简介:下面我们还是用表3.6.3产生的3/4收缩卷积码来进行Viterbi译码,表3.6.2中共108bit码元,卫星信道在QPSK调制时误码率pe=10-1~10-2,在108码元中选择8bit码元位置,使该码元处产生误码.用随机数方法产生8bit码元位置,分别在3,17,38,54,62,66,90,103.Pe=8/108=7.4×10-1(上述3,17,……103是用随机办法产生的一次结果,下一次再用随机数方法产生又会是另外的8个位置,但它们的分布符合卫星通道干扰噪声的分布规律.).把发送端的第3,17,38……103这8个bit码元的"0"变成"1"、"1"变成"0",使其误码,其余位置不变,就是接收码元.表3.6.7包含了步数、1/2码元、删除码元和接收码元,其中"X"表示该处不发送,"×"处表示该码元有错,"#"为在删除处插入空码符,它不参加分支度量比较.
简介:HandoverinDigitalVideoBroadcastingforHandhelds(DVB-H)aimstoprovidecontinuousmobilebroadcastingserviceswhenauseristravelingthroughcellboundaries.Agoodhandovercontrolcanimprovethepowerefficiencyandgainmuchbetterreceptionquality.ThisletterprovidesanovelapproachforDVB-HhandoverbasedonDVB-H/UniversalMobileTelecommunicationsSystem(UMTS)hybridnetwork,whichmovesthemainhandoverfunctionfromtheterminalstothenetworks,sothatitreducestheoperationcomplexityoftheterminalsandincreasesthepowersaving.WhentheterminalcannotreceivetheDVB-Hsignalinthetransmissionshadowareasorbecauseofsomeotherreasons,theUMTSnetworksmayofferthesameservicetouserstomaketheservicecontinuous.AstheUMTSnetworkshavethetopologyoftheDVB-Hnetworks,bycommunicatingwiththeterminals,theUMTSnetworkscanhelptheterminalstopredictthehandover,andavoidunnecessaryhandover.
简介:Thereactivityratiosofvinylacetate(VAc)anddivinylbenzene(DVB)werecalculatedfromtheQandevalues.Thepossibilityofthecopolymerizationofthesetwomonomerswaspredictedandthecopolymerizationwascarriedoutbysuspensionpolymerizationtechniqueinthepresenceofporeproducingagent(tolueneandgasoine).TherelativeratioofacetoxygroupandbenzeneringinthecopolymerweremonitoredbyIRmeasurementduringthepolymerization.Thevariationofporeproperties,suchasspectificsurfacearea,porosityandaverageporediameter,withpolymerizationtimeweredetermined.Thecopolymersatvariouspolymerizationtimewerealcoholyzedandthusthevariationofthehydroxylgroupcontentwithpolymerizationtimewasstudied.
简介:Internet应用的迅速推广,使他陷人了自身难以克服的困境。这是因为Internet是一个“网间网”,他是由许许多多IP自治域系统通过互联构成的复合网络系统。传输带宽的增加、交换速度的提高以及流量工程的引入,并没有从根本上改变传递信息过程中的多跳、存储转发和点到点传输的工作模式,因而阻塞现象的发生在所难免。