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简介:May21toMay24,2012TheOCEANS’12Conference,jointlysponsoredbytheMarineTechnologySociety(MTS),theOceanicEngineeringSocietyoftheIEEE,andtheKoreanAssociationofOceanScienceandTechnologySocieties,isamajorinternationalforumforscientists,engineers,andresponsibleoceanuserstopresentthelatestresearch
简介:在无线局域网(WLAN)势头正劲之际,最近又出现了无线城域网(MAN)技术。与为无线局域网制定802.11标准一样,IEEE为无线城域网推出了802.16标准,同时业界也成立了类似WiFi联盟的WiMAX论坛。无线城域网技术为何会紧跟WLAN之
简介:Themediumaccesscontrol(MAC)protocolforindoorvisiblelightcommunication(VLC)withenergyharvestingisexploredinthispaper.Theunfairnessofthroughputexistsamongdevicesduetothesignificantdifferenceoftheirenergyharvestingrateswhichchangeswithdistance,acceptanceangleandtheobstructionprobability.Weproposeanenergyharvestingmodel,anewobstructionprobabilitymodelandanenergyadaptivecontentionalgorithmtoovercometheunfairnessproblem.Thisdevicecanadjustitscontentionwindowaccordingtotheenergyharvestingrate.Asaresult,thedevicewithlowerenergyharvestingratecangetshortercontentionwindowtoimproveitstransmissionopportunity.SimulationresultsshowthatourMACprotocolcanachieveahigherdegreeoffairness.
简介:Backoffmechanismisakeycomponentofcontention-basedmediumaccesscontrol(MAC)layerprotocol.IthasbeenshownthatthebackoffmechanismofIEEE802.11standardmaybeveryinefficientespeciallywhenthenetworkiscongested.Numbersofmethodshavebeenproposedtotunethecontentionwindow(CW)withtheaimtoachievetheoptimalthroughputinIEEE802.11WLANs.However,themechanismsdonotspecificallyaddresspropersettingsforthevariablepacketlengthinfluenceandCWdivergingproblem.Thispaperproposesanovelfour-wayhandshakingfull-feedbackbackoffalgorithmnamedadoptivecontentionwindowbackoff(ACWB)toovercomethesedrawbacks.Theperformanceoftheproposedalgorithmisinvestigatedthroughanalysisandsimulation.SimulationresultsdemonstratethattheACWBalgorithmprovidesaremarkableperformanceimprovementintermsofshort-termfairness,packetdelayanddelayjitter,whilemaintaininganoptimalthroughputclosetothetheoreticalthroughputlimitoftheIEEE802.11distributedcoordinationfunction(DCF)accessscheme.
简介:IEEE802.15.4protocolisproposedtomeetthelowlatencyandenergyconsumptionneedsinlow-ratewirelessapplications,however,fewanalyticalmodelsaretractableenoughforcomprehensiveevaluationoftheprotocol.ToevaluatetheIEEE802.15.4slottedCSMA/CAchannelaccessmechanisminthispaper,weproposeapracticalandaccuratediscreteMarkovchainmodel,whichcandynamicallyrepresentdifferentnetworkloads.Bycomputingthesteady-statedistributionprobabilityoftheMarkovchain,weobtainanevaluationformulaforthroughput,energyconsumption,andaccesslatency.Thenwefurtheranalyzetheparametersthatinfluenceperformanceincludingpacketarrivalrate,initialbackoffexponentandmaximumbackoffnumber.Finally,NS2simulatorhasbeenusedtoevaluatetheperformanceofthe802.15.4CSMA/CAmechanismunderdifferentscenariosandtovalidatetheaccuracyoftheproposedmodel.
简介:WLAN是计算机网络与无线通信技术相结合的产物,它速率高、接入灵活,有着广阔的市场应用前景。本文依据移动WLAN系统的设计思路,提出一个基于IEEE802.11b标准的GSM、3G、WLAN的“三网舍一”的室内覆盖系统设计方案。该方案能解决室内GSM移动手机信号的覆盖问题,同时兼容3G业务覆盖,并接入WLAN系统进行互补,较好的解决了异种移动通信系统相互干扰的问题。总体方案具有较高的性价比和较强的可扩展性。