多用户环境下的无线通信设计

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1、:+,7(3$3(5RFcommunicationinamulti-userenvironment*(1(5$/SincemoreandmoresystemsareusingRFcommunication,andmostofthemareoperatinginanISM(Industrial,Scientific,Medical)bandtheneedforawaytoharmonizethecoexistenceofsystemsusingthesamefrequencyresources,areurgent.Inthiswhitepaperwe

2、willdiscussdifferenttechniquesfordealingwiththeproblemscausedbyRFtrafficfromothersystemsthanourown.7(&+1,48(6)25+$1'/,1*',6785%,1*75$)),&TherearedifferentwaysonhowasystembasedonacombinationofTDMA(TimeDivisionMultipleAccess)andFDMA(FrequencyDivisionMultipleAccess)usesthetim

3、eandfrequencydomain.Mostofthesystemshavea“bursty”useofthetimedomain,meaningthattheytransmitinshortburstsandkeepquietinbetweeneachburst.Fortheuseofthefrequencydomainthereareinmajorthreedifferentwaysasystemcanoperate:xFixedsinglechannel(Lowcomplexity)xDynamicchannelassigning(Mediumc

4、omplexity)xFrequencyhopping(Highcomplexity)Afixedsinglechannelsystemistypicallyasystemwheretheunitsdonothavethepossibilitytonegotiatewhichchanneltheyshalluseordistributeacommonsystemclock.Normallythiswillbeasystemwithatransmitterinoneendandareceiverintheother.Suchasystemwillbeable

5、tousedifferentchannels,butthechannelforoperationwillbeselectedonceatstart-up.Anexampleofsuchasystemisawirelessmouse.Dynamicchannelassignmentisamethodwhereallunitsinvolvedmusthaveatransceiver.Thisenablesthepossibilityforthereceivingunittoacknowledgeallreceivedpackets,whichwillmaket

6、hetransmittingunitabletodetectpacketlossandinitiateare-transmissionofthelostpacket.Itwillalsomakethesystemabletocalculatethepacketlossratio(PLR.)AndthesystemcanbemadesothattheunitschangetrafficchannelifthePLRreachesagiventhreshold.Thechannelchangeplancanbeimplementedasatableorasa“

7、goNup/down”algorithm.Themostimportantpartofachannelchangeisthatbothunitsactuallychangechannel.SinceitisthetransmittingunitthatwillbeabletodetectthePLRitwillalsobethepartresponsibleofinitiatingthechannelchange.Thisisdonebysendinga“changechanneltoX”(Xrepresentthenewchannel)packettot

8、hereceiver.Thereceiverwillacknowl