Thetraditionalwayofallocatingasinglechannelamongmultiplecompetingusersistochopupits()byusingoneofthemultiplexingschemessuchasFDM(FrequencyDivisionMultiplexing).IfthereareNusers,thebandwidthisdividedintoNequal-sizedportions,witheachuserbeingassignedoneportion.Sinceeachuserhasaprivatefrequency(本题),thereisnointerferenceamongusers.Whenthereisonlyasmallandconstantnumberofusers,eachofwhichhasasteadystreamoraheavyloadof(),thisdivisionisasimpleandefficientallocationmechanism.AwirelessexampleisFMradiostations.EachstationgetsaportionoftheFMbandandusesitmostofthetimetobroadcastitssignal.However,whenthenumberofsendersislargeandvaryingorthetrafficis(),FDMpresentssomeproblems.IfthespectrumiscutupintoNregionswhilefewerthanNusersarecurrentlyinterestedincommunicating,alargepieceofvaluablespectrumwillbewasted.IfmorethanNuserswanttocommunicate,someofthemwillbedenied()forlackofbandwidth.??
A.band
B.range
C.domain
D.assignment
正确答案是B