessdevices,wirelesshigh-speednetworks,andsupportingsoftwaretechnologies.Weenvisagethatinthenea

3、rfuture,alargenumberofmobileuserscarryingportabledevices(e.g.,palmtops,laptops,PDAs,WAPphones,etc.)willbeabletoaccessavarietyofinformationfromanywhereandatanytime.Thetypesofinformationthatmaybecomeaccessiblewirelesslyareboundless,andincludenews,stockquote

4、s,airlineschedules,andweatherandtrafficinformation,tonamebutafew.Therearetwofundamentalinformationdeliverymethodsforwirelessdataap-plications:point-to-pointaccessandbroadcast.Inpoint-to-pointaccess,alogicalchannelisestablishedbetweentheclientandtheserver.Q

5、ueriesaresubmittedtotheserverandresultsreturnedtotheclientinmuchthesamewayasinawirednetwork.Inbroadcast,dataaresentsimultaneouslytoallusersresidinginthebroadcastarea.Itisuptotheclienttoselectthedataitwants.Laterwewillseethatinaspecialkindofbroadcastsystem

6、,namelyon-demandbroadcast,theclientcanalsosubmitqueriestotheserversothatthedataitwantsareguaranteedtobebroadcast.12DATABROADCASTComparedwithpoint-to-pointaccess,broadcastisamoreattractivemethodforseveralreasons:Asinglebroadcastofadataitemcansatisfyallthe

7、outstandingrequestsforthatitemsimultaneously.Assuch,broadcastcanscaleuptoanarbitrarynumberofusers.Mobilewirelessenvironmentsarecharacterizedbyasymmetriccommunica-tion,i.e.,thedownlinkcommunicationcapacityismuchgreaterthantheuplinkcommunicationcapacity.Da

8、tabroadcastcantakeadvantageofthelargedown-linkcapacitywhendeliveringdatatoclients.Awirelesscommunicationsystemessentiallyemploysabroadcastcomponenttodeliverinformation.Thus,databroadcastcanbeimplementedwithoutintro