电子与通信工程硕士专业英语part-7.pptx

2020 3 18 1 Lesson4数字信号处理的基本概念BasicConceptsofDSP UNIT9PassageA 2020 3 18 2 Lesson4数字信号处理的基本概念BasicConceptsofDSP 内容大纲Outline 1 Theessentialsofanalog to digitalanddigital to analogconversion A D anti aliasing sampling quantization digitization D A smoothing converting zeroorderhold 2020 3 18 3 Lesson4数字信号处理的基本概念BasicConceptsofDSP 内容大纲Outline 2 Technologiesfordigitalsignalprocessing Digitalsignalprocessorsareatthecenterofsignalprocessing someadvantagesofdesigningwithDSPsoverothermicroprocessors theotheralternativesavailablefordigitalsignalprocessing FPGA ASIC GPP 2020 3 18 4 Lesson4数字信号处理的基本概念BasicConceptsofDSP seepage115 Wordsandexpressions 2020 3 18 5 Lesson4数字信号处理的基本概念BasicConceptsofDSP Adigitalsignalisanumericalrepresentationoftheanalogsignal Itmaybeeasierandmorecosteffectivetoprocessthesesignalsinthedigitalworld Intherealworld wecanconvertthesesignalsintodigitalsignalsthroughtheanalog to digitalconverter processthesignals andifneeded bringthesignalsbackouttotheanalogworldthroughthedigital to analogconverter 精读详解Intensivereading 2020 3 18 6 Lesson4数字信号处理的基本概念BasicConceptsofDSP 1 Theessentialsofanalog to digitalanddigital to analogconversion Thefirstessentialstepinanalog to digital A D conversion asshowninFigure9 1 istosampleananalogsignal Thisstepisperformedbyasampleandholdcircuit whichsamplesatregularintervalscalledsamplingintervals Thelengthofthesamplingintervalisthesameasthesamplingperiod andthereciprocalofthesamplingperiodisthesamplingfrequencyfs 精读详解Intensivereading 2020 3 18 7 Lesson4数字信号处理的基本概念BasicConceptsofDSP Whenthisminimumisnotrespected distortioncalledaliasingoccurs Aliasingcauseshighfrequencysignalstoappearaslowerfrequencysignals Tobesurealiasingwillnotoccur samplingisalwaysprecededbylowpassfiltering Thelowpassfilter calledtheanti aliasingfilter removesallfrequenciesabovehalftheselectedsamplingrate 精读详解Intensivereading 2020 3 18 8 Lesson4数字信号处理的基本概念BasicConceptsofDSP 精读详解Intensivereading Afterabriefacquisitiontime duringwhichasampleisacquired thesampleandholdcircuitholdsthesamplesteadyfortheremainderofthesamplinginterval ThisholdtimeisneededtoallowtimeforanA Dconvertertogenerateadigitalcodethatbestcorrespondstotheanalogsample 2020 3 18 9 Lesson4数字信号处理的基本概念BasicConceptsofDSP 精读详解Intensivereading TheA Dconverterchoosesaquantizationlevelforeachanalogsample AnN bitconverterchoosesamong2Npossiblequantizationlevels Thelargerthenumberoflevels thesmallerthequantizationerrors calculatedasthedifferencebetweenthequantizedlevelandthetruesamplelevel MostquantizationerrorsarelimitedinsizetohalfaquantizationstepQ ThequantizationstepsizeiscalculatedasQ R 2N whereRisthefullscalerangeoftheanalogsignalandNisthenumberofbitsusedbytheconverter 2020 3 18 10 Lesson4数字信号处理的基本概念BasicConceptsofDSP 精读详解Intensivereading Finally eachdigitalsampleisassignedadigitalcode whichcompletestheA Dprocess Theresultisadigitalbitstream Itisthiscollectionofdigitalcodesthatis processedindigitalsignalprocessing Tosummarize A Dcomprisesanti aliasing sampling quantizationanddigitization 2020 3 18 11 Lesson4数字信号处理的基本概念BasicConceptsofDSP 精读详解Intensivereading Oncedigitalsignalprocessingiscomplete digital to analog D A conversion asshowninFigure9 2 mustoccur Thisprocessbeginsbyconvertingeachdigitalcodeintoananalogvoltagethatisproportionalinsizetothenumberrepresentedbythecode Thisvoltageisheldsteadythroughzeroorderholduntilthenextcodeisavailable onesamplingintervallater Thiscreatesastaircase likesignalthatcontainsfrequenciesaboveWHz Thesesignalsareremovedwithasmoothinglowpassfilter thelaststepinD Aconversion 2020 3 18 12 Lesson4数字信号处理的基本概念BasicConceptsofDSP 精读详解Intensivereading 2020 3 18 13 Lesson4数字信号处理的基本概念BasicConceptsofDSP 精读详解Intensivereading 2 Technologiesfordigitalsignalprocessing Adigitalsignalprocessor DSP isatypeofmicro processor onethatisincrediblyfastandpowerful ADSPisuniquebecauseitprocessesdatainrealtime Thisreal timecapabilitymakesaDSPperfectforapplicationsthatcannottolerateanydelays Forexample didyouevertalkonacellphonewheretwopeoplecouldn ttalkatonce Youhadtowaituntiltheotherpersonfinishedtalking 2020 3 18 14 Lesson4数字信号处理的基本概念BasicConceptsofDSP 精读详解Intensivereading Ifyoubothspokesimultaneously thesignalwascut youdidn theartheotherperson Withtoday sdigitalcellphones whichuseDSP youcantalknormally HerearejustsomeoftheadvantagesofdesigningwithDSPsoverothermicroprocessors 2020 3 18 15 Lesson4数字信号处理的基本概念BasicConceptsofDSP 精读详解Intensivereading Single cyclemultiply accumulateoperations Real timeperformancesimulationandemulation Flexibility Reliability Increasedsystemperformance Reducedsystemcost 2020 3 18 16 Lesson4数字信号处理的基本概念BasicConceptsofDSP 精读详解Intensivereading However therearesomeoftheotheralternativesavailablefordigitalsignalprocessing HowtheycomparetoDSPs TheFPGAAlternative Field ProgrammableGateArrays FPGA havethecapabilityofbeingreconfigurablewithinasystem whichcanbeabigadvantageinapplicationsthatneedmultipletrialversionswithindevelopment offeringreasonablyfasttimetomarket 2020 3 18 17 Lesson4数字信号处理的基本概念BasicConceptsofDSP 精读详解Intensivereading Theyalsooffergreaterrawperformanceperspecificoperationbecauseoftheresultingdedicatedlogiccircuit However FPGAsaresignificantlymoreexpensiveandtypicallyhavemuchhigherpowerdissipationthanDSPswithsimilarfunctionality Assuch evenwhenFPGAsarethechosenperformancetechnologyindesignssuchaswirelessinfrastructure DSPsaretypicallyusedinconjunctionwithFPGAstoprovidegreaterflexibility betterprice performanceratios andlowersystempower 2020 3 18 18 Lesson4数字信号处理的基本概念BasicConceptsofDSP 精读详解Intensivereading TheASICAlternative Application specificICs ASIC canbetailoredtoperformspecificfunctionsextremelywell andcanbemadequitepowerefficient However sinceASICSarenotfield programmable theirfunctionalitycannotbeiterativelychangedorupdatedwhileinproductdevelopment Assuch everynewversionoftheproductrequiresaredesignandtripsthroughthefoundry anexpensiveproposition andanimpedimenttorapidtime to market ProgrammableDSPs ontheotherhand canbeupdatedwithoutchangingthesilicon merelychangethesoftwareprogram greatlyreducingdevelopmentcosts andavailingaftermarketfeatureenhancementswithmerecodedownloads Consequently moreoftenthannot whenyouseeASICsinrealtimesignalprocessingapplications theyaretypicallyemployedasbusinterfaces gluelogic and orfunctionalacceleratorsforaprogrammableDSP basedsystem 2020 3 18 19 Lesson4数字信号处理的基本概念BasicConceptsofDSP 精读详解Intensivereading TheGPPAlternative IncontrasttoASICsthatareoptimizedforspecificfunctions general purposemicroprocessors GPPs arebestsuitedforperformingabroadarrayoftasks However forapplicationsinwhichtheendproductmustprocessanswersinrealtime ormustdosowhilepoweredbyconsumerbatteries GPPscom parativelypoorrealtimeperformanceandhighpowerconsump tionallbutrulesthemout Moreandmore theseprocessorsarebeingseenasthedinosaursoftheindustry tooencumberedwithPCcompatibilityanddesktopfeaturestoadapttothechangingrealtimemarketplace Astheworldembracestinyhand heldwireless enabledproductsthatrequirepowerdissipationmeasuredinmilliwatts notthewattsthattheseprocessorsconsume DSPsaretheprogrammabletechnologyofchoice ThattrendisboundtocontinueasdigitalInternetappliancesgetsmaller fasterandmoreportable 2020 3 18 20 Lesson4数字信号处理的基本概念BasicConceptsofDSP satellite basedcommunicationX based基于X的e g UNIX basedoperatingsystem 补充材料Supplementarymaterials AbebasedonB e g Thetheoryisbasedonaseriesofwrongassumptions e g Thecommunicationisbasedonsatellite e g Basedontheseprinciples 2020 3 18 21 Lesson4数字信号处理的基本概念BasicConceptsofDSP 补充材料Supplementarymaterials X oriented面向X的e g object orientedprogramming process orientedprogramming OOAD object orientedanalysisanddesign X free无X的 免除X的e g nuclear weapon freezone radio free interference freefree X自由的 免费的 易 的e g free oscillation free phone free fall free cutting 2020 3 18 22 Lesson4数字信号处理的基本概念BasicConceptsofDSP 补充材料Supplementarymaterials X independent与X无关的e g position independentcode distance independentcostindependent 独立的independentvariables 2020 3 18 23 Lesson5电路交换和分组交换CircuitSwitchingandPacketSwitching UNIT21PassageB 2020 3 18 24 Lesson5电路交换和分组交换CircuitSwitchingandPacketSwitching Wordsandexpressions circuitswitching电路交换 messageswitching报文交换 packetswitching分组交换 2020 3 18 25 Lesson5电路交换和分组交换CircuitSwitchingandPacketSwitching Wordsandexpressions seepage262 2020 3 18 26 内容大纲Outline Paragraph1 Lesson5电路交换和分组交换CircuitSwitchingandPacketSwitching Paragraph2 Paragraph3 Paragraph4 Paragraph5 circuitswitching messageswitching packetswitching avariationofmessageswitching featureanalysisbetweencircuitswitchingandmessageswitching addedfeaturesandproblemsinpacketswitching 2020 3 18 27 Therearetwobasictypesofswitchingtechniques circuitswitchingandmessageswitching Incircuitswitching atotalpathofconnectedlinessetupfromtheorigintothedestinationatthetimethecallismade andthepathremainsallocatedtothesource destinationpair whetherusedornot untilitreleasedbythecommunicatingparties Theswitches calledcircuitswitches orofficeexchangeintelephonejargon havenocapabilityofstoringormanipulatinguser sdataontheirwaytothedestination Lesson5电路交换和分组交换CircuitSwitchingandPacketSwitching 精读详解Intensivereading Paragraph1 2020 3 18 28 Thecircuitissetupbyaspecialsignalingmessagethatfindsitswaythroughthenetwork seizingchannelsinthepathasitproceeds Oncethepathisestablished arereturnsignalinformsthesourcetobegintransmission Directtransmissionofdatafromsourcetodestinationcanthentakeplacewithoutanyinterventiononthepartofthesubnet Lesson5电路交换和分组交换CircuitSwitchingandPacketSwitching 精读详解Intensivereading 2020 3 18 29 Inmessageswitching thetransmissionunitisawell definedblockofdatacalledamessage Inadditiontothetexttobetransmitted amessagecomprisesaheaderandachecksum Theheadercontainsinformationregardingthesourceanddestinationaddressesaswellasothercontrolinformation thechecksumisusedforerrorcontrolpurposes Lesson5电路交换和分组交换CircuitSwitchingandPacketSwitching 精读详解Intensivereading Paragraph2 2020 3 18 30 Theswitchingelementisacomputerreferredtoasamessageprocessor withprocessingandstoragecapabilities Messagestravelindependentlyandasynchronously timingtheirownwayfromsourcetodestination Firstthemessageistransmittedfromthehosttothemessageprocessortowhichitisattached Oncethemessageisentirelyreceived themessageprocessorexaminesitsheader andaccordinglydecidesonthenextoutgoingchannelonwhichtotransmitit Lesson5电路交换和分组交换CircuitSwitchingandPacketSwitching 精读详解Intensivereading 2020 3 18 31 Ifthisselectedchannelisbusy themessagewaitsinaqueueuntilthechannelbecomesfree atwhichtimetransmissionbegins Atthenextmessageprocessor themessageisagainreceived stored examined andtransmittedonsomeoutgoingchannel andthesameprocesscontinuesuntilthemessageisdeliveredtoitsdestination Thistransmissiontechniqueisalsoreferredtoasthestore and forwardtransmissiontechnique Lesson5电路交换和分组交换CircuitSwitchingandPacketSwitching 精读详解Intensivereading 2020 3 18 32 Avariationofmessageswitchingispacketswitching Herethemessageisbrokenupintoseveralpiecesofagivenmaximumlength calledpackets Aswithmessageswitching eachpacketcontainsaheaderandachecksum Packetsaretransmittedindependentlyinastore and forwardmanner Lesson5电路交换和分组交换CircuitSwitchingandPacketSwitching 精读详解Intensivereading Paragraph3 2020 3 18 33 Withcircuitswitching thereisalwaysaninitialconnectioncostincurredinsettingupthecircuit Itiscost effectiveonlyinthosesituationswhereoncethecircuitissetupthereisaguaranteedsteadyflowofinformationtransfertoamortizetheinitialcost Thisiscertainlythecasewithvoicecommunicationinthetraditionalway andindeedcircuitswitchingisthetechniqueusedinthetelephonesystem Lesson5电路交换和分组交换CircuitSwitchingandPacketSwitching 精读详解Intensivereading Paragraph4 2020 3 18 34 Communicationamongcomputers however ischaracterizedasbursty Burstinessisaresultofthehighdegreeofrandomnessencounteredinthemessage generationprocessandthemessagesize andofthelowdelayconstraintrequiredbytheuser Theusersanddevicesrequirethecommunicationresourcesrelativelyinfrequently butwhentheydo theyrequirearelativelyrapidresponse Lesson5电路交换和分组交换CircuitSwitchingandPacketSwitching 精读详解Intensivereading 2020 3 18 35 Ifafixeddedicatedend to endcircuitweretobesetupconnectingtheendusers thenonemustassignenoughtransmissionbandwidthtothecircuitinordertomeetthedelayconstraintwiththeconsequencethattheresultingchannelutilizationislow Ifthecircuitofhighbandwidthweresetupandreleasedateachmessagetransmissionrequest thentheset uptimewouldbelargecomparedtothetransmissiontimeofthemessage resultingagaininlowchannelutilization Lesson5电路交换和分组交换CircuitSwitchingandPacketSwitching 精读详解Intensivereading 2020 3 18 36 Therefore forburstyusers whichcanalsobecharacterizedbyhighpeak to averagedataraterequirements store and forwardtransmissiontechniquesofferamorecost effectivesolution sinceamessageoccupiesaparticularcommunicationslinkonlyforthedurationofitstransmissiononthatlink therestofthetimeitisstore