六级模拟试题2文档格式.docx
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swifter,higher,stronger."
ThePathto4G
Beijinghasthegoodfortuneoflookingatpreviousgenerationsofwirelessnetworksandavoidingthesamemistakesasitpreparesfor2008.Firstgeneration（1G）wirelesstelecommunications--thebrick-likeanalogphonesthatarenowcollector'
sitems-introducedthecellulararchitecturethatisstillbeingofferedbymostwirelesscompaniestoday.Secondgeneration（2G）wirelesssupportedmoreuserswithinacellbyusingdigitaltechnology,whichallowedmanycallerstousethesamemultiplexedchannel.But2Gwasstillprimarilymeantforvoicecommunications,notdata,exceptsomeverylowdata-ratefeatures,likeshortmessagingservice（SMS）.So-called2.5Gallowedcarrierstoincreasedatarateswithasoftwareupgradeatthebasetransceiversstations（BTS）,aslongasconsumerspurchasednewphonestoo.Thirdgeneration（3G）wirelessoffersthepromiseofgreaterbandwidth,basicallybiggerdatapipestousers,whichwillallowthemtosendandreceivemoreinformation.
Allofthesearchitectures,however,arestillcellular.Cellulararchitectureissometimesreferredtoasa"
stararchitecture"
becauseuserswithinthatcellaccessacommon,centralizedbasestation.Theadvantageisthatgivenenoughtimeandmoney,carrierscanbuildnationwidenetworks,whichmostofthebigcarriershavedone.Someofthedisadvantagesincludeasingularpointoffailure,noloadbalancing,andspectralinefficiencies.Thesinglebiggestdisadvantagetocellularnetworksgoingforwardisthatasdataratesincrease,outputpowerwillhavetoincrease--orthesizeofthecellswillhavetodecrease—tosupportthosehigherdatarates.Sincesignificantincreasesinoutputpowerscarebothconsumersandregulators,itisfarmorelikelythatwewillseesignificantlysmallercells.Thiswillfurtherreducethereturnoninvestmentinalreadyfragile3Gbusinessplans.
Fourthgeneration（4G）wirelesswasoriginallyconceivedbytheDefenseAdvancedResearchProjectsAgency（DARPA）,thesameorganizationthatdevelopedthewiredInternet.Itisnotsurprising,then,thatDARPAchosethesamedistributedarchitectureforthewirelessInternetthathadprovensosuccessfulinthewiredInternet.Althoughexpertsandpolicymakershaveyettoagreeonalltheaspectsof4Gwireless,twocharacteristicshaveemergedasallbutcertaincomponentsof4G:
end-to-endInternetProtocol（IP）,andpeer-to-peer（点对点）networking.AnallIPnetworkmakessensebecauseconsumerswillwanttousethesamedataapplicationstheyareusedtoinwirednetworks.Peer-to-peernetworks,whereeverydeviceisbothatransceiver（收发器）andarouter（路由器）forotherdevicesinthenetwork,eliminatestheweaknessofcellulararchitectures,becausetheeliminationofasinglenodedoesnotdisablethenetwork.Thefinaldefinitionof"
4G"
willhavetoincludesomethingassimpleasthis:
ifaconsumercandoitathomeorintheofficewhilewiredtotheInternet,thatconsumermustbeabletodoitwirelesslyinafullymobileenvironment.
Let'
sdefine"
as"
wirelesscollaboratedpeer-to-peernetworking"
.4Gtechnologyissignificantbecauseusersjoiningthenetworkaddmobilerouterstothenetworkinfrastructure.Becauseuserscarrymuchofthenetworkwiththem,networkcapacityandcoverageisdynamicallyshiftedtoaccommodatechanginguserpatterns.Aspeoplecongregateandcreatepocketsofhighdemand,theyalsocreateadditionalroutesforeachother,thusenablingadditionalaccesstonetworkcapacity.Userswillautomaticallyhopawayfromcongestedroutestolesscongestedroutes.Thispermitsthenetworktodynamicallyandautomaticallyself-balancecapacity,andincreasenetworkutilization.
Whatcould4GmeanforBeijinganditsOlympics?
Thereisastatistic（withoutanyknownattribution）thatestimatesthatthefirstphonecallmadebyamajorityofChinesealivetodaywaswithacellphone.ThiswouldmeanthatmostChineseskippedawholegenerationoftelephony（coppertwistedpair）andjumpedintotheworldofwirelesstelephony.SotoomighttheChineseskipagenerationofwirelessanddeploya4Gnetworkbefore2008.FollowingareafewapplicationsthatcouldfurtherenhancetheOlympicexperience,bothforthevisitorsduringtheGames,andfortheresidentsofBeijinglongafterwards.
Security
Beijinghasalreadydeployedcamerasthroughoutthecityandsendsthoseimagesbacktoacentralcommandcenter.Thisisgenerallydoneusingfiber,whichlimitswherethecamerascanbehung,i.e.,nofiber,nocamera.4GnetworksallowBeijingtodeploycamerasandbackhaul（回传）themwirelessly.Andinsteadofhavingtobackhauleverycamera,citiescanbackhauleverythirdorfifthortenthcamera,usingtheothercamerasasrouter/repeaters.
TrafficControl
Beijingisachallengingcityfordrivers,withorwithoutanOlympicsgoingon.Thegrowingmiddleclass,andtheirnew-foundabilitytopurchaseautomobiles,isincreasingthenumberofpassengervehiclesontheroadatastaggeringannualrateof30%.4Gnetworkscanconnecttrafficcontrolboxestointelligenttransportationmanagementsystemswirelessly.Thiswouldcreateatrafficgridthatcouldchangelightcycletimesondemand,e.g.,keepingsomelightsgreenlongertemporarilytoimprovetrafficflow.Italsocouldmakevehiclebasedondemand"
allgreen"
routesforemergencyvehiclesrespondingtotrafficaccidents,reducingthelikelihoodthatthosevehicleswillthemselvesbeinvolvedinanaccidentroute.
HotSpots
Beijingcoulddeployinformationkiosks（亭）aroundthecitytoallowvisitorstotheOlympicstogetreal-timeinformationonresults,venueupdates,andtrafficconditions.TheycouldbebackhauledtotheInternetviaexistingcableorDSL.Buttheycouldalsobehometo802.11accesspoints,providingfreeinformationtoanyonewithan802.11card.Andwith4G'
speer-to-peercapabilities,thecitycoulddeployaccesspointsevenwherethereisnofiber,byhavingthose"
remote"
accesspointshopthroughbackhauledaccesspoints.
MobileHotSpots
Toexploittherealpowerof4G,Beijingcouldcreatemobilehotspots.Thiswouldallowusersinthesubways.trains,andbusestoconnecttotheInternetviastandard802.11cardstalkingtostandard802.11accesspoints.Butsincethoseaccesspointsobviouslycannotbewiredtothenetwork,theyareconnectedvia4Gwirelessnetworks.
Conclusion
HostinganOlympicGamesis,well,anOlympiantask.ModernChinaismorethanuptothechallengeanditissafetopredictthatBeijing2008willbeoneofthemostimpressiveGamesofalltimes.ButoneotherwaytomeasurethesuccessoftheGamesistheimpactithasonthehostcityafterthetorchisextinguished.Bydeployinga4GmobilebroadbandnetworkfortheGames,Beijingwillensurethatitsresidentswillenjoyprofoundandlastingbenefits.
1.WhichofthefollowingisNOToneofthewordsoftheBeijingOlympicmotto?
A）swifterB）higherC）biggerD）stronger
2.Whichoneintroducedthecellulararchitecturethatisstillbeingofferedbymostwirelesscompaniestoday?
A）Firstgeneration（1G）wirelesstelecommunications.
B）Theso-called2.5G.
C）Secondgeneration（2G）wireless.
D）Thirdgeneration（3G）wireless.
3.WhichoneofthefollowingqualityCANNOTbeusedinthedefinitionof"
?
A）collaboratedB）peer-to-peerC）wiredD）networking
4.Ifmanypeoplehavedemandforthenetworkatthesametime,thenetworkwill______.
A）bedifficultinthedatacommunication
B）breakdowncompletely
C）keepdynamicallyandautomaticallyself-balancecapacity
D）givenoinformation
5.4Gwirelesscommunicationcantaketheplaceof______tosendimagesbacktocentralcommandcenter.
A）screenB）cellphoneC）televisionD）fiber
6.ThegrowingmiddleclassinBeijingisincreasingthenumberofpassengervehiclesontheroadatanannualrateof_______.
A）20%B）25%C）30%D）35%
7.4Gnetworkscankeepsomelights________longertemporarilytoimprovetrafficflow.
A）greenB）yellowC）redD）blue
8.DuringBeijingOlympics,touristscaneasilyobtaintheinformationaboutgameresultsandtrafficconditionsintimefrom___________________.
9.Evenontheirwaytodestinations,travelerscaneasilysurfinternetby802.11cardsifthereare_____________.
10.WhetherBeijing2008issuccessfulornotcanbeascertainedby__________onBeijingafteritisover.
PartIV.Reading
Passage1
Canyouwalkastraightline?
Thequestionismuchmoredifficulttoanswerthanyouthink.ArecentexperimentheldinJapanshowsthatitisalmost__1__forpeopletowalkexactlystraightfor60meters.Eachmanhadtowearsockssoakedwithredinkandwalkonwhitepaperfixed___2__tothefloor.The____3__showedthatallwalkedinawindingratherthanastraightline.Researchersfoundthatpeople__4___theirdirectionofwalkingregularly.However,therangedifferedfromsubjecttosubject.
Thissuggeststhatnoneofuscanwalkina__5__straightline.Rather,wemeander（散步）,mainlyduetoaslightstructuraloffunctional___6__ofourlegs.Sostepsbytheleftandrightlegsofapersonare___7___.
Asaresult,althoughwemaystartwalkingin
升级会员 