Throughput and delay limits of IEEE 802.11.pdf

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1、IEEECOMMUNICATIONSLETTERS,VOL.6,NO.8,AUGUST2002355ThroughputandDelayLimitsofIEEE802.11YangXiao,Member,IEEE,andJonRosdahl,SeniorMember,IEEEAbstract—TheIEEE802.11protocolfamilyprovidesuptoIEEE802.11employsacarriersensemultipleaccesswith54-Mbpsdatarate,whereastheindustryisseekinghigherdatacollisiona

2、voidance(CSMA/CA)MACprotocolwithbinaryrates.Thispapershowsthatatheoreticalthroughputupperlimitexponentialbackoff,calledDistributedCoordinationFunctionandatheoreticaldelaylowerlimitexistfortheIEEE802.11protocols.Theexistenceofsuchlimitsindicatesthatbysimply(DCF)andanoptionalPointCoordinationFuncti

3、on[1].DCFincreasingthedataratewithoutreducingoverhead,theenhanceddefinesabasicaccessmechanismandanoptionalRequest-To-performance,intermsofthroughputanddelay,isboundedevenSend/Clear-To-Send(RTS/CTS)mechanism.Weonlyconsiderwhenthedatarategoesintoinfinitelyhigh.Reducingoverheadisthebasicaccessmechan

4、isminthispaper.Ourmethodcanbevitalforgoodperformance.easilyappliedtotheRTS/CTSmechanism.IndexTerms—IEEE802.11protocol,multipleaccesscontrol,Astationwithapackettotransmitmonitorsthechannelac-performanceevaluation.tivitiesuntilanidleperiodequaltoadistributedinter-framespace(DIFS)isdetected.Aftersen

5、singanidleDIFS,thesta-NOTATIONStionwaitsforarandombackoffintervalbeforetransmitting.ThebackofftimecounterisdecrementedintermsofslottimeasNotationsaredefinedasfollowsandwillbeusedthroughoutlongasthechannelissensedidle.Thecounterisstoppedwhenthispaper.atransmissionisdetectedonthechannelandreactivat

6、edwhenAslottime.thechannelissensedidleagainformorethanaDIFS.Thesta-SIFStime.tiontransmitsitspacketwhenthebackofftimereacheszero.AtDIFStime.eachtransmission,thebackofftimeisuniformlychosenintheMinimumbackoffwindowsize.range,whereisthecurrentbackoffwindowTransmissiontimeofthephysicalpreamble.size.A

7、ttheveryfirsttransmissionattempt,equalsthemin-TransmissiontimeofthePHYheader.imumbackoffwindowsize.Aftereachunsuccessfultransmis-MACoverheadinbytes,i.e.,28bytes.sion,isdoubleduntilamaximumbackoffwindowsizeACKsizeinbyte