Domov technika Wireless communication

Wireless communication



History

Opticaltelephone

Thefirstwirelesstelephoneconversationintheworldappearedin1880.Atthattime,theopticaltelephonewasusedbyAlexanderGraham.BellandCharlesSumnerTianteinventedandappliedforapatent.Opticaltelephonestransmitvoicesignalsthroughmodulatedlightbeams.Atthattime,therewasnoequipmenttoprovideelectricity,andevensciencefictiondidnotevenmentionlasers.Theirinventiondidnotseemtobeofpracticalvalueatthetime,andtheeffectoftelephonecallswasalsolimitedbysunlightandweather.Opticalphonesandfree-spaceopticalcommunicationsystemsarethesame.Therecanbenoobjectsblockingthebeambetweenthetransmitterandthetransmitter.Decadeslater,theopticaltelephonewasappliedtothefieldofmilitarycommunications.

Earlywork

DavidE.Hughesusedatransmittertotransmitradioseveralhundredmetersawayin1878.AtthattimeMaxwell'selectromagnetictheorywasnotwellknowntotheworld,socontemporaryscientistsregardedthisinventionastheresultofinduction.In1885,ThomasEdisonusedvibratormagnetsasinductivetransmission.In1888,EdisondeployedasignaltransmissionsystemfortheHayeValleyRailway.In1891,heobtainedaradiopatentusinginductance(USPatent465,971).

In1888,HeinrichHertzdemonstratedtheexistenceofelectromagneticwaves,whichbecamethebasisformostofthelaterwirelesstechnologies.Hertzprovedthatelectromagneticwavestravelinastraightlineinspaceandcanbereceivedbyexperimentalequipment,buthedidnotcontinueotherrelatedexperiments.JagdishChandraBossdevelopedanearlyradiodetectiondevicethatalsohelpedtounderstandthecharacteristicsofelectromagneticwaveswithinafewcentimetersofwavelength.

Radio

"Wireless"originallyreferredtoradioreceivers,ortransceivers(devicesthatcanbeusedforbothtransmissionandreception),asearlyastheeraofwirelesstelegraphy.Similardeviceshavebeenapplied.Nowtheterm"wireless"referstomodernwirelesscommunications,suchascellularnetworksandwirelessbroadbandcommunications.Thetermwirelessalsoreferstoanyapplicationthatcanbecarriedoutwithoutwires,suchas"wirelessremotecontrol"and"wirelessenergy".Conversion”withoutdistinguishingwhethertheactualapplicationtechnologyisradio,infraredorultrasonic.

GuglielmoMarconiandKarlBraunwontheNobelPrizeinPhysicsin1909fortheircontributionstowirelesstelegraphy.

Mode

Wirelesscommunicationcanbecarriedoutinthefollowingways:

Radio

Mainarticle:Radio

Radiocommunicationandmicrowavecommunicationareusedinlong-distancecommunicationandneedtobeequippedwithahigh-directionalantennaorshort-distancecommunication.

Freespaceopticalcommunication

Mainarticle:Freespaceopticalcommunication

Freespaceopticalcommunicationsystem(FSO)useslightinfreespace(thatis,air,Wirelessopticalcommunicationtechnologythattravelsinouterspaceandvacuumtotransmitsignals.Thefreespaceopticalcommunicationsystemusesvisiblelightorinfrared,suchasremotecontrolandinfraredcommunication.

Acousticcommunication

Soundwavesandultrasonicwavesarecommonlyusedinshort-distanceapplicationsthatusesoundwavestotransmitsignals.

Electromagneticinduction

Electromagneticinductionismainlyusedinlow-energyandshort-distancecommunicationapplications,suchaspacemakersandshort-distanceRFIDtags.

Wirelessnetwork

Wirelessnetworkcanmeetmanydifferentneeds,themostcommononeistofacilitatelaptopuserstoconnecttotheInternetonthewaytoandfromdifferentplaces,anotherpurposeItisconnectedtotheInternetbymobilephones.Iftheactuallocationofacertainnetworksegmentoftenchanges,itismorereasonabletouseawirelessnetworktoconnect.Thewirelessnetworkcanbeusedinthefollowingsituations:

  • Thedistanceofthenetworkexceedsthelengthallowedbythegeneralwirednetwork.

  • Asabackupnetwork,itisusedwhenthenormalnetworkisabnormal.

  • Connectmobileortemporarynodes.

  • Ingeneralnetworkwiringisdifficultorthecostistoohigh.

  • Mobileusersconnectorconnecttomobilenetworks.

Whendevelopingradiofrequencywirelessnetworks,designersneedtoconsiderthefollowingfactors:

  • UsehundredstothousandsofMHzOrtheGHzband.

  • Operatingrangeandbatterylife.

  • Sensitivityanddatarate.

  • Networktopologyandnodeintelligence.

Theapplicationsofwirelessnetworksincludepoint-to-pointcommunication,point-to-multipointcommunication,broadcasting,cellularnetworksandotherwirelessnetworksandWi-Fitechnology.

Electromagneticwavespectrum

Light,color,AMandFMbroadcasting,andmanyelectronicdevicesalluseradiowavespectrum.Theradiofrequencyspectrumthatcanbeusedforcommunicationisregardedaspublicproperty.Itismanagedbynationalagencies,suchastheFederalCommunicationsCommissionintheUnitedStatesandOfcomintheUnitedKingdom.Theseagenciesdefinewhocanusewhichfrequencybandandwhattheirpurposeis.Ifthepublicfrequencybandisliketheelectromagneticspectrumforpersonaluse,theremaybeconfusionifthereisnosimilarcontroloralternativeconfigurationmeasures.Forexample,theaircraftdoesnothaveaspecialfrequencythatcanbeusedontheairtrafficcontrol,andthesignaloftheamateurradiooperatorinterfereswiththeairtrafficcontrolsignal,Makingitimpossibleforthepilottolandtheplanenormally.Thefrequencybandofwirelesscommunicationisfrom9kHzto300GHz.

Applicationofwirelesscommunicationtechnology

Mobilephone

Mobilephoneshouldbeoneofthemostwidelyknownapplicationsofwirelesscommunication.Attheendof2010,thereweremorethan4.6billionmobilephones.Mobilephonesuseradiowavestoenableusersindifferentplacestocalleachother.Theusercanusethemobilephonewithintherangeofthemobilecommunicationbasestation,andthebasestationwillpickupandreceivethesignalfromthemobilephone.

Wirelessdatatransmission

Wirelessdatatransmissionisanindispensablepartofmobilecomputing.Therearemanyavailabletechnologies.Thedifferenceistheavailability,coverage,andperformanceintheregion.Insomecases,usersmustbeabletodeploymultipleconnectionmethodsandswitchbetweendifferentmodes.Inordertosimplifythetimespentbyusers,connectionmanagementsoftwarecanbeused,orMVPNcanbeusedtoprocessseveralconnectionsintoasinglesecurevirtualnetwork..Thefollowingaresomewirelesscommunicationsusedinwirelessdatatransmission:

  • Wi-Fiisawirelesslocalareanetwork,allowingportablecomputingdevicestoconnecttotheInternetinasimpleway,throughIEEE802.11a,b,g,nandotherstandards,thespeedofWi-Fiisclosetosomewirednetworks.Wi-Fihasbecomethedefactostandardforhotspotsinhomes,officesandpublicspaces.SomecompanieschargeWi-Fionceamonth,andsomecompaniesprovideitforfree,becauseprovidingWi-Ficanincreasethesalesoftheirproducts.

  • Honeycombnetwork:Itcanbeusedaslongasitiswithintentofifteenkilometersfromthenearestbasestation.AndGPRS,to3GnetworkslikeW-CDMA,GSMEnhancedDataRateEvolution(EDGE)orCDMA2000.

  • Mobilesatellitecommunication:Itcanbeusedinsituationswhereotherwirelesstechnologiescannotbeused,suchaslargeruralareasorremoteplaces.Communicationsatellitesareparticularlyimportantintransportation,aviation,navigationandmilitaryaffairs.

  • Wirelesssensornetwork:Itcandirectlydetectrelatedphysicalquantities,monitorandcollectdata,producemeaningfuldisplaysforpeopletowatch,andprovidesomedecision-makingfunctions.

Wirelesspowersupply

Mainarticle:Wirelesspowersupply

WirelesspowersupplyreferstotheThepowerispassedtoanotherdevicethatdoesnothaveabuilt-inpowersupply.Therearetwobasicwirelesspowersupplymethods,whichcanusebeam/laser,radioormicrowavetransmission,orusenear-fieldinduction.Electromagneticwavemagneticfieldsareusedinseveralways.

Wirelessmedicaltechnology

Newtechnologieslikemobilebodyareanetworks(MBAN)canusewirelesstechnologytomonitorbloodpressure,heartbeat,oxygenconcentrationandbodytemperature.Thewirelessbodyareanetworksendsalow-powerwirelesssignaltothereceiver,andthentransmitsittothemonitoringequipmentornursingstation.Thistechnologyreducestheriskofinfection,whetherintentionallyorunintentionally,orproblemscausedbybrokenwires.

Computerinterfaceequipment

Theearliestkeyboards,miceandotherequipmentarewired,andthenwirelessinterfaceequipmentslowlyappeared,mostofwhichuseBluetoothtechnology.TheresponseItmaybeslightlyslowerthanwireddevices,butthegapbetweenthetwoisgettingsmallerandsmaller.

Wirelessinterfacedevicesofcomputerssuchaskeyboardsandmicearegenerallybattery-poweredandtransmitradiofrequencysignalstothereceiverconnectedtothecomputer’sUSBport.Becauseoftheuseofradiofrequencysignals,datacanbetransmittedwirelessly,andtherangeofusecanbeexpanded,generallyuptothreemeters.Distance,physicalobstacles,otherwirelesssignalsandeventhehumanbodymayreducethesignalquality.

Attheendof2007,theissueofwirelesskeyboardsecuritybegantobediscussed.Atthattime,itwasdiscoveredthatMicrosoftwasusingthe27MHzseries,anditsencryptionimplementationwashighlylackinginsecurity.

Therealization,equipmentandrelatedstandardsofwirelesscommunication

  • Radio.

  • Broadcast.

  • Amateurradio.

  • Landmobileradiosystemorprofessionalmobileradio:groundrelayradio,P25,OpensSky,EDACS,DMR,dPMR.

  • Wirelessphone:digitallyenhancedwirelessphonesystem.

  • Honeycombnetwork:0G,1G,2G,3G,4G.

  • Short-distancepoint-to-pointcommunication:wirelessmicrophone,remotecontrol,IrDA,radiofrequencyidentification(RFID),TransferJet,wirelessuniversalserialbus,DSRC,EnOcean,nearfieldcommunication.

  • Wirelesssensingnetwork:ZigBee,EnOcean,wirelesspersonalnetwork,Bluetooth,TransferJet,ultra-wideband(UWB).

  • Wirelessnetwork:wirelesslocalareanetwork(WLAN,likeWi-FiandHiperLAN,etc.),globalinteroperabilitymicrowaveaccess(WiMAX).

Relateditems

  • Radio

  • Hotspot(Wi-Fi),wirelesspowersupply,wirelessaccessdevice

  • LightInternetTechnology(Li-Fi)

  • PersonalAreaNetwork

  • p>
  • Antenna

  • TerrestrialTV

Tento článek je ze sítě, nereprezentuje pozici této stanice. Uveďte prosím původ dotisku
HORNÍ