在ALTIUM DESIGNER中，画PCB封装时想用CTRL+M来测量两个焊盘的距离，但是光标一直不能锁定焊盘的中心？-百谷歌simulationofdatapropagationinaVANET,weusedandextendedtheNetworkSimu-lator2(ns2),whichfeaturesawellvalidatedimplementationoftheIEEE802.11speci-ficationthatiscrucialforourpurposes,andalsoprovidesanadequateradiowaveprop-agationmodel(TwoRayGroundModel).Effectssuchasshadowingduetobuildingwallsaretakenintoaccountbyasimpleline-of-sightmodelwhichhasbeenintroducedin[12].Valuablehintsonstrengthsandweaknessesofthens2-specificimplementationoftheMAClayercanbefoundin[17,13,6].MinordeviationsfromtheIEEEspeci-ficationwithinthens2implementationhavebeencorrected.Thescenariowhichhasbeenusedforallofthesimulationsisasfollows:Withinanareaof8km2,300wire-lessenabledvehicles(allofwhichareassumedtobeabletodetectpotentialhazards)aremovingaround.Acommunicationrangeof400mhasbeenapplied.Thesimula-tiondurationwassetto100s.Foreveryscenario50independentiterationshavebeenconductedtoavoidstatisticalaberrations.Tosimulatehighlyloadednetworkscenarios,thenodescanonlyaccessabandwidthof0.3Mbit/s.Thisfacilitatesthesimulationofhighlyloaded,largenetworks,whilereducingthenumberofeventsinthesimulatortoareasonableextent.ThebenefitfunctionappliedforestimatingthebenefitforthereceiversurcomprisesparameterssuchasDistancefromInformationSource,MessageAge,InformationCategory,LatestBroadcast,LatestReception,ExpectedNewsValueandcanbestudiedindetailin[3].Pleasealsorefertothispublicationregardingtheappliedtrafficpattern,whichfollowsthewidelyacceptedstore-and-forwardapproach.Thebenefitfunctionappliedforestimatingthebenefitforthereceiversurcomprisesthefollowingparameters:DistancefromInformationSource(di,inm,withamaximumof300m),MessageAge(ma,ins,withamaximumof50s),InformationCategory(ic,integerID,between1and10),LatestBroadcast(lb,ins,withamaximumof50s),LatestReception(lr,ins,withamaximumof50s)andExpectedNewsValue(nv^thatis0whentheinformationislikelytobeknownbytherecipientsand1otherwise).TheresultingrelevancefunctionisEqn.4.ThefunctionfordeterminingreceiverbenefitvaluesisEqn.5.
50s-malblrm-di+1·(10-ic)+1·2·300+2·+1·u r=n v·300m-di50s-malr2·+2·+1·(10-ic)+1·ur=nv6(4)(5)
4.2SimulationResults
Ourapproachmodifiesthemediumaccessrulestoprovideausefulformof”controlledunfairness”.Datathathasbeenidentifiedtoprovidehighbenefittopotentialrecipi-entsisgivenpreferentialaccesstothemedium.Itwillthereforegainfasteraccessattheexpenseofthelowerprioritytraffic.Toinvestigatetheimpactsofadjustingcon-tentionwindowsinahighlyloadednetwork,thefollowingsimulationhasbeenrun:Onlytwomessages(stemmingfromtwodifferentapplications)arebeingdisseminatedthroughoutthenetworkaccordingtoanunrestrictedstore-and-forwardscheme,whereeachnoderelayseverymessageithasnotseenbeforetoallofitsneighbors.AssoonasamessageispasseddownfromthepacketqueuetotheMAClayer,thecontention
window(CW)oftherespectivenodeisadjustedaccordingtotheestimatedbenefitofthemessage.
Fig.3.TrafficdifferentiationduetoadaptedContentionWindows
AsshowninFig.3,thepropagationofmessageshasbeenexaminedwithrespecttothreedifferentparametrization:First,nodessendingatype-1messageapplyaverysmallcontentionwindowof1,wherenodesintendingtosendatype-2packetuseaCWof3000,whichisanextremeapplicationofunfairnesswithregardtomediumaccess.Second,10(CWfortype-1)and500(CWfortype-2)havebeenused.Third,10(CWfortype-1)and50(CWfortype-2)wereappliedtointroducetrafficdifferentiation,nowshowingsmallereffectthanwiththefirstparameterset.Inthishighloadscenario,thelengthofanode’sCWsignificantlyinfluencesitslikelihoodtogetaccesstothesharedmedium.Inallthreecases,type-1-messagesreachnodesmorequicklythanwithouttheprioritization,whereastype-2-messagesaredisseminatedslowerthanintheconven-tionalcase.Last,thedashedlineinthemiddleofthefiguredepictstheoverallnumberofmessagesfrombothtypessentincasetrafficisnottreateddifferentlydependingonitstype.
Asmeansforinvestigatingthedistributionofmessagebenefitvalues,wechosethefollowingsimulationsetup:Onaverage,about30newdatapacketsaregeneratedeachsecondandnodeshave0.3Mbit/sofbandwidthavailable,whereasimple,benefitag-nosticstore-and-forwardmechanismforrelayingthedatahasbeenappliedinthefirstrun.ThepacketqueuesateachofthenodesthusworkaccordingtothesimpleFIFOprinciple.Uponthereceptionofamessage,eachvehiclewithinthescenariostartsacomputationofthebenefitreceived.Theresultingvalues,combinedwiththecurrenttimestamps,arethenloggedinafileforevaluation.TheresultsaredepictedinFig.4,representingtheoutcomeofonlyonesimulationscenario.Theplotshowsthatbenefitvaluesofpacketsshortlyafterthefirstpackettransmissionsareratherhigh.Aftersometimehaspassedandmessageshavebeenpropagatedtoahighnumberofvehicleswithvaryinginterestininformation,manypacketswithverylowbenefitvaluesarebeing
Fig.4.Benefitvaluedistributionincaseofnotrafficdifferentiation
received.Duetothelackingtrafficdifferentiationbasedondatabenefit,networkre-sourcesaremainlyabsorbedbythetransmissionoflow-benefitdatapackets.Onlyveryrarely,newandhighlyrelevantpacketsaregrantedaccesstothesharedmedium.Afurthereffectcanbeinferredfromthisplot:Neighboringvehiclesestimatethebenefitofthesamemessagerathersimilarly(seealsoin[3]).Thenumerousverticalchainsofdotsrepresentthereceptionofonecertainmessagebyanumberofcarsatthesamepointintime.Withincreasingnetworkloadovertime,thebenefitoftheinformationreceivedbythedifferentvehiclesdecreasesfurther.Networkresourcesarewastedduetothetransmissionofmoreorlessdispensabledata,wherehighlyrelevantpacketsgetstuckinthegrowingpacketsqueues.
Asasecondstep,wesimulatedthesamescenariowhileapplyingareorganizationofthepacketqueuesaccordingtocurrentpacketbenefitvalues.AscanbeseeninFig.5,thebenefitofmessagesreachingthevehicleswithinthescenariocanbesignificantlyincreased.Still,somemessageswithrelativelylowbenefitvaluesarereceivedbythevehiclesinthescenario,whichcanbeputdowntomainlythreereasons:First,thebenefitestimationwithinthecarsmayfalselyevaluatethebenefitacertainpieceofinformationmightprovidetotheadjacentnodes.Second,incaseanodeonlyhasdatawithrelativelylowrelevanceavailableanditsneighborsdonotintendtosendmorerelevantmessagesaswell,messageswithlowbenefitwillgetaccesstothemedium.Third,nointer-nodebroadcastsequencehasbeenestablishedthatensuresthenodewiththecurrentlymostrelevantpacketwinsthemediumcontentionprocess.
Finally,theMACfunctionalityhasbeenadditionallyadapted:Insteadoftreatingpacketsthesamewayandthusgrantingthemthesamechancetogetaccesstothemedium,weadaptthelegacyCSMAmechanismsuchthatdefer-andbackoff-timersaredeterminedbasedonthebenefitapacketisexpectedtoprovidetoadjacentnodes.Also,timersarenewlyseteachtimethechannelwassensedtobeidletoguaranteeanoptimalalignmentofpacketbenefitandchannelaccessprobability(per-periodtimeradaptationasbrieflyexplainedabove.AsvisualizedinFig.6,thebenefitofthere-ceivedpacketscouldbeimprovedevenmore.Duetotheinter-vehiclecoordinationon
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《Altium_Designer》-第11-12讲_第5章_元器件封装库的创建
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实验六 Altium Designer Winter 09 集成库的操作
实验目的：
1、了解Altium Designer软件元件库的组成结构
2、学习和练习集成库的建立、元件的新建、元件的画法。 3、学习元件封装的画法。
4、学习从元件库中复制元件的方法
实验原理：
1、集成库概述
Altium Designer软件元件库分为集成库和独立库。其集成库将元件的符号和封装联系起来，构成统一的库，这样，在绘制原理图时即可选择并可视元件封装。集成库后缀名为：*.intLib。而独立库分为*.SCHlib和*.PCBlib。 2、集成库的创建过程
建立集成库：菜单：File-New-Project-Integrated Library，并保存、命名项目。
建立原理图库：菜单：File-New- Library-Schematic Library，并保存、命名。
建立封装库：菜单：File-New- Library-PCB Library，并保存、命名。创建后的结果如下：
然后在MyPcbLib.PcbLib中绘制元件封装，并命名。 在MySchLib.SchLib中绘制元件符号，并命名。 通过以下方式将元件符号和元件封装联系起来：
在原理图库中，所绘制元件下方的栏目空白处点击鼠标右键-Add-Footprint，点Browse..，选择MyPcbLib.PcbLib中的对应封装。同一个元件可反复添加多个封装。
添加完成后可以将库编译并生成集成库。
执行菜单Project中的Compile Integrated Library XXX.LibPkg 在该项目所在路径下会生成一个目录：.. \Project Outputs for XXX中，会有所编译后的集成库文件。
在后续绘图过程中，若需要加载该集成库，可在菜单：Design-Add/Remove Library中点install指定到集成库所在位置进行添加库操作。
3、元件封装的绘制
在PCB库中，点击菜单：Tools-New Blank Component建立新封装元件。
点击菜单：View-Workspace Panels-PCB-PCBLibrary（也可在屏幕左下方点PCB library标签进入）在PCB Library页面中，双击空文件“PCBFOOTPRINT1”对元件命名。
放大图纸，在图纸中央零坐标处放置焊盘。
一般讲元件第一个焊盘或者元件中心放置在零坐标上。 （1）、放置焊盘。
使用菜单：Place-Pad放置焊盘，在还未放下去之前，按Tab键弹出焊盘属性。焊盘属性中：
Hole Size中输入过孔直径，若是表面贴装元件，Hole Size为零。 Round：圆形过孔；Square：方形过孔；Slot：长条形过孔。 Designator：输入管脚的标号。一般用数字或字母。 焊盘的．．．Designator．．．．．．．．．．一定要与符号库中管脚的．．．．．．．．．．．Designator．．．．．．．．．．一致。．．．
Layer项：通孔元件用MultiLayer，表贴元件用TopLayer。 Locked：后面打勾。 （2）、绘制元件外形。
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