简介:提高紧耦合天线的隔离度是雷达、通信和电子对抗等许多领域中提升系统性能的技术之一,目前的方法大多以牺牲天线辐射效率为代价。研究了一种基于反相耦合相消理念的去耦方法,可以在极小间距情况下实现天线单元之间的高隔离度,并且保持较高的天线增益。利用一种微带双天线结构来验证这一方法,这种结构的两个天线都工作于1.8GHz,相互间的间隔为10mm(1/16波长),仿真和实验结果说明,两个天线间的隔离可以低于-20dB。经仿真结果显示该结构中的天线增益要大于0dB,与不经隔离设计时的同结构同尺寸天线差别约1dB。初步实现了在较小地影响辐射性能的前提下实现紧耦合天线之间的高隔离目标。
简介:ThisstudyconcernssecurityissuesoftheemergingWirelessBodySensorNetwork(WBSN)formedbybiomedicalsensorswornonorimplantedinthehumanbodyformobilehealthcareappli-cations.Anovelauthenticatedsymmetric-keyestablishmentschemeisproposedforWBSN,whichfullyexploitsthephysiologicalfeaturesobtainedbynetworkentitiesviathebodychannelavailableinWBSNbutnototherwirelessnetworks.Theself-definedIntrinsicSharedSecret(ISS)isusedtoreplacethepre-deploymentofsecretsamongnetworkentities,whichthuseliminatescentralizedservicesorau-thoritiesessentialinexistingprotocols,andresolvesthekeytransportprobleminthepuresymmet-ric-keycryptosystemforWBSNaswell.Thesecuritypropertiesoftheproposedschemearedemon-stratedintermsofitsattackcomplexityandthetypesofattacksitcanresist.Besides,theschemecanbeimplementedunderalight-weightwayinWBSNsystems.DuetotheimportanceoftheISSconcept,theanalysisonusingfalseacceptance/falserejectionmethodtoevaluatetheperformanceofISSforitsusageintheschemeisalsodemonstrated.
简介:Recently,ithasbeenseenthattheensembleclassifierisaneffectivewaytoenhancethepredictionperformance.However,itusuallysuffersfromtheproblemofhowtoconstructanappropriateclassifierbasedonasetofcomplexdata,forexample,thedatawithmanydimensionsorhierarchicalattributes.Thisstudyproposesamethodtoconstructeanensembleclassifierbasedonthekeyattributes.Inadditiontoitshigh-performanceonprecisionsharedbycommonensembleclassifiers,thecalculationresultsarehighlyintelligibleandthuseasyforunderstanding.Furthermore,theexperimentalresultsbasedontherealdatacollectedfromChinaMobileshowthatthekey-attributes-basedensembleclassifierhasthegoodperformanceonbothoftheclassifierconstructionandthecustomerchurnprediction.
简介:Histogramofcollineargradient-enhancedcoding(HCGEC),arobustkeypointdescriptorformulti-spectralimagematching,isproposed.TheHCGECmainlyencodesroughstructureswithinanimageandsuppressesdetailedtexturalinformation,whichisdesirableinmulti-spectralimagematching.Experimentsontwomulti-spectraldatasetsdemonstratethattheproposeddescriptorcanyieldsignificantlybetterresultsthansomestate-ofthe-artdescriptors.
简介:Timeefficiencyofkeyestablishmentandupdateisoneofthemajorproblemscontributorykeymanagementsstrivetoaddress.Toachievebettertimeefficiencyinkeyestablishment,weproposeaLocation-basedHuffman(L-Huffman)scheme.First,usersareseparatedintoseveralsmallgroupstominimizecommunicationcostwhentheyaredistributedoverlargenetworks.Second,bothuser'scomputationdifferenceandmessagetransmissiondelayaretakenintoconsiderationwhenHuffmancodingisemployedtoformingtheoptimalkeytree.Third,thecombinedweightsinHuffmantreearelocatedinahigherplaceofthekeytreetoreducethevarianceoftheaveragekeygenerationtimeandminimizethelongestkeygenerationtime.SimulationsdemonstratethatL-HuffmanhasmuchbetterperformanceinwideareanetworksandisalittlebetterinlocalareanetworkthanHuffmanscheme.
简介:Certificatelessencryptionattractsalotofattentionsofarbyeliminatingthekeyescrowprobleminidentity-basedencryptionandpublickeycertificatesinthetraditionalpublickeycryptography.Byconsideringthethreatfromthekeyexposure,itisdesirabletoincorporatetheideaofkey-insulatedcryptosystemintothecertificatelessencryption.Inthispaper,wehavedesignedanefficientcertificatelesskeyinsulatedencryption(CL-KIE)schemetoachievethisgoal.Byourapproach,thecomputationalperformanceofourschemehasbeenimprovedsignificantlyintermsofreductiononrunningtimeandstorage.WealsogavethesecurityproofofthenewCL-KIEschemeagainstthechosenplaintextattacks(CPAs)intherandomoracle,consideringtheassumptionofthecomputationalDiffie-Hellman(CDH)problem.
简介:Nowadays,thepassword-basedremoteuserauthenticationmechanismusingsmartcardisoneofthesimplestandconvenientauthenticationwaystoensuresecurecommunicationsoverthepublicnetworkenvironments.Recently,Liuetal.proposedanefficientandsecuresmartcardbasedpasswordauthenticationscheme.However,wefindthatLiuetal.’sschemeisvulnerabletotheoff-linepasswordguessingattackanduserimpersonationattack.Furthermore,italsocannotprovideuseranonymity.Inthispaper,wecryptanalyzeLiuetal.’sschemeandproposeasecurityenhanceduserauthenticationschemetoovercometheaforementionedproblems.Especially,inordertopreservetheuseranonymityandpreventtheguessingattack,weusethedynamicidentitytechnique.Theanalysisshowsthattheproposedschemeismoresecureandefficientthanotherrelatedauthenticationschemes.
简介:Withouttheassumptionthattheprivatekeysarekeptsecureperfectly,cryptographicprimitivescannotbedeployedintheinsecureenvironmentswherethekeyleakageisinevitable.Inordertoreducethedamagecausedbythekeyexposureintheidentity-based(ID-based)signaturescenariosefficiently,weproposeanID-basedkey-insulatedsignatureschemeinthispaper,whicheliminatestheexpensivebilinearpairingoperations.Comparedwiththepreviouswork,ourschememinimizesthecomputationcostwithoutanyextracost.Underthediscretelogarithm(DL)assumption,asecurityproofofourschemeintherandomoraclemodelhasalsobeengiven.
简介:Intheair-waterquantumkeydistribution(QKD),theirregularseasurfacehassomeinfluenceonthephotonpolariza-tionstate.Thewindisconsideredasthemainfactorcausingtheirregularity,sothemodelofirregularseasurfacebasedonthewindspeedisadopted.Therelationshipsofthequantumbiterrorratewiththewindspeedandtheinitialincidentanglearesimulated.Therefore,themaximumsecuretransmissiondepthofQKDisconfirmed,andthelimita-tionofthewindspeedandtheinitialincidentangleisdetermined.Thesimulationresultsshowthatwhenthewindspeedandtheinitialincidentangleincrease,theperformanceofQKDwillfalldown.Undertheintercept-resendattackcondition,themaximumsafetransmissiondepthofQKDisupto105m.Torealizesafecommunicationsinthesafedivingdepthofsubmarines(100m),theinitialincidentangleisrequestedtobenotexceeding26~,andwiththeinitialincidentan~leincreased,thelimitationofwindspeedisdecreased.
简介:Withparametricdown-conversionsources(PDCSs),thenonorthogonaldecoystateprotocolbasedononevacuumandtwoweakdecoystatesispresented.ThedetectioneventsonBob'ssidearedividedintotwogroupsdependingonwhetherAlicegetsatriggerornot:triggeredcomponentsandnontriggeredcomponents.Thetriggeredcomponentsareusedtoestimatethefractionsanderrorratesofsingle-photonandtwo-photonpulses,andthenthefinalsecurekeyrateisdeduced.Besides,bothtriggeredandnontriggeredcomponentsareusedtodeduceamoreaccuratevalueofthekeygenerationrate.Thesimulationofthefinalkeygenerationrateovertransmissiondistanceshowsthatthefirstmethodcanobtainakeygenerationrateclosetothetheoreticallimitoftheinfinitedecoystateprotocol,whilethesecondmethodisbetter.
简介:V型槽侧面耦合是目前双包层光纤抽运光耦合的方法之一。本文提出了一种二透镜光学系统的耦合模型,并利用几何光学的ABCD矩阵分析和计算了透镜焦距与激光二极管阵列(LD—Arrays),透镜,双包层光纤(DCF)三者之间间距的关系,同时通过计算确定了V型槽所开的最佳角度。通过数值模拟计算发现透镜焦距的选取在很小范围内会引起两透镜间距的剧烈变化而且激光二极管与透镜的间距以及两透镜间的间距主要取决于靠近激光二极管那个透镜的焦距大小。本文的分析和计算对V型槽侧面抽运的光学耦合系统中透镜焦距的选取以及LD,透镜,DCF三者之间间距的设置的最优化提供了理论指导。