802.11 Power-Saving Mode for Mobile Computing in Wi-Fi hotspots

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1、802.11Power-SavingModeforMobileComputinginWi-Fihotspots:Limitations,EnhancementsandOpenIssuesG.Anastasia,M.Contib,E.Gregorib,A.Passarellab,∗PervasiveComputing&NetworkingLaboratory(PerLab)aDept.ofInformationEngineering,UniversityofPisaViaDiotisalvi2-56

2、122Pisa,Italyg.anastasi@iet.unipi.itbCNR-IITInstituteViaG.Moruzzi,1-56124Pisa,Italy{marco.conti,enrico.gregori,andrea.passarella}@iit.cnr.itAbstract.NowadaysWi-Fiisthemostmaturetechnologyforwireless-Internetaccess.Despitethelarge(andeverincreasing)dif

3、fusionofWi-Fihotspots,energylimitationsofmobiledevicesarestillanissue.Todealwiththis,thestandard802.11includesaPower-SavingMode(PSM),butnotmuchattentionhasbeendevotedbytheresearchcommunitytounderstanditsperformanceindepth.Wethinkthatthispapercontribut

4、estofillthegap.WefocusonatypicalWi-Fihotspotscenario,andassessthedependenceofthePSMbehavioronseveralkeyparameterssuchasthepacketlossprobability,theRoundTripTime,thenumberofuserswithinthehotspot.WeshowthatduringtrafficburstsPSMisabletosaveupto90%oftheene

5、rgyspentwhennoenergymanagementisused,andintroducesalimitedadditionaldelay.Unfortunately,inthecaseoflonginactivityperiodsbetweenbursts,PSMisnottheoptimalsolutionforenergymanagement.WethusproposeaverysimpleCross-LayerEnergyManager(XEM)thatdynamicallytun

6、esitsenergy-savingstrategydependingontheapplicationbehaviorandkeynetworkparameters.XEMdoesnotrequireanymodificationtotheapplicationsortothe802.11standard,andcanthusbeeasilyintegratedincurrentWi-Fidevices.Dependingonthenetworktrafficpattern,XEMreducesthe

7、energyconsumptionofanadditional20−96%withrespecttothestandardPSM.Keywords:802.11,Wi-Fi,Power-SavingMode,NetworkArchitecture&Design,MobileComputing,NetworkProtocols,PerformanceofSystems1IntroductionSincetheintroductionofthe802.11standardin1997,802.11wi

8、relessLANs(alsoknownasWi-Fihotspots)havebecomemoreandmorepopular.InstallationsofWi-Fihotspotsarenowadaysveryfrequent,forexampleincompanyandeducationbuildings,coffeeshops,airports,andsoon.Figure1showsasimpleWi-Fiinstallation,whereuserscarryingm